veterinary anesthesia

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Every effort has been made to ensure that the drug dosage schedules withinthis text are accurate and conform to standards accepted at time of publication.However, as treatment recommendations vary in the light of continuingresearch and clinical experience, the reader is advised to verify drug dosageschedules herein with information found on product information sheets. This isespecially true in cases of new or infrequently used drugs.

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Library of Congress Cataloging-in-Publication DataCornick-Seahorn, Janyce L.

Veterinary anesthesia / Janyce L. Cornick-Seahorn.p. cm. — (The Practical veterinarian)

Includes bibliographical references (p. ).ISBN 0-7506-7227-7 (alk. paper)

1. Veterinary anesthesia. I. Title. II. Series.SF914 .C67 2000636.089’796—dc21 00-044452

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Series Preface

The Practical Veterinarian series was developed to help

veterinary students, veterinarians, and veterinary techni-

cians find answers to common questions quickly. Unlike

larger textbooks, which are filled with detailed informa-

tion and meant to serve as reference books, all the books

in The Practical Veterinarian series are designed to cut to

the heart of the subject matter. Not meant to replace the

reference texts, the guides in our series complement the

larger books by serving as an introduction to each topic

for those learning the subject matter for the first time or

as a quick review for those who already have mastered

the basics of each subject.

The titles for the books in our series are selected to

provide information for the most common subjects one

would encounter in veterinary school and veterinary

practice. The authors are experienced and established

clinicians who can present the subject matter in an easy-

to-understand format. This helps both the first-time stu-

dent of the subject and the seasoned practitioner assess

information often difficult to comprehend.

It is our hope that the books in The Practical Veteri-

narian series will meet the needs of readers and serve as

a constant source of practical and important informa-

tion. We welcome comments and suggestions that will

vii

help us improve future editions of the books in this

series.

Shawn P. Messonnier, D.V.M.

viii Series Preface

Preface

Veterinary Anesthesia summarizes what I hope is practical,

useful information for learning the basic and clinical

principles and the daily practice of anesthesia. I would

like to thank my husband, Tom, and my children, Brad

and Sam, without whom this project would not have had

such meaning. I would like to thank my parents, without

whom I would not have had the opportunity to achieve

my goals nor the desire to share my knowledge, as I hope

I have in this endeavor.

I thank my mentor in anesthesia, Dr. Sandee Harts-

field, who continues to be a friend and unending source

of knowledge and common sense regarding the art of

anesthesia. I thank my mentor in large animal internal

medicine, Dr. Kent Carter, who instilled in me a logical

and thorough approach to case management.

I also thank my editor, Leslie Kramer, whose opti-

mism and enthusiasm gave me support every step of the

way.

And, most of all, I thank God for my profession and

the opportunity to accrue the information and knowl-

edge that I feel are most pertinent to teach veterinary

students and guide practitioners, many of whom I have

been fortunate to interact with at some level of their

careers.

ix

The book is not comprehensive but includes those

drug dosages, techniques, and procedures I feel are per-

tinent to the daily practice of veterinary medicine. Many

of the recommendations and dosages are based on clini-

cal experience, which I hope will complement and

enhance the clinical practice of anesthesia.

J.L.C-S.

x Preface

1

Introduction to Anesthesiaand Patient Preparation

Anesthesia is defined as total loss of sensation in a bodypart or the whole body, induced by a drug or drug com-bination that depresses activity of nervous tissue periph-erally (local and regional anesthesia) or centrally(general anesthesia). Anesthesia and chemical restraintare reversible processes essential to the practice of vet-erinary medicine, providing safe and effective patientimmobilization to minimize stress and pain and facilitatea wide variety of procedures.

1

General Principles of Anesthetic Management

Regardless of species and procedure, these guidelinesshould be applied to all patients:

1. Critical evaluation of history, physical examination,and laboratory data. Know your patient!

2. Weigh the benefits of the procedure against thepotential detrimental effects of anesthesia.

3. Stabilize and correct any identified abnormalities, ifpossible, prior to anesthesia.

4. Be organized to minimize anesthesia time.

5. Identify and prepare for potential complications.

6. Select the anesthetic protocol based on the patientand existing abnormalities.

7. Establish intravenous access whenever possible andfeasible.

8. Secure and maintain a patent airway whenever pos-sible and feasible.

9. Use supplemental oxygen when indicated, based onpatient and duration of procedure.

10. Use a maintenance regimen that will minimizeadverse effects.

11. Provide ventilatory support.

12. Monitor vital body systems, including cardiovascular,respiratory, and central nervous systems.

2 Introduction to Anesthesia and Patient Preparation

13. Identify and correct any abnormalities that arise dur-ing the anesthetic period.

14. Continue monitoring and support until vital signsare stable.

15. Use appropriate analgesia and sedation postopera-tively to minimize pain and distress.

Patient Preparation

“For every mistake that is made for not knowing, a hundred are made for not looking.”

—Anonymous

Patient preparation includes evaluation of the signal-ment, history, and pertinent laboratory data that mightaffect the patient’s response to anesthesia. Patients thencan be categorized according to physical status, whichhelps in the selection of an anesthetic protocol anddetermines the likelihood (risk) for occurrence of a car-diopulmonary emergency during the anesthetic period(Table 1–1).

Physical examination should always include assess-ment of temperature, heart rate, respiratory rate, mucousmembrane color and moistness, pulse quality, thoracicauscultation, and abdominal palpation, even in seem-ingly healthy patients. Normal values for a variety ofspecies are listed in Table 1–2. Minimal laboratory data inphysical status I patients should include packed cell vol-ume (PCV) and total protein for all species (exceptions

Introduction to Anesthesia and Patient Preparation 3

being animals in which venipuncture cannot be per-formed without some level of anesthesia). Blood ureanitrogen (uric acid in avian species) is advised but prob-ably not necessary in most healthy patients. Normalranges of these values for a variety of species are given inTable 1–3. History and physical examination findings


Table 1–1 Classification of Physical Status

Category Physical Status Examples

I Normal healthy Patient presented forpatient elective procedure

II Patient with mild Skin tumor, fracturesystemic disease without shock

III Patient with severe but Fever, dehydration, not incapacitating anemia, cachexia, early systemic disease renal or cardiac disease

IV Patient with severe Uremia, cardiac life-threatening decompensation, systemic disease septicemia, emaciation

V Moribund patient not Profound shock, expected to survive terminal malignancy, with or without severe traumaintervention

E E is added to category to designate that anesthesia is being performed on an emergency basis.

Adapted from the American Society of Anesthesiologists.


Table 1–2 Normal Values for Temperature, Pulse Rate,and Respiratory Rate for Several Veterinary Species

Heart Respiratory Species Temperature ºF Rate/Minute Rate/Minute

Birds

Pet birds* 102–105 120–500 10–75

Raptors 102–104 107–310 12–25

Ratites 99–104 60–190 6–12 (resting, mild ambi-ent tempera-ture)

Cat 100.5–102.5 110–200 15–26

Cow 100.5–102.5 60–80 8–20

Dog 101–103 89–140 8–20

Ferret 100–104 200–400 33–36

Goat 101–103 70–135 12–25

Horse 99.5–101.5 25–50 8–12

Llama 99.5–102 60–80 10–30

Rabbit 101.5–104 130–325 30–60

Sheep 102–104 60–90 15–30

Pig 100–103 60–90 10–30

Pot-belly pig 102–103 70–80 13–18 (80–100: (25–40: neonates) neonates/

juveniles)

*Ranges tend to correlate inversely with the size of the bird.


Tab

le 1

–3

Norm

al (

Aw

ake)

Ran

ges

for

Hem

atocr

it, To

tal Pro

tein

, W

hite B

lood C

ell

Count, a

nd S

ele

cted C

hem

istr

y Val

ues

for

Seve

ral Ve

terinar

y Speci

es

Sp

eci

es

PC

V (

%)

TP

(gm

/dl)

WB

C �

10

3B

UN

(m

g/d

l)

Cre

ati

nin

e (

mg/d

l)

Bird

s* Pet

bird

s35–50

2.5

–5.0

3.0

–12.0

2.3

–14.0

mg/

dl (U

ric a

cid)

Rap

tors

43–49

2.6

5–5.1

4.6

–12

4.5

–14 m

g/dl (U

ric a

cid)

Rat

ites

40–50

2.4

–5.3

8–24

1–14 m

g/dl (U

ric a

cid)

Cat

27–45

6.0

–7.

55.5

–18

15–31

0.7

–1.8

Cow

23–43

6.0

–7.

54–12

7–30

0.6

–1.8

Dog

35–54

5.5

–7.

56.5

–18

6–30

0.5

–1.6

Ferret

48–50

6.0

7.0–9.3

19–27

0.4

–0.5

Goat

22–38

6.1

–7.

44–13

12–25

0.7

–1.5

Hors

e25–48

5.7

–7.

96–12

10–30

0.9

–1.8

Llam

a25–45

4.9

–7.

98–23

9–33

1.1

–3.2

Rab

bit

36–48

5.4

–7.

59–11

17–23

0.8

–1.8

Shee

p30–50

6.3

–7.

14–12

5–26

0.9

–2.0

Pig

30–50

6.0

–8.0

6.5

–20

8–24

0.8

–2.7

Note

: Th

ese

norm

al v

alues

should

be

use

d a

s ge

ner

al g

uid

elin

es, a

s va

riatio

n e

xist

s bet

wee

n r

efer

ence

ran

ges

for

indi-

vidual

labora

torie

s.

*Wid

e va

riatio

n e

xist

s am

ong

avia

n s

pec

ies.

Val

ues

list

ed a

re to b

e use

d o

nly

as

gener

al g

uid

elin

es.

(abnormal organ system function, geriatric patients) willdictate the need for more complete laboratory evalua-tion including a complete blood count; serum chemistrypanel, which should include total CO2 (metabolic acid-base status) and electrolyte concentrations; and urinaly-sis. Unprompted extensive laboratory screening has notbeen found to improve outcome for surgical patients ineither human or veterinary medicine. Further diagnosticevaluation, such as thoracic and abdominal radiographsor ultrasonography, echocardiography, and organ spe-cific evaluation (i.e., bile acid assay) should be based onabnormal physical examination and primary bloodchemistry findings.

Fasting

In general, patients should be fasted for 6–12 hours priorto induction of anesthesia, with water withheld for vari-able periods of time to minimize risk of aspiration andregurgitation and to decrease gastrointestinal volume.There is disparity in the literature regarding length offasting, due largely to personal experience and prefer-ence. Table 1–4 lists recommended fasting times for sev-eral common domestic species. Slightly longer periodsare recommended when prolonged or abdominal sur-geries are to be performed. Very young and very smallpatients should not be fasted due to risk of hypoglycemia.Water withholding is unnecessary in most species with theexception being ruminants and camelids (see Table 1–4).



Table 1–4 Recommended Fasting and Water WithholdingTimes for Several Veterinary Species

WaterSpecies Recommended Fasting Time* Restriction**

Birds

Pet birds 1–3 hr (the smaller the bird, ≤1 hrthe shorter the fast; >300 gms: maximum 10 hr usually is tolerated)

Raptors 6–12 hr (up to 24 hr in large 2 hrraptors)

Ratites 12–24 hr 2 hr

Cat 6–8 hr 6 hr

Cow 24–48 hr 12–24 hr

Dog 6–8 hr 6 hr

Ferret 4–6 hr 2 hr

Goat 12–24 hr 2–8 hr

Horse 6–12 hr Not necessary

Llama 12–24 hr 8 hr

Rabbit† 8 hr Not necessary

Sheep 12–24 hr 2–8 hr

Pig 8–12 hr Not necessary

Note: Fasting times for many species vary in the literature; as a general rule, thelonger the procedure, the longer is the fast.

*Fasting is not recommended for neonates of any species or for very small patientsbecause high metabolic rates and limited glycogen stores cause increased risk fordevelopment of hypoglycemia. Fasting should be abbreviated or omitted in animalswith diseases that can precipitate hypoglycemia, such as insulinoma and diabetesmellitus. (continues)

Record Keeping

Proper patient preparation minimizes but cannot elimi-nate the risk of anesthesia. Thorough record keepingwill encourage vigilant patient monitoring and allow theveterinarian not only to evaluate perianesthetic eventsretrospectively for future reference but to provide rele-vant and documented information should litigationoccur. The anesthetic record should include animalname and case number, owner name, signalment,weight, physical and laboratory examination results,physical status, procedure performed, all anestheticagents (premedications, induction agents, maintenanceagents) administered including dose (in mg) or concen-tration (inhalant agents), route and time of administra-tion, duration of anesthesia, supportive measures (i.e.,fluid type and rate of administration), a chronologicrecording of vital signs, postoperative analgesic agentsadministered, vital signs recorded during recovery andany complications encountered. Figure 1–1 provides anexample of an anesthetic record to facilitate completerecord keeping.


Table 1–4 (Continued)**Water deprivation should be eliminated or abbreviated in patients with significantrenal disease (unless IV fluids are provided to assure normal hydration preopera-tively) or during high ambient environmental temperatures (i.e., ruminants).†While the practice has been recommended in the literature, fasting of rabbits isconsidered unnecessary since this species does not vomit and a prolonged fastcan promote gastrointestinal stasis.

10

Figure 1-1 An example of an anesthetic record, which facili-tates sequential recording of vital signs and summarizes drugsadministered and events occurring during the anesthetic period.

2

Pharmacology and Application of Parenteral Anesthetic Agents

A plethora of injectable agents are available in veterinarypractice to fulfill the need for premedication, induction,maintenance, and postoperative analgesia; to alleviateanxiety and motor activity (chemical restraint); and toprovide profound muscle relaxation (neuromuscularblocking agents) when indicated. While some agents,such as the dissociative drugs, serve multiple roles (pre-medication, induction, and maintenance), parenteraldrugs are summarized according to primary effects andbriefly described in Table 2–1. The “ideal” anestheticagent is described in Table 2–2. Because no drug avail-able today possesses all the “ideal” qualities, anestheticselection is a compromise based on the patient, the

11

procedure, and the available agents, equipment, andexpertise. Inhalation agents come closest to possessingthe majority of qualities described for an “ideal” anes-thetic agent and will be discussed in Chapter 4.

Premedication agents are used to aid in animalrestraint (calming effect), reduce anxiety, provide anal-gesia, provide muscle relaxation, decrease the require-ments for potentially more dangerous drugs used forinduction and maintenance, promote smooth transitionfrom consciousness to unconsciousness and vice versaduring the induction and recovery periods, respectively,and minimize autonomic reflex activity. Induction agentsare used to provide a smooth transition from conscious-ness to unconsciousness, which facilitates intubation andtransition to the maintenance protocol. Some agents usedfor induction also are useful, as repeat boluses or con-stant rate infusion, for maintenance of anesthesia (seeTable 2–1). Other drugs (adjunct agents, Table 2–1)serve a variety of roles including sparing the more car-diorespiratory depressing drugs used for induction andmaintenance and muscle relaxation.

The following alphabetical list (by chemical name)summarizes drugs that might be used in veterinary anes-thesia (MOA is mechanism of action; DOA is duration ofaction, these numbers are only guidelines as DOA isinfluenced significantly by concurrently administereddrugs and individual patient status). Route of adminis-tration for every agent is listed in parentheses after DOAand includes intravenous (IV), intramuscular (IM),

12 Pharmacology and Application of Parenteral Anesthetic Agents

subcutaneous (SC), and per os (PO). In general, theonset of effect occurs within 5 minutes for drugs admin-istered intravenously. When drugs are administeredintramuscularly, onset of effect is in 15 minutes; subcuta-neous administration requires a slightly longer time totake effect (20–30 minutes). Common tradenames(USA; UK* or USA and UK**) for some of the agentshave been listed in parentheses after the chemical name.Drug dosages are listed in Appendix 1 and in those chap-ters discussing protocols for individual animal species.

Drug: Acepromazine (Promace; Acetylpro-mazine*)

Class: Phenothiazine tranquilizer (major)

MOA: Antiadrenergic, anticholinergic, antihist-aminic, antidopaminergic

DOA: Dose dependent; 2–3 hr (prolonged inhepatic-compromised, geriatric, andpediatric patients); (IV, IM, SC, PO)

Effect: Calming effect; decreased motor activity;antiemetic; no analgesia

Adverse: Hypotension, penile paralysis (equine),decreased seizure threshold, prolongedduration with liver disease; anecdotalreports of profound respiratory and car-diovascular depression in Boxers

Approved: Horses, cats, dogs

Pharmacology and Application of Parenteral Anesthetic Agents 13

Drug: Alfentanil (Alfenta; Rapifen*): Schedule II

Class: Opioid agonist

MOA: Activates µ opioid receptors

DOA: <30 minutes; used as constant rate infu-sion; (IV)

Effect: Analgesia, sedation

Adverse: Respiratory depression, bradycardia,excitement in some species

Approved: None; rarely used in veterinary medicine

Drug: Atipamezole (Antisedan)

Class: Alpha2 receptor antagonist

MOA: Blocks alpha1 and alpha2 receptors

DOA: >120 minutes; (IM)

Effect: Reverses effects of alpha2 agonists

Adverse: Excitement, tremors, salivation, vomiting,diarrhea

Approved: Dogs

Drug: Atracurium (Tracrium**)

Class: Competitive nondepolarizing neuromus-cular blocking agent

MOA: Competitive blockade of acetylcholinereceptors at neuromuscular junction

DOA: <30 minutes (undergoes Hofmann elimi-nation: spontaneous nonenzymatic


degradation at body pH; also metabo-lized by esterases); (IV)

Effect: Reversible skeletal muscle relaxation

Adverse: Respiratory paralysis (must support respi-ration), minimal cardiovascular effects,may cause histamine release

Approved: None

Drug: Atropine

Class: Anticholinergic

MOA: Competitive blockade of muscarinicreceptors

DOA: 60–90 min (some species variation); (IV,IM, SC)

Effect: Parasympatholytic: increased heart rate,decreased salivation/secretions, dilatedpupils; gastrointestinal stasis, increasesphysiologic dead space (bronchodilation)

Adverse: Tachycardia, arrhythmias, colic (equine)

Approved: Dogs, cats, cattle, horses, sheep

Drug: Azaperone (Stresnil**)

Class: Butyrophenone tranquilizer (major)

MOA: Antiadrenergic, anticholinergic, antihist-aminic, antidopaminergic

DOA: 2–4 hr; (IV, IM)


Effect: Calming effect; decreased motor activity;antiemetic; no analgesia

Adverse: Extrapyramidal effects (tremors, rigidity)are more common compared to acepro-mazine; personality change possible;hypotension

Approved: Swine

Drug: Bupivacaine (Marcaine**): 0.5%

Class: Local anesthetic agent (amide)

MOA: Blocks nerve transmission by blocking Nachannel and preventing excitation-conduction process

DOA: 4–6 hr; (epidural, local infiltration)

Effect: Reversible prevention of nerve transmis-sion; thus motor, sensory, and autonomicfunction is temporarily inhibited

Adverse: CNS excitation, seizures, respiratoryparalysis, hypotension, hypothermia, ven-tricular arrhythmias

Approved: None

Drug: Buprenorphine (Buprenex; Temgesic*;Vetergesic*): Schedule V

Class: Opioid partial agonist

MOA: Activates opioid receptors in brain andspinal cord


DOA: 6–12 hr; (IV, IM, SC)

Effect: Analgesia; minimal sedation

Adverse: Respiratory depression (less than withpure opioid agonists), bradycardia, flatu-lence, defecation, hypothermia; may bemore difficult to reverse due to highreceptor affinity

Approved: None

Drug: Butorphanol (Torbugesic**; Torbutrol**): Schedule IV

Class: Opioid agonist/antagonist

MOA: Activates (�) and blocks (µ) opioidreceptors in brain and spinal cord

DOA: 1–2 hr; (IV, IM, SC, PO)


Adverse: Respiratory depression (less than withpure opioids), bradycardia, flatulence,defecation, hypothermia

Approved: Horses, dogs

Drug: Carfentanil (Wildnil): Schedule II(requires DEA special user’s permit)


MOA: Activates opioid µ receptors

DOA: Prolonged if not reversed; (IM)


Effect: Analgesia, sedation, immobilization

Adverse: Hypoventilation, excitement (somespecies), hypothermia, muscle fascicula-tions

Approved: Animal use only, reserved for use inimmobilization of wildlife and exoticspecies

Drug: Chloral hydrate: Schedule IV

Class: Sedative-hypnotic

MOA: CNS depression is due to active metabolites

DOA: Dose dependent: <2 hr for sedativedosages; (IV, PO)

Effect: Sedation at low doses; general anestheticat high doses; poor analgesic effects

Adverse: Minimal at sedative dosages; anestheticdoses have high incidence of cardiopul-monary arrest

Approved: None; once available in combinationwith pentobarbital and magnesium sul-fate for use in large animals

Drug: cis-Atracurium (Nimbex)

Class: Competitive nondepolarizing neuromus-cular blocking agent


MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction

DOA: <20–30 min (undergoes Hofmann elimi-nation: spontaneous nonenzymaticdegradation at body pH); (IV)


Adverse: Respiratory paralysis (must control respi-ration), minimal cardiovascular effects

Approved: None

Drug: Desflurane (Suprane)

Class: Methyl ether inhalation agent

MOA: Reversible depression of central nervoussystem

DOA: Not applicable

Effect: Unconsciousness, analgesia, musclerelaxation

Adverse: Dose-dependent cardiopulmonarydepression (slightly less than otherinhalation agents at equivalent MAC con-centrations)

Approved: None

Drug: Detomidine (Dormosedan)

Class: Alpha2 agonist

MOA: Activates CNS alpha2 receptors, whichinhibit neurotransmitter release in brain


DOA: Dose dependent; 75–120 min; (IV, IM)

Effect: Sedation, analgesia, muscle relaxation

Adverse: Bradycardia, conduction disturbances,hypotension, respiratory depression,hypoxia

Approved: Horses

Drug: Diazepam (Valium**): Schedule IV

Class: Benzodiazepine tranquilizer (minor)

MOA: Activates CNS benzodiazepine receptors,which increase inhibitory neurotransmit-ters (i.e., GABA, glycine)

DOA: <3 hr; (IV, IM, PO)

Effect: Mild sedation, muscle relaxation,enhances effect of concurrently usedagents

Adverse: Excitement in some species (horses,dogs), hepatoxicity has been reportedwith PO administration in cats

Approved: Dog

Drug: Diprenorphine (Revivon*, M50-50)


MOA: Blocks opioid receptors

DOA: Short (renarcotization following reversalof potent opioids has been reported);(IV, IM)


Effect: Used to antagonize etorphine

Adverse: Opioid sedation and respiratory depres-sion may persist with overdose

Approved: Animal use only, for reversal of etorphinein wildlife and exotic species

Drug: Edrophonium (Tensilon)

Class: Acetylcholinesterase inhibitor

MOA: Inhibits acetylcholinesterase and allowsaccumulation of ACh, enhances AChrelease, induces repetitive firing of themotor nerve terminal

DOA: Onset of action is rapid (1–2 min); dura-tion relatively short; (IV)

Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission

Adverse: Parasympathetic stimulation: bradycar-dia, airway constriction, increased secretions

Approved: None

Drug: Enflurane (Ethrane**): an isomer of isoflurane

Class: Methyl ether: inhalation agent



DOA: Not applicable

Effect: Unconsciousness, muscle relaxation

Adverse: Dose-dependent cardiac and respiratorydepression

Approved: None

Drug: Etomidate (Amidate; Hypnomidate*)

Class: Imidazole

MOA: Nonbarbiturate sedative-hypnotic

DOA: <10 min; (IV)

Effect: Rapid loss of consciousness of short dura-tion, minimal cardiopulmonary depres-sion

Adverse: Pain on injection, myoclonus, vomiting(minimized with premedication); depres-sion of adrenal function

Approved: None

Drug: Etorphine (M-99): Schedule II



DOA: <2 hr; (IV, IM)

Effect: Sedation, analgesia, immobilization,80–1,000 times as potent as morphine

Adverse: Profound respiratory depression, brady-cardia, hypertension


Approved: Animal use only: exotic animal immobi-lization

Drug: Fentanyl (Sublimaze**): Schedule II



DOA: <1 hr; used as constant rate infusion (IV)or transdermal patch

Effect: Analgesia, sedation, 75–125 times aspotent as morphine


Approved: None

Drug: Flumazenil (Romazicon)

Class: Benzodiazepine receptor antagonist

MOA: Competes with benzodiazepines forreceptor

DOA: 2–3 hr; (IV)

Effect: Specific reversal of benzodiazepine tran-quilizers

Adverse: Rare

Approved: None

Drug: Gallamine (Flaxedil**): currently notavailable commercially


Class: Nondepolarizing neuromuscular blocker

MOA: Competitive blockade of acetylcholinereceptors of neuromuscular junction;prevents muscle contraction

DOA: <30 min; (IV)


Adverse: Respiratory paralysis, tachycardia, hyper-tension

Approved: None (has been used in reptiles forimmobilization)

Drug: Glycopyrrolate (Robinul)

Class: Anticholinergic

MOA: Blocks effect of acetylcholine at mus-carinic receptors


Effect: Parasympatholytic: increased heart rate,decreased respiratory secretions,increases physiologic dead space (bron-chodilation), does not cross placental orblood-brain barrier

Adverse: Ileus, sinus tachycardia

Approved: Dog, cat

Drug: Guaifenesin (Guailaxin; Glycerol guaiacolate)

Class: Central-acting muscle relaxant


MOA: Depresses internuncial neuron transmis-sion; central-acting muscle relaxant

DOA: Dose dependent; 30 min; (IV)

Effect: Muscle relaxation, sedation

Adverse: Very safe although overdose can occur,which manifests as forelimb rigidity fol-lowed by respiratory paralysis

Approved: Horses

Drug: Halothane (Fluothane**)

Class: Fluorinated hydrocarbon inhalationanesthetic


DOA: Not applicable


Adverse: Dose-dependent cardiopulmonarydepression, ventricular arrhythmias

Approved: Dogs, cats, nonfood animals

Drug: Isoflurane (Aerrane, Isoflo; Forane**)

Class: Methyl ether inhalation anesthetic


DOA: Not applicable



Adverse: Dose-dependent cardiopulmonarydepression (relatively less thanhalothane)


Drug: Ketamine (Ketaset; Ketalar*; Vetalar**)

Class: Dissociative agent

MOA: Depresses thalamoneocortical system;activates limbic system; analgesic effectsare associated with opioid (agonist) andN-methyl-D-aspartate receptor (antago-nist) interaction

DOA: Dose and species dependent; 15–60 min;(IV, IM)

Effect: Catalepsy, superficial analgesia, poorvisual analgesia, amnesia, immobility

Adverse: Muscle rigidity, seizures, increased secre-tions, negative inotropic agent but central catecholamine release causesincreased ABP and HR, increased ocularand intracranial pressure

Approved: Cats, primates

Drug: Lidocaine (Xylocaine**): 2.0%


MOA: Blocks sodium influx and thus preventsnerve depolarization and conduction


DOA: 90–200 min; (epidural, local infiltration)

Effect: Blocks pain, motor, and sympatheticfibers; also used IV to treat ventriculararrhythmias

Adverse: Hypotension due to vasodilation; respira-tory arrest is possible when given epidu-rally; seizures at high doses

Approved: None

Drug: Medetomidine (Dormitor)



DOA: Dose and species dependent; 60–120min; (IV, IM, SC)



Approved: Dogs

Drug: Meperidine (Demerol; Pethidine*):Schedule II


MOA: Activates µ receptors in CNS and otherorgans


DOA: <2 hr; (IM, SC)

Effect: Analgesia, sedation, increases venouscapacitance

Adverse: Respiratory depression, flatulence, con-stipation, bradycardia, can cause hista-mine release with rapid IV injection,excitement possible in cats, horses

Approved: None

Drug: Mepivicaine (Carbocaine-V): 1–2%



DOA: 120–240 min; (epidural, local infiltration)

Effect: Blocks pain, motor and sympatheticfibers

Adverse: Hypotension due to vasodilation and res-piratory arrest are possible when givenepidurally; seizures and cardiotoxicitywith overdose

Approved: None

Drug: Methohexital (Brevital; Brevane; Brietal*): Schedule IV

Class: Ultrashort-acting oxybarbiturate

MOA: Sedative-hypnotic; CNS depression byaction on barbiturate receptors


DOA: <15 min; (IV)

Effect: Sedation to unconsciousness (dosedependent)

Adverse: Respiratory depression (apnea), myocar-dial depression, excitement, muscletremors, seizures during recovery

Approved: None

Drug: Methoxyflurane (Metofane**;Penthrane)

Class: Methyl ether inhalation anesthetic


DOA: Not applicable

Effect: Unconsciousness, analgesia, musclerelaxation

Adverse: Dose-dependent cardiopulmonarydepression; prolonged recovery; renal toxi-city due to metabolites

Approved: Small and large animals, birds

Drug: Midazolam (Versed; Hypnovel*): Schedule IV

Class: Benzodiazepine tranquilizer (minor)

MOA: Activates CNS benzodiazepine receptors,which increase inhibitory neurotransmit-tors (i.e., GABA, glycine)


DOA: <2 hr (duration is slightly less thandiazepam); (IV, IM, SC)

Effect: Mild sedation, muscle relaxation; workswell IV or IM

Adverse: Excitement in some species, respiratorydepression

Approved: None

Drug: Morphine (Duromorph**): Schedule II


MOA: Activates µ opioid receptors in CNS andother organs

DOA: 4 hr; (IM, SC, PO)

Effect: Analgesia, sedation, alleviates pulmonaryedema by increasing venous capacitance;provides 10–24 hr of analgesia as far for-ward as the thoracic limbs when adminis-tered epidurally.

Adverse: Respiratory depression, flatulence, con-stipation, histamine release with IVadministration; excitement possible inhorses and cats

Approved: None

Drug: Nalbuphine (Nubain)



MOA: Antagonizes µ receptor, activates kappareceptors



Adverse: Minimal respiratory depression

Approved: None

Drug: Nalmefene (Revex)

Class: Opioid antagonist

MOA: Antagonizes all opioid receptors

DOA: Longer acting than naloxone; (IV, IM,SC)

Effect: Reverses effects of opioid agonists,including respiratory depression andanalgesia

Adverse: Stimulates sympathetic nervous system;potential for cardiac arrhythmias

Approved: None

Drug: Naloxone (Narcan**)



DOA: 30–45 min; (IV, IM, SC)

Effect: Reverses the effects of opioid agonists,including respiratory depression and


analgesia; has been used in the treatmentof hemorrhagic shock

Adverse: Stimulates sympathetic nervous system:potential for cardiac arrhythmias

Approved: None

Drug: Naltrexone (Trexonil)



DOA: Longer acting than naloxone; (IV, IM,SC)

Effect: Reverses the effects of opioid agonists,including respiratory depression andanalgesia; available as an oral prepara-tion for humans

Adverse: Stimulates sympathetic nervous system:potential for cardiac arrhythmias

Approved: Used for reversal of carfentanil in exoticspecies

Drug: Neostigmine (Prostigmine; Stiglyn)


MOA: Inhibits acetylcholinesterase and allowsaccumulation of ACh, enhances AChrelease, induces repetitive firing of themotor nerve terminal


DOA: Onset of action is 7–10 min; duration ofaction is relatively short; (IV)

Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission, onset of action is rapid

Adverse: Parasympathetic stimulation includingbradycardia, airway constriction,increased secretions

Approved: None

Drug: Oxymorphone (Numorphan):Schedule II


MOA: Activates µ receptors




Approved: Dogs, cats

Drug: Pancuronium (Pavulon**)

Class: Competitive nondepolarizing neuromus-cular blocker

DOA: 30–45 min; (IV)



Effect: Reversible skeletal muscle paralysis

Adverse: Respiratory paralysis (must control venti-lation), minimal cardiovascular effectsalthough may cause transient tachycar-dia; prolonged effect in renal- andhepatic-compromised patients

Approved: None

Drug: Pentazocine (Talwin): Schedule IV


MOA: Activates (�) and blocks (µ) opioidreceptors in brain and spinal cord: lowpotency

DOA: <2 hr; (IM, SC)

Effect: Analgesia, sedation; 0.1–0.3 timespotency of morphine

Adverse: Respiratory depression (less than withpure opioids), bradycardia, flatulence,defecation, hypothermia


Drug: Pentobarbital (Nembutal; Beuthanasia-D): Schedule II

Class: Short-acting oxybarbiturate

MOA: Sedative-hypnotic; CNS depression byaction on barbiturate receptors


DOA: Species and dose dependent; <1.5 hr;(IV, PO)

Effect: Sedation to unconsciousness

Adverse: CNS/respiratory depression (apnea),myocardial depression, leukopenia,splenic engorgement, excitement (stageII) due to inadequate quantity or rate ofdosing

Approved: Dogs

Drug: Phenobarbital: Schedule IV

Class: Long-acting oxybarbiturate; routesinclude IV and PO

MOA: Sedative/hypnotic; CNS depression byaction on barbiturate receptors

DOA: Dose dependent; 12–24 hr; (IV, PO)

Effect: Sedation to unconsciousness (dosedependent); used to control seizures: (16mg/kg IV, 2–4 mg/kg PO BID (small ani-mal); 2–10 mg/kg IV/PO every 8–12 hr(equine)

Adverse: CNS/respiratory depression (apnea),myocardial depression, polyuria/polydip-sia/polyphagia

Approved: None


Drug: Procaine (Novocaine)

Class: Local anesthetic (ester linked)


DOA: 60–90 min; (local infiltration)

Effect: Blocks pain, motor, and sympatheticfibers

Adverse: May cause allergic reaction

Approved: None

Drug: Propofol (Rapinovet**)

Class: Alkyl phenol structure

MOA: Sedative/hypnotic: CNS depression byenhancing GABA activity in the brainand decreasing cerebral metabolic rate

DOA: <15 min; (IV)

Effect: Sedation to unconsciousness dependingon dosage; muscle relaxation

Adverse: Respiratory depression (apnea) especiallyif administered rapidly, myocardialdepression, hypotension, Heinz body for-mation (oxidative injury) in cats whengiven repeatedly due to phenolic struc-ture

Approved: Dogs


Drug: Pyridostigmine (Regonol)


MOA: Inhibit acetylcholinesterase and allowaccumulation of ACh, enhance AChrelease, induce repetitive firing of themotor nerve terminal

DOA: Onset of action is 12–16 min and dura-tion 40% longer than neostigmine andedrophonium; (IV)

Effect: Antagonize nondepolarizing neuromus-cular blockers to restore neuromusculartransmission

Adverse: Parasympathetic stimulation, includingbradycardia, airway constriction,increased secretions

Approved: None

Drug: Romifidine (Sedivet*)



DOA: Dose dependent; >120 min; (IV, IM, SC)




Approved: Not currently approved in the UnitedStates, but studies have been publishedfor dosages in dogs and horses

Drug: Sevoflurane (Ultrane)

Class: Methyl ether inhalation agent


DOA: Not applicable


Adverse: Dose-dependent cardiopulmonarydepression (similar to isoflurane)

Approved: None

Drug: Succinylcholine (Anectine**; Sucostrin;Scoline*)

Class: Depolarizing noncompetitive neuromus-cular blocker

MOA: Depolarizes nicotinic receptors on mus-cle motor end plate and prevents neuro-muscular transmission.

DOA: <15 min; (IV)

Effect: Nonreversible (short-duration) skeletalmuscle paralysis

Adverse: Respiratory paralysis (necessary equip-ment to provide mechanical ventilationshould be available if this drug is used);


prolonged effect with hepatic-compromising diseases due to depend-ency on metabolism by the liver-derivedenzyme, pseudocholinesterase; muscle fasciculations; hyperkalemia; known trigger of malignant hyperthermia

Approved: None

Drug: Sufentanil (Sufenta): Schedule II



DOA: <1 hr; used as constant rate infusion;(IV)


Adverse: Respiratory depression, bradycardia,muscle twitching

Approved: None; rarely used in veterinary medicine

Drug: Thiopental (Pentothal; Intraval*):Schedule III

Class: Ultrashort-acting thiobarbiturate

MOA: Sedative/hypnotic; CNS depression byaction on barbiturate receptors

DOA: <15 min; (IV)

Effect: Sedation to unconsciousness (dosedependent), stage II delerium can occurwith inadequate or perivascular dosages


Adverse: Respiratory depression (apnea), myocar-dial depression, cardiac arrhythmias

Approved: Dogs

Drug: Tiletamine; Zolazepam (Telazol):Schedule III

Class: Dissociative agent combined with benzo-diazepine

MOA: Tiletamine: depresses thalamoneocorticalsystem; activates limbic system; analgesiceffects are associated with opioid (ago-nist) and N-methyl-D-aspartate receptor(antagonist) interaction; zolazepam actson benzodiazepine receptors

DOA: Dose and species dependent; 20–80 min;(IM, IV)

Effect: Catalepsy, superficial analgesia, amnesia,immobility, muscle relaxation

Adverse: Increased secretions, muscle rigidity insome species, negative inotrope but cen-tral catecholamine release promotesincreased BP and HR, increased ocularand intracranial pressure

Approved: Cats, dogs

Drug: Tolazoline (Tolazine)

Class: Alpha1 and alpha2 receptor antagonist


MOA: Occupies and antagonizes alpha2 recep-tors (least specific for the alpha2 recep-tor)

DOA: 2 hr; (IV, IM)


Adverse: Hypotension with rapid injection due tovasodilatory effect, excitement, tremors,salivation, tachypnea

Approved: Horses

Drug: Tubocurarine (Curare)



DOA: <30 min; (IV)


Adverse: Respiratory paralysis (must control respi-ration), causes histamine release thatresults in hypotension and bronchocon-striction

Approved: None

Drug: Vecuronium (Norcuron)




DOA: <30 min; (IV)


Adverse: Respiratory paralysis (must control respi-ration), minimal cardiovascular effects;significant hepatic dysfunction will pro-long effect

Approved: None

Drug: Xylazine (Rompun**; Ansed)



DOA: Dose and species dependent; 15–30 min(analgesia); 1–2 hr (sedation); (IV, IM,SC)



Approved: Horses (10% formulation); dogs and cats(2% formulation); deer and elk


Drug: Yohimbine (Yobine)

Class: Alpha2 antagonist

MOA: Blocks alpha2 receptors; also has antisero-tonin activity

DOA: <1 hr; (IV, IM)


Adverse: Hypotension with rapid injection due tovasodilatory effect, excitement, tremors,salivation, tachypnea

Approved: Dogs


Tab

le 2

–1

Cat

ego

ries

and M

ajor

Effect

s of

Inje

ctab

le A

nest

hetic

Age

nts

Use

d in

Vete

rinar

y M

edic

ine (

text

has

speci

fic

agent

info

rmat

ion)

Use

/Cate

go

ryEff

ect

s/C

om

men

ts

Pre

med

icati

on

s

Antic

holin

ergic

sD

ecre

ase

secr

etio

ns,

pre

vent

bra

dyc

ardia

Atropin

e

Gly

copyr

rola

te

Tranquili

zers

Alle

viat

e an

xiet

y an

d d

ecre

ase

moto

r ac

tivity

; pro

vide

no

anal

gesi

a, s

yner

gize

act

ivity

of

oth

er a

gents

; pro

mote

m

usc

le r

elax

atio

n

Maj

or

tran

quili

zers

:

Ace

pro

maz

ine

Use

is

rela

tivel

y co

mm

on in a

ll sp

ecie

s(p

hen

oth

iazi

ne)

Aza

per

one

Use

is

pre

dom

inan

tly in s

win

e an

d s

om

e ex

otic

spec

ies

(buty

rophen

one)

Min

or

tran

quili

zers

:

Dia

zepam

M

inim

al s

edat

ion u

nle

ss c

om

bin

ed w

ith o

pio

id o

r al

pha 2

(ben

zodia

zepin

e)ag

onis

t

Mid

azola

m

More

rap

id o

nse

t of

effe

ct a

nd n

ot

pai

nfu

l w

hen

giv

en IM

or


(ben

zodia

zepin

e)SC

(co

mpar

ed t

o d

iaze

pam

, w

hic

h is

reco

mm

ended

for

IVuse

only

)

Ben

zodia

zepin

eSp

ecifi

c re

vers

al a

gent

for

ben

zodia

zepin

esanta

gonis

t

Flum

azen

il

Alp

ha

2ag

onis

tsPro

vide

anal

gesi

a, s

edat

ion, an

d m

usc

le r

elax

atio

n; ca

rdio

vas-

cula

r ef

fect

s ar

e pro

found (

conduct

ion d

istu

rban

ces,

hyp

ote

nsi

on)

but

usu

ally

wel

l-tole

rate

d in h

ealth

y pat

ients

;si

gnifi

cant

spar

ing

effe

ct w

hen

use

d p

rior

to inhal

ant

anes

-th

esia

Xyla

zine

Short

est

dura

tion o

f ef

fect

; �

2:�

1se

lect

ivity

bin

din

g ra

tio

= 1

60

Det

om

idin

eLo

nge

st d

ura

tion o

f ef

fect

; �

2:�

1se

lect

ivity

bin

din

g ra

tio =

260

Med

etom

idin

eG

reat

est

�2:�

1se

lect

ivity

bin

din

g ra

tio =

1620

Rom

ifidin

eN

ot

curren

tly a

ppro

ved f

or

use

in U

nite

d S

tate

s; �

2:�

1

sele

ctiv

ity b

indin

g ra

tio =

340

Alp

ha

2an

tago

nis

tsSp

ecifi

c re

vers

al a

gents

for

alpha 2

agonis

ts; m

ay p

rom

ote

hyp

ote

nsi

on t

hro

ugh

vas

odila

tory

effec

ts e

spec

ially

when

adm

inis

tere

d r

apid

ly IV

Yohim

bin

e�

2:�

1se

lect

ivity

bin

din

g ra

tio =

40

(contin

ues

)


Tab

le 2

–1

(Continued)

Use

/Cate

go

ryEff

ect

s/C

om

men

ts

Tola

zolin

eN

onsp

ecifi

c an

tago

nis

t of

�1

and �

2re

cepto

rs

Atip

amez

ole

�2:�

1se

lect

ivity

bin

din

g ra

tio =

8526

Opio

ids

Pro

vide

anal

gesi

a an

d s

edat

ion (

deg

ree

of

effe

cts

vary

with

ag

ent)

; use

d f

or

pre

emptiv

e an

d p

ost

oper

ativ

e an

alge

sia.

(Anal

gesi

c pote

nci

es r

elat

ive

to m

orp

hin

e [1

] ar

e lis

ted in

par

enth

eses

for

each

age

nt.)

Opio

id (

µ)

agonis

ts:

Maj

or

side

effe

ct is

resp

irato

ry d

epre

ssio

n; gr

eate

st p

ote

ntia

l fo

r ab

use

Morp

hin

e(1

)

Mep

erid

ine

(0.5

)

Hyd

rom

orp

hone

(5)

Oxy

morp

hone

(8–10)

Fenta

nyl

(75–125)

Alfe

nta

nil

(20–75)

Sufe

nta

nil

(600–1000)

Car

fenta

nil

(10,0

00)

Etorp

hin

e(8

0–1000)


Part

ial µ

agonis

t:Le

ss r

espira

tory

dep

ress

ion

Bupre

norp

hin

e(2

5–50)

Opio

id a

gonis

t (�

)/Le

ss r

espira

tory

dep

ress

ion c

om

par

ed t

o µ

agonis

tsan

tago

nis

ts (

µ):

Buto

rphan

ol

Com

monly

use

d in v

eter

inar

y m

edic

ine;

moder

ate

anal

gesi

a;

may

be

use

d t

o r

ever

se µ

agonis

ts; (2

–5)

Nal

buphin

eN

ot

sched

ule

d b

ut

min

imal

ly e

ffec

tive

as a

n a

nal

gesi

c ag

ent;

may

be

use

d t

o r

ever

se µ

agonis

ts; (0

.5)

Penta

zoci

ne

(0.1

)

Nal

orp

hin

eU

sed f

or

anta

gonis

t ef

fect

, ra

rely

use

d c

linic

ally

Dip

renorp

hin

eU

sed f

or

anta

gonis

t ef

fect

; sh

ort

dura

tion o

f ac

tion m

ay a

llow

”r

enar

cotiz

atio

n“

afte

r re

vers

al

Opio

id a

nta

gonis

ts:

Use

d “

to e

ffec

t” t

o r

ever

se o

pio

id a

gonis

ts a

nd a

gonis

t/an

tago

nis

ts

Nal

oxo

ne

Short d

ura

tion o

f ac

tion m

ay a

llow

“re

nar

cotiz

atio

n”

afte

r re

vers

al

Nal

trex

one

Nal

mef

ene

Dis

soci

ativ

e agen

tsD

ose

-dep

enden

t ef

fect

pro

vides

quie

ting

and im

mobili

zatio

n

at low

dose

s an

d g

ener

al a

nes

thes

ia a

t hig

her

dosa

ges,

som

atic

anal

gesi

a; p

oor

visc

eral

anal

gesi

a(c

ontin

ues

)


Tab

le 2

–1

(Continued)

Use

/Cate

go

ryEff

ect

s/C

om

men

ts

Ket

amin

e

Tile

tam

ine

(Tel

azol™

)C

om

mer

cial

pro

duct

com

bin

ed w

ith z

ola

zepam

in 1

:1 (

mg)

rat

io

Chlo

ral hyd

rate

Sedat

ive/

hyp

notic

: use

d f

or

larg

e an

imal

sed

atio

n; no longe

r use

d a

s la

rge

anim

al g

ener

al a

nes

thet

ic d

ue

to n

arro

wsa

fety

mar

gin a

nd p

rolo

nge

d r

ecove

ries;

effec

tive

IV, PO

,re

ctal

ly

Ind

uct

ion

/main

ten

an

ce a

gen

ts

Barb

ituate

sSh

ort a

nd u

ltras

hort-a

ctin

g; h

igh p

H m

akes

them

irrita

ting

to

tissu

es

Pento

bar

bita

lSh

ort-a

ctin

g oxy

bar

bitu

rate

; re

cove

ry >

6–24 h

r; r

arel

y use

d f

or

clin

ical

anes

thes

ia d

ue

to a

vaila

bili

ty o

f ag

ents

with

shorter

dura

tion o

f ef

fect

Met

hohex

ital

Ultr

ashort-a

ctin

g oxy

bar

bitu

rate

(ra

pid

ly m

etab

oliz

ed);

not

com

monly

use

d

Thio

pen

tal

Ultr

ashort-a

ctin

g th

iobar

bitu

rate

(ra

pid

ly r

edis

trib

ute

d):

ris

k of

rough

, pro

longe

d r

ecove

ry if

use

d a

s re

pea

ted b

olu

s or

inpre

sence

of

hep

atic

dis

ease

; co

mm

on u

se in v

eter

inar

ypra

ctic

e


Dis

soci

ativ

e agen

tsSe

e ea

rlier

; w

hile

met

abolis

m is

rela

tivel

y ra

pid

, re

pea

t dosa

ges

of

dis

soci

ativ

es w

ill c

ontrib

ute

to r

ough

, pro

longe

dre

cove

ries

(esp

ecia

lly t

ileta

min

e)

Pro

pofo

lPro

duce

s ra

pid

loss

of

consc

iousn

ess;

rec

ove

ry is

fast

due

to

rapid

met

abolis

m, m

akin

g it

use

ful fo

r in

duct

ion a

nd

mai

n-

tenan

ce

Etom

idat

ePro

duce

s ra

pid

loss

of

consc

iousn

ess;

rec

ove

ry is

fast

due

to

rapid

met

abolis

m, m

akin

g it

use

ful fo

r in

duct

ion a

nd

mai

n-

tenan

ce

Ad

jun

ct a

gen

ts

Gly

cery

l gu

aiac

ola

te

Cen

tral

-act

ing

musc

le r

elax

ant

use

d in lar

ge a

nim

als

to r

educe

(g

uai

fenes

in)

require

men

ts o

f in

duct

ion a

nd m

ainte

nan

ce a

gents

; 5 a

nd

10%

(hors

es o

nly

) so

lutio

ns—

10%

solu

tion c

ause

s hem

ol-

ysis

in s

pec

ies

oth

er t

han h

ors

es

Neu

rom

usc

ula

r Act

at

neu

rom

usc

ula

r ju

nct

ion t

o b

lock

neu

rotran

smis

sion,

blo

ckin

g a

gen

tsre

sulti

ng

in m

usc

le p

aral

ysis

; ve

ntil

atory

support is

require

d;

use

ful ad

junct

for

ocu

lar,

orthoped

ic, an

d a

bdom

inal

pro

ce-

dure

s an

d f

or

pat

ients

that

res

ist

mec

han

ical

ven

tilat

ion;

spar

ing

effe

ct o

n c

oncu

rren

tly u

sed d

rugs

; no inher

ent

analg

esic

effec

ts

(contin

ues

)


Tab

le 2

–1

(Continued)

Use

/Cate

go

ryEff

ect

s/C

om

men

ts

Nondep

ola

rizin

g C

om

pet

itive

(re

vers

ible

) in

terfer

ence

with

ace

tylc

holin

e at

co

mpet

itive

post

synap

tic m

usc

le m

embra

ne;

man

y ag

ents

curren

tly

agen

ts:

avai

lable

with

var

iable

dura

tion o

f ac

tion, ca

rdio

vasc

ula

r

effe

cts,

abili

ty t

o induce

his

tam

ine

rele

ase,

dura

tion a

nd

onse

t of

effe

ct a

nd c

ost

(te

xt d

escr

iptio

ns

are

give

n o

nly

for

those

with

curren

t or

his

toric

al, an

d r

elat

ivel

y co

mm

on, use

in v

eter

inar

y m

edic

ine)

Turb

ocu

rarin

eU

se is

larg

ely

rese

rved

for

rese

arch

Gal

lam

ine

Use

is

larg

ely

rese

rved

for

rese

arch

and s

om

e ex

otic

spec

ies

Pancu

roniu

mRel

ativ

ely

long

dura

tion o

f ef

fect

Vecu

roniu

mIn

term

edia

te d

ura

tion o

f ef

fect

Atrac

uriu

mSh

ort

dura

tion o

f ef

fect

cis-

Atrac

uriu

mSh

ort

dura

tion o

f ef

fect

Miv

acuriu

mSh

ort

dura

tion o

f ef

fect

Rocu

roniu

mIn

term

edia

te d

ura

tion o

f ef

fect

Doxa

curiu

mRel

ativ

ely

long

dura

tion o

f ef

fect


Dep

ola

rizin

g N

onre

vers

ible

dep

ola

rizat

ion o

f post

synap

tic m

usc

le m

embra

ne

nonco

mpet

itive

ag

ents

:

Succ

inyl

cholin

eU

ltras

hort

act

ing,

rap

id o

nse

t; si

de

effe

cts

pre

clude

routin

e use

Ace

tylc

holin

este

rase

Rev

erse

com

pet

itive

NM

Bs

by

allo

win

g ac

etyl

cholin

e to

acc

u-

inhib

itors

:m

ula

te a

t sy

nap

tic c

left a

nd r

esto

re n

orm

al m

usc

le f

unct

ion;

side

effe

cts

are

asso

ciat

ed w

ith s

timula

tion o

f m

usc

arin

icre

cepto

rs a

nd p

reve

nte

d b

y prio

r ad

min

istrat

ion o

f an

anti-

cholin

ergi

c ag

ent

Edro

phoniu

m

Neo

stig

min

e

Pyr

idost

igm

ine


Table 2–2 Properties of an “Ideal” Anesthetic Agent

1. Does not require metabolism for termination of action andelimination (reversible or respiratory elimination).

2. Permits rapid and easily controlled induction, changes inanesthetic depth and recovery.

3. Is not irritating to any tissue.

4. Does not depress cardiopulmonary function.

5. Produces adequate muscle relaxation and analgesia for sur-gical procedures.

6. Is compatible with other drugs.

7. Is nontoxic to the patient and humans.

8. Is inexpensive, stable, and noninflammable.

9. Requires no special equipment for administration.


3

Local/Regional Anesthetic Techniques

Local and regional anesthesia always has been an inte-gral part of large animal practice for economic and prac-tical reasons. The availability and convenience of avariety of general anesthesia options minimized the needto apply these agents in small animals. However, with theever-increasing awareness of pain management in all vet-erinary species, local and regional techniques are gain-ing popularity in small animal practice. Application oflocal and regional agents in animals undergoing generalanesthesia will provide preemptive analgesia and spareanesthetic requirements. While historically such tech-niques have been associated with the local anestheticagents, other drugs, including opioids, alpha2 agonists,and ketamine have been reported to possess analgesic

53

properties when applied by these routes. This chapterdiscusses mainly the application of local anestheticagents used to produce local and regional anesthesia(complete loss of sensation to a body part or region) butalso includes dosage and application of the alpha2 ago-nists. Clinical application of opioids to produce regionalanalgesia (loss of sensitivity to pain) is discussed in Chap-ter 8 (“Pain Management”).

Local anesthetic agents reversibly block actionpotentials along nerve axons by interference with volt-age-gated sodium channels. Two classes (based on theintermediate chain of the molecule), the esters and theamides (Table 3–1), determine drug biotransformation.Esters are readily hydrolyzed in the blood by plasmacholinesterase made in the liver, while amides requirebiotransformation by liver microsomal enzymes. Eventhough lidocaine is well-known for its usefulness intra-venously to treat cardiac ventricular arrhythmias, it andlocal anesthetic agents have several potential adverseeffects, including formation of cardiac arrhythmias(Table 3–2). These adverse effects are minimized whenaccidental intravenous injection is avoided and dosagesremain within recommended maximum safe limits.

The time to effect, potency, and duration of effectdepend on the agent’s physical and chemical properties(see Table 3–1). Lipid solubility influences intrinsicpotency and protein binding is probably the primarydeterminant of duration. The dissociation constant(pKa) is thought to determine the speed of action. The

54 Local/Regional Anesthetic Techniques

Local/Regional Anesthetic Techniques 55

Tab

le 3

–1

Pro

pert

ies

of

Sele

cted L

oca

l A

nest

hetic

Age

nts

Use

d in V

ete

rinar

y M

edic

ine

Agen

tLip

id

pK

aP

rote

in

On

set

of

Du

rati

on

(T

rad

e N

am

e)

Cla

ssP

ote

ncy

*So

lub

ilit

yB

ind

ing

Eff

ect

(min

)

Pro

cain

eEs

ter

—1

8.9

6%

Slow

60–90

(Novo

cain

e)

Chlo

ropro

cain

eEs

ter

11

9.1

7%

Fast

30–60

(Nes

acai

ne)

Lidoca

ine

Am

ide

23.6

7.7

65%

Fast

90–200

(Xyl

oca

ine)

Mep

ivac

aine

Am

ide

22

7.6

75%

Fast

120–240

(Car

boca

ine)

Bupiv

acai

ne

Am

ide

830

8.1

95%

Inte

rme-

180–600

(Mar

cain

e)dia

te

Tetrac

aine

Este

r8

80

8.6

80%

Slow

180–600

(Ponto

cain

e)

*Pote

ncy

is r

elat

ive

to p

roca

ine

(1).


Table 3–2 Potential Toxic Effects of Local Anesthetics

• Central nervous system

Muscle tremors

Convulsions

Respiratory depression

Generalized CNS depression

• Cardiovascular system

Depression of myocardial contractility

Hypotension

Bradycardia

Ventricular tachycardia/fibrillation: This response hasbeen reported with bupivacaine and may be refractory totreatment and fatal

• Methemoglobinemia

This response most often is linked to benzocaine buthas been reported with other agents

• Allergic reactions

Associated with para-aminobenzoic acid (PABA), ametabolite of the ester local anesthetics and of methyl-paraben, a preservative used in many of the local anesthetics

• Tissue toxicity

Local anesthetic injection has been shown to causereversible skeletal muscle damage and, rarely, neuronaldamage

uncharged base form is most lipid soluble, diffusingreadily across the nerve sheath; dissociation is favored byincreasing pH. This is why efficacy is decreased ininflamed and infected (low pH) tissues.

Local anesthetic agents show a preferential effect onnerve fibers with the order (most to least sensitive) beingpreganglionic sympathetic (B fibers) > small sensory (A-delta fibers) > motor (A-alpha fibers). Sensitivity ofunmyelinated pain (C) fibers to local anesthetic agents issimilar to B fibers, but blockade may be affected by fac-tors other than those influencing the myelinated fibers.Sensation disappears in the order of pain, cold, warmth,touch, then joint and deep pressure and recovers in thereverse order.

Of the many local anesthetic agents available, only afew are commonly used in veterinary medicine, includ-ing lidocaine, mepivacaine, and bupivacaine. A topical5% eutectic mixture of lidocaine and prilocaine (EMLAcream, Astra Pharmaceuticals) applied to unbroken skinalso is effective when applied to animals for such proce-dures as venipuncture but must be applied at least 15–30min in advance. While many techniques have beendescribed for the common domestic species, Tables 3–3through 3–5 describe selected local anesthetic tech-niques that have shown relatively common applicationfor local/regional anesthesia or pain management. Fig-ures 3–1 through 3–4 illustrate the sites for injection forseveral techniques described in Table 3–3.


Tab

le 3

–3

Sele

cted L

oca

l A

nest

hetic

Tech

niq

ues

in D

ogs

and C

ats

Nerv

es

Are

a A

nest

heti

zed

Tech

niq

ue*

Do

sage

Infrao

rbita

lU

pper

lip

, nose

, ro

of

of

Inse

rt n

eedle

1 c

m c

rania

l0.5

–2 m

l**

(Fig

. 3–1A)

nas

al c

avity

, sk

in c

rania

l to

(an

d a

dva

nce

to)

to infrao

rbita

l fo

ram

enin

frao

rbita

l fo

ram

en e

ither

in

tra-

or

extrao

rally

Trig

emin

alEy

e, o

rbit,

conju

ctiv

a, e

ye-

Inse

rt n

eedle

ven

tral

to z

ygo-1–2 m

l**

(ophth

alm

ic

lids,

ski

n o

f fo

rehea

d:

mat

ic p

roce

ss a

t le

vel of

div

isio

n)

glove

aki

nes

ia m

ay o

ccur

late

ral ca

nth

us,

cra

nia

l to

(Fig

. 3–1C

)ra

mus

of

man

dib

le in

med

ioca

udal

dire

ctio

n t

o

orb

ital fis

sure

Max

illar

y M

axill

a, u

pper

tee

th a

nd

Inse

rt n

eedle

at

90º

angl

e0.2

5–1 m

l**

(Fig

. 3–1B)

lip, nose

ventral

to b

ord

er o

f zy

gom

atic

arc

h, 0.5

cm

caudal

to lat

eral

can

thus

Men

tal

Low

er lip

Inse

rt n

eedle

rost

ral to

1–2 m

l**

(Fig

. 3–1E)

men

tal fo

ram

en a

t le

vel

of

2nd p

rem

ola

r


Man

dib

ula

rC

hee

k, c

anin

e, inci

sor

teet

h,

Inse

rt n

eedle

at

low

er0.5

–1 m

l**

(infe

rior

muco

sa a

nd s

kin o

f ch

inan

gle

of

jaw

, 1.5

cm

al

veola

r br.)

ro

stra

l to

angu

lar

pro

cess

;(F

ig. 3–1D

)ad

vance

1.5

cm

dors

ally

al

ong

med

ial su

rfac

e of

ram

us

Bra

chia

l ple

xus

Are

a dis

tal to

and incl

udin

g22 g

a, 7

.5 c

m n

eedle

4–6 m

g/kg

(F

ig. 3–2)

the

elbow

inse

rted

med

ial to

(L

)sh

ould

er join

t to

war

d

1.5

–2 m

g/kg

cost

och

ondra

l ju

nct

ion

(B)

par

alle

l to

ver

tebra

e.

Inje

ct w

hile

with

dra

win

g nee

dle

. Asp

irate

firs

t. O

nse

t re

quire

s 20–30

min

IV r

egio

nal

Are

a dis

tal to

tourn

iquet

Apply

tourn

iquet

after

2–3 m

l L

(BIE

R-b

lock

)des

angu

inat

ion o

f lim

b

dilu

ted t

o

with

Esm

arch

ban

dag

e.

5–10 m

l In

ject

into

super

ficia

l w

ith s

alin

eve

in. Li

mit

to 2

hr

(contin

ues)


Tab

le 3

–3

(Continued)

Nerv

es

Are

a A

nest

heti

zed

Tech

niq

ue*

Do

sage

Inte

rcost

alFo

r th

ora

coto

my,

rib

Blo

ck m

inim

um

of

50.2

5–1 m

l B

frac

ture

s, p

leura

l sp

ace

(2 c

rania

l an

d

per

site

dra

inag

e2 c

audal

to s

ite).

B:

≤3

Cau

dal

bord

er o

f rib

m

g/kg

nea

r in

terv

erte

bra

l fo

ram

en

Inte

rple

ura

lSa

me

as f

or

inte

rcost

al

Req

uire

s pla

cem

ent

of

1–2 m

l B

regi

onal

blo

ckin

terp

leura

l ca

thet

er

Epid

ura

l Anes

thes

ia c

audal

to

22 g

a, 2

.5–7.

5 c

m s

pin

al1 m

l/5 k

g re

gional

um

bili

cus

nee

dle

(25 g

a hyp

o-

L,B; M

axi-

(Fig

. 3–3)

der

mic

nee

dle

for

mum

of

6

pat

ients

<2 k

g). Lu

mbo-

ml has

sa

cral

spac

e: n

eedle

bee

nin

troduce

d o

n d

ors

al

advi

sed

mid

line

just

cau

dal

to

line

bet

wee

n ilia

c w

ings

. N

eedle

adva

nce

d u

ntil

dis

tinct

“pop”

is f

elt

(inte

r-


arcu

ate

ligam

ent)

. M

ay

obse

rve

tail

flick

. C

hec

k fo

r C

SF (

if pre

sent

dec

reas

e dose

by

50%

or

with

dra

w 1

–2 m

m)

Dig

ital blo

ck

Pro

vide

anal

gesi

a fo

rSu

per

ficia

l ra

dia

l n:

0.1

–0.3

ml

(Fig

. 3–4)

onyc

hec

tom

ydors

om

edia

l ca

rpus;

B p

er s

ite

uln

ar n

(dors

al

≤3 m

g/kg

cuta

neo

us

br)

: la

tera

l ca

rpus;

med

ian n

&

uln

ar n

(pal

mar

br)

: pal

mar

car

pus

L =

lidoca

ine;

B =

bupiv

acai

ne

*U

se 2

5 g

a nee

dle

unle

ss o

ther

wis

e in

dic

ated

.

**D

ose

is for

2%

lidoca

ine

or

0.5

% b

upiv

acai

ne

in d

ogs

. The

dose

in c

ats

is 0

.25–0.5

ml.

Tota

l dosa

ge for

lidoca

ine

should

not ex

ceed

4–5 m

g/kg

for

lidoca

ine

and 2

mg/

kg for

bupiv

acai

ne

for

eith

er s

pec

ies.


Tab

le 3

–4

Sele

cted L

oca

l A

nest

hetic

Tech

niq

ues

in H

ors

es

Nerv

e(s

)A

rea A

nest

heti

zed

Tech

niq

ue

Do

sage*

Supra

orb

ital

Upper

lid

Inse

rt 2

5 g

a nee

dle

into

5 m

l(f

ronta

l)su

pra

orb

ital fo

ram

en loca

ted

5–7 c

m a

bove

med

ial

canth

us

at d

epth

of

1.5

–2 c

m,

inje

ctin

g sh

allo

w t

o d

eep

Auric

ulo

pal

peb

ral

Aki

nes

ia o

f upper

In

sert n

eedle

into

dep

ress

ion

5 m

llid

only

caudal

to m

andib

le a

t ve

ntral

edge

of

zygo

mat

ic a

rch

Cau

dal

epid

ura

lTa

il, p

erin

eum

In

sert 1

8–22 g

a hyp

oder

mic

0.2

–0.3

caudal

nn.

incl

udin

gor

spin

al n

eedle

into

1st

mg/

sacr

al n

n.

rect

um

, vu

lva,

in

terc

occ

ygea

l sp

ace

with

kgva

gina,

pre

vents

nee

dle

per

pen

dic

ula

r to

stra

inin

gsk

in s

urf

ace

or

poin

t dire

cted

ve

ntrocr

ania

l (3

0°)

. Pla

cing

dro

p o

f ag

ent

into

nee

dle

hub

will

ver

ify p

roper

loca

tion a

s flu

id is

aspira

ted into

epid

ura

l sp

ace.

Addin

g xy

lazi

ne

(0.1

7


mg/

kg)

or

det

om

idin

e (0

.06

mg/

kg)

to t

he

lidoca

ine

will

in

crea

se d

ura

tion o

f an

alge

sia

Note

: Th

ese

are

just

a few

com

monly

use

d lo

cal a

nes

thet

ic tec

hniq

ues

in h

ors

es. F

or

des

crip

tions

of ad

diti

onal

blo

cks

for

the

hea

d, f

or

dia

gnost

ic n

erve

and jo

int blo

cks,

and tec

hniq

ues

for

lapar

oto

my, r

efer

to “

Rec

om

men

ded

Rea

din

g.”

*Dosa

ge is

for

2%

lidoca

ine.

Tab

le 3

–5

Sele

cted L

oca

l A

nest

hetic

Tech

niq

ues

in R

um

inan

ts a

nd S

win

e

Nerv

e(s

)A

rea A

nest

heti

zed

Tech

niq

ue

Do

sage*

Infil

trat

ion

Para

lum

bar

foss

aLi

ne

blo

ck o

f in

cisi

on s

ite.

50 m

lIn

verted

L t

echniq

ue:

cra

nia

l 50–100 m

lan

d d

ors

al t

o inci

sion s

ite.

Des

ensi

tize

skin

firs

t, th

en inje

ct

dee

per

to d

esen

sitiz

e m

usc

le

and p

erito

neu

m

Pro

xim

al

Para

lum

bar

foss

aD

esen

sitiz

e su

bcu

taneo

us

site

s 15 m

l dee

p,

para

vertebra

lfo

r nee

dle

entry

with

1–2 m

l L.

5 m

l af

ter

(dors

al a

nd

Use

14 g

a nee

dle

to g

uid

ew

ithdra

w-

ing

(contin

ues)


Tab

le 3

–5

(Continued)

Nerv

e(s

)A

rea A

nest

heti

zed

Tech

niq

ue

Do

sage*

ventral

br.

of

16–18 g

a, 1

1–15 c

m n

eedle

.nee

dle

T1

3, L1

, L2

)En

try

site

s ar

e 5 c

m o

ff m

idlin

e 1–2 c

m,

(2.5

–3 c

m f

or

smal

l ru

min

ants

).

per

site

Pass

nee

dle

dow

n t

o c

rania

l Sm

all

aspec

t of

tran

sver

se p

roce

ss

rum

inan

ts:

and “

wal

k off”

front

edge

of

2–3 m

l/pro

cess

(+

1 c

m).

site

T13: front

of

tran

sver

se

(tota

l pro

cess

of

L1dose

)

L1: front

of

tran

sver

se p

roce

ss

of

L2L2

: front

of

tran

sver

se p

roce

ss

of

L3

Dis

tal

Para

lum

bar

foss

aN

erve

s ar

e des

ensi

tized

at

dis

tal

20 m

l para

vertebra

l en

ds

of

tran

sver

se p

roce

sses

of

ventral

,(s

ame

as f

or

L1, L2

, an

d L

3. 18 g

a, 7

.5 c

m5 m

l pro

xim

al b

lock

)nee

dle

is

inse

rted

ven

tral

to

dors

alpro

cess

and inje

ctio

n m

ade


in f

an-s

hap

ed p

atte

rn. N

eedle

is

with

dra

wn a

nd r

einse

rted

dors

al t

o p

roce

ss

IV r

egio

nal

in

Are

a dis

tal to

Apply

tourn

iquet

or

cuff (

>200

30 m

l; ca

ttle

and

tourn

iquet

mm

Hg)

to lim

b. In

ject

into

3–10 m

l sm

all ru

mi-

super

ficia

l ve

in w

ith 2

0–25 g

afo

r sm

all

nan

tsnee

dle

clo

se t

o s

urg

ical

site

. ru

min

ants

Apply

pre

ssure

to s

ite t

o a

void

an

d s

win

ehem

atom

a. A

nes

thes

ia o

nse

t is

5–10 m

in a

nd p

ersi

sts

until

tour-

niq

uet

is

rem

ove

d (

max

: (≤

2 h

r).

Pete

rson e

ye

Eye,

orb

it, o

rbic

u-

SC infil

trat

ion a

t notc

h f

orm

ed15 m

lblo

ckla

ris o

culi

musc

le.

by

zygo

mat

ic a

nd t

empora

l ab

duce

ns,

Fa

cilit

ates

pro

cess

es o

f m

alar

bone.

troch

lear

, en

ucl

eatio

nU

se 1

4 g

a nee

dle

inse

rted

at

ocu

lom

oto

r, w

hen

com

bin

edsa

me

site

as

guid

e fo

r 18 g

a,ophth

alm

ic,

with

auric

ulo

-11 c

m n

eedle

dire

cted

horiz

onta

lm

axill

ary

and

pal

peb

ral blo

ckan

d s

lightly

post

erio

r to

man

dib

ula

r brr.

reac

h s

olid

bone

(site

of

of

trig

emin

al

orb

itoro

tundum

wher

e ner

ves

ner

veex

it) a

nd inje

ct(c

ontin

ues)


Tab

le 3

–5

(Continued)

Nerv

e(s

)A

rea A

nest

heti

zed

Tech

niq

ue

Do

sage*

Auric

olo

pal

peb

ral

Eyel

ids

Sam

e si

te a

s ab

ove

. W

ithdra

w

10 m

lnee

dle

and r

edire

ct p

ost

eria

lly,

late

ral to

zyg

om

atic

arc

h a

nd

inje

ct d

urin

g in

sertio

n t

o 5

–7.

5

cm. U

pper

lid

may

req

uire

lo

cal in

filtrat

ion 2

–3 c

m f

rom

lid

mar

gin.

Bovi

ne d

ehorn

Horn

and b

ase

Tem

pora

l rid

ge, 2 c

m f

rom

horn

5–10 m

lco

rnual

bra

nch

of

horn

bas

e, d

epth

of

1–2.5

cm

.of

zygo

mat

ico-

Ner

ve is

pal

pab

le h

ere.

Inje

ctte

mpora

l n.

2–3 c

m r

ost

ral to

horn

with

(of trig

emin

al n

.)18 g

a nee

dle

. Asp

irate

firs

t.An S

C r

ing

blo

ck a

round t

he

horn

bas

e m

ay b

e nee

ded

fo

r co

smet

ic d

ehorn

and

larg

e horn

s

Caprine d

ehorn

Horn

and b

ase

1. H

alfw

ay b

etw

een lat

eral

sa

me

ner

ve a

sof

horn

canth

us

and lat

eral

horn

pre

vious

(1)

bas

e: inse

rt n

eedle

(22


plu

s co

rnual

br.

ga, 2.5

cm

) cl

ose

to c

audal

2–3 m

l/si

teof

infrat

roch

lear

rid

ge o

f su

pra

orb

ital pro

cess

(<10 m

g/n. (2

)1–1.5

cm

dee

p.

kg m

axi-

2. H

alfw

ay b

etw

een m

edia

l m

um

)ca

nth

us

and m

edia

l horn

bas

e: inse

rt n

eedle

dors

al

and p

aral

lel to

dors

om

edia

l m

argi

n o

f orb

it, inje

ct in lin

e.

Deb

uddin

g of

kids:

rin

g blo

ck,

0.5

ml/

horn

Caudal epid

ura

lTa

il, p

erin

eum

Inse

rt 1

8–22 g

a hyp

oder

mic

or

5–6 m

l:(c

occ

ygea

l an

d

incl

udin

g re

ctum

,sp

inal

nee

dle

into

1st

inte

r-ca

ttle

sacr

al n

n.)

vu

lva,

vag

ina,

cocc

ygea

l sp

ace

with

nee

dle

0.2

2 m

g/kg

rum

inan

ts

pre

vents

per

pen

dic

ula

r to

ski

n s

urfac

efo

r lla

mas

cam

elid

sst

rain

ing

or

poin

t dire

cted

ven

trocr

ania

lan

d s

mal

l(3

0º)

. Pla

cing

dro

p o

f ag

ent

rum

inan

tsin

to n

eedle

hub w

ill v

erify

pro

per

loca

tion a

s flu

id is

aspira

ted into

epid

ura

l sp

ace.

Addin

g xy

lazi

ne

(0.0

5 m

g/kg

fo

r ca

ttle

, 0.1

7 m

g/kg

for


(contin

ues)

Tab

le 3

–5

(Continued)

Nerv

e(s

)A

rea A

nest

heti

zed

Tech

niq

ue

Do

sage*

llam

as)

to lid

oca

ine

will

in

crea

se d

ura

tion o

f an

alge

sia

Cra

nia

l epid

ura

lAnes

thes

ia c

audal

Te

chniq

ue

is s

imila

r to

that

use

d2–4 m

g/kg

(sm

all

to d

iaphra

gmin

dog.

Site

is

bet

wee

n L

9(r

umin

ant)

rum

inan

ts

and S

1. O

nse

t: 2–15 m

in.

0.8

–1 m

g/kg

and p

igs)

Rea

r lim

b p

aral

ysis

per

sist

s up

(pig

s)to

2 h

r. Red

uce

dose

by

50%

if

CSF

is

note

d in n

eedle

. Req

uire

s 18–20 g

a, 6

–16 c

m

nee

dle

, sh

ortes

t fo

r sm

all

rum

inan

ts; lo

nge

st f

or

larg

e pig

s. S

win

e: x

ylaz

ine

(1–2

mg/

kg)

or

det

om

idin

e 0.5

m

g/kg

) to

lid

oca

ine

will

incr

ease

dura

tion o

f an

alge

sia

SC: su

bcu

taneo

us

*Dosa

ge is

for

2%

lidoca

ine

(L).


69

Figu

re 3

–1

Needle

pla

cem

ent

for

loca

l an

est

hetic

inje

ctio

n o

f th

e (

A)

infr

aorb

ital

, (B

) m

axil-

lary

, (C

) ophth

amic

div

isio

n o

f th

e t

rige

min

al, (D

) m

enta

l, an

d (

E)

man

dib

ula

r (i

nfe

rior

alve

ola

rbra

nch

) nerv

es.

(R

eprinte

d w

ith p

erm

issi

on f

rom

Thurm

on, et

al.,

eds.

, Lu

mb a

nd J

ones’

Vete

ri-

nary

Anest

hesi

a, 3rd

ed.,

Bal

tim

ore

: W

illia

ms

& W

ilkin

s, 1

996, pag

e 4

30.)

70

Figure 3–2 Needle placement for brachial plexus block medialto shoulder joint, lateral aspect of left thoracic limb; 2 is the sec-ond rib. (Reprinted with permission from Muir and Hubbell, eds.,Handbook of Veterinary Anesthesia, 2nd ed., St. Louis: Mosby,1995, page 100.)

71

Figu

re 3

–3

Needle

pla

cem

ent

(A)

into

the lum

bosa

cral

epid

ura

l sp

ace o

f dogs

and c

ats.

Pal

pat

ion

of

the d

ors

al ilia

c w

ings

and d

ors

al p

roce

ss o

f lu

mbar

vert

ebra

7 w

ill g

uid

e p

lace

ment

on t

he m

idlin

eju

st c

audal

to a

lin

e d

raw

n b

etw

een t

he w

ings

and just

cra

nia

l to

the f

irst

sac

ral ve

rtebra

. (R

eprinte

dw

ith p

erm

issi

on f

rom

Thurm

on e

t al

., eds.

, Lu

mb a

nd J

ones’

Vete

rinary

Anest

hesi

a, 3rd

ed.,

Bal

tim

ore

:W

illia

ms

& W

ilkin

s, 1

996, pag

e 4

35.)

72

Figure 3–4 Diagram of right forepaw of a cat illustrating sitesfor injection of local anesthetic to provide analgesia for onychec-tomy. (Reprinted with permission from Pascoe, Local and regionalanesthesia and analgesia, in Seminars in Veterinary Medicine andSurgery (Small Animal) 1997;12(2):435.)

4

Inhalation Agents

Inhalation agents provide the most versatile and readilycontrolled method of general anesthesia and are espe-cially well suited for prolonged and complex proceduresand for common as well as uncommon veterinaryspecies. The anesthetic agents are carried in oxygen;thus, patients receive an enriched oxygen mixture andmost often are intubated, which assures a protected air-way and provides a method for ventilatory support. Themain disadvantages of these agents are the expense ofequipment necessary to deliver the agent and, despitethe ability to readily control the concentration delivered,vigilant monitoring is essential to avoid excessive anes-thetic depth, which can rapidly lead to patient mortality.

73

Inhalant anesthetics are vapors (a liquid at ambienttemperature and pressure; these include all potentinhalant agents) or gases (a gas at ambient temperatureand pressure, such as nitrous oxide) administered intothe respiratory tract and absorbed from alveoli into theblood to create a partial pressure (tension). This partialpressure allows the gas to pass from the blood to the brain, wherethe agents exert reversible generalized central nervous systemdepression, the degree of which has been described asdepth of anesthesia (Table 4–1).

Some of the physicochemical characteristics deter-mine the action and margin of safety of the agents anddictate how they are supplied and the equipmentneeded for safe delivery, as well as how they are taken upby the lung, distributed within the body, and eliminated.Vapor pressure is a measure of the agent’s ability to evapo-rate (volatility) and must be sufficient to provide ade-quate concentration in the vapor state to produceanesthesia under ambient conditions. Saturated vaporpressure represents the maximum achievable vapor con-centration for a given liquid at a given temperature (andbarometric pressure); it is determined by dividing vaporpressure by barometric pressure (e.g., Halothane:244/760 = 32% saturated vapor pressure). The greater isthe vapor pressure, the greater the concentration ofinhalant deliverable to the patient (and environment).

The boiling point, defined as the temperature atwhich the vapor pressure is equal to atmospheric pres-sure, is greater than room temperature for all inhalant

74 Inhalation Agents

Inhalation Agents 75

Tab

le 4

–1

Sta

ges

and C

har

acte

rist

ics

of

Genera

l A

nest

hesi

a

Sta

ge/

Pu

lse

Refl

exe

s O

cula

r

Mu

scle

To

ne

Desc

rip

tio

nR

ate

AB

PR

esp

irati

on

Lo

stR

efl

exe

s Lo

st

I/Anal

gesi

a⇑

⇑Reg

ula

r ±

⇑*

All

pre

sent

All

pre

sent

Norm

al

II/D

eler

ium

⇑⇑

Erra

tic ±

⇑*

All

pre

sent

Pre

sent:

Exce

ssiv

enys

tagm

us

move

men

t

III/S

urg

ical

Pla

ne

1,

⇓**

N⇓

Lary

nge

alD

imin

ished

⇓

light

Pla

nes

2

⇓⇓

**⇓

⇓Pe

dal

Lacr

imat

ion,

⇓⇓

and 3

, pal

peb

ral

med

ium

Pla

ne

4,

⇓⇓

**⇓

⇓⇓

, irr

egula

rC

orn

eal

⇓⇓

⇓

dee

p

IV⇓

⇓⇓

Bar

ely

Apnea

⇓⇓

⇓

pal

pab

le

Note

: W

hen

unaf

fect

ed b

y par

ente

ral a

gents

adm

inis

tere

d (

antic

holin

ergi

c ag

ents

, opio

ids)

, pupils

are

dila

ted d

urin

gst

ages

I a

nd II,

are

norm

al o

r co

nst

ricte

d in

pla

nes

1–3, a

nd a

re d

ilate

d in

pla

ne

4 a

nd s

tage

IV.

In c

attle

, eye

posi

tion is

a re

liable

indic

ator

of dep

th. T

he

eye

move

s from

cen

tral

to v

entral

as

surg

ical

anes

thet

ic d

epth

is a

chie

ved. A

s an

esth

e-si

a bec

om

es d

eeper

, the

eye

retu

rns

to c

entral

loca

tion.

(contin

ues

)

agents except nitrous oxide (N2O); therefore, all are liq-uids at room temperature except N2O, which is suppliedfor use in blue cylinders compressed to its liquid state at750 psi. Hence, the pressure gauge on a tank of N2Odoes not indicate the quantity of gas remaining until allliquid is converted to a gas state and pressure begins todecrease as the gas empties.

The quantity of inhalant agent delivered is discussedclinically as concentration in volume percentage, which rep-resents the percentage of the agent in relation to the car-rier gas mixture (oxygen alone or combined with N2O).

The molecular weight, unique for each vapor, is thatweight which occupies 22.4 liters under standard condi-tions (0°C [273 K, absolute scale] and 760 mmHg [baro-metric pressure at 1 atmosphere sea level]). The specificgravity is the ratio of the weight of a unit volume of onesubstance to a similar volume of water under similar con-ditions (20°C). Molecular weight and agent specific grav-ity are properties that allow determination of the volumeof vapor yielded by 1 ml of anesthetic liquid (Figure4–1). From this calculation, the cost of using an inhalantagent may be approximated, based on percentage deliv-ered, total carrier gas flow, and time (see Figure 4–1).


Table 4–1 (Continued)

ABP = arterial blood pressure

N = normal

*Breath holding may occur.

**Rate depends on other contributing factors, including premedications, body temperature, fluid balance.

77

Figure 4–1 Calculations to determine volume of vapor from 1ml of anesthetic liquid at 20ºC (calculations 1–4) and averageanesthetic liquid usage per unit time (calculations 5 and 6), usingisoflurane as an example.

1. 1 ml liquid isoflurane � 1.49 g/ml (spe-cific gravity) � 1.49 gm

2. 1.49 gm � 185 (molecular weight) �0.0081 mol of liquid

3. 0.0081 mol � 22400 ml/mol (1 mol of gas� 22.4 L) � 181.4 ml at 273 K (0°C)

4. 181.4 ml vapor � 293/273 K � 194.7 mlvapor/ml liquid isoflurane at 20°C and 760 mmHg

For example, assume 2% isoflurane deliverywith total flow (flowmeter setting) of 2L/minute.

5. 2% � 100 � 2 L/minute � 60 min � 2400ml isoflurane vapor per hour

6. 2400 ml isoflurane vapor/hr � 194.7 mlvapor/ml liquid � 12.3 ml liquid/hr

The solubility (partition) coefficient, the extent to whicha gas will dissolve in a given solvent, is expressed as a con-centration ratio of the anesthetic in the solvent and gasphases. The blood/gas solubility coefficient (Table 4–2)predicts the speed of induction, recovery, and change inanesthetic depth for an inhalant. The lower is the coeffi-cient, the more rapid the action of the agent. Theoil/gas solubility coefficient is the ratio of the concen-tration of an inhalant in oil and gas phases at equilib-rium, correlates inversely with anesthetic potency (asrepresented by the minimum alveolar concentration),and describes the capacity of lipids for the inhalant. Thelower is the oil/gas solubility coefficient, the lower thepotency and thus the higher the MAC value.

Several factors control anesthetic delivery to thelungs and uptake by the blood; these are summarized inTable 4–3. When equilibrium between delivery anduptake (by blood and tissue) is achieved and the alveolarpartial pressure reaches a steady state, the partial pres-sure in the brain is controlled by the partial pressure inthe alveoli.

The minimum alveolar concentration (MAC) is a meas-urement of inhalation agent potency, which refers to thequantity of an agent required to produce a desiredeffect. MAC, which provides a method for comparing thepotency of one agent to another (see Table 4–2), isdefined as the minimum alveolar concentration of ananesthetic agent at one atmosphere that produces immo-bility in 50% of patients exposed to a noxious stimulus.



Tab

le 4

–2

Phys

icoch

em

ical

Pro

pert

ies

and M

inim

um

Alv

eola

r C

once

ntr

atio

n(M

AC

) of

Inhal

ant

Anest

hetic

Age

nts

Halo

-Is

o-

Meth

o-

Sevo

-P

rop

ert

yD

esf

lura

ne

En

flu

ran

eth

an

efl

ura

ne

xyfl

ura

ne

flu

ran

eN

2O

Mole

cula

r168

185

197

185

165

200

44

wei

ght

Liquid

1.4

71.5

21.8

61.4

91.4

21.5

2—

spec

ific

grav

ity

(20°C

; gm

/ml)

ml va

por/

209.7

197.

5227

194.7

206.9

182.7

—m

l liq

uid

(2

0°C

)

Boili

ng

poin

t 23.5

57

50

49

105

59

–89

(°C

)

Vapor pre

ssure

664

172

243

240

23

160

—m

mH

G

at 2

0°C

(contin

ues

)


Tab

le 4

–2

(Continued)

Halo

-Is

o-

Meth

o-

Sevo

-P

rop

ert

yD

esf

lura

ne

En

flu

ran

eth

an

efl

ura

ne

xyfl

ura

ne

flu

ran

eN

2O

Blo

od/g

as

0.4

22.0

2.5

41.4

615.0

0.6

80.4

7par

titio

n

coef

ficie

nt

(37°C

)

Oil/

gas

18.7

96

224

91

970

47

1.4

0par

titio

n

coef

ficie

nt

(37°C

)

MAC

* (%

)7.

1–9.7

2.0

–2.3

0.8

–1.1

1.3

–1.6

0.2

3–0.2

92.1

–2.6

150– 200

Bio

tran

s-0.0

22.4

20–25

0.1

750

3.0

0.0

04

form

atio

n(%

of

met

abolit

es)

*M

AC

var

ies

slig

htly

am

ong

spec

ies

and in

div

idual

s. T

he

valu

e gi

ven is

an a

vera

ge o

r ra

nge

der

ived

fro

m v

alues

reported

for

seve

ral s

pec

ies.

As

a gen

eralr

ule

, conce

ntrat

ions

require

d for

clin

ical

purp

ose

s ar

e ap

pro

xim

atel

y 2–3

times

the

MAC

val

ue

imm

edia

tely

follo

win

g in

duct

ion (

mas

k in

duct

ion m

ay r

equire

3–5 tim

es M

AC

) an

d 1

.5–2 tim

esM

AC

val

ue

for

anes

thet

ic m

ainte

nan

ce.


Table 4–3 Factors That Increase the Rate of Rise ofInhalant Anesthetic Tension (Partial Pressure) in the Alveoli

I. Increased delivery of anesthetic to the lungs

A. Increased inspired concentration (the higher is theinspired concentration administered, the more rapid therate of rise of the alveolar concentration)

1. Increased vaporizer setting

2. Increased fresh gas inflow (this effect is significant dur-ing the induction phase when uptake is significant)

3. Decreased breathing circuit volume (the smaller isthe circuit volume, the more rapidly the inspired con-centration is affected by concentration delivered fromthe vaporizer)

4. Second gas effect: Passive increase in inspired con-centration of an anesthetic gas due to rapid uptake oflarge volumes of a less soluble agent used in a highconcentration (N2O), therefore the increased concen-tration accelerates the rate of rise of the second gasin the alveoli; 50% N2O augments inflow into alveoliand accelerates uptake of the second gas in mixture(e.g., halothane, isoflurane), which is used at muchlower concentrations

B. Increased alveolar ventilation

1. Occurs with application of mechanical ventilation

2. Occurs with a decrease in dead space ventilation

3. Relative to functional residual capacity (FRC; volumeremaining in lungs after normal expiration). Thesmaller is the FRC, the less time it takes to “wash in”

(continues)

Therefore, methoxyflurane (MAC = 0.23) currently isthe most potent inhalant agent available. Anestheticrequirements are altered by a variety of factors, which arelisted in Table 4–4, but not by duration of anesthesia, sex,or metabolic acid/base or potassium imbalance.

Inhalation agents affect organ systems in addition tothe central nervous system. Inhalant agents decreaseelectrical activity of the cerebral cortex as brain concen-tration increases, as indicated by decreased frequencyand amplitude of EEG activity; however, due to extremevariability, the EEG alone is not a reliable index of anes-thetic depth. And, the agent enflurane has epileptogenicpotential, which greatly limits its usefulness in veterinarymedicine.



the “new” gas mixture. FRC is decreased in pregnancy and in a variety of primary respiratorydiseases

II. Decreased removal (uptake) from the alveoli

A. Decreased blood/gas solubility coefficient

B. Decreased cardiac output

C. Decreased alveolar to venous anesthetic partial pres-sure difference: the magnitude of difference is relatedto the amount of anesthetic uptake by the tissues andthe largest gradient occurs during induction when tis-sue uptake is greatest


Inhalants depress respiratory function in a dose-dependent manner and respiratory arrest occurs at 2–3MAC. Of the currently available agents, respiratorydepression occurs in the following order from most toleast at equipotent concentrations: enflurane >desflurane ≥ isoflurane = methoxyflurane ≥ sevoflurane> halothane. Halothane has been reported to produce aparadoxic tachypnea in some patients, and the mecha-nism is unknown.

Table 4–4 Factors That Affect Anesthetic Requirements(MAC)

Increase in requirements:

Hyperthermia

Hypernatremia

CNS stimulants: amphetamine, ephedrine, physostigmine

Decrease in requirements:

Hypothermia

Hyponatremia

Pregnancy

PaO2 <40 mmHg

Pa CO2 >95 mmHg

Mean arterial blood pressure <50 mmHg

Old age

CNS depressants: N2O, opioids, acepromazine, benzodi-azepines, alpha2 agonists, ketamine, thiopental, propofol


All agents depress cardiovascular performance in adose-dependent manner, associated with a negativeinotropic effect, decreased sympathoadrenal activity, andvasodilation. Halothane is noted for its cardiac sensitiza-tion to epinephrine-induced arrhythmias. This occurs toa much lesser extent with methoxyflurane and isnegligible with the other agents. Vasodilation increaseswith increasing depth of isoflurane anesthesia, whichcontributes to hypotension. Myocardial depression is rel-atively less with isoflurane, desflurane, and sevofluranethan halothane, methoxyflurane, and enflurane. Desflu-rane, while similar to isoflurane in cardiovascular effects,is reported to sustain autonomic activity better and main-tain a relatively constant heart rate and, overall, is mostsparing of cardiovascular function.

While all of the inhalation agents are capable ofcausing hepatocellular injury due to reduced oxygen deliv-ery, isoflurane, sevoflurane, and desflurane better main-tain hepatic blood flow and oxygenation, especiallyduring prolonged periods. Halothane has been specifi-cally though rarely associated with fulminant hepaticnecrosis in humans and some animal species and shouldbe avoided in animals with identified hepatic abnormal-ities. This effect is probably influenced by such concur-rent factors as hypoxemia, N2O administration, priorinduction of hepatic drug-metabolizing enzymes, andmechanical ventilation.

All agents decrease renal blood flow and glomerularfiltration rate in a dose-related manner. The effect is


exacerbated by preexisting dehydration and hemody-namic abnormalities and may be minimized by intraop-erative fluid therapy. Methoxyflurane is most nephrotoxicand was removed from human use for this reason. Thecause is associated with methoxyflurane biotransforma-tion, which releases free fluoride ions that cause directtubular damage resulting in nonoliguric renal failure.Enflurane and sevoflurane also produce free fluorideions secondary to biotransformation, and sevofluraneyields a nephrotoxic compound, olefin, when it reactswith carbon dioxide absorbents; however, neither seemsto result in concentrations great enough to cause signifi-cant renal damage.

All potent volatile anesthetic agents can triggermalignant hyperthermia but halothane is the most potentof the commonly used agents. Malignant hyperthermiais a pharmacogenetic, often fatal, myopathy of humansand swine typically characterized by increased tempera-ture, muscle rigidity, metabolic acidosis, hyperkalemia,and striated muscle deterioration due to a defect in cal-cium homeostasis at the cellular level. It has beenreported in horses, dogs, cats, birds, deer, and otherwildlife species, but a genetic link has not been eluci-dated in these species. In wildlife species, the syndromeis referred to as capture myopathy.

Anesthetic elimination (and recovery) is influencedby alveolar ventilation, cardiac output, agent solubility,and duration of anesthesia (the longer is the duration,the greater the extent of tissue saturation). When a


rebreathing circuit is used (Chapter 5), purging the cir-cuit with oxygen by engaging the oxygen flush valve orincreasing oxygen flow rate will facilitate elimination aswill continued assisted ventilation. While it may seemintuitive to simply disconnect the patient from thebreathing system, this deprives the patient of oxygen sup-plementation and increases contamination of the workenvironment with exhaled anesthetic agent.

Biotransformation is unique to each anesthetic agent(see Table 4–2) and occurs primarily in the liver. Thepotential for acute and chronic toxicities (Table 4–5)associated with environmental exposure to inhaledagents increases with increased biotransformation tometabolites. This is a major reason why methoxyflurane(metabolized up to 50%) no longer is used in human

Table 4–5 Adverse Side Effects Associated with Environmental Exposure to Inhalation Agents

Reproduction disorders Abortion, malformations

Malignancy

Vital organ dysfunction Hepatopathy, renal pathologicchanges, behavioral changes(headache, fatigue, decreasedperformance)

N2O Neutropenia, megaloblastic anemia (decreased vitamin B12 &methionine synthetase synthesis


medicine and has lost favor in veterinary medicine, rep-resenting a significant health hazard to patients and per-sonnel. Practices to minimize workplace contamination(Table 4–6) with inhalant agents should be utilized tominimize human exposure.

Table 4–6 Work Practices That Help Minimize Environ-mental Contamination of the Workplace with InhalantAnesthetics

1. Use a scavenger system

2. Educate all personnel about the potential health hazards

3. Keep equipment and vaporizers in good condition

4. Identify and repair leaks in system by an established routine

5. Fill vaporizers at the end of the day

6. Fill vaporizers in a well-ventilated area

7. Inflate endotracheal tube cuffs adequately

8. Avoid the use of mask and chamber inductions and main-tenance whenever possible

9. Keep patients on O2 as long as possible to scavengeexpired anesthetic gases

10. Avoid or minimize exposure with the use of respiratorswith organic vapor cartridges (available from medical sup-ply companies) during the first trimester of pregnancy(while the first trimester is the most vulnerable period,steps to minimize exposure should be practiced through-out the pregnancy)

Nitrous oxide will not provide general anesthesiaalone due to its low potency (see Table 4–2) but is usedas a percentage of the carrier gas (50–70%) to decreaserequirements of the more potent agents and speedinduction, due to its second gas effect (see Table 4–3).While cardiopulmonary effects are minimal, somecontraindications are associated with its use and it hasbeen associated with specific toxic effects (see Table4–5). Nitrous oxide rapidly diffuses into closed gasspaces (while nitrogen slowly diffuses out) and will causeexpansion of the space and respiratory compromise(e.g., pneumothorax, intestinal obstruction); therefore,it is contraindicated in these situations. Nitrous oxiderarely is used in large animal species because of the largevolume of gas contained in the gastrointestinal tract andpotential for excessive distension as well as the need for100% oxygen to maintain adequate oxygenation duringinhalation anesthesia. Diffusion hypoxia can occur withN2O use, due to its rapid exit from the blood into thelungs when delivery is ended. It is essential that 100%oxygen delivery be continued for at least 5 min after N2Ois discontinued.

Inhalant agents offer the most versatile method formaintenance of anesthesia available today. Isofluranecurrently is the most commonly used and favored agentin veterinary medicine, although sevoflurane, with itslower solubility, offers benefits that may rival isofluranewhen it becomes a more economical option. Halothane


remains in common use, despite its arrhythmogenicpotential, slower onset and cessation of action, andgreater potential for cardiovascular depression.Halothane historically has been preferred in equineanesthesia, at least for elective procedures, due toreports of smoother recoveries (than isoflurane).Recently, use of sevoflurane has been reported to pro-duce smooth, rapid recoveries and may gain widespreaduse in equine anesthesia in the future. Inhalant anesthe-sia requires vigilant monitoring (Chapter 6) and is notwithout potential detrimental effects to both the patientand the work environment.


5

Anesthetic Equipment

The Anesthesia Machine

Basic components of an anesthesia machine include acompressed gas source, pressure-reducing valve (pres-sure regulator), flowmeter, and vaporizer. Compressed(carrier, fresh) gas sources are oxygen and N2O. WhileN2O commonly is used in human anesthesia, use in vet-erinary medicine is limited mainly to dogs and cats tospare requirements for the more potent inhalant agents.In addition to liquid bulk tanks for oxygen, sourcesinclude large tanks (e.g., H tanks with 6,910 L capacity foroxygen or 14,520 L for N2O) connected by high-pres-sure, color-coded (green for oxygen, blue for N2O) hose

91

known as DISS (diameter index and safety system) andsmall tanks (E tanks: 655 L capacity for oxygen, 1,590 Lfor N2O), which may be connected, via a hanger yolkwith a self-contained pressure regulator and pressuregauge, directly to a small animal machine. A pin indexsystem configuration (Figure 5–1) prevents inadvertentinterchange of medical gases. Compressed gas tanks arefilled under pressure (2200 psi for oxygen; 750 psi forN2O) and always must be handled carefully. The pres-sure gauge reading for oxygen tanks decreases linearlywith decreasing content, providing an indication ofavailable oxygen remaining.

Pressure regulators reduce the pressure exiting thecompressed gas source to a constant and safe pressure of50–60 psi to provide a constant pressure to the flowmeter.Flowmeters control and indicate the rate of flow of oxygenand N2O delivered to the common gas outlet or throughan out-of-system vaporizer. Gas moves from bottom totop around a float, which indicates flow rate in L (orml)/min. Most flowmeter floats are cylindrical and readin the middle; alternate-shaped floats are read at the top.Flowmeters are calibrated at 20°C and 760 mmHg. Flowknobs usually are color coded and oxygen flowmeterknobs usually are larger than other knobs on themachine to minimize human error.

Vaporizers deliver a controlled concentration of potentinhalant to the patient breathing system. Currently, thesafest vaporizers are out of (breathing) circle (VOC;Figure 5–2), precision, agent specific, concentration

92 Anesthetic Equipment

93

Figure 5–1 Diagram of the pin index safety system, illustratingthe spacing between the valve outlet and pin holes in the valvebodies for oxygen and N2O cylinders. The numbering system iden-tifies each pin hole site. (Reprinted with permission from CE Short,Principles and Practice of Veterinary Anesthesia, Baltimore:Williams & Wilkins, 1987, page 397.)

calibrated, and variable bypass, which are temperature,flow, and back-pressure compensated. Because vaporiz-ers different than those just described remain in use inveterinary practice, we provide a brief review of thesevaporizers.

The two major exceptions that remain in veterinarymedical use are nonprecision in-the-circle vaporizers(Stephens, Ohio #8) and multiagent measured-flow, out-of-circle vaporizers (Copper Kettle, Vernitrol). In-the-cir-cle vaporizers (VIC) almost always are located on theinspiratory side of the breathing system and the patientbreathes through the vaporizer. Vaporization and anes-thetic concentration in the breathing system is con-trolled by patient ventilation (increased ventilation willincrease vaporization); the arbitrary settings on thevaporizers (Ohio #8, 0–10; Stephens, off–8) indicate theamount of inspiratory flow diverted into the vaporizationchamber. These vaporizers are nonprecision, low resist-ance, and not temperature compensated, meaning thedelivered concentration is unknown and can changeunpredictably, the anesthesia often being referred to asqualitative (versus quantitative). Inspired concentrationincreases with increased temperature, increased ventila-tion (spontaneous or mechanical), and decreased freshgas flow into the breathing circuit. Mechanical ventila-tion is contraindicated with VICs. The Ohio #8, with itswick to increase surface area, was designed specificallyfor methoxyflurane (low volatility). Guidelines for use


95

Figu

re 5

–2

Dia

gra

m o

f va

porize

r an

d b

reat

hin

g co

mponent

loca

tion f

or

VO

C (

vaporize

r out

of

circ

le).

(R

eprinte

d w

ith p

erm

issi

on f

rom

CE S

hort

, Pri

nci

ple

s and P

ract

ice o

f Ve

teri

nary

Anest

hesi

a,

Bal

tim

ore

: W

illia

ms

& W

ilkin

s, 1

987,

pag

e 4

03.)

with isoflurane and halothane (with wick removed) havebeen published; however, this practice is discourageddue to the high volatility of these agents and theincreased potential to deliver fatal concentrations. TheStephens vaporizer has been used for halothane andisoflurane (and sevoflurane) and is intended for use witha low-flow circle breathing system. A wick is provided foruse with methoxyflurane as well. Vigilant monitoring willhelp assure that excessive concentrations are not deliv-ered to the patient.

Measured-flow vaporizers allow use of multipleagents because they contain two oxygen flowmeters, onefor diluent flow and one for vaporizer flow. The appro-priate flow setting for both flowmeters must be calcu-lated to deliver the desired concentration of the specificagent used (Figure 5–3). Originally, a special circularslide rule to determine flowmeter settings was includedwith these vaporizers (see Figure 5–3).

Two other features of anesthesia machines needmention. While not essential, most anesthesia machineshave an oxygen flush valve (OFV), which supplies oxygento the common gas outlet or directly to the breathing cir-cuit at an unmetered rate of 35–75 L/min. The OFV flowbypasses the vaporizer in contemporary machines, butolder machines to which precision vaporizers wereadded later may direct oxygen, with flush activation,through the vaporizer, with the potential to increaseanesthetic output if the vaporizer is turned on. Whenusing an anesthesia machine, the circuitry should be


97

Figure 5–3 Circular slide rule for calculation of oxygen flowsfor an anesthetic machine with a measured-flow VOC vaporizer(Verni-trol, Copper Kettle). The rule can be used for multiple anes-thetic agents and a variety of total oxygen flow rates over a rangeof temperatures. Calculations can be made according to the fol-lowing equations (using halothane as the anesthetic agent):

1. Saturated vapor pressure (halothane) � 243 � 760 � 32%;desired TGF (total gas flow) � 2 L/min; desired halothane con-centration [%Hal] � 1.5%

2. Halothane vapor leaving vaporizer � desired %Hal � TGF � 1.5% � 2000 ml � 30 ml

(continues)

followed and understood prior to use. The OFV is usedto flush (remove) anesthetic from the rebreathing sys-tem during recovery or when problems with anestheticdepth are identified; using it to fill the rebreathing bagin an attempt to ventilate and deepen the patient’s anes-thesia is ineffective, as its purpose is to dilute anestheticconcentration within the breathing circle. The OFVshould not be used in pediatric circuits or nonrebreath-ing systems, both of which have small volumes, due to thedanger of overpressurizing the patient’s respiratory sys-tem. The common gas outlet is the site from which gasesthat have passed through the flowmeter, vaporizer(VOC), or OFV exit the anesthesia machine for deliveryto the breathing system. Some vaporizers, purchased sep-arately and added to a machine, have been placedbetween the common gas outlet and the breathing cir-cuit, which increases the risk of delivering excessive con-


Figure 5–3 (Continued)

3. To provide 30 ml halothane vapor leaving vaporizer: TGF exitingvaporizer � 30 ml � 32%(sat VP) �94 ml.

4. 94 ml (TGF exiting vaporizer) � 30 ml (halothane vapor) � 64ml oxygen entering vaporization chamber (vaporizer flowmetersetting).

5. Bypass oxygen flowmeter setting � 2000 ml (total flow) � 94ml � 1906 ml

(Reprinted with permission from Thurmon et al., eds., Lumb andJones’ Veterinary Anesthesia, 3rd ed., Baltimore: Williams andWilkins, 1996, page 387.)

centrations should the vaporizer be tilted or the oxygenflush valve engaged when the vaporizer is on.

Anesthesia Breathing Systems

The breathing system connects the anesthesia machine(via the fresh gas inlet) to the patient (via mask or endo-tracheal tube). Two types of circuits are used in veteri-nary medicine. The circle rebreathing system is the mostcommon circuit used and is standard equipment onmost anesthesia machines. Pediatric, standard adult(small animal), and large animal circuits differ primarilyin their internal diameters, rebreathing bag, and overallvolume and size of the carbon dioxide absorbent canis-ter. Pediatric and adult circuits have the same sizeabsorbent canister and differ only in the size of thebreathing tubes and rebreathing bag used (Table 5–1).

Circle systems have the same basic components,including:

• The Y-piece (patient connection). • Two breathing tubes (between the Y-piece and one-

way valves).

• Paired one-way valves (inspiratory and expiratory),which prevent rebreathing of exhaled gases beforethey pass through the absorbent canister.

• Fresh gas inlet (site of entry of gases from the com-mon gas outlet).

Anesthetic Equipment 99


Tab

le 5

–1

Siz

es

and R

eco

mm

endat

ions

for

Fresh

Gas

Flo

w R

ates

of

Circl

e S

yste

ms

and N

onre

bre

athin

g Sy

stem

s Bre

ath

ing

Dia

mete

rR

eb

reath

ing

Fresh

Gas

Flow

Syst

em

Tub

e

Bag V

olu

me*

Pati

en

t Siz

eR

ate

(m

l/kg/m

in)

Circ

le Pedia

tric

15 m

m0.5

–1 L

<7kg

4–11 (

close

d)

Adult

22 m

m1 L

8–15 k

g10–20 (

low

flo

w)

2 L

16–30 k

g25–35 (

sem

i-cl

ose

d)

3 L

31–45 k

g5 L

46–135 k

gLa

rge

anim

al50 m

m15 a

nd 2

0 L

135–330 k

g6–10

30 L

>330

Nonre

bre

ath

ing

<5–7 k

g200–600**

Bai

ns

syst

em (

Map

leso

ncl

assi

ficat

ion T

ype

D,

modifi

ed)

Ayr

e’s

T-pie

ce

(Map

leso

n c

lass

ifica

tion

Type

E) N

orm

an e

lbow


(Map

leso

n c

lass

ifica

tion

Type

E) J

acks

on-R

ees

Syst

em (

a m

odifi

ed

Ayr

e’s

T-pie

ce; M

aple

son

clas

sific

atio

n T

ype

E)

*Reb

reat

hin

g bag

siz

e m

ay b

e es

timat

ed b

y m

ulti

ply

ing

6 �

tidal

volu

me

(10 m

l/kg

) �

BW

(kg

).

**Rec

om

men

dat

ions

for

tota

l fre

sh g

as flo

w a

re q

uite

var

iable

in the

liter

ature

but,

in g

ener

al, a

re 2

–3 tim

es m

inute

ventil

atio

n (

170–350 m

l/kg

/min

ute

for

dogs

and c

ats)

to p

reve

nt re

bre

athin

g of ca

rbon d

ioxide.

• Pop-off (relief) valve, which vents gases to the scav-enger system and prevents excessive pressure withinthe system.

• Rebreathing bag, which provides peak demands dur-ing inspiration, a mechanism for manually assistingventilation, and a method for observing sponta-neous ventilation.

• Pressure manometer, usually attached at absorbentcanister and calibrated in cm H2O to assess pressureachieved during assisted ventilation.

• Absorbent canister.

The absorbent canister is filled with either soda limeor barium lime granules (calcium hydroxide is the pri-mary component of both), which neutralize exhaledCO2. The reaction (CO2 � H2O → H2CO3 � 2NaOH �Ca(OH)2 → CaCO2 � Na2CO3 � 4H2O � heat) isexhaustive and produces a change in the granules,including heat generation, soft to hard, and a colorchange (most often white to violet). As a general rule,absorbent granules should be changed after 6–8 hr ofuse or when the color reaction is apparent in approxi-mately two thirds of the granules.

Nonrebreathing systems have no chemical absorbentand depend on a high fresh-gas flow rate to removeexhaled CO2 from the breathing system. They are lessefficient than the rebreathing system; the oxygen andanesthetic agent are wasted; more anesthetic agent must


be scavenged, with a greater potential for environmentalcontamination; and patient heat and humidity is notconserved, so that patient cooling due to convective heatloss is greater. The main advantage is less resistance to breath-

ing; hence, the recommendation for use in small (<5–7kg) patients. They also are lightweight, easy to position,inexpensive (to purchase), and allow rapid changes ininspired anesthetic concentration. Several systems, classi-fied collectively by the Mapleson system, are available; ingeneral, only four are used in veterinary medicine (seeTable 5–1), with the Bains coaxial system being the mostpopular. The Bains system is a tube (inspired fresh gasdelivery) within a tube (carries exhaled gases away fromthe patient to the reservoir bag and scavenging system)and can be fitted with a pressure manometer (with anadditional equipment piece that also has a relief valveand accommodates the reservoir bag).

Waste Gas Scavenging

Several medical problems have been linked to exposureto waste anesthetic gases (see Table 4–5). Guidelines tominimize workplace contamination (see Table 4–6)include a scavenging system on all anesthesia machines tocollect and eliminate waste gases from the workplace. Agas-collecting connection (the pop-off or relief valve), aninterface, and a disposal system compose the scavengingsystem assembly. The interface prevents transfer of pres-sure changes from the disposal system to the breathing



system. It includes positive and negative pressure reliefmechanisms and, for active systems, a reservoir bag toprovide visual assessment of its proper function.

Disposal systems are passive or active. Passive systemsinclude piping waste gases into nonrecirculating ventila-tion systems, directly to the atmosphere, and throughabsorption devices (F/air canisters are portable and neu-tralize inhaled gases with the exception of N2O but havea limited useful life, making them expensive and variablein effectiveness).

Active systems include piped vacuum and active ductsystems. A piped vacuum system is convenient whenalready in place and when location of exit for passive dis-charge is inconvenient. An active duct system with highvolume flow and low negative pressure is ideal for wastegas removal. Tubing for the connecting parts of the scav-enging system ideally should be readily discernible fromthe breathing circuit. Table 5–2 is a simple guide to per-forming routine checks of the anesthesia machine andto detecting leaks from the breathing circuit.

Ventilators

Controlled ventilation is unnecessary for the majority ofanesthetized veterinary patients, but a variety of patientcircumstances will prompt the need for intermittent pos-itive pressure ventilation (IPPV). Indications includeapnea; documentation of severe hypoventilation(↑PaCO2); intrathoracic surgery; patient factors such as


Table 5–2 Recommendations for Routine Assessment ofAnesthesia Machine and Breathing Circuit to Minimize Riskof Malfunction and Environmental Pollution

1. Machine check

a. Check anesthetic level in vaporizer and fill if indicated(preferably, at time when room is not in use).

b. Check tightness of filler cap.

c. Make sure vaporizer setting is in off position.

2. Oxygen supply and delivery

a. Check cylinder pressure (50–60 psi) and assess quan-tity of oxygen available.

b. For machines equipped with N2O source and flowmeter,turn on N2O flow and turn off oxygen supply; N2O floatshould drop to zero. (This should be performed at leastweekly.)

c. Verify proper flowmeter function. Float should movefreely the entire length of flowmeter tube.

3. Check breathing circuit

a. Assure all fittings are tight.

b. Check absorbant canister for need to change soda limeand assure canister is properly positioned and tightly fitted.

c. Confirm proper function of unidirectional valves of circleby inhaling and exhaling through Y-piece and observingappropriate movement.

d. Check for leaks: Close the relief valve, occlude the Y-piece, pressurize the circuit to 30 cm H2O; pressureshould remain stable or drop slowly (<250 ml/min).Open the relief valve to assure release of pressure.

(continues)

obesity, abdominal distention, or primary lung dysfunc-tion; use of an intraoperative neuromuscular blockingagent; surgery lasting more than 90 min; the need forhyperventilation in cases of head trauma; and facilitationof a stable plane of surgical anesthesia by enhancinganesthetic agent delivery and uptake.

Maintaining a PaCO2 between 35 and 45 mmHg isthe general goal of IPPV; however, there is controversyregarding the desired high-end range for PaCO2, with 50mmHg commonly recommended. Moderate increases inPaCO2 support arterial blood pressure through endoge-nous catecholamine release. Intermittent positive pres-sure ventilation decreases cardiovascular function by



4. Check waste gas scavenging system

a. Confirm connection to relief valve.

b. Connect or activate active scavenging system or verifypatency of passive system.

5. Check ventilator function (when applicable).

a. Turn on prior to connection to breathing circuit (mayrequire partially occluding connecting tubing) to assurefunction and appropriate settings.

b. Verify proper connection to breathing circuit, whichincludes closing the relief valve.

c. The scavenging system must be connected to the venti-lator relief valve when in use.

impeding venous return to the heart (and therefore dias-tolic filling). The benefits of IPPV, compared to thepotential detrimental effects, should be considered inevery patient. High-risk patients with inadequate vascu-lar volume or compromised cardiac function may nottolerate IPPV well, as evidenced by exacerbation of lowarterial blood pressure values.

Even though IPPV has a negative effect on cardio-vascular performance, this is minimized by assuring ade-quate intravascular volume, using inotropes to enhancecardiovascular performance (Chapter 7), and applyingIPPV within the recommended guidelines (Table 5–3).

Ventilators are classified broadly, based on mode ofoperation, including pressure cycled and volume cycled.Ventilators require electricity, compressed gas, or bothfor operation. The timing of pressure-cycled ventilators isinfluenced by a preset peak inspiratory pressure limit.Inspiration will continue until a preset pressure isachieved, regardless of the volume delivered. While thistype of operation is safer, in that it will not allow deliveryof excessive pressure during the inspiratory phase, tidalvolume delivered may be inadequate (depending onlung and breathing system compliance). The tidal vol-ume delivered tends to decrease over time unless theventilator periodically is reset to compensate for the tem-poral decrease in lung compliance.

Volume-cycled ventilators deliver a preset tidal volumeregardless of peak pressure achieved. Most ventilators of


this type have settings that limit the maximum pressureachieved to assure patient safety. Maximum pressure dur-ing the inspiratory phase increases as patient compliancedecreases. Leaks in the breathing circuit do not becomereadily apparent with volume-cycled operation, while


Table 5–3 Recommended Settings for Mechanical Ventilation

Setting Guidelines

Tidal volume* 15–20 ml/kg (small animals)

10–15 ml/kg (large animals)

Inspiratory time <1.5 sec (small animals)

<3 sec (large animals)

I:E (inspiratory to expiratory) ≤1:2ratio

Peak inspiratory pressure 12–20 cm H2O (small animals)

20–30 cm H2O (large animals)

Respiratory frequency 8–14 (dogs)

10–14 (cats)

6–10 (horse and cow)

8–12 (small ruminants and pigs)

*Ventilator tidal volume is set slightly higher than the actual patient needs, to allowfor increases in breathing system and airway volume when positive pressure isdelivered. Setting tidal volume too low will permit development of atelectasis. Whenlower tidal volume must be used (e.g., on animals with abdominal distention ordiaphragmatic hernia), the rate should be increased accordingly.

leaks usually are readily apparent with pressure-cycledventilators.

While ventilators historically have been classified aspressure or volume cycled, the terms are somewhat mis-leading because most often a timing mechanism controlsthe change from the inspiratory phase to the expiratoryphase, with inspiratory time being a major determinantof the cycle. Ventilators also are classified according todirection of bellows movement during expiration. Ascending(during expiration) bellows are considered safer,because they will not fill if a disconnection occurs in thebreathing circuit, thus quickly alerting the anesthetist toa problem.

Even though an anesthetized animal may appear tobe ventilating adequately, as indicated by a normal spon-taneous respiratory rate and a “normal”-appearing tidalvolume, some degree of respiratory depression is pres-ent. The subsequent elevation of PaCO2 may be quanti-tated by arterial blood gas analysis or continuouslyreading capnometers, which visually display a value forend-tidal carbon dioxide, an indirect measure of PaCO2.Anesthesia-associated hypercapnia during spontaneousventilation tends to increase with the duration of theanesthesia. This stresses the importance of minimizinganesthesia time and providing ventilatory support, eithermanually or mechanically, for prolonged proceduresand high-risk patients.


6

Monitoring Anesthesia

Based on suggestions by the American College of Veteri-nary Anesthesiologists (ACVA) for monitoring anes-thetized veterinary patients, personnel should be “awareof the patient’s status at all times during anesthesia andrecovery.” No monitoring tool or device can take theplace of constant human observation; available equip-ment is meant to enhance the observation skills of theattending anesthetist. Keeping a record of perianestheticevents (see Figure 1–1) will provide a legal documentand facilitate appropriate observation and temporalrecording of relevant measured parameters and events.Monitoring provides ongoing determination of patientphysiologic status, allowing early recognition and treat-ment of abnormalities and a way to assess therapeutic

111

efficacy. Recommended monitoring methods anddevices are targeted to assure adequate circulation, oxy-genation, and ventilation. The best treatment for anes-thetic complications is prevention. But, when they dooccur, early recognition usually will allow correction withminimal intervention and long-term detrimental effects.

Monitoring efforts concentrate on three bodysystems—the central nervous system (including ocular,musculoskeletal, and other reflexes), the cardiovascularsystem, and the respiratory system—and should includeperiodic temperature assessment. The following guide-lines should be considered:

1. Evaluation of integrated responses, using one ormore parameters for multiple body system assess-ment, allows more accurate and representativeongoing patient assessment than reliance on a singleparameter.

2. Even though a variety of monitoring devices is avail-able, it is best to choose one or two for routine useand become familiar with their benefits and limita-tions, remembering that they are a supplement tomonitoring not a replacement.

3. The monitoring plan should increase in complexity(more quantitative measurements) as patient andprocedure risk increase.

4. Noninvasive monitors are relatively easy to use butresults can be highly variable; the data provided are

112 Monitoring Anesthesia

best viewed as trends (qualitative) over time ratherthan quantitative measurements.

5. In general, invasive monitoring techniques are moreaccurate but more expensive to provide, requiregreater technical skill, and usually are reserved forhigh-risk patients and procedures (horses are anexception, for which invasive arterial blood pressuremonitoring is used routinely during inhalation anes-thesia regardless of patient status).

6. Keeping an anesthetic record provides a method oftracking trends in measured parameters (e.g., heartrate, respiratory rate, blood pressure) and providesinformation for subsequent anesthetic episodes inthat patient.

Signs of the various stages of inhalation anesthesiaare listed in Table 4–1. General anesthesia includes uncon-

sciousness, insensitivity to pain, muscle relaxation, and absence

of reflex response. The degree required for each of theseeffects depends largely on the procedure. While no clearline divides stages and planes of anesthesia, planes 2 and3 of stage III are the desired levels for most procedures.Confounding factors that complicate evaluation accord-ing to stage, include variation in species response toanesthetic agents, premedication agents administered,PaO

2and PaCO

2values, and the patient’s physical status.

Monitoring Anesthesia 113

Tab

le 6

–1

Par

amete

rs M

onitore

d a

nd A

pplic

able

Tech

niq

ues

Use

d D

uring

Genera

lA

nest

hesi

a

Para

mete

rM

eth

od

Co

mm

en

ts

Res

pira

tory

monito

ring

Res

pira

tory

rat

e,

Thora

cic

move

men

tSu

bje

ctiv

e only

. N

o indic

atio

ndep

th, an

d c

har

acte

rReb

reat

hin

g bag

of

adeq

uac

y of

ventil

atio

n.

move

men

tAppro

pria

te f

or

asse

ssin

g ch

ange

s ove

r tim

e.

Esophag

eal st

etho-

May

be

atta

ched

to e

arpie

ces

or

scope

amplif

ier; a

lso d

etec

ts h

eart s

ounds

Res

pira

tory

(ap

nea

) In

terfac

ed b

etw

een E

T tu

be

monito

ran

d b

reat

hin

g sy

stem

. D

etec

tsex

hal

ed b

reat

h b

y ch

ange

in t

em-

per

ature

and p

rovi

des

an a

udib

lebee

p. M

ay n

ot

be

sensi

tive

enough

for

very

sm

all pat

ients

.

Tidal

and m

inute

volu

me

Ventil

om

etry

Ventil

om

eter

is

applie

d t

o e

xpira

tory

side

of

pat

ient

bre

athin

g ci

rcuit

End-tid

al C

O2

(ETC

O2)

Cap

nom

etry

Pro

vides

bre

athin

g ra

te a

nd

ETC

O2

valu

e.


Cap

nogr

aphy

Als

o d

ispla

ys g

raph o

f ex

pire

d C

O2

(Fig

ure

6–1)

Hem

ogl

obin

sat

ura

tion

Puls

e oxi

met

erH

emogl

obin

oxy

gen s

atura

tion a

nd

(SaO

2or

SpO

2)

puls

e ra

te

Arter

ial blo

od g

as a

nal

ysis

Labora

tory

blo

od g

as

Most

acc

ura

te a

sses

smen

t of

(PaC

O2

and P

aO2)

anal

yzer

adeq

uac

y of

ventil

atio

n a

nd

Han

dhel

d a

nal

yzer

sblo

od o

xyge

nat

ion

Card

iova

scula

r m

onito

ring

Hea

rt r

ate

Pre

cord

ial au

sculta

tion

Esophag

eal st

etho-

Als

o a

vaila

ble

with

sel

f-sc

ope

conta

ined

ECG

lea

ds

(Hes

ka

Corp

., Fo

rt C

olli

ns,

CO

)

ECG

Rec

ord

s m

yoca

rdia

l el

ectric

al a

ctiv

itybu

t gi

ves

no in

dica

tion

of a

dequ

acy

of p

erfu

sion

Puls

e ra

te a

nd q

ual

ityPa

lpat

ion

Subje

ctiv

e; s

ites

vary

am

ong

spec

ies:

Can

ine—

dors

al p

edal

, lin

gual

, fe

mora

l

Felin

e—fe

mora

l, �

lingu

al a

nd

dors

al p

edal

(contin

ues

)


Tab

le 6

–1

(Continued)

Para

mete

rM

eth

od

Co

mm

en

ts

Equin

e—fa

cial

, tran

sver

se f

acia

l, dors

al m

etat

arsa

lRum

inan

t—au

ricula

r, co

ccyg

eal,

dig

ital

Swin

e—fe

mora

l, au

ricula

r, co

ccyg

eal,

bra

chia

lPuls

e oxi

met

ryPro

vides

puls

e ra

te a

nd indire

ct

asse

ssm

ent

of

blo

od o

xyge

nat

ion

(SaO

2; Fi

gure

6–2)

Art

eria

l blo

od p

ress

ure

N

onin

vasi

veTw

o m

ethods

(both

req

uire

cuff*)

:(A

BP)

1. O

scill

om

etric

—pro

vides

hea

rt r

ate

plu

s sy

stolic

, m

ean, an

d d

iast

olic

AB

P a

t pre

set

inte

rval

s.2. D

opple

r cr

ysta

l pro

be—

applie

d

ove

r ar

tery

dis

tal to

a c

uff w

ithm

anom

eter

. Sk

in o

ver

arte

ry m

ust

be

close

ly c

lipped

, ge

l ap

plie

d

and p

robe

taped

in p

lace

, w

hic

ham

plif

ies

sound o

f puls

e. R

elia

bly


mea

sure

s sy

stolic

AB

P o

nly

.**Als

opro

vides

contin

uous

audito

ryin

form

atio

n o

n p

uls

e rh

ythm

and

qual

ity. Le

ss a

uto

mat

ed t

han

osc

illom

etric

tec

hniq

ue.

Inva

sive

†Pro

vides

contin

uous,

acc

ura

te

read

out

of

SAP,

MAP,

and D

AP.

Req

uire

s ar

teria

l ca

thet

er a

ttac

hed

to a

pre

ssure

tra

nsd

uce

r an

dre

cord

ing

dev

ice

or

sphyg

mo-

man

om

eter

(M

AP o

nly

) vi

asa

line-

fille

d t

ubin

g. S

ensi

tive

mon-

itor

of

anes

thet

ic d

epth

, es

pec

ially

use

ful in

hors

es.

Site

s fo

r arter

ial ca

thet

eriz

atio

n:

Can

ine—

dors

al p

edal

, lin

gual

, fe

mora

lFe

line—

fem

ora

l, dors

al p

edal

Equin

e—fa

cial

, tran

sver

se f

acia

l, dors

al m

etat

arsa

l(c

ontin

ues

)


Tab

le 6

–1

(Continued)

Para

mete

rM

eth

od

Co

mm

en

ts

Rum

inan

t—au

ricula

rSw

ine—

auric

ula

r, fe

mora

l

Cen

tral

ven

ous

pre

ssure

Mea

sure

d w

ith c

athet

erRef

lect

s th

e bal

ance

bet

wee

n b

lood

(CVP)

pla

ced into

ante

rior

volu

me

and c

apac

ity a

nd h

elps

vena

cava

via

jugu

lar

avoid

pulm

onar

y ed

ema

and

vein

and c

onnec

ted

ove

rhyd

ratio

n w

ith r

apid

flu

idto

man

om

eter

or

adm

inis

trat

ion in h

igh-ris

kpre

ssure

tra

nsd

uce

r pat

ients

.ze

roed

at

thora

cic

Norm

al va

lues

:in

let

0–10 c

m H

2O

(sm

all an

imal

)5–15 c

m H

2O

(aw

ake

hors

es)

25–35 c

m H

2O

(an

esth

etiz

ed

hors

es)

Urin

e outp

ut

Urin

ary

cath

eter

con-

Indire

ct m

easu

re o

f org

annec

ted t

o c

lose

d

per

fusi

on. Es

pec

ially

colle

ctio

n s

yste

mim

portan

t in

ren

al d

isea

se.

Norm

al:

1–2 m

l/kg

/hr


Note

s: T

he

goal

of re

spira

tory

monito

ring

is to d

eter

min

e an

d m

ainta

in a

deq

uac

y of ve

ntil

atio

n (

norm

al P

aCO

2an

dPa

O2). T

he

goal

of ca

rdio

vasc

ula

r m

onito

ring

is to m

onito

r th

e el

ectric

al a

ctiv

ity o

f th

e hea

rt a

nd e

nsu

re a

deq

uat

e per

fu-

sion o

f vi

tal o

rgan

s, p

artic

ula

rly the

bra

in, h

eart, a

nd k

idney

s.

SAP =

sys

tolic

AB

P; M

AP =

mea

n A

BP; D

AP =

dia

stolic

AB

P.

*C

uff

wid

th is

appro

xim

atel

y 40%

the

circ

um

fere

nce

of th

e ap

pen

dag

e.

**As

a ge

ner

al r

ule

, when

the

syst

olic

AB

P is

90–100 m

mH

g, m

ean A

BP is

60–70 m

mH

g.†A m

inim

um

mea

n A

BP o

f 60–70 m

mH

g is

consi

der

ed n

eces

sary

to a

ssure

per

fusi

on o

f vi

tal o

rgan

s in

all

spec

ies.

Cat

-tle

may

dem

onst

rate

hig

her

val

ues

durin

g ge

ner

al a

nes

thes

ia a

nd r

ecum

ben

cy, e

spec

ially

as

dura

tion o

f an

esth

esia

incr

ease

s (e

.g.,

mea

n A

BP =

100–150 m

mH

g). H

ors

es h

ave

bee

n r

eported

to e

xhib

it hig

h v

alues

, whic

h in

crea

se o

ver

time

in a

ssoci

atio

n w

ith tourn

iquet

applic

atio

n (

star

ting

appro

xim

atel

y 45 m

in a

fter

tourn

iquet

pla

cem

ent)

.


Assessment of the cardiovascular and respiratorysystems incorporate subjective and objective data thatindicate the state of circulation, oxygenation, and venti-lation. Table 6–1 lists the parameters that may beassessed and methods and equipment available. Table6–2 provides details on the principles and operation ofthe capnograph and pulse oximeter. Table 6–3 lists nor-mal values for some measured parameters in a variety ofspecies. Table 6–4 lists some potential abnormalities thatmay develop during general anesthesia, potential causesto be investigated, and an approach to management.


Tab

le 6

–2

Princi

ple

s of

Opera

tion a

nd S

ignific

ance

of

Info

rmat

ion P

rovi

ded b

yM

onitoring

Equip

ment

Use

d in V

ete

rinar

y M

edic

ine

Eq

uip

men

tP

rin

cip

les

of

Op

era

tio

nP

rob

e S

ite(s

)/So

urc

e o

f Err

or

Cap

nogr

aphy

Infrar

ed a

bso

rptio

n is

the

most

Tw

o a

nal

yzer

typ

es p

lace

d b

etw

een

(Fig

ure

6–1)

com

mon m

easu

ring

met

hod

ET t

ube

and b

reat

hin

g ci

rcuit:

to d

eter

min

e CO

2in

exp

ired

1. Si

des

trea

m—

aspira

tes

gase

s in

toga

ses.

ETC

O2

repre

sents

an

alyz

er v

ia t

ubin

g (5

0–250 m

l/al

veola

r CO

2, w

hic

h

min

), r

esulti

ng

in lag

tim

e.eq

uili

bra

tes

with

PaC

O2,

2. M

ainst

ream

—m

easu

res

CO

2

refle

ctin

g ve

ntil

atory

effi

cien

cy.

dire

ctly

in a

irway

, no lag

tim

e.N

orm

al c

apnogr

am r

equire

s Er

ror: E

TCO

2under

estim

ates

PaC

O2

met

abolis

m, ci

rcula

tion, an

d

by

appro

xim

atel

y 5 m

mH

gve

ntil

atio

n a

nd it

thus

(up t

o 1

4 in h

ors

es)

due

tom

onito

rs m

ulti

ple

vita

l al

veola

r dea

d s

pac

e. Idea

lly,

funct

ions.

it

is a

good idea

to a

sses

s ac

tual

PaC

O2 p

erio

dic

ally

durin

g use

.

Puls

e oxi

met

ry

Estim

ates

oxy

genat

ed h

emo-

Two p

robe

types

:(S

aO2

or

globin

(H

gb)

as a

per

cent

of

1. Tr

ansm

ittan

ce—

sends

and

SpO

2)

tota

l hem

ogl

obin

. Bas

ed o

n

rece

ives

lig

ht

acro

ss t

issu

e:(F

igure

6–2)

prin

ciple

that

oxy

genat

ed a

nd

tongu

e, t

oe

web

, ea

r, vu

lva.

(contin

ues

)


Tab

le 6

–2

(Continued)

Eq

uip

men

tP

rin

cip

les

of

Op

era

tio

nP

rob

e S

ite(s

)/So

urc

e o

f Err

or

deo

xyge

nat

ed H

gb a

bso

rb

2. Ref

lect

ance

—se

nds

and r

ecei

ves

light

diff

eren

tly a

t diff

eren

t lig

ht

on t

he

sam

e pla

ne:

wav

elen

gths,

660 n

m (

red)

esophag

us,

rec

tum

, m

uco

us

and 9

40 n

m (

infrar

ed).

m

embra

nes

.Req

uire

s puls

atile

blo

od.

Erro

r:H

emogl

obin

sat

ura

tion

1. Lo

w p

uls

e pre

ssure

.re

flect

s blo

od o

xyge

nat

ion

2. In

crea

sed v

enous

puls

atio

ns

(PaO

2)

as r

epre

sente

d b

y th

e (e

.g.,

right-hea

rt f

ailu

re,

oxy

hem

ogl

obin

dis

soci

atio

n

tourn

iquet

).cu

rve

(Fig

ure

6–2).

3. C

ardia

c ar

rhyt

hm

ias.

4. M

ove

men

t.5. D

yshem

ogl

obin

s (e

.g.,

met

he-

mogl

obin

, ca

rboxy

hem

ogl

obin

).6. D

yes

(e.g

., m

ethyl

ene

blu

e).

7. A

nem

ia (

<5 g

m/d

l).

8. Ex

tern

al lig

ht.

9. El

ectroca

ute

ry u

nits

.10. Po

or

pro

be

posi

tionin

g


123

Figure 6–1 Diagram of normal expired CO2 waveform. Thethree phases of the normal waveform include apparatus andanatomical series dead space (phase I), mixture of anatomicalseries and alveolar parallel gas (phase II), and the alveolar plateau(phase III), a mixture of gases from well-perfused alveoli and alve-olar dead space (unperfused alveoli). (Reprinted with permissionfrom KK Tremper, Interpretation of noninvasive oxygen and carbondioxide data. Can J Anaesth 1990;37(4):Slxxxi.)

124

Figure 6–2 (A) The oxyhemoglobin dissociation curve illus-trates the relationship between blood oxygen tension (PO2) andhemoglobin saturation (SaO2). A simple guide summarizing therelationship between PaO2 and SaO2 follows for interpretation ofpulse oximeter readings obtained during clinical monitoring.

PaO2 (mmHg) SaO2 (%) Interpretation

>80 >95 Normal

<60 <90 Significant hypoxemia

<40 <75 Serious life-threatening hypoxemia

(B) A combination pulse oximeter and electrocardiograph. (Courtesy of SurgiVet Inc., Waukesha, WI.)

Plateau Phase

Arterial

Blood

Steep

Phase

Venous

Blood

Oxygen Tension (PO2)

He

mo

glo

bin

Sa

tura

tio

n (

SO

2)

20

0 20 30 40 60 80 120

40

60

80

100

(A)

(B)

Tab

le 6

–3

“Norm

al”

Val

ues

for

Sele

cted M

eas

ure

d P

aram

ete

rs in a

Var

iety

of

Speci

es

Para

mete

rD

og

Cat

Ho

rse

Cow

Go

at/

Sh

eep

Pig

Rab

bit

Tem

per

ature

37–40

37–40

37–38

37–39

37–40

38–40

38–40

(core

°C

)

Hea

rt

70–140

100–200

25–50

60–80

60–90

60–90

200–325

rate

/min

*

Res

pira

tory

10–30

12–40

8–15

12–30

15–30

10–30

30–60

rate

/min

Min

ute

170–350

200–350

NA

NA

100–130

300–400

190–240

ventil

atio

n(m

l/kg

/min

)

Blo

od v

olu

me

75–90

45–65

70–100

57–60

60–70

50–70

55–65

(ml/

kg)

Note

s: T

he

follo

win

g va

lues

are

com

mon to a

ll sp

ecie

s:

ET C

O2

(mm

Hg)

30–40

SpO

2(%

)>

95%

Arter

ial p

H7.

35–7.

45

PaCO

2(m

mH

g)35–45

*Rat

es ten

d to b

e hig

her

in n

eonat

es.


PaO

2(m

mH

g)80–100 (

room

air:

FIO

2=

.21)

>300 (

100%

oxy

gen: F IO

2=

1.0

)

Bic

arbonat

e (m

Eq/L

)17–25 (

smal

l anim

als)

25–31 (

larg

e an

imal

s)Bas

e ex

cess

(m

Eq/L

)–4–

+4

Tab

le 6

–4

Trouble

shooting

Identified P

roble

ms

During

Anest

hetic

Monitoring

Co

mp

lica

tio

nP

ote

nti

al

Cau

ses

Man

agem

en

t

Tach

ypnea

Too lig

ht

or

too d

eeply

Ass

ess

anes

thet

ic d

epth

anes

thet

ized

Hyp

oxe

mia

, hyp

erca

rbia

, Ass

ess

arte

rial pH

and b

lood g

asac

idosi

sH

yper

ther

mia

Ass

ess

tem

per

ature

Dru

g in

duce

d (

opio

ids,

Ass

ess

com

plia

nce

, dep

thhal

oth

ane)

Ate

lect

asis

, pneu

moth

ora

x,

Asp

irate

ple

ura

l sp

ace

if in

dic

ated

ple

ura

l ef

fusi

on

Dec

reas

ed

Too d

eeply

anes

thet

ized

Ass

ess

anes

thet

ic d

epth

resp

irato

ry r

ate,

apnea

, ch

ange

in c

har

acte

r

Pre

ssuriz

atio

n in b

reat

hin

g C

hec

k an

esth

esia

mac

hin

eci

rcuit

Tube

occ

lusi

on

Ass

ure

pat

ent

ET t

ube

Effe

ct o

f in

ject

ed a

nes

thet

ic

Pro

vide

ventil

atory

support

until

agen

tssp

onta

neo

us

bre

athin

g re

sum

es


Hyp

oth

erm

iaAss

ess

tem

per

ature

, dec

reas

e dep

th, pro

vide

hea

t

Iatroge

nic

hyp

erve

ntil

atio

nAllo

w C

O2

to incr

ease

to t

rigge

r sp

onta

neo

us

ventil

atio

n

Sinu

s br

adyc

ardi

a:*

Dru

g-in

duce

d (

alpha 2

Adm

inis

ter

antic

holin

ergi

cD

ogs

: <

60–

agonis

ts, opio

ids)

agen

t (A

ppen

dix

1)

70/m

inEx

cess

ive

anes

thet

ic d

epth

, Ass

ess

tem

per

ature

, pro

vide

hea

t,C

ats:

<90–

hyp

oth

erm

ia**

dec

reas

e an

esth

etic

dep

th,

100/m

in

adm

inis

ter

antic

holin

ergi

c ag

ent

Hors

es: <

20–

25/m

inC

attle

: <

40–

50/m

in

Sm. R

um

inan

ts:

Hyp

erte

nsi

on, in

crea

sed IC

P<

50/m

inSu

rgic

ally

induce

d v

agal

O

cula

r an

d v

isce

ral m

anip

ula

tion:

stim

ula

tion

stop m

anip

ula

tion

Hyp

ote

nsi

on, m

yoca

rdia

l Ass

ess

AB

P, o

xyge

nat

ion s

tatu

sis

chem

ia

Hyp

erka

lem

iaRev

iew

his

tory

; as

sess

ser

um

[K

+]

(contin

ues

)


Tab

le 6

–4

(Continued)

Co

mp

lica

tio

nP

ote

nti

al

Cau

ses

Man

agem

en

t

Sinus

tach

ycar

dia

Too lig

htly

anes

thet

ized

(pai

n)

Ass

ess

anes

thet

ic d

epth

Hyp

ote

nsi

on

Ass

ess

puls

e qual

ity/A

BP

Pro

vide

inotropic

support

Hyp

erca

pnia

, hyp

oxe

mia

Ass

ess

arte

rial blo

od g

ases

Dru

g in

duce

d (

antic

holin

ergi

c,

dis

soci

ativ

e ag

ents

; th

iobar

bitu

rate

s, c

atec

hola

-m

ines

)

Hyp

ote

nsi

on

Too d

eeply

anes

thet

ized

Ass

ess/

reduce

anes

thes

ia d

epth

†

Blo

od o

r flu

id loss

Incr

ease

flu

id a

dm

inis

trat

ion r

ate

Pro

vide

blo

od/c

ollo

id s

upport

Endoto

xem

ia, se

psi

sRev

iew

his

tory

, pro

vide

inotropic

su

pport: dobuta

min

e (2

–10 m

cgor

µg/

kg/m

in);

dopam

ine

(5–10

mcg

or

µg/

kg/m

in);

ephed

rine

(0.0

3–0.1

mg/

kg IV b

olu

s, low

erdose

ran

ge f

or

larg

e an

imal

s)


Ventric

ula

r Prim

ary

myo

card

ial dis

ease

/Rev

iew

his

tory

; trea

t w

hen

PVC

sar

rhyt

hm

ias

trau

ma

mee

t lis

ted c

riter

ia(P

VCs)

Hyp

ovo

lem

ia, hyp

ote

nsi

on

Ass

ess

fluid

req

uire

men

ts; AB

PH

yper

capnia

, hyp

oxe

mia

Ass

ess

arte

rial blo

od g

as, pro

vide

ventil

atio

n a

s in

dic

ated

Inad

equat

e an

esth

etic

dep

th

Ass

ess

dep

th; su

pple

men

t an

esth

esia

(pai

n)

as n

eeded

Elec

troly

te im

bal

ance

sRev

iew

his

tory

; as

sess

ser

um

el

ectroly

te c

once

ntrat

ions

Crit

eria

for

PVC

tre

atm

ent:

Lidoca

ine

ther

apy:

1–2 m

g/kg

>

15–20/m

in, m

ulti

foca

l,(0

.2–0.5

mg/

kg f

or

cats

, hors

es):

occ

urren

ce in r

uns,

bolu

s IV

2–4 t

imes

ove

r 20 m

in.

acco

mpan

ied b

y poor

For

repea

ted r

eturn

of

PVC

s: S

tart

puls

e qual

ityin

fusi

on a

t 50–100 m

cg o

r µg/

kg/m

in (

add 1

mg/

ml to

cr

ysta

lloid

flu

id; gi

ve a

t 0.0

5–0.1

m

l/kg

/min

)

ICP =

intrac

rania

l pre

ssure

AB

P =

arter

ial b

lood p

ress

ure

(contin

ues

)


Tab

le 6

–4

(Continued)

*G

uid

elin

es for

hea

rt r

ate

are

for

adults

. A h

igher

val

ue

should

be

consi

der

ed a

s “m

inim

um

” hea

rt r

ate

in n

eonat

es.

Neo

nat

es a

re m

ore

dep

enden

t on h

eart r

ate

for

adeq

uat

e ca

rdia

c outp

ut,

and in

gen

eral

, bra

dyc

ardia

should

be

trea

ted

more

agg

ress

ivel

y w

ith a

ntic

holin

ergi

c ag

ent su

pport.

**Anim

als

with

pro

found h

ypoth

erm

ia m

ay n

ot re

spond e

ffect

ivel

y to

antic

holin

ergi

c ag

ents

. Dec

reas

ing

anes

thes

iadep

th a

nd a

ttem

pts

to r

ewar

m a

re im

portan

t as

pec

ts o

f m

anag

emen

t.† A

dm

inis

trat

ion o

f in

trao

per

ativ

e opio

ids

may

hel

p to s

par

e ge

ner

al a

nes

thet

ic r

equire

men

ts w

ith m

inim

al e

ffect

on

myo

card

ial c

ontrac

tility

.130 Monitoring Anesthesia

7Supportive Care During Anesthesia

Supportive care during general anesthesia contributessignificantly to a successful outcome. Many factors, suchas increased patient risk and prolonged, complex, andinvasive procedures, increase the critical need for sup-portive measures that will assure patient homeostasisduring the anesthetic period. Supportive care beginspreoperatively with a thorough patient evaluation,including physical examination and appropriate diag-nostic evaluation and correction of any abnormalitiesidentified, especially fluid and electrolyte deficits and pHabnormalities. Intraoperative support includes appropri-ate fluid administration, assurance of acid-base balance,ventilatory support (Chapter 5), administration ofadjunct drugs as indicated, provision of external heat,

131

and positioning considerations. The most critical factorguiding supportive care during the anesthetic period isadequate monitoring (Chapter 6). Monitoring is the linkbetween recognition of developing problems and rapidcorrection before the problem becomes life threatening.

Fluid Therapy

Fluid therapy usually is unnecessary for short proceduresin healthy patients, although it is always advisable to haveintravenous access established for any anesthetizedpatient, in case of unexpected blood loss, the need forcardiorespiratory supportive drugs, or additionalinjectable anesthetic agents. For high-risk patientsundergoing invasive, prolonged procedures, fluidadministration provides replacement for intraoperativeevaporative losses and third space losses associated withsurgical trauma or the existing primary disease process,and it helps maintain cardiovascular stability and organperfusion, which are altered by anesthetic agents.

Most commonly and for most species, a balancedcrystalloid fluid similar in composition to extracellularfluid (e.g., LRS or Normosol-R) is administered at a rateof 10 ml/kg/hr. After the initial two hours of anesthesia, ifblood loss is minimal and arterial pressure stable,decreasing the fluid rate to 4–8 ml/kg/hr is recom-mended to avoid excessive dilution of packed cell vol-ume (PCV) and total protein, especially duringprolonged procedures. These fluid rate guidelines must

132 Supportive Care During Anesthesia

be adjusted, based on the individual patient, blood orother body fluid loss (e.g., third space loss), and bloodpressure monitoring, to assure adequate tissue perfu-sion. Normal body water percentage and distributionand electrolyte composition of body water and severalcommercially available fluids are listed in Table 7–1.

The following guidelines are for fluid therapy in theperioperative period:

1. Abnormalities identified on preoperative evaluation,including dehydration and acid-base and electrolyteimbalances, should be corrected prior to inductionof anesthesia, whenever possible. Table 7–2 providesa general guide for clinical and laboratory assess-ment of dehydration.

2. Fluids that do not contain an alkalinizing agent (i.e.,0.9% saline, 5% dextrose, Ringer’s) tend to promotemetabolic acidosis (by dilution) if used for pro-longed periods.

3. Blood loss may be replaced with crystalloid fluids atthree times the estimated blood volume as long asPCV remains above 20%. This guideline is based onthe fact that crystalloid fluids distribute to the entireextracellular fluid volume (ECF), which is approxi-mately three times the blood volume.

4. Fluids to which glucose has been added (for 2.5%,add 25 mg/ml; for 5%, add 50 mg/ml) should beadministered to neonates, small patients (<2 kg),

Supportive Care During Anesthesia 133


Tab

le 7

–1

Body

Wat

er

Com

par

tment

Perc

enta

ges,

the E

lect

roly

te C

om

posi

tion o

fB

ody

Wat

er,

and C

om

monly

Use

d P

arente

ral Fl

uid

s Ele

ctro

lyte

Co

mp

osi

tio

n (

mEq

/L)

Perc

en

tage (

% �

Na

Cl

KH

CO

3*

Ca

+2

MG

+2

Osm

**B

W i

n k

g y

ield

s L)

Body

wate

r sp

ace

Tota

l body

wat

er60%

(60–75%

: hig

her

in n

eo-

nat

es; lo

wer

w

ith o

bes

ity)

ECF

(ext

race

llula

r20–30%

fluid

)

Pla

sma

volu

me

5%

142

106

524

52

282

Blo

od v

olu

me

8–10%

(dep

ends

on h

emat

ocr

it)

Inte

rstit

ial flu

id15–25%

145

115

430

32

(EC

F—pla

sma

volu

me)

ICF

(intrac

ellu

lar flu

id)

30–40%

13

2155

10

22

35


Com

mer

cial flu

ids

LRS

130

109

428

30

272

Rin

ger’s

147

156

40

50

312

Norm

oso

l-R

148

98

527(a

)5

0296

23(g

)

Multi

sol-R

140

98

527(a

)3

3294

23(g

)

5%

dex

trose

(5 g

m0

00

00

0252

/dl gl

uco

se)

0.9

% s

alin

e154

154

00

00

308

Hyp

erto

nic

sal

ine

1200

1200

00

00

2400

(7%

)

1.3

% N

aHCO

3156

00

156

00

312

5%

NaH

CO

3600

00

600

00

1200

8.4

% N

aHCO

31000

00

1000

00

2000

(1 m

Eq/L

)

*O

r bic

arbonat

e-lik

e pre

curs

or:

LRS

(lac

tate

); N

orm

oso

l-R, o

r M

ulti

sol-R

(ac

etat

e [a

] or

gluco

nat

e [g

]).

**m

Osm

ol/

L.


Tab

le 7

–2

Clin

ical

and L

abora

tory

Ass

ess

ment

of

Dehyd

ration

Sk

in

TP

**%

Deh

yd

rati

on

*Te

nt

MM

Mo

istu

reEye

CR

TP

CV

**(%

)(g

m/d

l)

5–6%

2–3 s

ecM

ois

t but

Brig

ht,

slig

htly

<3 s

ec40–60

7.0–8.0

stic

kysu

nke

n

7–9%

3–5 s

ecSt

icky

to d

ryD

ull,

sunke

n3–4 s

ec60–65

8.0

–9.0

>9%

>5 s

ecD

ry, cy

anotic

Corn

ea d

ry>

4 s

ec>

65%

>9.0

Note

: Fl

uid

req

uire

men

ts for

deh

ydra

tion a

re c

alcu

late

d b

y th

e eq

uat

ion

Fluid

to a

dm

inis

ter

(L)

= %

deh

ydra

tion �

body

wei

ght (k

g)

When

tim

e per

mits

, it is

bes

t to

rep

lace

flu

id d

efic

it sl

ow

ly, o

ver

12–24 h

r to

allo

w w

hole

body

redis

trib

utio

n.

MM

= m

uco

us

mem

bra

ne

CRT

= c

apill

ary

refil

l tim

e

PC

V =

pac

ked c

ell v

olu

me

TP =

tota

l pro

tein

*≤

5%

deh

ydra

tion is

not cl

inic

ally

det

ecta

ble

.

**N

orm

al P

CV a

nd T

P v

alues

var

y am

ong

spec

ies

(Tab

le 1

–3)

and w

ill b

e af

fect

ed b

y under

lyin

g

conditi

ons

that

affe

ct n

orm

al v

alues

, such

as

anem

ia a

nd h

ypopro

tein

emia

.

avian patients, and animals at risk for hypoglycemia(e.g., those with insulinoma, diabetes mellitus, por-tal caval shunt) to avoid a hypoglycemic crisis. It isadvisable to monitor blood glucose levels duringprolonged anesthetic periods.

5. Administration of large quantities of fluids at roomtemperature can contribute significantly to hypother-mia. Efforts should be taken to warm fluids (cocoon-ing the administration line in hot water bottles,warming the fluids, using commercially availableinfusion warmers during prolonged administration;Figure 7–1), especially in small patients.

6. Administration of large quantities of fluids can con-tribute to the development of cerebral and pul-monary edema (this depends on many factors,including fluid administration rate, patient’s serumprotein concentration, and cardiac function). In at-risk patients, consider administration of a colloid, ifnecessary, to maintain adequate circulating volumeand blood pressure.

7. Animals that may not handle volume overload (e.g.,those with mitral insufficiency) should receive fluidsat 50% or less the standard rate.

8. Maximum rate of fluid administration is 90 ml/kg/hr for most domestic species; cats should notreceive greater than 50 ml/kg/hr. Higher rates (upto 360 ml/kg/hr) probably will be tolerated inrelatively healthy patients; administer fluids as rap-


138

Figure 7–1 Infusion warmers are available in two sizes toaccommodate fluid and blood administration sets. These devicesare especially useful for administering blood products or large vol-umes of fluid during prolonged procedures to help minimizehypothermia. (Reprinted with permission from Thurmon et al.,eds., Lumb and Jones’ Veterinary Anesthesia, 3rd ed., Baltimore:Williams & Wilkins, 1996, page 579.)

idly as necessary to achieve hemodynamic stabilityand decrease the rate as soon as this occurs.

9. For hypokalemic animals, it is best to correct thedeficit prior to anesthesia; K+-supplemented fluidsadministered during anesthesia could result in car-diac conduction disturbances, if fluid administrationwere suddenly increased. Potassium supplementa-tion is common (adding 10–30 mEq/L) duringsupportive care of patients with a variety of abnor-malities, such as anorexia, diarrhea, or vomiting.Intravenous potassium administration must notexceed 0.5 mEq/kg/hr.

10. Intraoperative serial assessment of packed cell vol-ume and total protein is advisable in prolonged pro-cedures and necessary when significant blood lossoccurs. While numbers vary in the literature, bloodloss greater than 20% of total blood volume (i.e.,8–10% of body weight; Table 6–3) in healthy patientsand greater than 10% loss in critical patients shouldbe replaced with whole blood, packed red cells, or anartificial blood solution, depending on availability.Colloids should be administered when hypopro-teinemia is present or when crystalloid fluids fail tomaintain adequate blood pressure (i.e., minimum of60 mmHg, mean arterial pressure). Table 7–3 listssome available blood and colloid products and basicindications and guidelines for use.



Tab

le 7

–3

Adju

nct

s to

Flu

id T

hera

py

During

Anest

hesi

a: I

ndic

atio

ns,

Sid

e E

ffect

s,an

d G

enera

l G

uid

elin

es

for

Use

Pro

du

ctIn

dic

ati

on

sSid

e E

ffect

sD

osa

ge/C

om

men

ts

Blo

od r

epla

cem

ents

Whole

blo

od*

Anem

ia,

Imm

une

reac

tion

1. Bas

ed o

n e

stim

ated

loss

hem

orrhag

ecr

oss

-mat

ch is

2. Bas

ed o

n e

quat

ion:

reco

mm

ended

es

pec

ially

with

re

pea

t tran

s-fu

sions

3. Em

piri

cal:

10–40 m

l/kg

(d

og)

and 5

–20 m

l/kg

(cat

s), freq

uen

t re

asse

ss-

men

tPa

cked

red

cel

ls**

Anem

ia,

Sam

e as

pre

vious

Sam

e as

pre

vious.

Dilu

te

hem

orrhag

ew

ith s

alin

e to

adm

inis

ter.

Blo

od s

ubst

itute

†Anem

ia,

Urin

e/tis

sue

15–30 m

l/kg

: ra

te <

10 m

l/hem

orrhag

edis

colo

ratio

n,

kg/h

r vo

lum

e ove

r-lo

ad, ar

ryth

mia

s,

renal to

xici

ty

Amou

nt =

desi

red

PCV

– ac

tual

PC

V

dono

r PC

V

�re

cipi

ent b

lood

vol

ume


Collo

ids

Pla

sma*

Hyp

opro

tein

emia

,Alle

rgic

rea

ctio

n,

10–20 m

l/kg

, in

itial

em

piri

cal

volu

me

volu

me

ove

r-dose

. C

alcu

latio

n m

ay b

eex

pan

sion

load

bas

ed o

n t

he

equat

ion:

End p

oin

t dire

cted

by

seria

l TP

ass

essm

ent.

Intrav

ascu

lar

life-

span

: 4–15

day

s

Dex

tran

(40 a

nd 7

0)

Sam

e as

for

Sam

e as

for

5–20 m

l/kg

ove

r 24 h

rpla

sma

pla

sma,

(m

ore

rap

id f

or

shock

)co

agulo

pat

hy

End p

oin

t is

dire

cted

by

stab

iliza

tion o

f AB

P.In

trav

ascu

lar lif

e-sp

an: 2–24 h

r

Het

asta

rch

Sam

e as

for

Sam

e as

for

5–20 m

l/kg

ove

r 24 h

rpla

sma

pla

sma,

(m

ore

rap

id f

or

shock

)co

agulo

pat

hy

End p

oin

t is

dire

cted

by

stab

iliza

tion o

f AB

P.(c

ontin

ues

)

Amou

nt =

desi

red

TP –

act

ual T

P

dono

r pl

asm

a TP

�re

cipi

ent p

lasm

a vo

lum

e


Tab

le 7

–3

(Continued)

Pro

du

ctIn

dic

ati

on

sSid

e E

ffect

sD

osa

ge/C

om

men

ts

Intrav

ascu

lar

life-

span

: 6 h

r (l

onge

r fo

r Pe

nta

star

ch)

Alk

alin

izin

g a

gen

ts

Bic

arbonat

eM

etab

olic

In

trac

ellu

lar

1. Adm

inis

ter

if pH

<7.

2 o

rac

idosi

sac

idosi

sbas

e def

icit

is >

—10 m

Eq/L

. Avo

id in t

he

pre

sence

of

hyp

ove

ntil

atio

n b

ecau

se

hyp

erca

pnia

is

exac

erbat

ed

and p

H f

urt

her

dec

reas

ed

by

incr

ease

d f

orm

atio

n o

f C

O2

when

HCO

3co

mbin

es

with

H+

ions.

Do n

ot

coad

-m

inis

ter

with

Ca+

+or

blo

od p

roduct

s.2. Q

uan

tity

to a

dm

inis

ter

is

bas

ed o

n b

ase

def

icit.

Q

uan

tity

(mEq

/L)

= B

ase

def

icit

�0.3

�body


wei

ght

(kg)

. G

ive

1/4

–1/2

of

calc

ula

ted d

efic

it ove

r 30 m

in a

nd r

eass

ess.

Trom

etham

ine

Met

abolic

O

smotic

diu

resi

s,1. D

osa

ge (

ml)

= b

ase

def

icit

org

anic

am

ine

acid

osi

shyp

ogl

ycem

ia�

1.1

�body

wei

ght

(kg)

buffer

(0.3

M)

incr

ease

s 2. Adm

inis

ter

slow

ly; ra

pid

coag

ula

tion

infu

sion c

an c

ause

ECG

tim

esch

ange

s si

mila

r to

hyp

er-

kale

mia

.

3. Adm

inis

trat

ion is

contrai

n-

dic

ated

with

ure

mia

and

anuria

.

Car

diov

ascu

lar

drug

s

Lidoca

ine

Ventric

ula

r Se

e cr

iteria

in t

ext

Dosa

ges

liste

d in T

able

6–4.

arrh

ythm

ias,

Avo

id w

hen

hea

rt r

ate

isve

ntric

ula

r lo

w (

<120–140/m

in f

or

tach

ycar

dia

dogs

); it

may

induce

pro

-fo

und b

radyc

ardia

and

hav

e si

gnifi

cant

neg

ativ

e ef

fect

on c

ardia

c outp

ut.

(contin

ues

)


Tab

le 7

–3

(Continued)

Pro

du

ctIn

dic

ati

on

sSid

e E

ffect

sD

osa

ge/C

om

men

ts

Dobuta

min

eH

ypote

nsi

on

Sinus

tach

ycar

dia

,2–10 µ

g/kg

/min

ute

arrh

ythm

ias

Dopam

ine

Hyp

ote

nsi

on,

Sinus

tach

ycar

dia

,5–10 µ

g/kg

/min

: lo

w d

ose

dec

reas

ed

arrh

ythm

ias

(2–5 µ

g/kg

/min

) is

urin

e re

com

men

ded

for

pro

duct

ion

incr

easi

ng

renal

per

fusi

on to

impro

ve u

rine

form

atio

n.

Ephed

rine

Hyp

ote

nsi

on

Sinus

tach

ycar

dia

0.0

3–0.1

mg/

kg IV b

olu

s:

low

er d

ose

ran

ge f

or

larg

ean

imal

s. R

eported

to s

par

eute

rine

blo

od f

low

, w

hic

hm

ay b

e par

ticula

rly b

enef

i-ci

al f

or

pre

gnan

t pat

ients

.

Epin

ephrin

eRef

ract

ory

Arr

hyt

hm

ias

0.0

1–0.0

3 µ

g/kg

/min

hyp

ote

nsi

on

Sinus

tach

ycar

dia

Contrai

ndic

ated

durin

g hal

oth

ane

anes

thes

ia


Isopro

tere

nol

Bra

dyc

ardia

Arrhyt

hm

ias,

0.0

1–0.1

µg/

kg/m

inhyp

ote

nsi

on

(B2 e

ffec

t)

Note

: Blo

od a

nd p

lasm

a m

ust

be

adm

inis

tere

d thro

ugh

in-li

ne

filte

r to

rem

ove

clo

ts a

nd c

ellu

lar

deb

ris. B

lood s

hould

not be

mixed

with

cal

cium

- or

bic

arbonat

e-co

nta

inin

g flu

ids.

*Fre

sh w

hole

blo

od a

nd fre

sh fro

zen

pla

sma

also

are

effe

ctiv

e in

tre

atin

g co

agulo

pat

hy, in

cludin

g vo

n W

illeb

rand’s

dis

-ea

se. T

he

form

er a

lso is

effe

ctiv

e in

tre

atm

ent of th

rom

bocy

topen

ia. T

he

latte

r al

so is

effe

ctiv

e in

tre

atin

g pla

tele

t dys

-fu

nct

ion a

nd s

pec

ific

clotti

ng

fact

or

def

icits

.

**Pa

cked

cel

ls a

re b

ette

r fo

r an

emia

notac

com

pan

ied b

y hyp

ovo

lem

ia, w

hile

whole

blo

od o

r pac

ked c

ells

plu

s co

lloid

are

bet

ter

for

acute

(si

gnifi

cant)

hem

orrhag

e.† S

ever

al p

roduct

s ex

ist,

incl

udin

g free

-hem

ogl

obin

-bas

ed, l

iposo

me-

enca

psu

late

d h

emogl

obin

and p

erflu

roro

carb

ons;

and o

ne

pro

duct

, Oxy

globin

™ (

free

-hem

ogl

obin

bas

ed), c

urren

tly is

appro

ved for

use

in v

eter

inar

y m

edic

ine.

11. Metabolic acidosis may be preexisting or developduring anesthesia due to poor perfusion orhypothermia and may require treatment in somecases. Alkalinizing agents should be considered ifthe pH is <7.2 and the acidosis is due to the meta-bolic component (i.e., PCO2 is within normal limits;see the acid-base section later).

Routes of Administration

While subcutaneous fluid replacement with isotonicfluid (preferably without dextrose or at concentrations≤2.5%) is acceptable for mild dehydration, moderate tosevere dehydration requiring relatively rapid correctionshould be treated with intravenous fluids. While venousaccess usually is no problem in most species under rela-tively normal conditions, neonates and severely volume-depleted animals can present a challenge. For very smalland very hypotensive patients or patients with throm-bosed peripheral vasculature, the intraosseous route offluid administration may provide the necessary access toreestablish fluid balance prior to and during anesthesia.This route also is effective for infusion of a variety ofanesthetic agents and cardiosupportive drugs. The mostcommon access sites in small animals include the medialsurface of the proximal tibia 1–2 cm distal to the tibialtuberosity, the tibial tuberosity, the trocanteric fossa ofthe femur, the wing of the ilium, the ischium, and thegreater tubercle of the humerus. In birds, access sites


include the distal ulna and the proximal tibiotarsus (see Figure 11–2). A spinal needle (20–22 ga) is pre-ferred if patient size will accommodate placement. Hypo-dermic needles (22–25 ga) are more appropriate forvery small patients, but these have a tendency to becomeblocked with a bone piece during entry through the cor-tex. The needles are placed aseptically, capped, and uti-lized like IV catheters; they usually are sewn or taped tothe skin using a tape butterfly and protected with a bulkywrap to prevent bending or breaking. Fluid rate is lim-ited to 11 ml/min and can be doubled using pressuriza-tion (300 mmHg). Contraindications for intraosseouscannulation include recent fractures, pneumatic bones,infection over the access site, and sepsis.

Acid-Base Balance

Normal blood pH (7.35–7.45) is maintained throughthree general mechanisms: buffer systems (bicarbonate isthe major extracellular buffer, where pH = 6.1 + logHCO3

–/H2CO3–; hemoglobin, plasma protein, and phos-

phate play a lesser role) cushion insults that alter the pH;the lungs (respiratory mechanism) alter the pH throughchanges in PCO2 (normal PaCO2 = 35–45 mmHg;hypoventilation will increase PaCO2, and hyperventila-tion will decrease PaCO2); and the kidney (metabolicmechanism) affects the pH through excretion of H+ andgeneration and resorption of HCO3

– (normal: HCO3– =

17–31 mEq/L).


The acid-base status should be assessed prior to anes-thetic induction in high-risk patients. If preexisting meta-bolic disorders are identified, anesthesia should bepostponed until the disorders are corrected, as generalanesthesia can exacerbate an acid-base imbalance. Dis-orders of the pH can affect electrolyte concentrations(the pH affects potassium concentration inversely:decreased pH ⇒ increased K+ and vice versa; pH affectsionized calcium inversely: decreased pH ⇒ increasedionized Ca++ and vice versa), cardiac contractility, vascu-lar responsiveness, and normal cellular function.

Four primary disturbances in pH balance can occur(Table 7–4), and the complexity of interpretation isincreased by compensatory responses (the opposing sys-tem responds to turn pH back toward the normal range)and the potential for a mixed disorder in some patients.

Oxygenation

Arterial oxygen tension (PaO2), included in routine arte-rial blood gas analysis, provides accurate assessment ofthe patient’s ability to oxygenate the blood and provideadequate tissue oxygenation during anesthesia. Tissueoxygenation is determined by hemoglobin concentra-tion, hemoglobin saturation (SpO2, which is determinedby PaO2; Figure 6–2A), and blood delivery (cardiacoutput as reflected by arterial blood pressure). Five factorscontribute to decreased arterial oxygen tension (PaO

2):



Tab

le 7

–4

Altera

tions

in, C

ause

s of,

and C

om

pensa

tory

Mech

anis

ms

Invo

lved in

Aci

d-B

ase B

alan

ce

Pri

mary

Dis

ord

er/

No

nco

mp

en

sate

dC

om

pen

sate

d**

Co

mp

en

sato

ry

pH

PC

O2

HC

O3*

pH

PC

O2

HC

O3

Cau

ses

Resp

on

se

Res

pira

tory

aci

dosi

s/↓

↓↑

↑↓

↑↑

↑Anes

thes

ia, obes

ity,

met

abolic

alk

alosi

sth

ora

cic

or

bra

in d

isea

se

Res

pira

tory

alk

alosi

s/↑

↑↓

↓↓

↓↓

↓Ia

troge

nic

, ex

cess

ive

met

abolic

aci

dosi

s IP

PV,

fev

er, hyp

o-

xem

ia, an

xiet

y

Met

abolic

aci

dosi

s/↓

↓Ν

↓↓

↓↓

Poor

per

fusi

on,

resp

irato

ry a

lkal

osi

ssh

ock

, re

nal

dis

-ea

se, ke

toac

ido-

sis,

dia

rrhea

Met

abolic

alk

alosi

s/

↑↑

Ν↑

↑↑

↑Acu

te v

om

iting,

re

spira

tory

aci

dosi

supper

GI o

bst

ruc-

tion (

rum

inan

ts),

hyp

oka

lem

ia

(contin

ues

)


Tab

le 7

–4

(Continued)

Note

: Tw

o a

cid-b

ase

dis

turb

ance

s ca

n o

ccur

indep

enden

tly (

e.g.

, tra

um

a re

sulti

ng

in s

hock

and s

ever

e pulm

onar

y hem

-orrhag

e re

sulti

ng

in m

etab

olic

and r

espira

tory

aci

dosi

s) w

ith in

crea

sed s

ever

ity in

the

pH

chan

ges,

or,

in the

case

of tw

oopposi

ng

indep

enden

t dis

ord

ers

(met

abolic

alk

alosi

s as

soci

ated

with

upper

GI obst

ruct

ion w

ith a

nes

thet

ic-in

duce

d r

es-

pira

tory

dep

ress

ion), c

an e

xist

with

a n

ear

norm

al p

H. K

now

ledge

of th

e ca

se h

isto

ry a

nd la

bora

tory

fin

din

gs w

ill h

elp to

dis

cern

com

pen

sato

ry r

esponse

ver

sus

two p

rimar

y dis

ord

ers.

Durin

g an

esth

esia

, correc

tion o

f re

spira

tory

-induce

d p

H c

han

ges

invo

lves

an a

ppro

pria

te c

han

ge in

ven

tilat

ory

support.

Met

abolic

aci

dosi

s is

bes

t co

rrec

ted p

rior

to a

nes

thes

ia. T

reat

men

t w

ith b

icar

bonat

e sh

ould

be

consi

der

ed if

the

bas

eex

cess

val

ue

(norm

al v

alues

are

list

ed in

Tab

le 6

–3)

is g

reat

er than

–10 m

Eq/L

and o

nly

if n

orm

al P

aCO

2va

lues

are

esta

blis

hed

. Bic

arbonat

e dosa

ge in

mEq

/L =

Bas

e ex

cess

val

ue

�BW

(kg

) �

0.3

.

Giv

e ap

pro

xim

atel

y one

fourth the

dose

and r

eass

ess

blo

od g

as a

nal

ysis

. Rep

eat until

pH

and b

ase

exce

ss r

eturn

to

norm

al li

mits

. Met

abolic

alk

alosi

s is

tre

ated

by

adm

inis

trat

ion o

f bic

arbonat

e-free

flu

ids

(e.g

., 0.9

% s

alin

e).

*H

CO

3in

crea

ses

with

res

pira

tory

aci

dosi

s an

d d

ecre

ases

with

res

pira

tory

alk

alosi

s by

appro

xim

atel

y 1–2 m

Eq/L

for

each

10 m

mH

g ch

ange

in P

CO

2ac

cord

ing

to the

equat

ion:

CO

2+

H2O

←→H

2CO

3←→

HCO

3–

+ H

+

**As

a ge

ner

al r

ule

, the

com

pen

sato

ry r

esponse

occ

urs

when

the

prim

ary

dis

turb

ance

bec

om

es c

hro

nic

and a

cts

tobrin

g th

e blo

od p

H b

ack

tow

ard

(but usu

ally

not co

mple

tely

into

) th

e norm

al r

ange

, whic

h h

elps

diff

eren

tiate

prim

ary

from

com

pen

sato

ry c

han

ges.

Com

pen

sato

ry r

espira

tory

mec

han

ism

s ar

e m

axim

al w

ithin

8–12 h

r. C

om

pen

sato

ry m

eta-

bolic

mec

han

ism

s ar

e m

axim

al w

ithin

3–5 d

ays

and m

ore

effe

ctiv

e (t

han

res

pira

tory

) in

ret

urn

ing

the

pH

to n

orm

al.

decreased inspired concentration (FIO

2), hypoventilation,

diffusion abnormality, ventilation-perfusion (VQ) mismatch,and right-to-left shunt. All but the last benefit fromenriched oxygen delivery (FIO2 = 1.0 or 100% versusroom air; FIO2 = 0.21 or 21%). Anesthetized patients aresusceptible to hypoventilation and VQ mismatch, espe-cially horses, and supplemental oxygen is recommendedin all patients, especially those at increased risk for devel-opment of hypoxemia (e.g., those with respiratoryabnormalities). Hypoxemia is defined as PaO2 <60mmHg (which corresponds approximately to SpO2 =90%). The PaO2 value should be maintained at leastabove 60 mmHg and preferably above 100 mmHgthroughout the perianesthetic period.

Intraoperative Adjunct Drugs

The use of various agents to support cardiac perform-ance during general anesthesia is guided by the moni-toring devices applied during the anesthetic period.Continuous electrocardiography detects rhythm distur-bances that might benefit from therapeutic intervention,and quantitative blood pressure monitoring (either inva-sive or noninvasive) guides the need for inotropic sup-port. Ventricular premature complexes should be treated ifthey are multiform, appear to be superimposed on theprevious T wave, occur in runs, are >15–20/min infrequency, or have a significant detrimental effect onarterial blood pressure. Lidocaine dosages are listed in


Table 6–4. Ventricular tachycardia may respond to lido-caine if a pulse is present and the rate is ≥150/minute.

Hypotension not responsive to fluid bolus anddecreasing the depth of anesthesia may benefit frominotropic agent administration. Dobutamine anddopamine must be administered as an infusion due totheir short duration of effect. Ephedrine, as an IV bolus,will provide blood pressure support by both direct andindirect effects at both alpha and beta receptors; theeffects may persist for 10–30 min. Dosages are listed inTable 6–4. An ECG should be monitored during admin-istration, as these agents can promote arrhythmias. Infu-sion of epinephrine has been suggested for hypotensionthat fails to respond to the more commonly usedinotropes. Due to its inherent arrhythmogenicity, epi-nephrine should be reserved for refractory cases andavoided during halothane anesthesia.

Prevention of Hypothermia

Hypothermia occurs commonly during general anesthe-sia, especially in small and neonatal patients, due to therelatively large body surface to mass ratio and contribut-ing factors including inhalation of dry, cold anestheticgases; contact with cold surfaces; wet skin from surgicalsite preparation; exposure of body cavities during theprocedure; anesthetic-induced vasodilation; and ther-moregulatory depression. Severe hypothermia can causebrain damage, ventilatory depression, life-threatening


cardiac arrhythmias and conduction disturbances, and acid-base and electrolyte derangements, whichcontribute significantly to delayed recoveries. Severalmethods are available to limit heat loss during anesthe-sia, including maintaining the ambient temperaturebetween 21 and 25°C, keeping the patient on a circulat-ing water blanket, applying “space” wraps or forced airblanket heaters when possible, and using warmed intra-venous crystalloid fluids when relatively large quantitiesare administered. Minimizing anesthesia time is one ofthe most critical factors in the prevention of severehypothermia. Monitoring the patient’s temperature withan esophageal probe to assess the core temperature isthe most accurate representation of the patient’s heatbalance. Small patients benefit from recovery in incuba-tors, if available. Measures to facilitate return to nor-mothermia during recovery include providing a warmambient temperature, using water-circulating blankets to“cocoon” the patient, using heat lamps, and administer-ing warm IV fluids, if therapy is continued into the post-operative period. As patients recover, shivering invariablyoccurs as part of the warming process and can increaseoxygen consumption fivefold, often at a time when res-piration still is depressed. Providing supplemental oxy-gen until the body temperature has returned to nearnormal helps prevent development of hypoxemia and isespecially important in high-risk patients, such as thosewith underlying respiratory or cardiac abnormalities.Temperature monitoring should be continued until the


temperature returns to normal. To avoid hyperthermia,it is advisable to remove heating devices once the bodytemperature reaches 98–99°F and the patient is awakeand showing spontaneous movement.

Positioning Considerations

Padding and positioning are of greater concern in largeanimal patients, but some considerations for positioningsmall animal patients deserve mention. Considerationsfor both large and small patients assume even greaterimportance during prolonged procedures. Tiltingpatients to a “head-down” position, as for ovariohysterec-tomy, has minimal adverse effects in the short term andin healthy patients but should be avoided for prolongedperiods and in high-risk patients due to respiratory com-promise. Positioning the forelimbs forward is commonand not detrimental if done loosely. However, extremeextension of the forelimbs can interfere with respiratorymovement and cause brachial neuropathy if applied forlong periods of time. The dependent lung (lateralrecumbency) becomes atelectic over time, and this effectis exacerbated with duration of anesthesia. In patientswith unilateral lung disease, it is beneficial to place themore “normal” lung up, when possible. Assure that theairway stays patent by keeping the neck and head slightlyextended and assure unrestricted respiratory movement(equipment and elbows should not be placed on thethoracic area).


Large animal patients should be placed on apadded surface to minimize the risk of postanestheticmyopathy—this is essential for equine patients during gasanesthesia. Available padding includes bags that can befilled with air once the animal is positioned (dunnagebags) and thick (4 in. minimum) foam- or water-filledpads. Laterally recumbent animals should have the lowerforelimb extended forward to minimize the risk ofentrapping the brachial plexus with resultant neuropa-thy. The upper limbs should be supported to maintainthem parallel to the table surface (see additional species-specific recommendations in species chapters). Theseconsiderations are of lesser importance in small rumi-nants and camelids, but padding (2 in. minimum)should be provided for these patients.


8

Pain Management

The definition, recognition, and management of painhas become a central issue in veterinary practice due toincreased awareness and knowledge by veterinarians andpet owners. Pain is an unpleasant sensory or emotionalexperience associated with actual or potential tissuedamage and has been described as “an experience forwhich there is no direct measure.” Pain causes distressand suffering, which contributes greatly to the stressassociated with hospitalization and anesthesia. A series ofbehavioral, physiologic, endocrine, metabolic, and cellu-lar responses accompany pain, which maintain andamplify the pain response. Except to warn that some-thing is wrong, pain rarely, if ever, has beneficial effects,and unmanaged pain interferes with normal behavior

157

patterns. Activation of the sympathetic nervous systemsecondary to pain may result in protein catabolism,abnormal renal function, electrolyte disturbances,immune suppression, and delayed healing.

Pain is difficult to quantitate because many animalsare stoic; and signs of pain vary greatly with species,breed, age, health status, behavioral patterns, and painintensity. Table 8–1 lists physiologic and behavioral signsthat may be (but are not exclusively) associated with painas well as some specific painful insults and the expecteddegree of associated pain. Because signs of pain are oftennonspecific and sometimes discrete, management ofpain in veterinary patients often is inadequate. It isimportant to maintain a liberal attitude regarding anal-gesic therapy. While overtreatment may occur, the con-sequences of unnecessary analgesia and side effects mustbe weighed against the detrimental effects of unrelievedpain. In general, any procedure known to be painful inhumans should be assumed to be painful in animals andtreated appropriately.

Physiology of Pain

Nociceptive signals are transmitted to the spinal cord byfine myelinated A-delta fibers and unmyelinated C fibers,with their cell bodies contained in the dorsal root gan-glia. Two neuron types have been identified: nociceptivespecific neurons (which respond to input from discrete

158 Pain Management

Pain Management 159

Tab

le 8

–1

Phys

iolo

gic

and B

ehav

iora

l Sig

ns

That

May

Be A

ssoci

ated w

ith P

ain a

nd

Som

e E

xam

ple

s of

Pai

nfu

l In

sults

and t

he E

xpect

ed D

egre

e o

f A

ssoci

ated P

ain

Ph

ysi

olo

gic

Sig

ns*

Beh

avio

ral

Sig

ns

Pain

ful

Insu

lt/D

egre

e o

f P

ain

**

Tach

ypnea

Voca

lizat

ion

Surg

ery† :

mild

, m

oder

ate,

sev

ere

Tach

ycar

dia

Res

tless

nes

sM

ild t

o m

oder

ate

surg

ical pain

:

Hyp

erte

nsi

on

Agi

tatio

nC

astrat

ion, ova

riohys

tere

ctom

y,

explo

rato

ry

Dila

ted p

upils

Abnorm

al p

ost

urin

gLa

par

oto

my,

onyc

hec

tom

y

Saliv

atio

nPe

rsonal

ity c

han

geSe

vere

to d

istres

sing s

urg

ical pain

:

Pale

muco

us

Anore

xia

Am

puta

tions,

orthoped

ic

mem

bra

nes

pro

cedure

s, t

hora

coto

mie

s,

Car

dia

c D

ecre

ased

gro

om

ing

Spin

al s

urg

ery,

auric

ula

r su

rger

y,

arrh

ythm

ias

per

ianal

surg

ery

Hyp

ergl

ycem

iaEx

cess

ive

licki

ng

or

chew

ing

Trau

ma—

mild

to d

istres

sing

Obliv

ious

to s

urroundin

gsPa

ncr

eatit

is—

dis

tres

sing

Perit

oniti

s—dis

tres

sing

*M

any

sign

s m

ay b

e diff

icult

to d

iffer

entia

te fro

m e

ffect

s of an

esth

etic

em

erge

nce

and d

rugs

adm

inis

tere

d d

urin

g th

ean

esth

etic

per

iod e

spec

ially

in the

imm

edia

te p

ost

oper

ativ

e per

iod.

**D

egre

e of pai

n a

ssoci

ated

with

a s

pec

ific

insu

lt va

ries

grea

tly w

ith in

div

idual

anim

al a

nd s

urg

ical

tec

hniq

ue.

†Su

rgic

al p

ain is

div

ided

into

the

thre

e ca

tego

ries,

with

more

inva

sive

pro

cedure

s an

d m

ore

ext

ensi

ve tis

sue

trau

ma

causi

ng

grea

ter

pai

n.

topographical areas) and wide dynamic range neurons(which respond to a wide range of stimuli). It is believedthat the latter type is more important in nociception andresponsible for central sensitization of receptive fieldswith long-term activation of afferent pathways, which hasbeen referred to as wind up. This mechanism is believedto be due to repeated C-fiber stimulation, which leads tocontinued release of neurotransmitters that facilitatenociception (e.g., substance P, glutamic acid, N-methyl-D-aspartate [NMDA], neurotensin, cholecystokinin).Once activated, transmission of afferent signals to higherbrain centers, including the thalamic, medullary, pon-tine, and cortical regions, occurs via the spinothalamic,spinocervical, spinomesencephalic, and spinoreticulartracts.

Pain perception is a complex process that may bemodified clinically at several sites, including reduction ofafferent input (local techniques), signal integration andtransmission (regional techniques), or integration andrecognition at higher centers (parenterally administeredagents). Analgesic administration before the onset of pain(preemptive analgesia) provides better control of pain inthe postoperative period. Combining agents that act atdifferent sites (multimodal therapy) may provide supe-rior pain management for both acute and refractorypain with fewer side effects. With these considerations inmind, the following agents and techniques provide sev-eral options for pain management.

160 Pain Management

Therapeutic Options

Agents for pain management may be administered on ascheduled basis or dictated by dynamic patient assess-ment. Available drugs for analgesia include the opioidsand alpha

2agonists, applied epidurally or parenterally;

local anesthetic agents; ketamine; and nonsteroidal anti-inflammatory agents (NSAIDs).

Opioids

Opioid agonists and agonist-antagonists are effective inthe management of acute moderate to severe pain andalso provide variable degrees of sedation. Opioids areclassified according to the specific opioid receptor thatthey modulate, vary in their analgesic and sedative prop-erties, and are scheduled according to their potential foraddiction (Appendix 2). Pure agonists, including mor-phine, oxymorphone, hydromorphone, meperidine,and fentanyl, provide analgesia with variable durations ofaction (Table 8–2). Side effects include dose-dependentrespiratory depression and a vagomimetic effect, whichpromotes bradycardia. Myocardial contractility is well-maintained with opioids.

Morphine and meperidine may cause histaminerelease, resulting in hypotension, when administeredintravenously (IV); therefore, the subcutaneous or intra-muscular routes are preferred. The short duration ofaction and low potency of meperidine makes it less

Pain Management 161

162 Pain Management

Tab

le 8

–2

Dosa

ges

of

Anal

gesi

c A

gents

in D

ogs

and C

ats

Do

se (

mg/k

g)

Do

gC

at

Ro

ute

Du

rati

on

(h

r)C

om

men

ts

Syst

emic

opio

ids

Morp

hin

e0.0

5–0.6

0.0

5–0.2

IM, SC

2–6

Use

with

tra

nquili

zer

(cat

s)SR

(su

stai

ned

-1.0

–3.0

–PO

12

rele

ase)

Oxy

morp

hone

0.0

5–0.2

0.0

5–0.1

IM, SC

, 2–6

Use

with

tra

nquili

zer

IV(c

ats)

, 4 m

g m

axdose

Hyd

rom

orp

hone

0.1

–0.2

0.0

5–0.1

IM, SC

2–4

Use

with

tra

nquili

zer

(cat

s)

Mep

erid

ine

1.0

–4.0

1.0

–3.0

IM, SC

0.5

1

Fenta

nyl

25 µ

g Tr

ans-

Up t

o 7

212–24 h

r onse

t of

(<10 k

g)der

mal

ef

fect

(an

ecdota

l50 µ

g (1

0–

reports

of

20 k

g)dys

phoria

in

75 µ

g (2

0–

both

spec

ies)

30 k

g)

Pain Management 163

100 µ

g (>

30 k

g)2–6 µ

g/kg

IV<

1 (

prio

r bolu

s to

CRI)

2–6 µ

g/IV

CRI

kg/m

in(s

am

e)2–6 µ

g/kg

/hr

Buto

rphan

ol

0.1

–0.4

0.1

–0.4

IM, SC

, 1–3

IV

Bupre

norp

hin

e0.0

05–

0.0

05–

IM, SC

, 4–8

0.0

20.0

1IV

Epid

ura

l opio

ids

Dilu

te w

ith s

alin

e (1

ml/

5 k

g)

Morp

hin

e0.1

0.1

10–20

Or

use

Bupiv

acai

ne

(1 m

l/5 k

g)

Oxy

morp

hone

0.1

0.1

10

(6 m

l m

ax. vo

lum

e has

bee

n r

ecom

-m

ended

)

(contin

ues

)

164 Pain Management

Tab

le 8

–2

(Continued) D

ose

(m

g/k

g)

Do

gC

at

Ro

ute

Du

rati

on

(h

r)C

om

men

ts

Fenta

nyl

0.0

04

0.0

04

<1

Buto

rphan

ol

0.2

50.2

52–4

Bupre

norp

hone

0.0

03–

0.0

03–

12–18

0.0

05

0.0

05

Intra-a

rtic

ula

r opio

ids

Morp

hin

e0.1

mg/

kg

–12–24

in 0

.5 m

l/kg

bupiv

a-ca

ine

Syst

emic

alp

ha

2

agonis

ts*

Xyla

zine

0.0

1–0.2

0.0

1–0.2

IM, SC

, 1–3

IV

Med

etom

idin

e0.0

02–

0.0

02–

IM, SC

, 1–4

0.0

10.0

1IV

Pain Management 165

Epid

ura

lalp

ha

2

agonis

ts

Xyla

zine

0.2

0.2

1–3

Med

etom

idin

e0.0

10.0

14

Ket

amin

e 0.2

50.2

5IV

1–2

(with

dia

zepam

, 0.2

0.2

IVeq

ual

volu

me)

Infu

sion

Load

ing

dose

0.2

5–0.5

Sam

eIV

–m

g/kg

Intrao

per

ativ

e10 µ

g/kg

/Sa

me

IV–

min

Rec

ove

ry2 µ

g/kg

/Sa

me

IV≤

24 h

rReq

uire

s co

ntin

uous

min

obse

rvat

ion

Nonst

eroid

al anti-

infla

mm

ator

ydru

gs

Car

pro

fen**

2.0

–4.0

2.0

PO

24

One

dose

only

(ca

ts)

2.0

–4.0

2.0

IV, SC

24

One

dos

e on

ly (

both

)

Etodola

c10–15

–PO

24

Ket

opro

fen

0.5

–1.0

0.5

–1.0

PO

24

One

dos

e on

ly (

both

)

(contin

ues

)

166 Pain Management

Tab

le 8

–2

(Continued) D

ose

(m

g/k

g)

Do

gC

at

Ro

ute

Du

rati

on

(h

r)C

om

men

ts

Asp

irin

10–25

10–15

PO

8–12 (

dog)

24 (

cat)

Phen

ylbuta

zone

10–25

10–15

PO

8–12

Lim

ited u

se (

both

)

Mel

oxi

cam

**0.1

–0.2

0.1

–0.3

24

0.2

SC

(or

0.3

PO

) PO

and

PO

fo

r fir

st d

ose

,SC

only

then

0.1

PO

; 4

day

s m

ax (

cats

)

Nap

roxe

n1.0

–2.0

–PO

24

Piro

xica

m0.2

–0.4

–PO

48

Flunix

in m

eglu

min

e0.5

–1.0

–IM

, IV

One

dose

only

Ace

tam

inophen

10–15

–PO

12

Note

: Se

e sp

ecie

s-sp

ecifi

c ch

apte

rs for

reco

mm

endat

ions

for

hors

es, r

um

inan

ts, s

win

e, b

irds,

rep

tiles

, and s

mal

l mam

-m

als.

CRI =

const

ant ra

te in

fusi

on

*Do n

ot use

alp

ha 2

agonis

ts in

hig

h-ris

k pat

ients

.

**In

ject

able

car

pro

fen is

not cu

rren

tly a

vaila

ble

in the

Unite

d S

tate

s. M

eloxica

m is

not cu

rren

tly a

vaila

ble

in the

Unite

dSt

ates

.

useful than other opioids. Fentanyl is a potent agonistwith a short duration of effect. It is available for trans-dermal application in four sizes and for IV use asrepeated bolus or constant rate infusion (see Table 8–2).The latter use requires constant patient observation butis very effective in acute, severe pain management. Opi-oid agonists can cause dysphoria in cats, but concurrentuse of a tranquilizer (a benzodiazepine or acepro-mazine) minimizes this side effect; tranquilizers are alsobeneficial in dogs when pain relief afforded by an opioidresults in increased activity or (rarely) dysphoria. Theopioid agonist-antagonist butorphanol provides moder-ate analgesia and minimal sedation in both dogs and catsand rarely causes excitement in cats. Buprenorphine is apartial opioid agonist, useful for dogs and cats, that pro-vides moderate analgesia and has a duration of action of6–12 hr. An advantage of the opioids is reversibility withopioid antagonists, including naloxone and nalmefene,should an adverse response occur. Butorphanol may beused to reverse excessive respiratory depression inducedby an opioid agonist while preserving some analgesia.

Opioids, including morphine, oxymorphone, fen-tanyl, butorphanol, and buprenorphine, have been usedepidurally to provide analgesia of variable duration (seeTable 8–2) while minimizing sedation and the adverseeffects that may accompany systemic opioid administra-tion. The technique for epidural injection of opioids isidentical to that for local anesthetic agents (described inChapter 3) and the two are often combined for a more

Pain Management 167

profound and prolonged effect. The advantage ofepidural opioids over local anesthetic agents is thatmotor and sympathetic nerve functions are preservedand duration is longer when morphine, buprenorphine,and oxymorphone are used. Normal rear limb activity ismaintained and hypotension secondary to vasodilation,seen with local anesthetics, does not occur. An epiduraltechnique is contraindicated in the presence of bleedingabnormalities, sepsis, or infected skin at the site of injec-tion; epidural administration of local anesthetics is con-traindicated for hypovolemic patients.

Alpha2

Agonists

Alpha2

agonists, including xylazine, detomidine(horses), and medetomidine, provide good short-termanalgesia and sedation. The side effects of alpha

2ago-

nists are listed in Chapter 2, and these effects are exac-erbated by concurrently used anesthetic agents. Due tothe cardiovascular effects and the relatively short dura-tion of analgesia, use of these agents for analgesia shouldbe reserved for healthy animals recovering from electiveprocedures or suffering from relatively minor trauma.Concurrent administration with opioids will enhance theanalgesic effect and allow for use of minimal effectivedosages. Alpha

2agonists are reversible with alpha

2antag-

onists, including yohimbine, atipamezole, and tolazoline(see Table 8–2). Both xylazine and medetomidine (anddetomidine in horses and swine; see Tables 3–4 and 3–5)

168 Pain Management

have been used epidurally. While of lesser concern inhorses and swine, the potential for systemic side effectsand the relatively short duration of action make themless useful than the opioids in small animals, with oneadvantage being easy accessibility (not scheduled).

Ketamine

Subanesthetic doses of ketamine have been used inhumans for relief of acute and chronic pain. Ketamineprovides somatic analgesia in animals and is not recom-mended as the sole agent for visceral pain management.Undesirable side effects, including dysphoria, seizures,and muscle rigidity, may be minimized by using ketaminein combination with a tranquilizer. Specific contraindica-tions are listed in Chapter 2. Dosages have not beendefinitively established for pain management in animals,but suggested guidelines are included in Table 8–2.

Nonsteroidal Anti-Inflammatory Agents

NSAIDs are used for the treatment of mild to moderatepain. The side effects are due to inhibition of physiologic(protective) prostaglandins and include gastrointestinalulceration and renal tubular necrosis. With developmentof more selective NSAIDs, which are more potentinhibitors of inflammation and less organ toxic, theseagents, in combination with an opioid, have beenapplied for preemptive and perioperative managementof acute surgical pain.

Pain Management 169

Carprofen is a more specific inhibitor of cyclooxyge-nase-2. It is approved for oral use in dogs in the UnitedStates, but cat dosages have been reported (see Table8–2). While side effects are less likely than from otherNSAIDs, gastrointestinal disturbances have beenreported and acute hepatopathy has been described.

Etodolac is another specific cyclooxygenase-2inhibitor with fewer side effects. It is approved for use indogs in the United States for management of osteoarthri-tis pain.

Ketoprofen is a relatively new NSAID with potent anti-inflammatory activity but greater potential for sideeffects than carprofen. It is approved for use in cats anddogs in Europe. Ketoprofen causes gastrointestinal andrenal effects at therapeutic doses and should be avoidedin high-risk patients and in the preoperative period.

Meloxicam is approved for use in dogs in Europe. It ismarketed for treatment of chronic skeletal pain but hasbeen shown to be effective in the management ofmoderate postoperative pain. Dosages are available forcats; however, data regarding its safety currently areunavailable.

Aspirin is a potent analgesic and anti-inflammatoryagent that may be used in both dogs and cats. Gastriculceration can occur at therapeutic doses with a lesserrisk when buffered preparations are used. Dosing fre-quency is less in the cat due to prolonged plasma elimi-nation.

170 Pain Management

Use of other NSAIDs, including phenylbutazone,naproxen, piroxicam, and flunixin meglumine, in dogsand cats has been reported and dosages are listed inTable 8–2. Flunixin is a potent visceral analgesic that alsomay modulate the pathophysiologic response to endo-toxin. While dosages are available, data supporting theuse of these agents are lacking and there is a greaterincidence of adverse side effects; therefore, these drugsshould not be used unless safer agents are unavailableand the need outweighs the potential for adverse effects.

Acetaminophen is an atypical NSAID with excellentanalgesic effects but limited anti-inflammatory activity.Its use in cats is contraindicated due to methemoglobinformation.

Local and Regional Techniques

Application of local anesthetic techniques has beenshown to decrease the intensity of postoperative pain.Blocking nocioceptive impulse entry into the cord prob-ably prevents development of the sustained hyperex-citable state of the central nervous system largelyresponsible for sustained postoperative pain. Severallocal techniques and their applications are described inChapter 3. Bupivacaine is the local anesthetic of choicefor pain management due to duration of effect; sug-gested dosages for the specific techniques are includedin Chapter 3.

Pain Management 171

Selection of appropriate analgesic drugs and tech-niques for pain management is influenced by many fac-tors, including the animal’s previous behavior pattern;the type, duration, and invasiveness of the procedure orextent and location of the traumatic injury; mental sta-tus; and overall patient condition. Like anesthetic man-agement, no one agent or technique is applicable forevery situation; however, every case should be assessedand treated according to the preceding considerations.

172 Pain Management

9

Introduction to Anesthetic Management in Specific Species

Chapters 10–17 provide brief overviews of anestheticmanagement for a variety of veterinary species, includ-ing considerations that might be unique to that particu-lar species, such as restraint, venous access, intubation,positioning, monitoring, and recovery, as well as sug-gested protocols for premedication, induction, and totalparenteral anesthesia. Anesthetic protocols should beformulated to produce the desired result safely, effec-tively, and economically, based on the patient’s tempera-ment, physical status, a thorough physical examination,

appropriate laboratory and diagnostic tests, and proce-dure duration and complexity, regardless of species.

173

4. Eye lubrication should be applied to all anesthetizedanimals, as general anesthesia obtunds tearing andthe ability to blink, so as to maintain a moist cornea.

5. Monitoring may be simple or complex, dependingon the length and invasiveness of the procedure.Available techniques (Chapter 6) apply to all veteri-nary species with some species-specific considera-tions.

6. As a general rule, anticholinergic agents are not con-sidered a routine part of the preanesthetic protocolin any species but can be used as such in healthysmall animals, especially when drugs known todecrease heart rate (e.g., opioids) are part of theprotocol. Anticholinergics may precipitate colic inhorses, and horses are rarely susceptible to brady-cardia during the anesthetic period; therefore,routine perioperative use is contraindicated. Anti-cholinergic administration will not eliminate rumi-nant salivation and, in fact, may increase the viscosityof secretions, making them harder to clear; there-fore, routine use is not recommended.

Introduction to Anesthetic Management in Specific Species 175

10

Anesthetic Management of Dogs

A variety of protocols are available to provide chemical

restraint/premedication, induction of anesthesia, and

total parenteral anesthesia in dogs (Table 10–1). A neu-

roleptanalgesic (tranquilizer plus opioid) combination

will minimize anxiety and struggling for catheterization,

minimize requirements for induction and maintenance

agents, and provide preemptive analgesia. Popular and

economical combinations are acepromazine with mor-

phine (moderate to severe pain), hydromorphone (mod-

erate to severe pain), or butorphanol (mild to moderate

pain).

Diazepam can be substituted for acepromazine

when the latter is contraindicated (see Chapter 2). Mida-

zolam provides a convenient (but expensive) alternative

177

178 Anesthetic Management of Dogs

Tab

le 1

0–1

Reco

mm

ended D

osa

ges

and P

roto

cols

for

Chem

ical

Rest

rain

t,

Pre

anest

hetic

Pro

toco

ls, In

duct

ion A

gents

, an

d T

ota

l Par

ente

ral A

nest

hesi

a fo

r D

ogs

Do

sages

(mg/k

g)

Pro

toco

l(I

V,

IM,

SC

)*C

om

men

ts

Chem

ical re

stra

int/

Anim

als

can b

e ar

ouse

d d

urin

g ch

emic

alpre

med

icatio

nre

stra

int.

Opio

id p

lus*

*Ace

pro

maz

ine

or

0.0

5M

ax d

ose

: 2 m

g (p

rem

ed),

4 m

g (r

estrai

nt)

.D

iaze

pam

or

0.2

Max

rec

om

men

ded

dose

: 10 m

g.M

idaz

ola

m0.1

–0.2

Max

rec

om

men

ded

dose

: 10 m

g.

Ben

zodia

zepin

es a

re p

refe

rred

for

hig

h-

risk,

neo

nat

al, an

d g

eria

tric

pat

ients

.

Morp

hin

e0.4

–1.0

Avo

id IV r

oute

, pote

ntia

l fo

r his

tam

ine

rele

ase.

Oxy

morp

hone

0.1

–0.2

Hyd

rom

orp

hone

0.1

–0.2

Buto

rphan

ol

0.2

–0.4

Hig

h e

nd d

osa

ge f

or

smal

ler

pat

ients

. Le

ss

anal

gesi

a th

an p

ure

opio

ids

(for m

ild p

ain).

Bupre

norp

hin

e0.0

2–0.0

4

Anesthetic Management of Dogs 179

Alp

ha

2agonis

tsPro

vide

pro

found s

edat

ion a

nd a

nal

gesi

a an

d g

reat

ly s

par

e (≥

50%

) an

esth

esia

nee

ded

. U

se a

lpha 2

agonis

ts o

nly

inhea

lthy

young

anim

als.

Xyla

zine

0.2

–0.4

Med

etom

idin

e0.0

1–0.0

2

Tela

zol

2 IM

Good f

or

imm

obili

zatio

n o

f ag

gres

sive

dogs

.

Induct

ion

Adm

inis

tere

d “

to e

ffec

t” t

o f

acili

tate

unco

nsc

iousn

ess

and intu

bat

ion f

or

inhal

ant

anes

thes

ia.

Thio

pen

tal

5–10 IV

Apnea

is

com

mon.

Dia

zepam

-ket

amin

e1 m

l/10 k

g IV

Can

follo

w p

rior

tran

quili

zer

adm

inis

trat

ion.

Tela

zol

0.5

–1.0

IV

Can

follo

w p

rior

tran

quili

zer

adm

inis

trat

ion.

Pro

pofo

l2–6 IV

Apnea

is

com

mon if

not

give

n s

low

ly.

Etom

idat

e0.5

–2.0

IV

Expen

sive

but

spar

ing

of

card

iore

spira

tory

fu

nct

ion.

Tota

l pare

nte

ral

Less

control ove

r an

esth

esia

dep

th a

nd

anes

thes

iadura

tion t

han

inhal

atio

n m

ainte

nan

ce.

(contin

ues

)


Tab

le 1

0–1

(Continued)

Do

sages

(mg/k

g)

Pro

toco

l(I

V,

IM,

SC

)*C

om

men

ts

Xyla

zine

0.4

Adm

inis

trat

ion o

f X/

B p

rior

to k

etam

ine

min

imiz

es p

ain o

f IM

ket

amin

e or

keta

-m

ine

can b

e ad

min

iste

red IV “

to e

ffec

t.”

Buto

rphan

ol

0.4

Ket

amin

e10

Med

etom

idin

e0.0

1–0.0

2Adm

inis

trat

ion o

f M

/B p

rior

to k

etam

ine

min

imiz

es p

ain o

f IM

ket

amin

e or

keta

-m

ine

can b

e ad

min

iste

red IV “

to e

ffec

t.”

Buto

rphan

ol

0.4

Ket

amin

e10

Buto

rphan

ol

0.4

Dia

zepam

-ket

amin

e1 m

l/10 k

g IV

Dia

zepam

-ket

amin

e is

titr

ated

to e

ffec

t. N

ot

for

seve

rely

pai

nfu

l pro

cedure

s.

Pre

med

icat

ions

as

2–6 (

induct

ion)

Intu

bat

ion a

nd o

xyge

n d

eliv

ery

isab

ove

plu

s pro

pofo

l0.4

CRI (c

onst

ant

reco

mm

ended

rate

infu

sion)

or

repea

t bolu

s of

0.5

–1.0

ml “t

o e

ffec

t”


Opio

id a

nta

gonis

ts

Nal

oxo

ne

0.0

01–0.0

15 IV

May

be

give

n IV “

to e

ffec

t” w

hen

dilu

ted

(1 m

l in

9 m

l sa

line)

. G

ive

mat

chin

g (I

V)

dose

SC

.

Nal

mef

ene

0.0

01 IV

Longe

r dura

tion o

f ac

tion t

han

nal

oxo

ne.

Alp

ha

2anta

gonis

ts

Yohim

bin

e0.0

5–0.1

IV

May

be

give

n IM

but

less

effec

tive.

Atip

amez

ole

0.0

7–0.1

5 IV,

IM

Tola

zolin

e1–2 IV

May

be

give

n IM

but

less

effec

tive.

CRI (m

g/kg

/min

).

*As

a ge

ner

al r

ule

, use

low

er d

osa

ge r

ange

for

IV a

dm

inis

trat

ion. A

ll ro

ute

s ac

cepta

ble

unle

ss o

ther

wis

e sp

ecifi

ed.

**U

se o

f an

opio

id w

ith o

ne

of th

ese

med

icat

ions

is c

alle

d n

euro

lepta

nalg

esia

. The

com

bin

atio

n h

as a

syn

ergi

stic

effe

ct, p

rovi

din

g bet

ter

sedat

ion than

eith

er a

gent al

one.

to diazepam when SC or IM administration is needed,

since diazepam causes tissue irritation and has unreliable

absorption when given by these routes. Thiopental and

diazepam-ketamine are economical and effective induc-

tion agents, but repeated bolus administration can con-

tribute to a rough, prolonged recovery and both

thiopental and ketamine have specific contraindications

(Chapter 2). Thiopental causes prolonged recovery in

sighthounds due to an inherent inability to metabolize

the drug efficiently; alternatives include diazepam-keta-

mine and propofol.

Propofol has become a popular drug in veterinary

medicine due to its rapid effect, short duration, and lack

of cumulative effect, which allows it to be used as

repeated boluses or constant rate infusion without sig-

nificantly increasing recovery time. Even though more

expensive than thiopental, propofol’s rapid recovery and

lack of arrhythmogenic effect make it an excellent alter-

native agent.

Applying local and regional anesthetic techniques

appropriate to the procedure (most conveniently follow-

ing anesthetic induction) provides preemptive and post-

operative analgesia and further decreases anesthetic

maintenance requirements.

Dogs are prone to regurgitation and aspiration.

Anesthetized patients should be intubated to assure a

patent and protected airway, especially if fasting status is

unknown or time will not permit an adequate fast (emer-

gencies). Dogs are relatively easy to intubate by direct


visualization of the larynx, which is aided by adequate

anesthetic depth and use of a laryngoscope. Intubation

provides a route for oxygen delivery with or without

inhalant administration and an effective means for pro-

viding ventilatory support. Appropriate tube sizes for

dogs cover a wide range from 3.0 to 14.0 mm internal

diameter.

An intravenous catheter should be placed in a periph-

eral vein for procedures anticipated to take longer than

30 min and when administration of additional anesthetic

agent is likely. The most common sites are the cephalic

and lateral saphenous veins. A secure access provides a

route for intraoperative fluid and supportive drug

administration and for emergency drug administration,

should cardiopulmonary arrest occur.

Recovery should occur in a warm quiet area with

external heat provided in most cases. Extubation is per-

formed with the cuff deflated when swallowing is noted.

When there is evidence of regurgitation or when blood

has collected in the pharyngeal region, the oral cavity

should be swabbed and the tube removed with the cuff

still inflated once swallowing is observed to remove any

debris that has settled around the tube within the tra-

chea. Patients with underlying airway compromise

(brachycephalic breeds, history of a collapsing trachea)

should remain intubated as long as possible and closely

observed until recovery is complete. Animals should be

observed until vital signs have returned to normal

(Chapter 1).


11

Anesthetic Management of Cats

Total parenteral anesthetic protocols seem to be morepopular and widely used in cats than dogs for a variety ofreasons, including greater resistance to handling andrestraint, more difficult venous access, more difficultintubation, and greater effectiveness with less occur-rence of side effects associated with dissociative agents.Several protocols are available for short-term injectableanesthesia (Table 11–1). However, for complicated, pro-longed procedures and high-risk cats, inhalation mainte-nance following premedication and induction is morecontrollable and safer (see Table 11–1).

For tractable patients, neuroleptanalgesic combina-tions like those used for dogs are effective. Pure opioidagonists have been reported to cause excitement in cats,

185

186 Anesthetic Management of Cats

Tab

le 1

1–1

Reco

mm

ended D

osa

ges

and P

roto

cols

for

Chem

ical

Rest

rain

t, P

re-

anest

hetic

and I

nduct

ion P

roto

cols

, an

d T

ota

l Par

ente

ral A

nest

hesi

a fo

r C

ats

Do

sages

(mg/k

g)

Pro

toco

l(I

V,

IM,

SC

)*C

om

men

ts

Chem

ical re

stra

int/

Anim

als

can b

e ar

ouse

d d

urin

g ch

emic

alpre

medic

atio

nre

stra

int.

Ace

pro

maz

ine

or

0.0

5–0.1

Dia

zepam

or

0.2

Ben

zodia

zepin

es a

re p

refe

rred

for

hig

h-ris

k,

Mid

azola

m0.1

–0.2

neo

nat

al, an

d g

eria

tric

pat

ients

.

Use

d w

ithM

orp

hin

e0.4

–1.0

Oxy

morp

hone

0.1

–0.2

Hyd

rom

orp

hone

0.1

–0.2

Buto

rphan

ol

0.4

Less

anal

gesi

a th

an p

ure

opio

ids

(for

mild

to

moder

ate

pai

n).

Induct

ion

Adm

inis

tere

d “

to e

ffec

t” t

o f

acili

tate

unco

nsc

iousn

ess

and intu

bat

ion.

Thio

pen

tal

5–10 IV

Apnea

is

com

mon.

Dia

zepam

-ket

amin

e1 m

l/10 k

g IV

Can

be

use

d e

ven w

ith p

rior

tran

quili

zer

adm

inis

trat

ion.

Anesthetic Management of Cats 187

Tela

zol

0.5

–1.0

IV

Can

be

use

d e

ven w

ith p

rior

tran

quili

zer

adm

inis

trat

ion.

Pro

pofo

l2–6 IV

Apnea

is

com

mon e

spec

ially

with

rap

id

inje

ctio

n.

Etom

idat

e0.5

–2.0

IV

Expen

sive

but

spar

ing

of

card

iore

spira

tory

fu

nct

ion.

Pare

nte

ral anest

hesi

a

Xyla

zine

0.4

Adm

inis

trat

ion o

f X/

B p

rior

to k

etam

ine

will

Buto

rphan

ol

0.4

min

imiz

e pai

n o

f IM

ket

amin

e or

keta

-Ket

amin

e10–15

min

e ca

n b

e ad

min

iste

red IV “

to e

ffec

t.”

Med

etom

idin

e0.0

1–0.0

2Adm

inis

trat

ion o

f M

/B p

rior

to k

etam

ine

will

Buto

rphan

ol

0.4

min

imiz

e pai

n o

f IM

ket

amin

e or

keta

-Ket

amin

e10–15

min

e ca

n b

e ad

min

iste

red IV “

to e

ffec

t.”

Pro

pofo

l2–6 (

induct

ion)

Ace

pro

maz

ine

or

ben

zodia

zepin

e plu

s 0.4

const

ant

rate

opio

id f

ollo

wed

by

pro

pofo

l.in

fusi

on o

r re

pea

t bolu

s of

0.2

5–0.5

“t

o e

ffec

t”

Note

: D

osa

ges

for

reve

rsal

age

nts

are

sim

ilar

to those

list

ed for

dogs

(se

e Ta

ble

10–1 o

r Appen

dix 1

).

*As

a ge

ner

al r

ule

, use

low

er d

osa

ge r

ange

for

IV a

dm

inis

trat

ion.

but risk of this side effect is minimized with concurrentuse of a tranquilizer or when an agonist-antagonist(butorphanol) is used. Adding a low dose of ketamine tothe neuroleptanalgesic combination (see Table 11–1)will provide immobilization for less tractable patients tofacilitate catheterization and will further decrease induc-tion requirements. While mask induction following pre-medication is effective in cats, induction quality isimproved and intubation facilitated by using a rapidinduction method such as thiopental, diazepam-keta-mine, telazol, or propofol. The feline respiratory centeris more susceptible to the depression associated withthiopental and propofol and transient apnea is common.Some cats will produce excessive respiratory secretionswhen the dissociative agents are used, which may becounteracted by anticholinergic agent administration.

As a rule, cats tend to resent and resist restraintmore than dogs. Various devices, such as cat bags andfeline muzzles, often are necessary to ensure the safety ofpersonnel and the animal. Always close the doors toavoid escape when working with cats. Most cats can berestrained adequately with scruffing and stretching(holding the skin behind the neck with one hand andthe rear limbs with the other and applying gentle ten-sion) for injection of premedication. For resistant ani-mals, adding ketamine or telazol in low dosage to thepremedication protocol improves the quality of thecatheterization/induction sequence. Many of the local


and regional techniques, such as epidural and localnerve blocks, are effective and feasible in cats to providepreemptive and postoperative analgesia (Chapter 3).

When indicated (high-risk animal, repeat injections,prolonged procedures), an IV catheter should beinserted. Cats seem to resist the necessary restraint asmuch as the actual catheter placement so premedicationusually is required. Sites include the cephalic, medialsaphenous, and femoral veins. Laying the animal in lat-eral recumbency for placement in the medial saphenousvein seems to be less stressful for some anxious, aggres-sive patients.

Feline intubation is more challenging than in dogs.While visualization usually is good, the feline larynx isreactive and prone to laryngospasm, which makes intu-bation more difficult and increases the risk of trauma.Patience is essential, and the process is facilitated byapplication of 0.1 ml of 2% lidocaine dropped from asyringe to desensitize the area. Commercial human spraypreparations containing benzocaine (e.g., Cetacaine™)should be avoided because of reports of methemoglo-binemia associated with its use. Once visualized anddesensitized, using a guide tube (canine polyethyleneurinary catheter) will help to stiffen the ET tube andgain access between the arytenoid cartilages and into thetrachea so that the tube may be passed, rotating slightlyif needed, to allow the bevel to pass into the trachea.Stiffer stylets are available, but the risk of trauma is


greater if care is not taken to maintain the stylet pointinside the ET tube. The tube is secured around the backof the neck with tie gauze.

While a standard rebreathing circle can be usedeffectively in cats, a pediatric circle or nonrebreathingsystem is more appropriate for their size. The latter willminimize resistance to breathing but is more likely tocontribute to intraoperative hypothermia. If a rebreath-ing circuit is used, ventilatory support becomes evenmore important (due to added resistance to breathing),especially during prolonged procedures.

Cats are more challenging to monitor. The smallertidal volume makes movement of the rebreathing bagmore difficult to observe. Esophageal stethoscopes arehelpful for ausculting both respiration and heart sounds.Respiratory monitors and capnometers usually are effec-tive but add to dead space. Pulse quality is more difficultto assess; the best site for pulse palpation is the femoralartery, which may not always be accessible. The dorsalpedal artery can be palpated in some cats; clipping thearea over this artery is beneficial. Pulse oximeters andoscillometric blood pressure monitors may fail to workconsistently, due to the small vessel size. The Dopplerapparatus is effective when applied to either a forelimbor hindlimb but takes time and experience to apply effi-ciently. The feline lead II electrocardiogram is small andsometimes difficult to assess.


Recovery usually is rapid in cats following inhalationanesthesia, unless severe hypothermia has developed.Providing a warm environment and thermal supportfacilitate recovery. Close attention to body temperatureis important, as cats seem prone to hyperthermia as bodyactivity increases during recovery, seemingly independ-ent of the protocol used. As a general rule, once thebody temperature reaches 99°F, thermal support shouldbe removed. Cats with elevated temperature (>104°F)benefit from the application of alcohol to the pads and afan to dissipate heat; animals act seemingly normal dur-ing this period of increased temperature; thermoregula-tion returns to normal usually within 24 hr.


12

Anesthetic Management of Birds

Birds frequently require general anesthesia for a veteri-narian to perform procedures normally accomplishedwith physical restraint in most other species as well ascomplicated and invasive procedures. General anesthe-sia is challenging in birds due to less familiarity withavian anatomy, greater resistance to restraint, lower mar-gin of safety for injectable agents, less experience withcatheterization and intubation techniques, more diffi-culty in monitoring, and currently, limited informationon effective analgesic agents.

Capture and restraint should be performed in a quietand safe environment and done quickly to minimize thestress of chasing. Passeriformes may be restrained withthe bird cradled in the palm of the hand and the head

193

gently restrained between the index and middle fingers.For the larger Psittaciformes, a two-hand technique isrequired (Figure 12–1). Head restraint is vital to avoidbites to the handler and accomplished by creating a ringaround the bird’s neck with one hand and applying gen-tle pressure against the base of the skull and lowermandible. The other hand is placed around the legs togently support the body. A towel can be used to protectthe hand near the head. It is essential to not restrict tho-racic movement or compromise the airway. Restrainttechniques for adult ratites cannot be described in theconfines of this reference book; for information, readersare referred to the recommended reading list.

Anesthetic induction and maintenance with isoflu-rane is the protocol of choice for pet birds and raptors.Sevoflurane also appears to be effective and currently isgaining popularity. Dosages for some injectable proto-cols are available and listed in Table 12–1; however, theseagents usually fail to produce stable and safe levels ofanesthesia and should not be used unless gas anesthesiais unavailable. Larger birds, such as ratites, will requirean injectable premedication and induction protocol (seeTable 12–1) because mask induction is prolonged anddangerous except in debilitated patients.

Intubation is relatively easy to perform in avianspecies as the glottis is readily apparent at the base of thetongue when the beak is opened. Psittaciformes have afleshy tongue, which must be pulled forward carefully toexpose the glottis. Birds >350 grams can be intubated

194 Anesthetic Management of Birds

195

Figure 12–1 Restraint technique for Psittaciformes, demon-strating hand positioning. (Reprinted with permission from TGCurro, Anesthesia of pet birds, in: Seminars in Avian and ExoticPet Medicine: Anesthesia and Analgesia, AM Fudge, ed.,1998;7(1):12.)

Table 12–1 Reported Dosages for Injectable AnestheticAgents in Pet Birds, Raptors, and Ratites (Injectable proto-cols are not recommended in birds unless inhalant anes-thesia is unavailable.)

Drug Combination Dosage (mg/kg)*

Pet birds**

Ketamine-xylazine 10–50/1.0–10

Ketamine-diazepam 10–50/0.5–2.0

Ketamine-midazolam 10–40/0.5–1.5

Ketamine-acepromazine 10–25/0.5–1.0

Telazol (tiletamine-zolazepam) 7.7–26.0

Yohimbine 1.0

Analgesic optionsButorphanol 1–4 IV, SC, IMFlunixin 1–10 IM (not critically

evaluated)Aspirin 5 gr/250 ml drinking water

(not critically evaluated)

Raptors†

Buteo Hawks350 g 0.04–0.08 ml650–1500 g 0.08–0.15 ml900–1700 g 0.1–0.3 ml

Accipiter Hawks100–250 g 0.04–0.06 ml250–500 g 0.08–0.1 ml600–1200 g 0.05–0.07 ml

(continues)




Eagles3–5 kg 0.1–0.2 ml

Falcons90–250 g 0.03–0.06 ml500–950 g 0.07–0.2 ml950–1500 g 0.12–0.3 ml

Owls60–130 g 0.03–0.05150–350 g 0.05–0.1700–2500 g 0.1–0.25 (not recommended

for surgery on great hornedor snowy owls)

Osprey 0.12–0.2 ml

Turkey vulture 0.15–0.2 ml

Ratites

Xylazine 0.2–2.2 IM

Detomidine 1.5 IM

Medetomidine 0.1 IM

Butorphanol 0.05–0.5 IV, IM

Diazepam 0.1–0.3 IV0.22–1.0 IM

Midazolam 0.15 IM

Ketamine-xylazine 2.2 IV/0.25 IV2.2–3.3 IV/2.2 IM

Carfentanil-xylazine 0.03 IV/0.5 IM

(continues)

Anesthetic Management of Birds 197



Ketamine-diazepam 5.0/0.25 IV (mixed)2.2–3.3 IV/0.22–0.5 IM

(ketamine given 15–30 min after diazepam)

Telazol 2–10 IM; 1–3 IV

Antagonists:Naloxone 2 mg IV (total dose adminis-

tered to adult ostriches)Yohimbine 12.5 mg IV (total dose admin-

istered to adult ostriches)Atipamezole 5–20 mg IV (total dose admin-

istered to adult ostriches)Naltrexone 300 mg IV (total dose adminis-

tered to adult ostriches)

*Dosages are for intramuscular administration in the pectoral muscles unless other-wise indicated.

**Lower dosage range is for larger birds (>250 g) and sedation in smaller birds;higher dosage range is for smaller birds (<250 g) and for a “surgical plane” ofanesthesia in larger birds.†Dosage in mls of a mixture of 1 ml ketamine (100 mg/ml) and xylazine (20mg/ml). Low-end range represents minimal effective dose, high-end range repre-sents surgical anesthesia. As with pet birds, injectable anesthesia is not recom-mended for raptors. A dosage range for the xylazine-ketamine mixture (100 mg/20mg) has been published and dosages in ml are summarized. For details on anes-thetic management of raptors and other species, see PT Redig, Recommendationsfor anesthesia in raptors with comments on trumpeter swans, in: Seminars in Avianand Exotic Pet Medicine: Anesthesia and Analgesia, AM Fudge, ed.,1998;7(1):22–29.


with a cuffed tube (smallest: 3.0–5.0 mm ID). Larger rap-tors may require slightly larger tubes, and the adult ratitetrachea accommodates tube sizes up to 18 mm ID. Birds100–350 g require uncuffed tubes (2.0–3.0 mm ID), Coletubes (uncuffed tubes with a tapered end), or largegauge IV catheters (14–18 ga). Birds smaller than 100 gare best maintained by mask with the head gentlyextended because there is an increased likelihood oftube occlusion and significant impedance to air move-ment associated with the small diameter cathetersrequired in this size bird. Endotracheal tubes with a sideopening near the bevel (Murphy tubes) help minimizethe risk of mucus occlusion. Once in place, the tube iseffectively secured with a thin piece of tape around thetube, which then is encircled around the closed beak.

For cases with airway obstruction or to perform pro-cedures in the oral cavity, inhalant anesthesia can bedelivered into the air sacs. Percutaneous catheters(14–18 ga; 2–3 cm) may be placed in the caudal thoracicor abdominal air sacs using sterile technique. A smallskin incision is required to expose the air sac membrane.The catheter is inserted and the skin secured around thecatheter; the catheter is connected to an endotrachealtube adaptor for delivery of the anesthetic agent. Theapproximate site of entry is at the last intercostal space.Apnea is common when this technique is used, makingmonitoring of cardiovascular parameters critical.

Anesthetic Management of Birds 199

For prolonged procedures or debilitated patientsand when significant hemorrhage is anticipated, intra-operative fluids should be administered. Intravenousaccess is possible in birds weighing ≥250 grams; sitesinclude the jugular, cutaneous ulnar, and medialmetatarsal veins. When fluid administration is essentialand IV access unsuccessful, the intraosseous route also iseffective. Sites of entry include the distal ulna and theproximal tibiotarsus (Figure 12–2). Spinal or hypoder-mic needles are used, depending on the size of the bird;the former minimizes the risk of needle occlusion by abone core during placement. Once placed, the needle iscapped and secured as for an IV catheter. Subcutaneousfluid administration sites include the propatagium (wingweb), intrascapular, and inguinal regions. Dextrose-con-taining fluids (LRS or Normosol with 2.5–5.0% dextrose,half strength LRS, or saline with 2.5% dextrose) are rec-ommended. Fluids administered SC should contain≤2.5% dextrose.

Sensitivity to anesthesia is variable among avianspecies and individual birds can develop complicationsrapidly; therefore, monitoring heart and respiratoryrates is essential. Effective aids to anesthetic monitoringinclude direct or esophageal auscultation, a lead II elec-trocardiogram (Figure 12–3), and respiratory (apnea)monitor; the last may not function effectively in verysmall patients, adds dead space to the breathing circuit,and usually is ineffective during mask delivery. Place-ment of ECG leads include the skin of the propatagium


201

Figure 12–2 Sites for intraosseous catheterization of birds forintraoperative fluid administration: (A) site for placing spinal orhypodermic needle via the distal ulna; (B) site for placing spinal orhypodermic needle via the proximal tibiotarsus. (Reprinted withpermission from DJ Harris, Therapeutic avian techniques, in: Semi-nars in Avian and Exotic Pet Medicine: Clinical Techniques, AMFudge, ed., 1997;6(2):61.)

(A)

(B)

(LA and RA) and the skin of the stifle (LL). Alligatorclips should be padded with alcohol-soaked gauze toavoid skin damage or, alternatively and effective, snap-onsticky ECG pads can be applied. Heart rates shouldremain between 200 and 400 beats/min depending onthe size of the bird (less for large ratites: 60–120beats/min). During surgical anesthesia, birds should berelaxed and unresponsive to painful stimulation; cornealand pedal reflexes are slow and the palpebral reflex islost. Respiration should be slow, regular, and deep, withrates usually ranging from 12–30 breaths/min. Temper-ature should be monitored, especially during long pro-cedures, to avoid development of hypothermia. Externalheat sources should be provided; maintaining a bodytemperature of 101–103°F is recommended.

Recovery usually occurs within 5–15 min afterinhalant delivery is discontinued and should occur in awarm, quiet, and dimly lit environment. Birds should bewrapped loosely in a towel and gently restrained untilextubated and able to stand. For prolonged recovery,birds may be left in a padded enclosure with close obser-vation, once extubated. For extubation, the oral cavityshould be checked for regurgitation or excessive secre-tions and swabbed if needed. Extubation should be per-formed when the bird resists its presence. Informationon analgesic agent dosages for birds is limited but shouldbe considered for painful invasive procedures andadministered either intraoperatively or just prior torecovery. Dosages for butorphanol have been reported


203

Figu

re 1

2–3

Norm

al E

CG

(w

ith a

sim

ultan

eous

arte

rial

pre

ssure

wav

e)

from

a 2

60 g

His

pan

iola

n A

maz

on p

arro

t. H

ear

t ra

te w

as a

bout

400 b

eat

s/m

in.

for pet birds and probably can be extrapolated toraptors. Flunixin meglumate and aspirin also have beenrecommended but not critically evaluated. Dosages arelisted in Table 12–1. Birds should be offered food andwater when able to perch.


13

Anesthetic Management of Small Mammals

This chapter primarily addresses anesthetic managementof rabbits and ferrets with additional comments on man-agement and analgesic options for other small mammals.

Ferrets

Ferrets are effectively restrained (and often resent it less)by techniques established for use in cats; namely, “scruff-ing” the skin of the neck and gently stretching the ani-mal by grasping the rear limbs. Premedication isrecommended in all but extremely debilitated animals;protocols are listed in Table 13–1. Most ferrets can be

205

catheterized for IV induction following a neuroleptanal-gesic combination, although healthy, uncooperativepatients will benefit from the addition of ketamine to thepreanesthetic protocol. Induction may be accomplishedby inhalant anesthetic, preferably isoflurane, deliveredby mask, or with an IV protocol such as thiopental,diazepam-ketamine, or propofol; IV induction will pro-vide more reliable access and increased duration of timefor intubation.

Sites for intravenous catheterization in ferretsinclude the cephalic, lateral saphenous, and (last) thejugular veins. Skin is tough, so making an “introductionhole” through the skin over the vein with a hypodermicneedle to facilitate entry of the catheter (22 or 24 ga) isbeneficial. Placing a tourniquet above the site will helpmaximally raise the vessel, which is very difficult to visu-alize due to its small size and the usual presence of alarge amount of SC fat. Catheterization is recommendedfor prolonged procedures and high-risk patients to pro-vide access for administration of intraoperative fluidsand anticipated supportive measures.

Intubation is relatively easy in ferrets. Visualization issimilar to cats and the ferret larynx usually will accom-modate a 2.5–3.0 mm ID tube. The larynx is less reactivethan cats, making local anesthetic desensitization unnec-essary; visualization is facilitated by a laryngoscope. Thetube should be secured around the back of the head withtie gauze as it is in cats.

206 Anesthetic Management of Small Mammals

Anesthetic Management of Small Mammals 207

Tab

le 1

3–1

Dosa

ges

of

Pre

medic

atio

n P

roto

cols

and I

nduct

ion A

gents

for

Ferr

ets

and R

abbits

Pro

toco

lD

osa

ge (

mg/k

g)

Co

mm

en

ts

Ferr

ets

Prem

edic

atio

n/

chem

ical re

stra

int

Atropin

e0.0

5 S

C, IV

, IM

Routin

e use

not

reco

mm

ended

.

Gly

copyr

rola

te0.0

1 S

C, IV

, IM

Routin

e use

not

reco

mm

ended

.

Ace

pro

maz

ine/

0.1

/0.4

SC

Avo

id a

cepro

maz

ine

in d

ebili

tate

d p

atie

nts

.buto

rphan

ol

Add k

etam

ine

(5–10 m

g/kg

IM

) to

pro

-vi

de

imm

obili

zatio

n t

o f

acili

tate

cat

het

eri-

zatio

n, in

duct

ion, an

d m

inor

pro

cedure

s.

Mid

azola

m/

0.2

–0.4

/0.4

SC

Good f

or

deb

ilita

ted p

atie

nts

. D

iaze

pam

buto

rphan

ol

(0.2

–2.0

mg/

kg)

may

be

use

d in p

lace

of

mid

azola

m b

ut

is les

s w

ell ab

sorb

ed a

nd

cause

s pai

n o

n inje

ctio

n. Add k

etam

ine

(5–10 m

g/kg

IM

) to

pro

vide

imm

obili

za-

tion t

o f

acili

tate

cat

het

eriz

atio

n, in

duct

ion,

and m

inor

pro

cedure

s.

(contin

ues

)


Tab

le 1

3–1

(Continued)

Pro

toco

lD

osa

ge (

mg/k

g)

Co

mm

en

ts

Xyla

zine

0.5

–1.0

SC

For

hea

lthy

pat

ients

only

. N

ot

reco

mm

ended

as

a p

rem

edic

atio

n f

or

inhal

ant

anes

thet

icm

ainte

nan

ce.

Med

etom

idin

e0.0

8 S

CFo

r hea

lthy

pat

ients

only

. N

ot

reco

mm

ended

as

a p

rem

edic

atio

n f

or

inhal

ant

anes

thet

icm

ainte

nan

ce.

Tela

zol

6–12 IM

Rec

ove

ry m

ay b

e pro

longe

d (

>4 h

r).

Rep

orted

sid

e ef

fect

s in

clude

snee

zing

and

pad

dlin

g durin

g in

duct

ion a

nd rec

ove

ry.

Faci

litat

es m

inor nonin

vasi

ve p

roce

dure

s.

Induct

ion*

Thio

pen

tal

8–12 IV

Giv

e sl

ow

ly “

to e

ffec

t.”

Ket

amin

e plu

s 0.1

ml/

kg IV

Dru

g m

ixtu

re is

mad

e by

com

bin

ing

equal

dia

zepam

or

volu

mes

of ke

tam

ine

and b

enzo

dia

zepin

e.m

idaz

ola

mG

ive

“to e

ffec

t.”

Pro

pofo

l2–5 IV

Giv

e sl

ow

ly “

to e

ffec

t.”

Inje

ctable

mix

ture

s**

Ace

pro

maz

ine/

0.2

–0.3

/20–30 IM

keta

min

e


Xyla

zine/

keta

min

e2.0

/25 IM

Anec

dota

l re

ports

of

dea

th in a

ppar

ently

norm

al a

nim

als

hav

e bee

n a

ssoci

ated

with

xyl

azin

e-ke

tam

ine.

Ace

pro

maz

ine/

0.0

5/1

–2/2

0–30 IM

xyla

zine/

keta

min

e

Med

etom

idin

e/0.0

8/0

.1/1

0 IM

Giv

ing

oth

er a

gents

SC

prio

r to

IM

ket

amin

ebuto

rphan

ol/

will

hel

p m

inim

ize

the

pai

n o

f IM

ke

tam

ine

inje

ctio

n.

Rab

bit

s†

Prem

edic

atio

n/

chem

ical re

stra

int

Atropin

e0.0

4–0.5

SC

, IV

, IM

Routin

e use

not

reco

mm

ended

.

Gly

copyr

rola

te0.0

1 S

C, IV

, IM

Routin

e use

not

reco

mm

ended

.

Ace

pro

maz

ine/

0.1

SC

/0.0

4 S

C/

Giv

e ke

tam

ine

10–15 m

inute

s af

ter

oth

er

bupre

norp

hin

e/5–10 IM

agen

ts o

r gi

ve a

ll IM

; ke

tam

ine

may

not

keta

min

e be

nec

essa

ry in t

ract

able

pat

ients

. Fa

cili-

tate

s ca

thet

eriz

atio

n, in

duct

ion, an

d m

inor

nonin

vasi

ve p

roce

dure

s.

(conntin

ues

)


Tab

le 1

3–1

(Continued)

Pro

toco

lD

osa

ge (

mg/k

g)

Co

mm

en

ts

Mid

azola

m o

r 0.2

SC

(IM

for

Mid

azola

m p

rovi

des

more

rel

iable

abso

rptio

ndia

zepam

/dia

zepam

)/0.4

and les

s pai

n o

n inje

ctio

n. Ket

amin

e m

aybuto

rphan

ol/

SC/5

–10 IM

not

be

nee

ded

for

trac

table

or

dep

ress

edke

tam

ine

pat

ients

. G

ood a

ltern

ativ

e fo

r deb

ilita

ted

pat

ients

. Fa

cilit

ates

cat

het

eriz

atio

n, in

duc-

tion, an

d m

inor

nonin

vasi

ve p

roce

dure

s.

Tela

zol

5–11 IM

Faci

litat

es c

athet

eriz

atio

n, in

duct

ion, an

d

min

or

nonin

vasi

ve p

roce

dure

s. R

ecove

ries

may

be

pro

longe

d. N

ephro

toxi

city

has

bee

n r

eport

ed b

ut

unlik

ely

at t

hes

e dose

s.

Induct

ion*

Dia

zepam

/ket

amin

e1 m

l/5–10 k

g IV

A 1

:1 (

volu

me)

mix

ture

giv

en t

o e

ffec

t.

Pro

pofo

l4–10 IV

Adm

inis

ter

slow

lyto

avo

id a

pnea

.

Inje

ctable

mix

ture

s**

Xyla

zine/

keta

min

e5/3

5Fo

r hea

lthy

anim

als

only

. Pro

vides

≤30 m

in-

ute

s of

surg

ical

anes

thes

ia. Res

ponse

is

varia

ble

and inef

fect

ive

in s

om

e pat

ients

.


Pro

found h

ypoxe

mia

is

report

ed w

ith t

his

com

bin

atio

n; su

pple

men

tal oxy

gen is

reco

mm

ended

.

*Mas

k in

duct

ion is

effe

ctiv

e in

fer

rets

and r

abbits

follo

win

g pre

med

icat

ion a

nd r

ecom

men

ded

in d

ebili

tate

d p

atie

nts

.M

ask

induct

ion is

par

ticula

rly a

ppro

pria

te in

rab

bits

bec

ause

mai

nte

nan

ce o

f an

esth

esia

via

mas

k is

ver

y co

mm

on d

ue

to d

iffic

ult

intu

bat

ion. R

apid

act

ing

IV a

gents

pro

vide

super

ior

rela

xatio

n a

nd v

isual

izat

ion o

f th

e la

rynx

and m

ore

tim

e to

succ

essf

ully

com

ple

te in

tubat

ion. T

elaz

ol a

nd c

om

bin

atio

ns

incl

udin

g ke

tam

ine

may

allo

w in

tubat

ion w

ithout m

aski

ng

or

additi

onal

inje

ctab

le a

gents

.

**In

ject

able

com

bin

atio

ns

pro

vide

short d

ura

tion a

nes

thes

ia for

min

or

pro

cedure

s an

d the

dosa

ges

liste

d a

re n

ot th

ose

reco

mm

ended

for

adm

inis

trat

ion p

rior

to in

hal

ant m

ainte

nan

ce. P

atie

nts

should

be

close

ly m

onito

red w

hen

com

bin

a-tio

ns

that

incl

ude

alpha 2

agonis

ts a

re u

sed a

nd a

lpha 2

agonis

t-co

nta

inin

g co

mbin

atio

ns

are

not re

com

men

ded

prio

r to

inhal

ant m

ainte

nan

ce.

† Effe

ctiv

enes

s of in

tran

asal

adm

inis

trat

ion o

f se

vera

l anes

thet

ic p

roto

cols

has

bee

n r

eported

in r

abbits

and p

rovi

des

an

alte

rnat

ive

route

for

pre

med

icat

ion a

dm

inis

trat

ion. E

ffect

ive

(and r

elat

ivel

y sa

fe)

pro

toco

ls (

mg/

kg)

incl

ude

xyla

zine

(3)/

keta

min

e (1

0);

mid

azola

m (

2);

ket

amin

e (2

5);

mid

azola

m (

1)/

keta

min

e (2

5);

tel

azol (

10). O

nse

t tim

e w

as w

ithin

3 m

in. N

one

of th

e pro

toco

ls p

rovi

ded

consi

sten

t ev

iden

ce o

f ad

equat

e an

esth

esia

for

inva

sive

pro

cedure

s.

Effective monitoring devices include an esophagealstethoscope, ECG, respiratory monitor, capnometer, andpulse oximeter.

Ferrets lose body heat rapidly, and external heatmust be provided. Recovery should occur in a warm,quiet environment; an incubator is ideal, especially whensignificant hypothermia has developed, which is com-mon during abdominal procedures. Options for postop-erative analgesia are listed in Table 13–2.

Rabbits

Rabbits are easily stressed by handling, which can have anegative impact on the anesthetic period. When fright-ened, they may hold deceptively still then struggle toescape, which can predispose them to traumatic frac-tures of the vertebral column (due to the massive rearlimb muscles and low-density skeletal system) or exhibita rapid ventilatory rate (200 breaths/min), which mightbe misinterpreted as a respiratory abnormality. Safe

restraint is essential to avoid injury, performed by gentlygrasping the skin of the neck and supporting the bodyon the forearm or a nonslip table. Loosely wrapping therabbit in a towel or restraint bag also helps minimizeinjury. The immobility reflex (“hypnosis”) has beendescribed for rabbits and can facilitate minor proce-dures, such as physical examination and blood collec-tion. Briefly, the rabbit is placed in dorsal recumbencyand gentle traction applied to the neck while rubbing



Tab

le 1

3–2

Dosa

ges

of

Sele

cted A

nal

gesi

c A

gents

for

a Var

iety

of

Sm

all M

amm

alSpeci

es

Rat,

Ham

ster,

Gu

inea P

ig,

Dru

gFe

rret

Rab

bit

Gerb

ilC

hin

chil

laM

ou

se

Opio

ids

Bupre

norp

hin

e0.0

1–0.0

3/

0.0

1–0.0

5/

0.0

1–0.0

5/

0.1

–0.2

5/

0.0

5–0.1

/8–12 IV,

SC

8–12 S

C, IV

8–12 S

C, IV

8–12 P

O12 S

C0.0

5/

8–12 S

C

Buto

rphan

ol

0.4

/4–6 S

C0.1

–0.5

/2.0

/4 S

C1.0

–2.0

/4 S

C1.0

–5.0

/SC

2–4 S

C

Morp

hin

e0.5

–5.0

/2.0

–5.0

/2.0

–5.0

/2.0

–5.0

/2.0

–5.0

/6 S

C2–4 S

C2–4 S

C2–4 S

C2–4 S

C

NSA

IDs

Asp

irin

200/*

PO

100/*

PO

100/*

PO

87/

* PO

120/*

PO

Car

pro

fen**

2.0

–4.0

/1.5

/12 P

O5.0

/24 S

CN

A5.0

/ * S

C24 S

C

Flunix

in

0.5

–2.0

/1.1

/12 S

C2.5

/12 S

C1–2/*

SC

2.5

/12 S

Cm

eglu

mat

e12–24 S

C

(contin

ues

)


Tab

le 1

3–2

(Continued)

Rat,

Ham

ster,

Gu

inea P

ig,

Dru

gFe

rret

Rab

bit

Gerb

ilC

hin

chil

laM

ou

se

Ket

opro

fen

NA

3.0

/* IM

, SC

5.0

/* S

CN

AN

A

Note

: N

um

ber

s re

pre

sent dosa

ge in

mg/

kg /

inte

rval

(in

hr)

for

each

spec

ies

cate

gory

. Consi

der

able

indiv

idual

var

iatio

nin

res

ponse

exist

s in

thes

e sp

ecie

s an

d fre

quen

t as

sess

men

t of ef

ficac

y is

crit

ical

.

*Rel

iable

dat

a re

gard

ing

dosa

ge in

terv

al is

unav

aila

ble

. Conse

rvat

ive

dosi

ng

at 1

2–24 h

r in

terv

al is

rec

om

men

ded

. In

gener

al, N

SAID

s sh

ould

not be

use

d for

more

than

1–3 d

ays,

due

to the

pote

ntia

l adve

rse

side

effe

cts

and p

auci

ty o

fin

form

atio

n r

egar

din

g sa

fety

in thes

e sp

ecie

s.

**C

arpro

fen c

urren

tly is

not av

aila

ble

in the

inje

ctab

le form

in the

Unite

d S

tate

s.

Route

s of ad

min

istrat

ion:

IV =

intrav

enous

SC =

subcu

taneo

us

IM =

intram

usc

ula

r

PO

= o

ral

NA =

not av

aila

ble

Dosa

ges

are

adap

ted fro

m P

A F

leck

nel

l, Anal

gesi

a in

sm

all m

amm

als,

in: Se

min

ars

in A

vian a

nd E

xotic

Pet

Med

icin

e:Anes

thes

ia a

nd A

nalg

esia

, AM

Fudge

, ed.,

1998;7

(1):

41–47.

(D

osa

ges

for

ham

ster

s, g

erbils

, and c

hin

chill

as a

re b

ased

on e

xtra

pola

tion fro

m o

ther

spec

ies

and in

itial

dose

s sh

ould

util

ize

the

low

er d

osa

ge r

ange

.)

the abdomen. The hypnotized rabbit usually stays still fora short period of time, unless aroused by loud noises orrough handling.

Premedication usually is required to facilitatesmooth induction of anesthesia, and protocols are listedin Table 13–1. Most of the agents may be administeredsubcutaneously (over the skin of the back), and this ispreferred, due to occasional occurrence of lameness andtissue necrosis associated with IM administration. Disso-ciative agents should be administered IM, and the mostcommon sites include the anterior and posterior thigh.A significant percentage of rabbits (30–50%) possessatropinesterase, which results in rapid metabolism andabbreviated effective duration of atropine. Because ofthis, a wide range of dosages has been recommended inthe literature; however, routine use is unnecessary andanticholinergic agent administration in rabbits is bestreserved for treatment of intraoperative bradycardia(HR <70–80/min or an abrupt, marked decrease[≥20%] in HR). Dosages for atropine and glycopyrrolateare listed in Table 13–1.

Intravenous catheterization following premedica-tion usually is possible in rabbits over 2 kg and recom-mended for prolonged procedures, debilitated patients,and to facilitate IV induction of anesthesia. Sites includethe cephalic, lateral saphenous, and marginal ear veins,using a 22–24 ga catheter. The ear vein is particularlyfragile and more difficult to catheterize than the othertwo sites.


Mask induction, preferably with isoflurane, is aneffective method when the rabbit is adequatelyrestrained and sedated; and it is particularly applicablewhen intubation is not planned. For prolonged proce-dures, intubation is recommended; and a rapid-actinginduction agent, such as diazepam-ketamine, propofol,or thiopental, will facilitate the process. Intranasaladministration of anesthetic agents for sedation or toinduce anesthesia also has been reported for rabbits andmay provide an alternative route for some agents in spe-cific individuals (Table 13–1).

Rabbits are difficult to intubate and it takes practiceand anatomical knowledge to master the technique. Theendotracheal tube size for rabbits ranges 2.0–4.0 mm ID.The oral cavity is small but long, with limited ability forthe animal to open its mouth. The tongue tends toobscure the larynx. The epiglottis is long and pliable,often remaining dorsal to the soft palate. The pharynx islocated at a right angle to the larynx, and the larynx issusceptible to laryngospasm and trauma.

Adequate anesthetic depth is essential to facilitateatraumatic intubation, and several methods and animalpositions (with sternal recumbency being most com-mon) have been described. The head and neck shouldbe kept in full extension; a length of roll gauze placedbehind the upper incisors will help hold the mouthopen; and retraction of the tongue lateral to the lowerincisors will minimize risk of laceration during the pro-cedure. Techniques include blind (passing the tube to


the point of maximum intensity of breath sounds eitherwith the ear or with stethoscope earpieces attached tothe end of the tube, then passing the tube during inspi-ration when the larynx is maximally abducted) and direct

visualization (with a small lighted laryngoscope or oto-scope to guide the tube into place). Use of an introduc-tory tube, such as a small urinary catheter, placed visuallyinto the larynx may facilitate the process. A drop of 1%or 2% lidocaine on the glottis will help minimize laryn-gospasm. Evidence of proper placement includes acough reflex with passage and those signs previouslynoted in Chapter 9. Roll gauze tied around the tube andaround the back of the head will secure the tube inplace.

Once induction is complete, epidural administrationof local anesthetic agents, with or without an opioid, iseffective and relatively easy to perform in rabbits to pro-vide preemptive analgesia for procedures involving theabdomen and hind limbs. Dosages and technique aresimilar to those described for dogs and cats (Chapter 3).

Monitoring tools, to enhance observation of breath-ing rate (>15 breaths/min) and pattern and ausculta-tion/palpation of pulse rate (auricular, femoral, ordorsal pedal), include the ECG and, in larger rabbits,noninvasive blood pressure monitors placed over aperipheral artery. Pulse oximetry has limited use (due tofrequent use of a mask for maintenance and limitedexposure of the tongue for probe placement), but maywork on the ear in light-skinned rabbits. Respiratory


devices and the esophageal stethoscope require intuba-tion and, so, often are not applicable. Respiratory dys-function probably is the most common anestheticcomplication in rabbits and close observation of thebreathing rate and pattern is essential. A sudden changein these parameters should prompt assessment of ETtube patency (if in place) or the oropharynx for exces-sive secretions (if a mask is used), and anesthetic deliveryshould be decreased or stopped. Reflexes used to assessanesthetic depth include the pinna (“ear pinch”) andpedal reflexes with the former considered to be mostreliable. The palpebral reflex has been reported to beunreliable in rabbits; loss of the corneal reflex, as inother species, indicates excessive anesthetic depth.

Monitoring should continue into the recoveryperiod, until the animal is extubated and vital signs arestable, and should proceed in a warm environment (withincubator or heat lamp support) until the animal’s tem-perature returns to normal (Chapter 1). Analgesic agentdosages have been reported (see Table 13–2) and shouldbe applied to rabbits subjected to painful procedures tohelp minimize stress and suffering.

Other Small Mammals

A variety of “pocket pets” may be presented with the needfor general anesthesia. Some general statements regard-ing management in clinical situations can be made:


1. For small mammals, anesthetic management is bestaccomplished by mask or chamber induction(depending on tractability) with isoflurane orsevoflurane. Designing a mask to work effectivelymay require some innovative modification of stan-dard feline or canine masks or syringe cases. Intuba-tion may be attempted if the necessary tube sizes andadjunct equipment are available.

2. When dealing with species for which anestheticdosage and technique information is limited, effortsto minimize anesthesia time is essential.

3. Established monitoring tools often are effective; it isalways worthwhile to apply available equipment,especially during prolonged procedures.

4. Venous access is not always possible with small mam-mals, but when fluid therapy is indicated, alternativeroutes, including SC and intraosseous, should beconsidered.

5. Analgesic therapy should be considered for any ani-mal undergoing a painful procedure; when specificdosages are not readily available, extrapolation orscrutiny of the literature may provide safe, effectiveguidelines. Table 13–2 provides dosages of analgesicagents in a variety of small mammal species.


14

Anesthetic Management of Reptiles

A variety of reptilian species may be presented with theneed for chemical restraint and general anesthesia, andthis represents a unique challenge, including limitedsites for parenteral agent injection and IV access, a majortendency to become apneic during anesthesia (whichoften prevents use of mask induction), difficulty in car-diac auscultation, and limited usefulness of availablemonitoring tools.

Restraint techniques are relatively simple for most rep-tiles but may become more challenging in infrequentlyencountered aggressive patients. Lizards are restrainedby enclosing in the hand if small or securing on a flat sur-face then applying gentle pressure to the neck and cau-dal body. For snakes, a hand should secure the head and

221

the remainder of the body supported with the otherhand or on a flat surface. Turtles require minimalrestraint but present a unique problem in that the headusually is inaccessible for physical examination. To viewthe head, applying a gentle pinch to a front limb usuallywill cause it to emerge from the shell. Two preanestheticconsiderations are important for reptiles. Allow at least24 hr of hospitalization prior to anesthesia for acclima-tion. The optimal temperature for most species is86–88°F. Second, an accurate weight is important to cal-culate dosages for premedication, which is necessary forinduction in most reptile patients. Fasting in reptilesgenerally is not recommended; the exception is snakes,for which a large meal ingested just prior to anesthesiacould impede cardiovascular function; therefore, a 24-hr(minimum) fast is recommended.

Various sites for blood collection have beenreported—lizards (toenail, ventral tail vein); snakes (ven-tral tail vein, heart, palatine vein); turtles (toenail,brachial plexus)—and may be required for the workupof complicated cases.

Induction and intubation for maintenance withinhalant anesthesia (preferably isoflurane) is facilitatedby IM administration of ketamine. Dosages for ketamineand other adjunct drugs are listed in Table 14–1. Noneof the agents listed provides adequate analgesia aloneand inhalant supplementation is necessary for painfulprocedures. Because many species of reptiles can convertto anaerobic metabolism and become apneic, mask

222 Anesthetic Management of Reptiles

induction is prolonged without the benefit of aninjectable agent. Like birds, reptiles have a renal portalsystem and the caudal half of the body should be avoidedfor IM drug administration. Sites for IM injectioninclude the front legs (lizards, chelonians) and the par-avertebral muscles (lizards, snakes). A nonrebreathingsystem for inhalant delivery is recommended for reptilesweighing <5 kg.

Intubation is important in anesthetic managementof reptiles to provide ventilatory support during theanesthetic period and maintain an adequate depth ofanesthesia. Intubation is relatively easy to perform andcan be accomplished in some awake reptiles, includingsnakes and some iguanas. The glottis is located rostrallyand hence easy to view. However, the glottis is closed atrest and patience is required to wait for an inspiration toallow passage of the tube. The tube may be passedthrough the closed glottis if extreme care is taken and maybe facilitated by passage of a soft stylet (urinary catheter)to guide the entry of the endotracheal tube. Tube sizesfor reptiles range from 2.0–4.0 mm ID, but smallerpatients may require other options, such as IV catheters.Short tubes should be used in turtles, due to their rela-tively short trachea. Chelonians have complete trachealrings, making them susceptible to mucosal damage dueto an overinflated cuff; snakes and lizards have incom-plete tracheal rings. When a cuffed tube is used in anyreptile, care should be taken to not overinflate the cuff.

Anesthetic Management of Reptiles 223


Tab

le 1

4–1

Dosa

ges

for

Inje

ctab

le A

nest

hetic

Age

nts

in R

eptile

s

Agen

tD

osa

ge (

mg/k

g)*

Co

mm

en

ts

Atropin

e0.0

1–0.0

4Routin

e use

is

not

reco

mm

ended

.

Gly

copyr

rola

te0.0

1Routin

e use

is

not

reco

mm

ended

.

Tranquili

zers

/alp

ha

2D

osa

ge a

nd e

ffic

acy

info

rmat

ion is

limite

d.

agonis

ts/a

nta

gonis

ts

Ace

pro

maz

ine

0.1

–0.5

Dia

zepam

0.2

–1.0

Mid

azola

m0.2

–2.0

Xyla

zine

0.1

–1.2

5

Med

etom

idin

e0.1

–0.1

5

Atip

amez

ole

0.5

–0.7

5

Neu

role

pta

nalg

esia

Buto

rphan

ol/

mid

azola

m0.4

/2.0

Dis

soci

ativ

e agen

ts

Ket

amin

eKet

amin

e is

the

most

com

mon a

nes

thet

ic

adju

nct

util

ized

.Li

zard

s30–50

Snak

es20–40


Turtle

s30

Tela

zol

5–10

May

contrib

ute

sig

nifi

cantly

to a

pro

longe

d

reco

very

.

Oth

er a

gen

ts

Pro

pofo

lLi

zard

s10 IO

Snak

es10 IV,

IC

Turtle

s5–10 IV

Analg

esic

agen

ts

Buto

rphan

ol

0.4

IM

, IV

, SC

Bupre

norp

hin

e0.0

1

Car

pro

fen

2.0

–4.0

PO

once

ev

ery

1–3 d

ays

Flunix

in0.1

–0.5

IM

once

dai

ly (

max

imum

of

3 d

ays)

IO =

intrao

sseo

us

IC =

intrac

ardia

c

*Adm

inis

trat

ion is

IM

unle

ss o

ther

wis

e note

d.

Intraoperative fluid administration is not routine,unless the procedure is prolonged or the animal debili-tated. Intravenous access is a daunting task in reptiles,requiring a cutdown in most cases. The exception islarge snakes, in which the palatine vein can be easily visu-alized and catheterized with a 24 ga catheter followinginduction and intubation. When needed, the intra-osseous route is feasible. Intraosseous catheter sites inlizards include the humerus and tibia. In chelonians, thejugular vein may be catheterized in some patients (some-times without a cutdown); the long bones lack a distinctmedullary canal, limiting IO sites to the bridge betweenthe plastron (bottom of shell) and carapace (top ofshell), which may be difficult to enter without penetrat-ing the coelomic cavity.

Ventilatory support at a rate of 6–12 breaths/minshould be provided for all reptiles, regardless of the indi-vidual’s spontaneous rate, to help maintain an adequateplane of anesthesia.

Monitoring anesthetized reptiles is the ultimate chal-lenge. Apnea is common, making respiratory monitor-ing undependable. Heart sounds are extremely difficultto auscultate, and peripheral pulses rarely are palpable.Useful tools include the ECG (Figure 14–1) and theDoppler blood flow probe (apparatus), which providesan audible signal of cardiac function. The crystal isplaced over the heart in snakes and lizards and at thethoracic inlet in chelonians. Reptiles relax in a cranial tocaudal direction during anesthesia, and function returns


in the opposite direction during recovery. The rightingreflex is lost first, followed by the tail- and toe-pinchwhen a surgical plane of anesthesia is reached. Whileconsiderable variation exists, loss of the vent reflex (tailor toe movement when the vent is squeezed), thecorneal reflex, and tongue withdrawal all may indicateexcessive depth of anesthesia, which should prompt crit-ical patient assessment.

Recovery from inhalation anesthesia often is pro-longed in reptiles compared to mammals, commonlytaking 1 hr or more, especially following prolonged pro-cedures. Animals should recover in a quiet environment,ideally with the ambient temperature near the species’optimal range. Ventilatory support should be continuedto aid in elimination of the anesthetic agent; animals thatdo not resume spontaneous ventilation within 15 min ofdiscontinuation of anesthetic delivery may benefit fromdoxapram (5 mg/kg IM). Voluntary movement andincreased muscle tone usually are the first signs to indi-cate extubation, which should be delayed, if possible,until the righting reflex returns. While information islimited, analgesia should be provided for painful proce-dures. Suggested agents and dosages are listed in Table14–1.


228

Figu

re 1

4–1

Lead

II

ele

ctro

card

iogra

m f

rom

an igu

ana

during

isoflura

ne a

nest

hesi

a. L

ead

s w

ere

pla

ced o

n t

he f

ore

limbs

and left

rear

lim

b.

15

Anesthetic Management of Horses

Horses are an anesthetic challenge due to their size, widerange of temperaments, tendency to react explosively tofear and stress, increased risk of trauma associated withinduction and recovery (which can both be rough andunpredictable), susceptibility to hypotension, andincreased risk for development of postoperative myopa-thy and neuropathy following inhalant anesthesia. Mostshort procedures (<60 min) in horses are performedwith total parenteral anesthesia, using the same agentsthat provide induction for inhalant anesthesia; recom-mended protocols are listed in Table 15–1.

Fasting is controversial in horses. Horses cannotvomit, so risk of regurgitation and aspiration is negligi-ble; however, a minimum of 6 hr is recommended. It is

229

230 Anesthetic Management of Horses

Tab

le 1

5–1

Pro

toco

ls f

or

Chem

ical R

est

rain

t, I

nduct

ion o

f A

nest

hesi

a, and

Inje

ctable

Anest

hesi

a in H

ors

es

Agen

t/P

roto

col

Do

sages

(mg/k

g)

Co

mm

en

ts

Ad

ult

s

Chem

ical re

stra

int

Ace

pro

maz

ine

0.0

2–0.0

6M

ay b

e co

mbin

ed w

ith a

lpha 2

agonis

t or

opio

id.

Xyla

zine

0.2

–1.0

May

be

com

bin

ed w

ith a

cepro

maz

ine

or

opio

id.

Det

om

idin

e0.0

1–0.0

4M

ay b

e co

mbin

ed w

ith a

cepro

maz

ine

or

opio

id.

Buto

rphan

ol

0.0

2–0.0

4U

sual

ly c

om

bin

ed w

ith a

lpha 2

agonis

t.

Morp

hin

e0.0

5D

o n

ot

use

alo

ne

due

to lik

elih

ood o

f ex

cite

-m

ent;

usu

ally

com

bin

ed w

ith a

lpha 2

agonis

t.

Induct

ion/s

hort-

term

ane

sthe

sia

Xyla

zine/

keta

min

e 1.1

*/2.2

IV

Giv

e xy

lazi

ne

first

and p

roce

ed in 5

min

or

when

sed

atio

n a

ppea

rs a

deq

uat

e. F

or

unru

lyan

imal

s, x

ylaz

ine

may

be

adm

inis

tere

d IM

(2.2

mg/

kg)

and m

ay r

equire

additi

onal

IV

xyla

zine

(0.2

–0.4

mg/

kg)

prio

r to

ket

amin

ead

min

istrat

ion. Adju

nct

dru

gs t

o im

pro

ve

Anesthetic Management of Horses 231

sedat

ion p

rior

to k

etam

ine

incl

ude

acep

ro-

maz

ine

(0.0

2 m

g/kg

IV o

r IM

) or

buto

r-phan

ol (0

.02–0.0

4 m

g/kg

IV).

Xyla

zine/

0.5

–1.1

/0.0

5–

Good f

or

deb

ilita

ted p

atie

nts

and

dia

zepam

/0.1

/2.2

neo

nat

es; xy

lazi

ne

adm

inis

trat

ion s

hould

ke

tam

ine

pre

cede

induct

ion a

nd d

ose

is

bas

ed o

npat

ient

aler

tnes

s. M

ix d

iaze

pam

and k

eta-

min

e an

d g

ive

as b

olu

s. In v

ery

dep

ress

ed,

recu

mben

t an

imal

s or

neo

nat

es, xy

lazi

ne

may

be

om

itted

. If

sedat

ion is

consi

der

ednec

essa

ry, 0.0

1–0.0

3 m

g/kg

buto

rphan

ol is

reco

mm

ended

.

Xyla

zine/

5%

0.5

–1.1

/”to

effec

t”/

Inco

rpora

ting

guai

fenes

in w

ill h

elp d

ecre

ase

guai

fenes

in/

0.7

5–2.2

xyla

zine

and k

etam

ine

require

men

ts.

keta

min

e

Xyla

zine/

5%

0.5

–0.6

/to e

ffec

t/Th

iopen

tal ca

n f

ollo

w g

uai

fenes

in a

s a

bolu

s or

guai

fenes

in/

3.0

–4.0

2 g

added

to g

uai

fenes

in a

nd g

iven

to

thio

pen

tal

recu

mben

cy.

Xyla

zine/

Tela

zol

1.1

/1.1

Rep

orted

to c

ause

a m

ore

pro

longe

d a

nd s

lightly

rough

er r

ecove

ry t

han

xyl

azin

e/ke

tam

ine.

(contin

ues

)


Tab

le 1

5–1

(Continued)

Agen

t/P

roto

col

Do

sages

(mg/k

g)

Co

mm

en

ts

Inje

ctable

U

se f

ollo

win

g in

duct

ion w

ith x

ylaz

ine-

keta

min

eanes

thet

ic

(with

or

with

out

dia

zepam

, buto

rphan

ol,

main

tenance

or

acep

rom

azin

e).

Xyla

zine/

0.5

mg/

ml xy

lazi

ne

“Trip

le d

rip”:

adm

inis

tere

d a

t ap

pro

xim

atel

ygu

aife

nes

in/

and 1

mg/

ml

2.2

ml/

kg/h

our

keta

min

eke

tam

ine

added

May

be

use

d f

or

induct

ion o

f an

esth

esia

to 5

% g

uai

fenes

in(0

.5–0.6

ml/

kg)

in h

ors

es w

eigh

ing

<200 k

g.

Guai

fenes

in/

2 m

g/m

l ad

ded

C

an b

e use

d f

ollo

win

g in

duct

ion w

ith x

ylaz

ine-

thio

pen

tal

to 5

% g

uai

fenes

inke

tam

ine

or

guai

fenes

in-thio

pen

tal.

Anes

-th

etic

dep

th b

ecom

es m

ore

diff

icult

toas

sess

if

the

form

er is

use

d.

Avo

id u

sing

more

than

2 g

thio

pen

tal fo

r m

ain-

tenan

ce t

o m

inim

ize

risk

of

rough

rec

ove

ry.

Foals

Induct

ion/s

hort-

dura

tion

main

tenance


Buto

rphan

ol/

0.0

6/0

.06 IV

Induce

anes

thes

ia b

y m

ask

or

nas

otrac

hea

ldia

zepam

intu

bat

ion, pre

fera

bly

with

iso

flura

ne

(or

sevo

flura

ne)

.

Buto

rphan

ol/

0.0

6/0

.1/2

.2Xy

lazi

ne

(0.2

–0.5

mg/

kg)

may

be

added

for

dia

zepam

/hea

lthy

foal

s w

hen

they

res

ist

rest

rain

t or

keta

min

ea

pai

nfu

l pro

cedure

is

to b

e per

form

ed.

Dura

tion o

f an

esth

esia

: 10–20 m

in.

Analg

esic

optio

ns

Dosa

ge inte

rval

s ar

e gu

idel

ines

to b

e ta

ilore

d t

o

indiv

idual

pat

ients

bas

ed o

n o

ngo

ing

asse

ss-

men

t.

Bupre

norp

hin

e0.0

05 IM

, SC

Inte

rval

: 6–12 h

r

Buto

rphan

ol

0.0

2 IV,

IM

Inte

rval

: 2–4 h

r

Morp

hin

e0.2

IM

Inte

rval

: 4–6 h

r

The

pre

sence

of

pai

n o

btu

nds

the

exci

tato

ry

resp

onse

that

can

occ

ur

with

morp

hin

ead

min

istrat

ion t

o h

ors

es; how

ever

, ag

itatio

nan

d e

xcite

men

t ca

n o

ccur,

whic

h a

re c

on-

trolle

d b

y xy

lazi

ne

(0.2

–0.4

mg/

kg IV).

(contin

ues

)


Tab

le 1

5–1

(Continued)

Agen

t/P

roto

col

Do

sages

(mg/k

g)

Co

mm

en

ts

Morp

hin

e (c

ont.)

0.1

(ep

idura

l M

ay b

e use

d a

lone

or

com

bin

ed w

ith x

ylaz

ine

adm

inis

trat

ion)

or

det

om

idin

e (s

ee d

osa

ges

in T

able

3–4)

for

pai

n r

elie

f as

far

forw

ard a

s th

ora

x fo

r 8–24 h

r.

Avo

id f

orm

ula

tions

that

conta

in t

he

pre

serv

ativ

e fo

rmal

in (

the

pre

serv

ativ

e m

ethyl

par

aben

is

acce

pta

ble

). U

se o

f th

e pre

serv

ativ

e-free

pre

par

atio

n (

Duro

morp

h™

) is

optim

al b

ut,

due

to t

he

low

conce

ntrat

ion, ad

equat

edosa

ge m

ay b

e diff

icult

to d

eliv

er d

ue

to t

he

larg

e quan

tity

require

d.

Fenta

nyl

Tw

o 1

00 µ

g pat

ches

Dura

tion o

f ef

fect

: 48 h

r.(t

ransd

erm

al)

per

adult

hors

e(a

pplie

d o

ver

tho-

rax

beh

ind e

lbow

)

Phen

ylbuta

zone

2.2

–4.4

IV,

PO

Inte

rval

: 12 h

r

Flunix

in m

eglu

min

e1.1

IV

Inte

rval

: 8–12 h

r

Ket

opro

fen

1.1

–2.2

IV

Inte

rval

: 12–24 h

r

Note

: D

osa

ges

are

most

com

monly

adm

inis

tere

d IV.

*D

raft

bre

eds

rare

ly r

equire

more

than

600 m

g (t

ota

l IV d

ose

) xy

lazi

ne

pre

med

icat

ion for

keta

min

e in

duct

ion.


advisable but unnecessary to remove shoes prior to anes-thetic induction; shoes with toe clips or devices that maycause significant body injury or excessive slipping duringrecovery should be removed. Covering shoes left in placewith padding and tape will help minimize these risks.

Adequate preanesthetic sedation is essential in adulthorses. Induction of anesthesia in an inadequatelysedated animal will increase the risk of injury to bothhorse and handler. The most commonly used drug isxylazine. Combining a second agent with xylazine, such asbutorphanol, acepromazine, or diazepam, will helpassure a smooth induction (see Table 15–1). Avoidxylazine (at least high dosages) in foals less than 1 monthof age if other agents are available (see Table 15–1). Theinduction agent most commonly used is ketamine, aloneor in combination with guaifenesin or diazepam.Thiopental also is used, largely dependent on experiencewith the drugs and the occasional contraindication asso-ciated with ketamine in individual patients (e.g., headtrauma, descemetocoele). As a general rule, protocolsusing ketamine produce a more reliable and smootherrecovery; however, some animals—such as excitable, hot-blooded breeds, donkeys, mules, and ponies—may fail torespond to ketamine induction and short-term mainte-nance, making it necessary to use other or additionalagents for induction and maintenance. Donkeys andmules appear sensitive to the effects of guaifenesin;incorporating guaifenesin into the induction protocol is


effective, but care must be taken to avoid high-enddosages, which could precipitate apnea.

Because their response to anesthetics can be unpre-dictable, placing a catheter in the jugular vein, eitherbefore or after premedication, will provide easy access toadminister additional drugs when needed to smoothinduction, prolong the anesthetic period in field situa-tions, and quickly obtund voluntary movement duringinhalation anesthesia.

Intubation is performed blindly in the horse, withthe head, neck, and back extended in a straight line.Inserting a speculum, such as a short piece of PVC pipewith the edges smoothed, will facilitate passage of thetube between the cheek teeth into the larynx. Once thetube reaches the larynx, it is retracted slightly, rotated90°, and advanced again until it can pass by the arytenoidcartilages and “fall into” the trachea. This may need to berepeated, rotating in the same direction, one or severaltimes before the tube bevel can pass into the trachea.

Endotracheal tubes also can be passed nasally; thispractice is common in foals to facilitate an inhalantinduction and may be indicated in adult horses for pro-cedures of the oral cavity. Desensitizing the floor of thenasal opening with lidocaine jelly will facilitate tubeintroduction into the ventral nasal meatus. The disad-vantage of nasotracheal intubation is that a smaller tubemust be used, which will increase resistance to breathing.Orotracheal tube sizes range from 10 mm ID (newbornfoals) to 30 mm ID for draft breeds. For nasotracheal


intubation, 8–12 mm ID is used in foals and 16–20 mmID can be passed in adult horses. Intubation is unneces-sary during parenteral anesthesia. However, horses areobligate nasal breathers, and some individuals maydevelop stridorous inspiration during general anesthe-sia, which may require placement of an ET tube (nasal isconvenient) to maintain airway patency. Appropriatelysized tubes always should be available for quick intuba-tion should a respiratory emergency develop.

Halothane, isoflurane, and, most recently, sevoflu-rane are used in horses. Halothane historically has beenthe agent of choice for elective procedures, due to itseffectiveness and lower cost, despite a greater negativeeffect on cardiac performance and greater likelihood ofhypotension. Isoflurane is a better choice for high-riskpatients (e.g., those with colic or needing a cesarean sec-tion) and foals. Reports have suggested a rougher recov-ery associated with isoflurane anesthesia when used inrelatively healthy horses. This potential undesirableeffect can be minimized by administration of a sedativeor tranquilizer (e.g., alpha2 agonist, butorphanol, ace-promazine) at the low-end dosage range, IV or IM, in thepostoperative period. Intramuscular administration willprovide a longer duration with less negative cardiovascu-lar effects but should be given 15–30 min prior to therecovery period. Sevoflurane has been reported to pro-duce smooth recoveries, even in healthy patients, due toits lower solubility (compared to isoflurane andhalothane) and rapid clearance.


Supportive care considerations include adequatepadding and proper positioning to minimize risk of myo-pathy and neuropathy, crystalloid fluid administration tocounteract the hypotensive effects of inhalant anesthet-ics, provision of mechanical ventilation during inhalantanesthesia (especially for respiratory-compromisedpatients and during prolonged procedures), and admin-istration of inotropic agents when indicated. Minimizingdowntime is a critical factor in decreasing the risk ofmyopathy in all horses and especially important in largebreeds, such as draft horses. The most commonly usedinotrope in horses is dobutamine, administered “toeffect” at an approximate infusion rate of 2–5µg/kg/min. An easy method is to add 50 mg of dobuta-mine to a 500 ml bag of 0.9% saline or 5% dextrose andadminister at a rate of 1–2 drop/sec (10 drop/ml dripset for adults; 60 drop/ml set for foals) until the desiredblood pressure is achieved. Dobutamine may be usedintermittently as needed or the administration rate canbe adjusted to maintain a stable and adequate mean arte-rial pressure. Greater accuracy is provided by use of asyringe pump when available.

During parenteral anesthesia, the eyes should becovered to minimize external stimulation, the halterremoved to minimize risk of damage to nerves lyingsuperficially in the head, and oxygen supplemented(10–15 L/min) for procedures anticipated to exceed 60min. Demand valves, which function at 50–80 psi to

deliver 200–280 L/min of oxygen, provide supplementaland emergency ventilatory support for large animalpatients during injectable anesthesia and recovery frominhalation anesthesia when an anesthesia machine is notreadily accessible. The demand valve, connected to theendotracheal tube, is triggered by negative pressure cre-ated by the animal’s spontaneous breath or manually bythe operator. It adds resistance to breathing and shouldnot be left on the ET tube for prolonged periods of time.It can be used connected to a stomach tube with the tipplaced in the nasopharynx, but this is less efficient.

Vigilant monitoring is important in horses, as volun-tary movement, sometimes without obvious warning, iscommon. Horses may exhibit transient apnea in theimmediate postinduction period, which will delay anes-thetic uptake if ventilatory support is not provided. Res-piration is easy to observe in horses by directvisualization of the thorax and rebreathing bag. Normalrates should be 6–12 breaths/min, higher for foals(12–20 breaths/min). Horses are prone to hypoventila-tion and hypoxemia during anesthesia. Although of min-imal consequence during short field procedures, thesechanges can become significant and affect cardiac per-formance during prolonged procedures. Arterial bloodgas analysis, when available, will help guide ventilatorysupport and optimize homeostasis during the intraoper-ative period and is advised for procedures in excess of 60min and for high-risk patients.



The heart rate (HR) tends to remain stable in adulthorses (25–50 beats/min; performance animals mayhave even lower rates), even when anesthesia is inade-quate, so it is not an effective indicator of anestheticdepth. Foals are the exception: a marked increase in HRis likely to occur during inadequate anesthesia. Invasivearterial blood pressure monitoring is a reliable and nec-essary monitoring tool during equine inhalation anes-thesia to assure adequate perfusion pressure (minimalmean arterial pressure >60–70 mmHg, which will helpminimize the risk of myopathy), provide information oncardiac performance, and signal inadequate anestheticdepth, with a sudden and rapid increase in pressureoften (but not always) preceding voluntary movement.Both of the noninvasive arterial blood pressure monitor-ing techniques (Chapter 6) are applicable for short anes-thetic duration (<1 hr) and seem to be especiallyeffective in foals, although less reliable and accurate.

Eye signs used to assess inhalant anesthetic depth inhorses include the palpebral reflex, which shouldremain slow but present; rapid nystagmus, which oftensignals impending movement (slow nystagmus may per-sist in some individuals without accompanying voluntarymovement); and tearing, which may signal a light planeof anesthesia. These signs should be assessed in conjunc-tion with cardiopulmonary parameters whenever criticalassessment of anesthetic depth is made.

Recovery following inhalant anesthesia should occurin a dark and padded enclosure. Recovery may be assisted

with a tail rope and halter if there is adequate room in therecovery area for personnel to escape injury and amethod to secure the ropes. Assisted recovery is especiallyindicated for patients at risk of injury during recovery,such as orthopedic patients. Recovery is facilitated byplacing animals on a large pad, to maintain padding, andto discourage attempts to stand until the animal is able.Postanesthetic sedation helps to delay attempts to standuntil the animal can do so unattended or with minimalassistance. Two approaches to extubation are used,depending on personal preference and available facili-ties. The tube can be removed before swallowing isobserved and replaced with a smaller nasotracheal tube,which should be taped securely to the muzzle to assure apatent airway throughout the recovery process. Or, theanimal can be attended until swallowing is observed andthen the tube removed, assuming a patent airway can bemaintained at that time. Regardless of the preferredapproach, oxygen supplementation (15 L/min) shouldbe provided throughout recovery because a tendency tohypoxemia will persist until the horse returns to standing.

For field procedures, a safe and grassy area is pre-ferred for recovery. The eyes should remain covered andthe animal attended until it can be assisted to stand whena coordinated attempt is made.


16

Anesthetic Management of Ruminants and Camelids

Ruminants are amenable to standing chemical restraintand local techniques (Chapter 3) for a variety of proce-dures due to temperament (there are exceptions) andestablished effective restraint techniques. Table 16–1 listsdosages for agents to provide chemical restraint, induc-tion, and parenteral maintenance of anesthesia. Anti-cholinergic administration is controversial and routineadministration is not recommended. Bradycardia rarelyis a complication of general anesthesia and administra-tion of atropine will not significantly decrease salivationbut will increase its viscosity and may contribute to devel-opment of bloat.

243

244 Anesthetic Management of Ruminants and Camelids

Tab

le 1

6–1

Dosa

ges

of

Inje

ctab

le A

nest

hetic

Age

nts

Use

d f

or

Chem

ical

Rest

rain

t,In

duct

ion, an

d M

ainte

nan

ce o

f A

nest

hesi

a in

Rum

inan

ts a

nd C

amelid

s

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

Ru

min

an

ts

Che

mic

al r

estrai

nt/

pre

med

icatio

n

Ace

pro

maz

ine

Cat

tle0.0

2–0.0

6In

effe

ctiv

e al

one

for

intrac

table

pat

ients

.G

oat

s, s

hee

p0.0

4–0.0

8M

ay incr

ease

occ

urren

ce o

f re

gurg

itatio

n.

Dia

zepam

(ca

lves

, 0.2

–0.5

Min

imal

ly e

ffec

tive

in a

dult

cattle

.sm

all ru

min

ants

)

Xyla

zine*

*C

attle

0.0

1–0.1

In g

ener

al, do n

ot

exce

ed 5

0 m

g to

tal dose

; ↑

dosa

ges

may

be

require

d f

or

intrac

table

pat

ients

.G

oat

s0.0

2–0.1

Do n

ot

exce

ed 0

.02 (

mg/

kg)

IM in k

ids.

Shee

p0.0

2–0.2

Hyp

oxe

mia

due

to p

atholo

gic

pulm

onar

y ch

ange

s has

bee

n r

eport

ed in s

hee

p; if

xyla

zine

adm

inis

trat

ion is

unav

oid

able

, use

min

imal

rec

om

men

ded

dosa

ges

and s

upple

-m

ent

oxy

gen w

hile

sed

ated

.

Anesthetic Management of Ruminants and Camelids 245

Chlo

ral hyd

rate

Cat

tle40–60 IV

80–100 P

O,

per

rec

tum

Goat

s30–50 IV

Buto

rphan

ol

Bes

t use

d in c

om

bin

atio

n w

ith a

cepro

maz

ine

or

xyla

zine.

Cat

tle0.0

1–0.0

4Sh

eep, go

ats

0.1

–0.2

Induct

ion/

main

tenance

Thio

pen

tal (s

mal

l 10–15 IV

Induct

ion o

f an

esth

esia

.ru

min

ants

)

5%

Guai

fenes

in

80–100 IV

When

use

d a

lone

for

recu

mben

cy.

(cat

tle)

50 IV

In c

om

bin

atio

n w

ith o

ther

age

nts

.

5%

Guai

fenes

in/

2–3 g

added

Adm

inis

tere

d “

to e

ffec

t”; al

so m

ay b

e use

d t

oth

iopen

tal

to 1

L 5

% G

Gm

ainta

in a

nes

thes

ia s

hort t

erm

. Add 3

g f

or

(cat

tle)

cattl

e >

1000 k

g. P

rem

edic

atio

n u

sual

ly u

nnec

-es

sary

. Intu

bat

e an

imal

durin

g m

ainte

nan

ce to

avoid

ris

k of re

gurg

itatio

n a

nd a

spira

tion.

(con

tinue

s)


Tab

le 1

6–1

(Continued)

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

5%

Guai

fenes

in/

2–3 g

added

to

Add 3

g f

or

cattle

>1000 k

g. P

rem

edic

atio

nke

tam

ine

1 L

5%

GG

usu

ally

unnec

essa

ry, but

if nee

ded

for

(cat

tle)

intrac

table

pat

ients

, xy

lazi

ne

is e

ffec

tive.

Induct

ion d

ose

: 0.5

–1.0

ml/

kgM

ainte

nan

ce d

ose

: 2.2

ml/

kg/h

r (“

to e

ffec

t”)

Xyla

zine/

keta

min

eFo

r ru

min

ant ne

onat

es, u

se ≤

0.0

2 m

g/kg

xyl

azin

e.C

attle

0.0

4/2

.2 IV

Can

mix

and a

dm

inis

ter

IV.

Goat

s0.1

IM

/5 IV

Xyla

zine

should

pre

cede

keta

min

e by

15 m

in.

Shee

p0.2

IM

/5 IV

Xyla

zine

should

pre

cede

keta

min

e by

15 m

in.

Dia

zepam

/0.2

5/5

IV

Mix

and a

dm

inis

ter

IV “

to e

ffec

t.” M

ay r

equire

keta

min

ead

diti

onal

dru

gs e

spec

ially

if

pre

med

icat

ion is

not

adm

inis

tere

d.

Lla

mas

Chem

ical re

stra

int/

pre

med

icatio

n

Xyla

zine

0.2

5–0.4

IV,

IM

Low

er d

osa

ge is

for

IV a

dm

inis

trat

ion. Avo

id in

neo

nat

es; if

nec

essa

ry t

o p

erfo

rm m

inor

pro

-ce

dure

s, u

se m

inim

um

dosa

ge r

ange

and


only

if

accu

rate

wei

ght

is d

eter

min

ed.

Buto

rphan

ol

0.1

–0.2

IV,

IM

Enhan

ces

sedat

ion a

nd a

nal

gesi

a w

ith x

ylaz

ine.

Ef

fect

ive

sedat

ion f

or

mas

k or

nas

otrac

hea

lin

duct

ion o

r dia

zepam

-ket

amin

e in

duct

ion in

neo

nat

es a

nd juve

nile

s.

Induct

ion/

main

tenance

Xyla

zine/

keta

min

e0.2

5/2

.2 IV

Inje

ct x

ylaz

ine

first

then

ket

amin

e. F

or

unco

op-

erat

ive

anim

als,

xyl

azin

e m

ay b

e ad

min

is-

tere

d IM

(0.4

).

5%

Guai

fenes

in/

1 m

g/m

l ke

tam

ine

1.1

–1.6

ml/

kg g

iven

“to

effec

t” t

o f

acili

tate

keta

min

ein

1 L

GG

IV

intu

bat

ion. Th

is d

ose

pro

vides

15–20 m

inan

esth

esia

and m

ay b

e tit

rate

d t

o m

ainta

inan

esth

esia

(if

nec

essa

ry).

5%

Guai

fenes

in/

2 m

g/m

l th

iopen

tal

1.1

–1.6

ml/

kg g

iven

to e

ffec

t to

fac

ilita

teth

iopen

tal

in 1

L G

G IV

intu

bat

ion. Th

is d

ose

pro

vides

15–20 m

inan

esth

esia

. M

ainte

nan

ce w

ith t

his

com

bin

a-tio

n is

not

reco

mm

ended

.

(contin

ues

)


Tab

le 1

6–1

(Continued)

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

Ru

min

an

ts a

nd

ca

meli

ds

Analg

esia

Dosa

ge inte

rval

s ar

e gu

idel

ines

only

: ad

min

istra-

tion s

hould

be

bas

ed o

n o

ngo

ing

asse

ssm

ent.

Bupre

norp

hin

e 0.0

05 IM

Inte

rval

: 12 h

r.(s

mal

l ru

min

ants

)

Buto

rphan

ol

Cat

tle0.0

1–0.0

2 IV,

IM

Inte

rval

: 2–4 h

r (o

r as

indic

ated

by

pat

ient)

.Sh

eep, go

ats

0.1

IV,

IM

Morp

hin

eSh

eep, go

ats

0.1

IM

, SC

Dose

should

not

exce

ed 1

0 m

g. Inte

rval

: bas

ed

on p

atie

nt

(eve

ry 6

–8 h

r?).

Rum

inan

ts,

0.1

(ep

idura

l Pro

vides

anal

gesi

a as

far

forw

ard a

s th

ora

x fo

rca

mel

ids

adm

inis

trat

ion)

8–24 h

r. D

ue

to t

he

syst

emic

sid

e ef

fect

s of

epid

ura

l xy

lazi

ne

in r

um

inan

ts, it

is n

ot

rec-

om

men

ded

to a

dd x

ylaz

ine

to m

orp

hin

e fo

rlo

ng-

term

pai

n m

anag

emen

t, how

ever

if


indic

ated

for

additi

onal

anal

gesi

a, d

osa

ge f

or

cattle

and c

amel

ids

is lis

ted in T

able

3–5.

Avo

id f

orm

ula

tions

that

conta

in t

he

pre

serv

ativ

e fo

rmal

in (

the

pre

serv

ativ

e m

ethyl

par

aben

is

acce

pta

ble

). U

se o

f th

e pre

serv

ativ

e-free

pre

par

atio

n (

Duro

morp

h™

) is

optim

al, but

due

to t

he

low

conce

ntrat

ion a

nd c

ost

, ad

e-quat

e dosa

ge m

ay b

e diff

icult

to d

eliv

er d

ue

to t

he

larg

e quan

tity

require

d f

or

adult

cattle

and c

amel

ids.

Phen

ylbuta

zone

NSA

IDs

are

not

routin

ely

use

d in r

um

inan

ts;

adm

inis

trat

ion m

ay b

e bas

ed e

mpiri

cally

on

equin

e dosa

ges

and u

sed s

par

ingl

y.C

attle

2.2

IV,

PO

Shee

p, go

ats

5–10 P

O

Flunix

in0.5

–1.0

IV

*Dru

gs m

ay b

e ad

min

iste

red IM

or

IV u

nle

ss o

ther

wis

e in

dic

ated

. Low

er d

osa

ges

should

be

util

ized

for

IV a

dm

inis

tra-

tion.

**G

reat

var

iatio

n e

xist

s am

ong

bre

eds

and in

div

idual

s. B

rahm

an b

reed

s an

d H

eref

ord

s m

ay d

emonst

rate

incr

ease

d s

en-

sitiv

ity to x

ylaz

ine

effe

cts

and lo

w-e

nd d

osa

ges

should

be

util

ized

and in

crea

sed a

s nee

ded

.

Fasting is essential in ruminants and camelids (seeTable 1–4) to decrease rumen/forestomach contentsand thus decrease risk of regurgitation and aspiration,bloat, and respiratory compromise during induction andmaintenance of general anesthesia. Neonates (less than1 month of age) need only a 2–4 hr fast.

The need for premedication to facilitate catheterplacement and anesthetic induction depends largely onpatient cooperation and availability of restraint facilities(adult cattle). Agitated adult cattle will benefit from pre-medication regardless of secure restraint facilities to pro-vide maximal safety to the animal and personnel andminimize movement during catheterization. In field sit-uations, it may be necessary to cast the animal with ropesto facilitate handling following sedation. Small rumi-nants and calves can be adequately restrained by placingthem in lateral recumbency, controlling the dependentlimbs, and applying gentle pressure to the head andneck. Camelids have a unique personality and are proneto spitting, striking, biting, and butting. Placing a towelloosely over the face (hooding) will aid handling andhelp avoid being spit on. Adult camelids, like cattle, maybe restrained in a chute or head gate. Premedication isindicated in all but the most tractable or debilitatedcamelid patients.

Vascular access in adult cattle and camelids is the jugu-lar vein. Both species require cutdown via a stab incisionthrough the skin to allow entry of the stylet and smoothpassage of the catheter shaft. The jugular furrow is


apparent and the vein usually easy to observe whenoccluded distally in cattle. However, in camelids, there isno discernible jugular groove and the vein does notbecome readily apparent, even when distally occluded,although a fluid wave may be observed with percussion.The optimal site for catheter entry into the internal jugu-lar vein in camelids is the right side (to avoid the esoph-agus) at the junction of the cranial and middle third ofthe neck. There is greater risk of accidental penetrationof the carotid artery compared to cattle. The jugular veinis used for small ruminants, calves, and young camelidsand cutdown usually is unnecessary; additionally, thecephalic vein, similar in location to dogs, can be utilized.

Induction of anesthesia should be performed withrapid-acting agents (see Table 16–1) in adult ruminantsand camelids to facilitate quick-sequence intubation andminimize risk of regurgitation and aspiration. Maskinduction and maintenance with inhalant anesthesia isacceptable for ruminant and camelid neonates for shortprocedures (<1 hr). In adult cattle, intubation is per-formed by digitally palpating the arytenoid cartilagesand guiding the ET tube through the larynx. Whenthere is inadequate room for the hand and ET tube, pass-ing a smaller long tube (a medium-sized equine naso-gastric tube) digitally into the trachea, to guide passageof the ET tube, may be necessary. Rotation of the tube tomanipulate the bevel will facilitate passage into the tra-chea. The cuff then should be inflated quickly to protectthe airway.


Orotracheal intubation of small ruminants,camelids, and calves requires visualization of the larynx.A flat, long blade (180–350 mm) laryngoscope facilitatesthe procedure. Positioning of the endotracheal tube mayobstruct the view of the ET tube passing through the lar-ynx; passing a small, long, stiff piece of polyethylene tub-ing visually into the trachea to guide the ET tube may bebeneficial in these cases. Use gauze loops to hold themouth open and extend the head and neck to maximizevisualization.

Blind orotracheal intubation is possible in llamas,small ruminants, and calves but more difficult than theprocedure in horses. Nasotracheal intubation has beendescribed for llamas and calves, and it also is more diffi-cult than the procedure in horses. Llamas have a largepharyngeal diverticulum, which may complicate nasotra-cheal intubation. Head and neck extension is essentialfor both techniques. Delivering 1.0–2.0 ml of lidocainethrough the tube with the tip positioned just over thelarynx may help obtund swallowing and facilitate suc-cessful intubation.

Endotracheal tube sizes for adult cattle range from20–30 mm ID and for adult camelids, 12–14 mm ID(10–12 mm ID for nasotracheal intubation). Calves andcrias usually require size 8–12 mm ID and size 7–9 mmID, respectively. Small ruminants accommodate size8.0–12 mm ID tube, while juveniles require size 5.0–7.0mm ID tube.


Adult ruminants and camelids should be positionedwith support under the neck so that the head will tiltdownward to prevent accumulation of saliva in theoropharynx and encourage drainage out of the oral cav-ity. Adequate padding of the down surface, positioningof the down forelimb forward and supporting the uplimbs parallel to the table are necessary in adult cattleand camelids during prolonged procedures to minimizerisk of myopathy and neuropathy. When adequatepadding is not feasible, placing an inner tube tire aroundthe down limb will help minimize risk of neuropathy.Small ruminants and neonates should be provided anexternal heat source for prolonged invasive procedures.Intraoperative fluids are indicated for prolonged proce-dures in all ruminants to replace intraoperative fluidlosses and provide a route for administration of adjunctdrugs.

Recovery in ruminants usually is uneventful; animalsgenerally recover quietly and smoothly. Endotrachealtubes should be removed when swallowing is observed,with residual cuff inflation to remove any saliva or regur-gitation that may have collected rostral to the cuff. Adultruminants should be positioned upright in sternalrecumbency as soon as possible, to facilitate eructationof collected rumen gases. Analgesic dosages are availablefor ruminants and should be administered when indi-cated (see Table 16–1).


17Anesthetic Management of Swine

Swine anesthesia presents a plethora of challenges,including resistance to physical restraint, which oftenprecludes adequate physical examination and collectionof blood for preoperative assessment; lack of easily acces-sible superficial veins, which makes IV anesthetic induc-tion challenging; difficult intubation; a tendency towardintraoperative hyperthermia, including an inability todissipate heat due to low body surface to mass ratio andthe risk of malignant hyperthermia; and lack of readilypalpable peripheral pulses, which increases the chal-lenge of effective intraoperative monitoring.

Pigs usually resist restraint. Neonates and compan-ion breeds (i.e., Vietnamese potbelly) usually can berestrained by holding the animal against the body and

255

wrapping with a towel. Safe restraint is critical in com-panion breeds to avoid damage to their relatively fragileskeleton. Restraint techniques used in food animalbreeds, such as nose snares and lifting by the rear limbs,is not recommended. An effective device for restrainingpigs of all sizes is a webbed stanchion with wheels to allowtransport (Figure 17–1). Using a board or moveable gateto squeeze pigs into a small confinement usually facili-tates IM premedication injection in larger swine.

Pigs vomit and an adequate fast (see Table 1–4) isimportant to minimize risk of regurgitation, especiallywhen intubation is not planned. It is best to delay anes-thesia, when possible, if fasting status is unknown orinadequate.

Intramuscular induction is the most commonmethod of anesthesia in swine. The minimal needlelength for injection is 11/2 in. to reach the muscle, sinceswine have a large quantity of superficial fat stores. Sitesinclude the neck muscles just behind the ear and themuscles of the hind limb; the latter site should beavoided in pigs destined for human consumption. Intra-venous induction by use of the auricular vein is possiblefollowing adequate premedication and restraint (Table17–1). Pigs that can be safely restrained are amenable tomask induction with inhalation anesthetic agents. Pigsusually accept the mask and transition smoothly withminimal movement (3–5 min). The process is facilitatedby premedication (see Table 17–1).

256 Anesthetic Management of Swine

257

Figure 17–1 A web-topped mobile table for restraint andtransport of swine for physical examination and induction of anes-thesia. (Reprinted with permission from JC Thurmon and GJ Ben-son, Special anesthesia considerations of swine, in: Principles andPractice of Veterinary Anesthesia, CE Short, ed., Baltimore:Williams and Wilkins, 1987, page 311.)


Tab

le 1

7–1

Anest

hetic

Age

nts

for

Pre

medic

atio

n, In

duct

ion, an

d A

nal

gesi

a in

Sw

ine

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

Chem

ical re

stra

int/

pre

med

icatio

n

Ace

pro

maz

ine

0.0

3–0.2

Do n

ot

exce

ed 1

5 m

g. M

inim

al t

ranquili

zatio

n.

Aza

per

one

0.4

–3.0

Low

er d

osa

ge r

ange

for

larg

er s

win

e; e

ffec

ts

may

per

sist

for

seve

ral hours

.

Dia

zepam

0.4

–1.0

Inef

fect

ive

alone.

Undep

endab

le a

bso

rptio

n.

Mid

azola

m0.1

–0.5

Quic

k onse

t. M

inor

effe

ct w

hen

use

d a

lone.

Xyla

zine

0.5

–2.0

Hig

her

dosa

ge f

or

smal

l sw

ine

and v

ice

vers

a.

Xyla

zine

is les

s ef

fect

ive

in s

win

e th

an o

ther

sp

ecie

s.

Med

etom

idin

e0.0

1–0.0

5Appea

rs t

o b

e m

ore

effec

tive

than

xyl

azin

e.

Buto

rphan

ol

0.1

–0.2

May

be

com

bin

ed w

ith t

ranquili

zer

or

alpha 2

agonis

t to

enhan

ce s

edat

ion.

Induct

ion/

main

tenance

Xyla

zine/

keta

min

e0.5

–2.0

/2.2

–4.4

Induct

ion is

often

pro

longe

d a

nd inco

mple

te.

Scal

e to

pig

siz

e: B

igge

r pig

tak

es low

er d

osa

ge.

Anesthetic Management of Swine 259

Usi

ng

med

etom

idin

e (0

.02–0.0

4)

in p

lace

of

xyla

zine

may

pro

vide

a sm

ooth

er, bet

ter

qual

ity induct

ion.

Addin

g buto

rphan

ol m

ay im

pro

ve induct

ion a

nd

qual

ity o

f an

esth

esia

.

In g

ener

al, th

is p

roto

col is

inad

equat

e fo

r su

rgi-

cal m

ainte

nan

ce; re

pea

ted d

osi

ng

is n

eces

-sa

ry if

move

men

t per

sist

s.

Ket

amin

e dose

for

PB

P is

5–10 m

g/kg

.

Xyla

zine/

keta

min

e/2.0

/2.0

/0.0

75

For

juve

nile

s an

d P

BP.

oxy

morp

hone

Good a

nal

gesi

a an

d m

usc

le r

elax

atio

n f

or

min

or

surg

ical

pro

cedure

s; d

ura

tion o

f ef

fect

is

20–30 m

in.

Rap

id s

hal

low

bre

athin

g is

a c

om

mon s

ide

effe

ct.

Xyla

zine/

tela

zol

0.5

–1.0

/2–6

Pro

vides

rap

id (

<5 m

in)

smooth

induct

ion.

Pre

ferred

induct

ion a

gent

but

expen

sive

.Rec

ove

ry m

ay t

ake

seve

ral hours

(>

4 h

r) w

hen

hig

h-e

nd d

ose

is

use

d.

(contin

ues

)


Tab

le 1

7–1

(Continued)

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

Med

etom

idin

e (0

.02–0.0

4)

may

be

use

d in

pla

ce o

f xy

lazi

ne,

and b

uto

rphan

ol m

ay b

e ad

ded

to p

roto

col.

Pro

vides

adeq

uat

e im

mobili

zatio

n f

or

min

imal

ly

pai

nfu

l, nonin

vasi

ve p

roce

dure

s.

Ace

pro

maz

ine/

0.1

/5–10

Aza

per

one

(0.4

–2)

may

be

subst

itute

d f

or

keta

min

eac

epro

maz

ine.

Incr

ease

ket

amin

e dosa

ge t

o

15 m

g/kg

for

PB

P.Se

par

ate

inje

ctio

ns

by

30 m

in, gi

ving

tran

quili

zer

first

.U

nre

liable

; m

ay p

rovi

de

adeq

uat

e im

mobili

za-

tion t

o g

ain IV a

cces

s.

Thio

pen

tal

5–10 IV

Req

uire

s se

cure

IV a

cces

s, u

sual

ly a

uric

ula

r ve

in.

Use

2.5

–5%

solu

tion t

o m

inim

ize

tissu

e irr

itatio

n a

t in

ject

ion s

ite.

Exce

llent

rela

xatio

n f

or

intu

bat

ion.

Guai

fenes

in (

GG

)/In

duct

ion: 1.0

ml/

Add 2

g t

hio

pen

tal per

1 L

of

5%

GG

.th

iopen

tal

kg IV


Mai

nte

nan

ce:

Del

iver

y (i

dea

lly)

should

not

exce

ed 1

hr

to≤4 m

l/kg

/hr

IVdec

reas

e ris

k of

rough

rec

ove

ry.

Guai

fenes

in (

GG

)/In

duct

ion: 0.5

–1.0

Add 1

mg/m

lxy

lazi

ne

and

1 m

g/m

lke

tam

ine

xyla

zine/

ml/

kg IV

to 5

% G

G.

keta

min

eM

ainte

nan

ce:

Min

imal

res

pira

tory

dep

ress

ion.

2.2

ml/

kg/h

r IV

Rec

ove

ry is

smooth

and r

elat

ivel

y ra

pid

eve

n

afte

r 2 h

r m

ainte

nan

ce.

Use

d f

or

induct

ion if

IV a

cces

s is

poss

ible

or

fol-

low

ing

IM induct

ion (

as p

revi

ousl

y outli

ned

).

Tela

zol/

keta

min

e/1.3

–2.0

mg/

kgTe

lazo

l (5

00 m

g) is

reco

nst

itute

d w

ith 2

.5 m

l xy

lazi

ne

(dis

soci

ativ

e)ea

ch o

f ke

tam

ine

and 1

0%

xyl

azin

e. (

The

liste

d(1

00 m

g/m

l dosa

ge e

quat

es t

o 1

ml/

50–75 k

g.)

dis

soci

ativ

e)Als

o e

ffec

tive

for

PB

P a

t a

dose

of

0.6

–1.2

m

g/kg

dis

soci

ativ

e, w

hic

h e

quat

es t

o 0

.006–

0.0

12 m

l/kg

.

An

tago

nis

ts

Alp

ha

2re

cepto

r

Yohim

bin

e0.0

5–0.2

IV,

IM

Tola

zolin

e1–2 IV

(contin

ues

)


Tab

le 1

7–1

(Continued)

Agen

t/P

roto

col

Do

sage (

mg/k

g)*

Co

mm

en

ts

Atip

amez

ole

0.2

IM

Ben

zodia

zepin

e

Flum

azen

il0.0

2–0.1

IV

Opio

id

Nal

oxo

ne

0.0

4 IV,

IM

, SC

Analg

esia

**

Bupre

norp

hin

e0.0

05–0.0

2In

terv

al: 12 h

r.

Buto

rphan

ol

0.1

–0.4

Inte

rval

: 2–4 h

r.

Morp

hin

e0.2

IM

Inte

rval

: 4–6 h

r.0.1

(ep

idura

l In

terv

al: 12–24 h

r.ad

min

istrat

ion)

Morp

hin

e m

ay b

e gi

ven a

lone

(dilu

ted t

o a

vol-

um

e of

3–5 m

l w

ith 0

.9%

sal

ine)

or

added

to lid

oca

ine,

with

or

with

out

alpha 2

agonis

t,as

des

crib

ed in T

able

3–5.

Note

: D

osa

ges

are

also

applic

able

for

potb

ellie

d p

igs

(PB

P)

unle

ss o

ther

wis

e note

d.

*D

osa

ges

are

for

IM in

ject

ion u

nle

ss o

ther

wis

e in

dic

ated

.

**D

osa

ge in

terv

als

are

extrap

ola

ted fro

m o

ther

spec

ies.

Adm

inis

trat

ion u

ltim

atel

y sh

ould

be

bas

ed o

n o

ngo

ing

pat

ient

asse

ssm

ent.

Pigs can be effectively maintained with inhalationagents delivered with a tight-fitting mask. However, forlong and complicated procedures and in high-riskpatients, endotracheal intubation is advised. Both sternaland dorsal recumbency have been recommended forswine intubation, with sternal being better when theexperience of the anesthetist is limited. Intubation is dif-ficult in swine for several anatomical reasons: The larynxis a long way from the tip of snout, the mouth does notopen widely, there is a large middle ventricle (middlelaryngeal ventricle) on the floor of the larynx and lateralopenings near vocal folds (lateral laryngeal ventricles)that tend to trap the tip of the ET tube, and the larynx issusceptible to laryngospasm. To assist the process:

1. Use gauze strips (versus fingers) behind upper andlower canine teeth to hold the mouth open to opti-mize visualization.

2. Extend the head moderately.

3. Use a flat long-blade (180–350 mm) laryngoscope tovisualize the larynx and pull the epiglottis forward.

4. Apply 2% lidocaine (0.2–0.5 ml) to the laryngealopening to minimize risk of laryngospasm.

When the pig is positioned sternally, the tip of the tubeshould point ventral until it meets resistance as it con-tacts the floor of the larynx. The tube should be rotated180° and advanced, with minimal pressure, just into the


trachea, at which time the tube should be returned tothe initial position and inserted to the appropriate level.Once proper placement is verified, the tube is securedwith gauze, around the tube and then the snout, and thecuff inflated to form an effective seal. Tube sizes rangefrom 3–4 mm ID in neonates up to 16–18 mm ID in largesows and boars, which is smaller (given comparable bodyweight) than for other species. Tube sizes for adult com-panion pigs usually are in the range of 5.0–7.0 mm ID.

For prolonged anesthetic procedures, an IV cathetershould be inserted to provide fluid therapy and a routefor administration of additional anesthetic agents whena parenteral protocol is being used. Sites include theauricular, cephalic (located on the dorsomedial aspect ofthe forelimb), femoral, and medial and lateral saphe-nous veins. Except for the auricular and femoral veins,these veins are difficult to visualize and successfullycatheterize but provide alternatives when the auricularveins are too small to visualize (many potbelly pigs havesmall ears) or have hematomas due to unsuccessfulcatheterization attempts.

Effective monitoring devices include esophagealstethoscopes and capnometers (if intubated), ECG, andpulse oximeter on the tongue (if accessible), or ear (innonpigmented individuals). Breathing rate should rangefrom 8–20/min but may be higher in neonates. Heartrate should stay above 40–50 beats/min and usually ismaintained at 70–100 when dissociative agents havebeen administered. Rates of 100–140 beats/min are


common in neonates. Pulse quality can be assessed bypalpation of femoral, brachial, metatarsal, coccygeal,and auricular arteries.

Temperature should be closely monitored in swinebecause of greater tendency to develop hyperthermiaand increased susceptibility to malignant hyperthermia(MH). White breeds historically have been linked to thedisease—specifically, Pietrain, Landrace, Hampshire,and (less commonly) Duroc. While hyperthemia follow-ing isoflurane anesthesia has been reported in a potbellypig, the existence of genetically linked MH has not beendemonstrated in this breed.

Malignant hyperthermia is an inherited predisposi-tion to uncontrolled generalized muscle rigidity trig-gered by stress, all inhalant anesthetics (halothane hasbeen the most commonly incriminated), and succinyl-choline. The genetic defect is at the level of the sar-coplasmic reticulum and associated with excessivecalcium release. Clinical signs include muscle rigidity,tachycardia, hyperthermia, tachypnea, metabolic acido-sis, hypoxia, and blotchy skin. The disease can rapidlyprogress to dyspnea, apnea, arrhythmias, and death ifnot treated immediately. Treatment includes discontinua-

tion of inhalant delivery, efforts to cool the animal (alcoholbath, chilled IV fluids), continued delivery of 100% oxy-gen to meet increased metabolic demands, bicarbonateadministration (1 mEq/kg) preferably guided by bloodpH analysis, corticosteroids, and dantrolene (2–5 mg/kgIV). Dantrolene is a peripheral muscle relaxant that


suppresses calcium ion release from the sarcoplasmicreticulum but has minimal effect on respiratory musclefunction. Oral dantrolene is less expensive than the IVpreparation. Administration (5 mg/kg PO) 8–10 hrbefore anesthetic induction in high-risk breeds may bebeneficial, especially when inhalant anesthetics must beused and a prolonged anesthetic period is anticipated.

Recovery in swine generally is uneventful andshould take place at a neutral ambient temperature in aquiet, safe area. Small patients may require an externalheat source, the need for which should be based on bodytemperature recorded at the end of anesthesia (seeTable 6–3). Animals should be monitored until extu-bated and able to maintain sternal recumbency unas-sisted with normal vital signs.


18

Overview of Cardiopulmonary Resuscitation

Prevention of cardiopulmonary arrest through appro-priate patient preparation (minimizing risk factors) andoptimal anesthetic management and monitoring is farbetter than cardiopulmonary resuscitation (CPR).Guidelines for CPR are summarized here. Resuscitationusually is successful in relatively healthy small animals(and large animal neonates) when arrest is recognizedearly; resuscitation in horses and adult cattle often is inef-fective, making prevention through early recognition ofand intervention for potential problems critical in thesespecies.

Quickly recognizing signs of impending cardiopul-monary arrest is optimized by monitoring vital signs at

267

5-min intervals. Indications include cyanosis (which can-not occur in anemic patients if [Hgb] <5 g/dl); pro-longed capillary refill time (CRT) (>2–3 sec); irregular,absent, or sudden change in pulse or heart sounds; car-diac arrhythmias; abnormal respiratory pattern orapnea; and loss of corneal reflex. When problems arenoted, the first step is to stop delivery of anesthesia, flushthe breathing system with 100% oxygen; and supportventilation to ensure adequate oxygen delivery. The ETtube should be checked for patency and the animalintubated if a tube is not already in place. Whenreversible agents have been used, administration of theirantagonist is usually indicated.

CPR guidelines include basic (A, B, C) andadvanced (D, E) steps for life support:

Step A. Airway Establish or assure patent airway withET tube for delivery of ventilation.

Step B. Breathing Provide 100% oxygen (150ml/kg/min for small animals; 15–20ml/kg/min for large animals); ventilate simul-taneous with chest compressions at a rate of12–20/min (6–12 for large animals).

Step C. Circulation (compressions) Deliver chest compres-sions at 80–120/min (40–80/min or as rapidlyas possible for large animals) in a “coughlike”manner, meaning rapid and forceful delivery ofpressure. Chest compressions should be initiated assoon as absence of effective blood flow is identified and

268 Overview of Cardiopulmonary Resuscitation

while the airway is being assured or established.External massage promotes forward movementof blood through one of two methods. In smallpatients or those with narrow thoracic width,the cardiac pump theory best explains forwardblood flow associated with actual compressionof the myocardium during chest compressions.In larger patients, the thoracic pump theoryexplains the resulting forward blood flow as aresult of sudden and significant increases ininternal thoracic pressure (associated withcompressions) being transmitted to the heart.Therefore, for small animals (<10 kg), com-press the chest directly over the heart withhands or fingers applied to both sides of thechest. For larger patients (>10 kg), compresschest over widest portion or at the seventhintercostal space at the junction of dorsal andmiddle thirds of chest. Ventral-dorsal compres-sions may be more effective in some patients.

In advanced CPR, step D includes drugs and/or defib-rillation and step E is recognition of the specific ECGabnormality. The initial drug to be administered is epi-nephrine followed by atropine and other agents (Table18–1), as indicated by the individual patient’s underlyingand identified problems and abnormalities identified onECG. Defibrillation is indicated for ventricular tachycar-dia and fibrillation and recommended dosages are listedin Table 18–1.

Overview of Cardiopulmonary Resuscitation 269


Tab

le 1

8–1

Dosa

ges

and I

ndic

atio

ns

for

Dru

gs U

sed D

uring

Car

dio

pulm

onar

yA

rrest

Agen

tD

osa

ge(m

g/k

g)*

Ind

icati

on

s/Eff

ect

s

Dru

g

Epin

ephrin

e (I

T)0.0

2–0.2

**

Alp

ha

agonis

t ef

fect

s in

crea

se p

erip

her

al r

esis

t-(s

mal

l an

imal

)an

ce a

nd intrat

hora

cic

blo

od f

low

to p

rom

ote

0.0

1–0.0

2

per

fusi

on w

hile

pre

fere

ntia

lly p

rese

rvin

g(l

arge

anim

al)

flow

to b

rain

and h

eart.

Bet

a ac

tivity

to im

pro

ve c

ontrac

tility

and t

o

rees

tablis

h n

orm

al c

ardia

c rh

ythm

(in

som

eca

ses)

.

Atropin

e (I

T)0.0

2–0.0

4

Incr

ease

s hea

rt r

ate.

(sm

all an

imal

)Tr

eats

bra

dyc

ardia

and a

syst

ole

.2–6 m

g to

tal dose

(l

arge

anim

als)

Lidoca

ine

(IT)

2–4 (

dogs

)Tr

eats

rec

urren

t ve

ntric

ula

r ar

rhyt

hm

ias

and

0.5

–1.0

(ca

ts,

tach

ycar

dia

.hors

es, ru

min

ants

)

Doxa

pra

m0.0

5–0.2

(bolu

s)C

entral

act

ing

resp

irato

ry s

timula

nt

indic

ated

for

5–10 µ

g/kg

/min

ap

nea

due

to a

nes

thet

ic o

verd

ose

.(i

nfu

sion)


Inotropes

Impro

ves

card

iac

contrac

tility

once

NSR

is

rees

tablis

hed

.

Dobuta

min

e2–10 µ

g/kg

/min

Dopam

ine

5–10 µ

g/kg

/min

Dire

ct r

enal

vas

odila

tory

effec

t (q

ues

tionab

le in

cats

).

Ephed

rine

0.0

3–0.1

IV b

olu

sLo

wer

dose

ran

ge f

or

larg

e an

imal

s.

Isopro

tere

nol

0.0

1–0.1

µg/

kg/m

inIn

crea

ses

hea

rt r

ate

in r

efra

ctory

cas

es.

Impro

ves

contrac

tility

but

may

dec

reas

e blo

od

pre

ssure

due

to b

eta 2

vaso

dila

tory

effec

ts.

Arrhyt

hm

oge

nic

: m

onito

r EC

G d

urin

g ad

min

istrat

ion.

Cal

cium

(ch

lorid

e 5–10 m

g/kg

(sm

all

Posi

tive

inotrope,

may

enhan

ce e

ffec

t of

or

gluco

nat

e)an

imal

)in

otropic

age

nts

but

can c

ause

asy

stole

2 m

g/kg

(la

rge

if ove

rdose

d.

anim

al)

Cal

cium

has

bee

n incr

imin

ated

in t

he

pat

hoge

n-

esis

of

post

resu

scita

tion s

yndro

me

(cer

ebra

lis

chem

ia)

and is

not

use

d in r

esusc

itatio

n(u

nle

ss t

he

under

lyin

g c

ause

of

arr

est

is d

ue

to h

ypoca

lcem

ia o

r hyp

erka

lem

ia). (c

ontin

ues

)


Tab

le 1

8–1

(Continued)

Agen

tD

osa

ge(m

g/k

g)*

Ind

icati

on

s/Eff

ect

s

Bic

arbonat

e1–2 m

Eq/k

g or

Correc

ts m

etab

olic

aci

dosi

s.dose

on c

al-

Usu

ally

unnec

essa

ry if

arre

st is

<10 m

in a

nd n

ocu

late

d d

efic

it†under

lyin

g im

bal

ance

was

pre

sent.

Adm

inis

trat

ion m

ay p

rom

ote

more

succ

essf

ul

resp

onse

to d

efib

rilla

tion.

If ad

min

iste

red w

hen

ven

tilat

ion is

inad

equat

e,

can p

rom

ote

intrac

ellu

lar

acid

osi

s (p

arad

oxi

cce

rebra

l ac

idosi

s) d

ue

to g

ener

atio

n o

f ca

r-bon d

ioxi

de.

Cortic

ost

eroid

sPro

tect

aga

inst

cer

ebra

l ed

ema

follo

win

g re

susc

itatio

n.

Solu

-med

rol™

30

Enhan

ces

ATP r

elea

se f

rom

the

mito

chondria

to

(met

hyl

pre

d-

faci

litat

e norm

al m

embra

ne

funct

ion.

nis

olo

ne

sodiu

msu

ccin

ate)

Solu

-del

ta-c

ortef

™30–60

(pre

dnis

olo

ne

sodiu

m s

ucc

inat

e)


Dex

amet

has

oneS

P2.0

–4.0

(sodiu

m

phosp

hat

e)

Ele

ctri

cal

(wat

t-se

c =

Joule

)Fo

r ve

ntric

ula

r ta

chyc

ardia

and f

ibril

lato

n.

defi

bri

llati

on

Exte

rnal

5–10 J

oule

/kg

Inte

rnal

0.5

–2.0

Joule

/kg

Ch

em

ical

When

ele

ctric

al d

efib

rilla

tor

is u

nav

aila

ble

.d

efi

bri

llati

on

Pota

ssiu

m

1 m

g/kg

Effic

acy

is q

ues

tionab

le.

chlo

ride

plu

sAce

tylc

holin

e6 m

g/kg

10%

Cal

cium

10 m

g/kg

Cal

cium

follo

ws

KC

l-ace

tylc

holin

e m

ixtu

re.

chlo

ride

Po

stre

susc

itati

on

th

era

py f

or

cere

bra

l p

rote

ctio

n

Cortic

ost

eroid

sAs

liste

d p

revi

ousl

yFu

rose

mid

e1 m

g/kg

More

effec

tive

in t

reat

ing

edem

a fo

llow

ing

man

nito

l.(c

ontin

ues

)


Tab

le 1

8–1

(Continued)

Agen

tD

osa

ge(m

g/k

g)*

Ind

icati

on

s/Eff

ect

s

Man

nito

l1 g

m/k

gC

ereb

ral ed

ema;

giv

e ove

r 20–30 m

in.

Dia

zepam

0.1

–0.2

Giv

en “

to e

ffec

t” t

o c

ontrol se

izure

s.0.5

mg/

kg/h

r in

fusi

on

Pro

pofo

l1 m

g/kg

bolu

sSe

izure

control;

anim

al u

sual

ly r

emai

ns

0.1

mg/

kg/h

r co

nsc

ious

at t

his

dosa

ge.

infu

sion

NSR

= n

orm

al s

inus

rhyt

hm

.

*Dru

gs s

hould

be

give

n in

trav

enousl

y or

intrat

rach

eally

(IT

), if

spec

ified

by

the

spec

ific

dru

g. D

osa

ges

for

the

IT r

oute

should

be

double

the

IV d

osa

ge. D

osa

ges

are

in m

g/kg

unle

ss o

ther

wis

e sp

ecifi

ed.

**Th

is d

osa

ge is

controve

rsia

l. Lo

w d

ose

sugg

ests

dilu

ting

epin

ephrin

e (1

mg/

ml) w

ith 9

ml o

f 0.9

sal

ine

and a

dm

inis

-te

ring

at 1

ml p

er 5

kg;

hig

h d

ose

sugg

ests

use

of undilu

ted e

pin

ephrin

e at

1 m

l per

5 k

g. It is

pru

den

t to

atte

mpt use

of lo

w d

ose

epin

ephrin

e fo

r one

or

two d

ose

s bef

ore

util

izin

g th

e hig

her

rec

om

men

ded

dosa

ge.

† Bic

arbonat

e re

quire

men

ts a

re c

alcu

late

d b

y th

is e

quat

ion:

Req

uire

d a

mount (m

Eq/L

) =

Def

icit

(bas

e def

icit

or

diff

eren

ce b

etw

een b

icar

bonat

e va

lue

and n

orm

al v

alue)

�BW

(kg)

�0.3

(EC

F vo

lum

e). G

ive

appro

xim

atel

y one

quar

ter

the

calc

ula

ted d

efic

it an

d r

eass

ess

blo

od p

H a

nd g

as v

alues

.

Intravenous access should be established early in theresuscitation efforts. While a central line (jugular vein) isideal, a peripheral vein usually is easier and faster toaccess (at least in small animal species). Other routes fordrug administration include intratracheal (epinephrine,atropine, lidocaine, naloxone) and intraosseous routes(also for fluid delivery). For intratracheal delivery,

1. Dose should be doubled.

2. Drug should be diluted in 3–10 ml of sterile saline orwater.

3. Drug should be deposited with a small long catheter(urinary catheter) with the tip positioned at thecarina.

4. Two or three breaths should be delivered immedi-ately following drug instillation before resumingcompressions.

Potential causes and specific treatment for electrocar-diogram traces identified during arrest are listed inTable 18–2.

Internal cardiac compression has been shown to bemore effective than external compression in promotingmyocardial and peripheral tissue perfusion during CPR.Internal compression requires a thoracotomy, althoughcardiac access may be gained through the diaphragmwhen arrest occurs during an abdominal procedure.Indications include the presence of pneumothorax or


Tab

le 1

8–2

Ele

ctro

card

iogra

m T

raci

ngs

Identified D

uring

Car

dio

pulm

onar

y A

rrest

,Pote

ntial

Pre

dis

posi

ng

Cau

ses,

and T

reat

ment

Ste

ps

Treatm

en

t Ste

ps

Trace

Po

ten

tial

Cau

ses

(in

ad

dit

ion

to

ste

ps

A,

B,

an

d C

)

Ventric

ula

r fib

rilla

tion

Exci

tem

ent

durin

g in

duct

ion

Early

def

ibril

latio

n (

3 c

onse

cutiv

eor

reco

very

(en

doge

nous

shock

s)ca

tech

ola

min

e re

leas

e)Rea

sses

s EC

G, re

pea

t co

unte

r-Anes

thet

ic o

verd

ose

shock

at

incr

ease

d lev

el.

Under

lyin

g m

yoca

rdia

l Adm

inis

ter ep

inep

hrin

e: lo

w d

ose

dis

ease

or

trau

ma

initi

ally

then

hig

h d

ose

if

no

Undet

ecte

d o

verp

ress

uriz

a-re

sponse

; re

pea

t sh

ock

.tio

n o

f bre

athin

g ci

rcuit

Lidoca

ine

for

refrac

tory

cas

es;

Hyp

oth

erm

ia, hyp

ovo

lem

iare

pea

t sh

ock

.Aci

dosi

s or

elec

troly

te

Iden

tify

and c

orrec

t pote

ntia

lim

bal

ance

under

lyin

g ca

use

s.

Ventric

ula

r ta

chyc

ardia

Sam

e as

for

fibril

latio

nTr

eat

like

fibril

latio

n if

no

pal

pab

le p

uls

e.If

puls

e is

pal

pab

le, lid

oca

ine

bolu

s.

Asy

stole

Anes

thet

ic o

verd

ose

Low

-dose

epin

ephrin

e, a

tropin

e.



Hyp

ote

nsi

on: sh

ock

, H

igh-d

ose

epin

ephrin

e.en

doto

xem

iaAdm

inis

ter flu

id b

olu

s (1

0–20 m

l/Va

gal st

imula

tion:

kg).

visc

eral

, ocu

lar

Dopam

ine

if rh

ythm

ret

urn

s but

puls

e w

eak.

Iden

tify

and c

orrec

t under

lyin

g ca

use

s.

Elec

trom

echan

ical

EC

G m

ay a

ppea

r norm

alSa

me

as f

or

asys

tole

.dis

soci

atio

n

or

show

idio

ventric

ula

rAdm

inis

ter

cortic

ost

eroid

ear

ly(p

uls

eles

s or

ventric

ula

r es

cape

Consi

der

bic

arbonat

e af

ter

elec

tric

al a

ctiv

ity)

rhyt

hm

with

no

asso

ciat

ed

10 m

in.

puls

ePro

gnosi

s is

poor

for

succ

essf

ul

Cau

ses:

hyp

ovo

lem

ia,

resu

scita

tion

tam

ponad

e, p

neu

moth

ora

x,

pulm

onar

y em

bolis

m,

hyp

oxi

a, a

nes

thet

ic

ove

rdose

broken ribs, inability to apply effective external com-pressions due to size and shape of the thorax, failure ofexternal compression to produce effective forwardblood flow, and absence of spontaneous rhythm after5–10 min CPR. Thoracotomy is performed, followingabbreviated aseptic preparation, by making a liberal inci-sion at the fifth intercostal space. The pleura is pene-trated with a finger or blunt tip to avoid damage tounderlying thoracic structures. Compression rate shouldbe coordinated with ventricular filling. Once sponta-neous stable rhythm is reestablished, the thorax shouldbe flushed with warm isotonic crystalloid fluid, the inci-sion closed in a routine manner, and thoracocentesisperformed to evacuate the pleural space.

Animals successfully resuscitated following CPAremain vulnerable to recurrence of myocardial instabil-ity and development of neurologic consequences associ-ated with tissue ischemia and reperfusion insult. Oxygensupplementation should be continued and the ECG andarterial blood pressure monitored for several hours fol-lowing resuscitation. Conservative fluid therapy (50ml/kg/24 hr; less for cats) should be continued to main-tain adequate perfusion and preload but minimize riskof contribution to edema formation. Glucose-containingfluids are contraindicated because glucose can exacerbateneurologic damage. Inotropic support may be necessary(see Table 18–1) and a suggested goal of therapy is tomaintain diastolic blood pressure above 60 mmHg. Mon-


itoring urine output provides an additional indicator ofadequate tissue perfusion. Ideally, arterial pH and bloodgas analysis should be performed to assure adequate ven-tilation and oxygenation and assess the metabolic acid-base status. When conscious, the animal’s neurologicstatus should be evaluated and findings recorded. Cere-bral edema may develop 24–48 hr following resuscitationand may be signaled by seizures, depression, coma, orblindness. Specific treatment for cerebral insult andedema are listed in Table 18–1.


Appendix 1

Approximate Dosages (mg/kg) ofAnesthetic Agents and Adjuncts for

Common Domestic Species

281

Dru

gD

og

Cat

Ho

rse

Cow

Sh

eep

, G

oat

Pig

Atropin

e0.0

2–0.0

40.0

2–0.0

40.0

04–0.0

10.0

1–0.0

20.0

4–0.0

60.0

4

Gly

copyr

rola

te0.0

10.0

10.0

02

0.0

02

0.0

05–0.0

10.0

03

Ace

pro

maz

ine

0.0

5–0.2

0.0

5–0.2

0.0

2–0.0

60.0

1–0.1

0.0

4–0.0

80.0

3–0.2

Aza

per

one

––

––

–0.4

–3.0

Dia

zepam

0.2

–0.4

0.2

–0.4

0.0

2–0.1

0.0

2–0.1

0.1

–0.2

0.4

–1.0

Mid

azola

m0.1

–0.4

0.1

–0.4

––

–0.1

–0.5

Flum

azen

il0.0

1–0.0

20.0

1–0.0

2–

––

0.0

1–0.0

8

Xyla

zine

0.2

–1.0

0.2

–1.0

0.2

–1.0

0.0

1–0.1

0.0

2–0.2

0.5

–2.0

Det

om

idin

e0.0

005–0.0

2–

0.0

1–0.0

40.0

1–0.0

2–

–

Med

etom

idin

e0.0

1–0.0

40.0

1–0.0

60.0

05–0.0

10.0

1–0.0

4–

0.0

1–0.0

5

Rom

ifidin

e0.0

1–0.0

4–

0.0

3–0.0

80.0

1–0.0

2–

–

Yohim

bin

e0.0

5–0.1

50.1

–0.2

0.0

7–0.1

0.2

–1.0

0.1

–0.2

0.0

5

Tola

zolin

e0.5

–2.0

1.0

–2.0

0.5

–2.0

2.0

–3.0

2.0

–3.0

1.0

–2.0

Atip

amez

ole

*0.0

7–0.2

0.2

–0.4

0.1

5–0.4

0.0

1–0.1

0.0

1–0.2

0.1

–0.2

Morp

hin

e*0.2

–0.6

0.2

–0.4

0.0

5–0.2

–0.1

–0.2

(10

0.2

mg

max

.)

Mep

erid

ine

2.0

–6.0

5.0

2.0

–4.0

2.0

2.0

(200 m

g 2.0

max

.)

Hyd

rom

orp

hone

0.2

–0.4

0.1

–0.2

––

––

282 Appendix 1

Oxy

morp

hone

0.1

–0.2

0.0

5–0.1

0.0

2–

–0.0

2

Fenta

nyl

0.0

02–0.0

06

––

––

–

Bupre

norp

hin

e0.0

05–0.0

40.0

05–0.0

10.0

05

–0.0

05

0.0

05–0.0

1

Buto

rphan

ol

0.2

–0.4

0.2

–0.4

0.0

2–0.0

40.0

1–0.0

40.1

–0.2

0.1

–0.2

Nal

buphin

e1.0

–3.0

1.0

–3.0

––

––

Penta

zoci

ne

2.0

2.0

–3.0

0.3

–0.5

––

2.0

Nal

oxo

ne

0.0

01–0.0

40.0

01–0.0

40.0

1–

0.0

05–0.0

20.0

1–0.0

5

Nal

mef

ene

0.0

01

0.0

01

––

––

Chlo

ral H

ydra

te–

–5–30**

40–60 IV

30–50 IV

–80–100 P

O

Met

hohex

ital†

3.0

–8.0

3.0

–8.0

5.0

–6.0

3.0

–6.0

2.0

–4.0

3.0

–10

Pento

bar

bita

l†30

30

3.0

–10.0

14.0

20.0

–30.0

10–30

Ket

amin

e2.0

–10.0

5–20

2.2

(IV

2.2

(IV

5.0

–15.0

2.0

–12.0

only

)only

)

Tela

zol

2.0

–8.0

2.0

–8.0

1.1

(IV

2.0

–4.0

(IV

)2.0

–6.0

(IV

)2.0

–6.0

IM

only

)

Thio

pen

tal†

10

10

4.0

–6.0

4.0

–8.0

4.0

–10.0

4.0

–8.0

Pro

pofo

l (b

olu

s)2.0

–6.0

2.0

–4.0

2.0

–4.0

––

–(i

nfu

sion m

g/0.4

0.4

0.0

5–0.1

––

–kg

/min

)

(contin

ues)

Appendix 1 283

Dru

gD

og

Cat

Ho

rse

Cow

Sh

eep

, G

oat

Pig

Etom

idat

e0.5

–2.0

0.5

–2.0

––

–0.5

–2.0

Guai

fenes

in–

–40–80

60–100

60–100

40–80

Pancu

roniu

m0.0

2–0.0

40.0

20.0

8–0.1

20.0

4–0.1

0.0

05

0.0

5–0.1

2

Vecu

roniu

m0.0

12–0.2

0.0

24–0.0

40.0

5–0.1

–0.0

05

0.1

–0.2

Atrac

uriu

m0.1

2–0.4

0.0

6–0.2

50.0

7–0.1

0.1

5

0.0

05/h

r0.5

(lla

ma)

(infu

sion)

cis–

Atrac

uriu

m0.0

50.0

5–

––

–

Edro

phoniu

m‡

1.0

1.0

0.2

5–0.5

0.5

0.5

0.5

Neo

stig

min

e‡0.0

40.0

40.0

2–0.0

40.0

2–0.0

40.2

–0.0

40.0

2–0.0

4

Pyr

idost

igm

ine‡

0.2

0.2

0.2

0.2

0.2

0.2

*Rec

om

men

ded

for

IM u

se o

nly, a

lthough

thes

e ag

ents

hav

e bee

n u

sed in

trav

enousl

y.

**Rec

om

men

dat

ions

sugg

est usi

ng

chlo

ral h

ydra

te in

incr

emen

tal l

ow

dosa

ges

to a

chie

ve d

esire

d e

ffect

, whic

h r

ange

sfrom

mild

to p

rofo

und s

edat

ion-h

ypnosi

s.† A

ll bar

bitu

rate

s sh

ould

be

titra

ted to e

ffect

. Pen

tobar

bita

l is

notre

com

men

ded

for

anes

thet

ic in

duct

ion a

nd m

ainte

-nan

ce in

clin

ical

pra

ctic

e as

rec

ove

ry is

pro

longe

d a

nd r

espira

tory

dep

ress

ion m

ay b

e si

gnifi

cant.

When

use

d, t

he

calc

u-

late

d d

ose

is g

iven

“to

effect

,” a

ppro

xim

atel

y one

quar

ter

to o

ne

hal

f is

giv

en r

elat

ivel

y ra

pid

ly a

nd the

rest

titr

ated

slow

ly to the

des

ired le

vel o

f an

esth

esia

. The

hors

e dosa

ge li

sted

for

pen

tobar

bita

l is

for

sedat

ion o

r co

ntrol o

f se

izure

s.A d

ose

of 15–30 m

g/kg

of pen

tobar

bita

l inje

cted

intrat

estic

ula

rly h

as b

een r

ecom

men

ded

for

cast

ratio

n o

f la

rge

boar

s.

284 Appendix 1

‡ Rev

ersa

l of neu

rom

usc

ula

r blo

ckad

e w

ith a

cety

lcholin

este

rase

inhib

itors

should

be

pre

ceded

by

an a

ntic

holin

ergi

cag

ent re

gard

less

of sp

ecie

s. R

esponse

to thes

e ag

ents

is h

ighly

var

iable

, dep

endin

g on the

deg

ree

of blo

ckad

e pre

sent

when

age

nts

are

giv

en; th

eref

ore

, the

dosa

ge r

ecom

men

dat

ions

should

be

consi

der

ed g

uid

elin

es a

nd e

ffect

iven

ess

of

reve

rsal

should

be

bas

ed o

n u

se o

f th

e trai

n-o

f-fo

ur

resp

onse

(sh

ould

be

retu

rned

to n

orm

al)

with

a n

erve

tw

itch s

tim-

ula

tor.

See

the

first

thre

e re

fere

nce

s in

“Rec

om

men

ded

Rea

din

g” for

det

ails

reg

ardin

g in

terp

reta

tion o

f m

onito

ring

with

the

ner

ve tw

itch s

timula

tor.

Appendix 1 285

Appendix 2

Drug Scheduling Classification andGuidelines for Storing, Dispensing,

and Administering Scheduled Agents

AgentSchedule Signification Description Examples

I C-I No accepted Heroin, marihuana,medical use. methaqualoneMajor potentialfor abuse.

II C-II Approved medical All pure opioid uses but high agonists (e.g., potential for morphine), abuse leading cocaine, to addiction. pentobarbital,

amphetamine

(continues)

287

AgentSchedule Signification Description Examples

III C-III Approved medical Thiopental, uses. High telazol™,potential for ketamine,abuse but less anabolicthan that for steroidsC-II.

IV C-IV Approved medical Diazepam, uses. Less midazolam, potential for oxazepam abuse than C-III butorphanol, but addiction pentazocine, is possible. chloral hydrate,

methohexital, phenobarbital

V C-V Approved medical Buprenorphineuses. Least potential for abuse of the scheduled agents.

1. To administer, prescribe or dispense scheduled drugs, veterinarians must be reg-istered (initial application: form DEA-224) with and approved by the DrugEnforcement Agency of the United States Department of Justice (Headquarters:1-800-882-9539).

2. To purchase Schedule II drugs for clinical use, triplicate order form DEA-222must be filled out and sent to the supplier. Upon receipt of Schedule II drugs,appropriate quantity should be verified by dating and completing the order form.

3. Schedule III-V drugs do not require the triplicate order form. However, records oftransactions should be maintained for two years by use of supplier’s invoices orlogbook, including date of receipt and quantities ordered and received.

288 Appendix 2

4. The DEA license is valid for only one office where controlled substances areadministered or dispensed. If multiple offices are used to administer and dis-pense controlled substances, each must be registered independently.

5. A record of transaction must be maintained for all controlled substances admin-istered or dispensed and should include patient name and identification, withdrug and amount used to account for all controlled substances.

6. Controlled substances stored in a clinic must be kept in a securely locked, sub-stantially constructed cabinet or safe. Ideally, stock should be kept to a minimumand maintained within a two- or three-lock system.

7. When controlled substances are dispensed, a record of each transaction isrequired.

8. For the prescription of controlled substances II-V, it is necessary to be registeredwith the DEA but it is not required to keep records of those transactions. Pre-scriptions must be signed and include the address and DEA registration number.The prescription order should be precise, legible, and alteration proof. Clearlyindicate refill authorization directions. Schedule II prescriptions may not berefilled.

Appendix 2 289

Appendix 3

Suggestions for Anesthetic Preparation and Management

of High-Risk Patients

General statements may be applied to all species. (Forspecific protocols, see species-specific chapters.)

Trauma Patients

Preparation

Treat shock

• Fluid/blood component therapy

• Corticosteroids

Assess lead II ECG throughout the anesthetic period

291

Assess thoracic/abdominal imagingEstablish baseline blood pressureCalculate lidocaine dosage

Management

Plan a rapid induction to gain control of airwayInduce with ECG if possible (small animal)Monitor arterial blood pressure throughout the anes-thetic periodBe ready to provide arrhythmia treatment and inotropicsupportManage pain appropriately

Cardiac Patients

Preparation

Identify potential problems

• Lead II ECG

• Thoracic radiographs

• Echocardiography

Plan for potential problems

• Arrhythmias

• Hypotension

292 Appendix 3

Management

Determine fluid needs (conservative with risk of volumeoverload)Premedicate to minimize anxietyOxygenate throughout anesthetic period (including pre-and postop)Assist ventilation to maintain normal PaCO2

Monitor cardiovascular parameters quantitatively ifpossible

Respiratory Patients

Preparation

Preoperative assessment

• Thoracic radiographs

• Arterial blood gas analysis

Thoracocentesis (when indicated)Preoxygenation (essential)Rapid (IV) premedication and induction

Management

Supervise entire premedication and induction processAssist ventilation throughout the procedure

Assess continuous ECG if possibleEvaluate arterial blood gases intraoperatively, if availableFacilitate a smooth and gradual recovery

Appendix 3 293

Provide oxygen supplementation throughout the recov-ery period

Neurologic Patients

Preparation

Record preoperative neurologic exam findingsTreat cerebral edema if necessary

• Solu-medrol/Solu-cortef: 20–30 mg/kg IV

• Furosemide: 1–2 mg/kg

• Mannitol: 1 g/kg over 20–30 min

Assure normal fluid balance to maintain normal MAP

Management

Provide smooth induction with minimal physicalrestraintUse conservative but adequate fluid therapy (avoid glu-cose-containing fluids)Provide IPPV to maintain PaCO2 at 30–35 mmHgMonitor ABP to assure adequate cerebral perfusionAvoid acepromazine and ketamine; isoflurane is the bestinhalant to useMonitor mentation postoperatively and assess neuro-logic status frequently

294 Appendix 3

Cesarean Section Patients

Preparation

Administer fluid bolus preoperatively (10–20 ml/kg)Prepare surgery site prior to inductionPreoxygenateAdminister premedications

• To minimize anxiety

• Choose reversible agents

Prepare to provide resuscitation for newborns

• Oxygen delivery

• Oropharynx suction

• Warmth

• Reversal agents (e.g., naloxone)

• Dopram

• Administer agents into umbilical stalk or sublin-gually

Management

Two general approaches to anesthetic management:

1. Rapid induction/intubation with propofol ordiazepam-ketamine following neuroleptanalgesiccombination; maintain on isoflurane or sevoflurane

Appendix 3 295

(halothane is acceptable but more cardiodepress-ing)

2. Neuroleptanalgesia (ruminants may not requirepremed) plus regional anesthesia: epidural, lineblock, paralumbar technique (Table 3–5)

Monitor and maintain adequate ABPEfficiency is essential to minimize time to delivery

Hepatic Disease Patients

Preparation

Assess chemistry panel for accompanying abnormalities

• Hypoproteinemia

• Hypoglycemia

• Coagulopathy (coagulation panel, bleeding time)

Assure adequate fluid balanceAvoid agents that depend on hepatic metabolism

Management

Choose reversible premedications (e.g., opioid)Benzodiazepine use is controversial and is best avoidedin the presence of hepatoencephalopathyPropofol or etomidate are good small animal inductionagents; guaifenesin-ketamine is suitable for large animals

296 Appendix 3

Isoflurane is most sparing of hepatic blood flow and isagent of choiceConsider glucose-containing fluids and colloids whenindicated

Renal Disease Patients

Preparation

Correct azotemia prior to inductionAssure normal fluid balanceAssess for accompanying disorders

• Anemia

• Hypoproteinemia

• Acid-base and electrolyte imbalances

Be prepared to minimize anesthesia time

Management

Choose a cardiac-sparing protocol: opioid-benzodi-azepine, ketamine, low-dose propofol, isoflurane main-tenanceAdminister fluids intraoperatively: (10 ml/kg/hr)Monitor ABP and urine production (normal: 1–2ml/kg/hr)Consider dopamine infusion: 2–5 µg/kg/minute

Appendix 3 297

Geriatric Patients

Preparation

Geriatric = the last 20–25% of natural lifespan

• <10 kg dogs >11 yr

• 10–25 kg dogs >10 yr

• 25–40 kg dogs >9 yr

• >40 kg dogs >7.5 yr

• cats >12 yr

Physiologic changes

• Decreased metabolic rate

• Decreased maximal cardiac output

• Decreased alveolar gas exchange

• Decreased organ reserve including liver and kidneys

• Increased fat

• Decreased anesthesia requirements

Complete physical exam, blood workup, other diagnos-tic tests as indicated by physical exam findings

Management

Select reversible premedication with minimal cardiacand respiratory effects: opioid + benzodiazepine

298 Appendix 3

PreoxygenateInduction: mask, propofol, thiopental, diazepam-keta-mineIsoflurane or sevoflurane for maintenanceConsider local/regional techniques to spare require-mentsMonitor ECG and ABPAdminister fluids at conservative rateSupport ventilation during anesthesiaProvide adequate analgesia and oxygen postoperatively

Neonates

Preparation

Considerations

• Age: ≤12 wks

• Increased metabolic demands

• Cardiac output is rate dependent

• Response to hypotension is less well-developed

• PCV and TP slightly less than adults

• More susceptible to hypothermia

increased surface area to body mass ratio

less body fat

poorly developed thermoregulatory center

Appendix 3 299

• Increased susceptibility to dehydration

greater body water content

less ability to concentrate urine

• Hepatic function not fully developed

limited ability to metabolize drugs

limited glycogen stores

Management

Select reversible premedication with minimal cardiaceffects: consider anticholinergic premedication whendrugs known to decrease HR are used (e.g., opioids)Premedication: opioid + benzodiazepineInduction: mask induction, propofol, diazepam-keta-mineMaintenance: isoflurane or sevoflurane, nonrebreathingsystemAdminister glucose-containing fluids (2.5–5%)Provide external heat sourcesPostoperative period: maintain oxygen delivery as longas possible and provide warm environment

300 Appendix 3

Recommended Reading

Altman RB, Clubb SL, Dorrestein GM, QuesenberryK, eds. Avian Medicine and Surgery. Philadelphia: WBSaunders Co.; 1997.

Fudge AM, ed. Seminars in Avian and Exotic Pet Medi-

cine: Anesthesia and Analgesia. Vol 7. Philadelphia:W.B. Saunders Co.; 1998.

Johnson-Delaney CA, Harrison LR, eds. Exotic Com-

panion Medicine Handbook for Veterinarians. LakeWorth, FL: Wingers Publishing; 1996.

Muir WW, Hubbell JAE, eds. Equine Anesthesia Moni-

toring and Emergency Therapy. St. Louis: Mosby Year-Book; 1991.

Muir WW, Hubbell JAE, eds. Handbook of Veterinary

Anesthesia. 2nd ed. St. Louis: Mosby Year-Book; 1995.

301

Seymour C, Gleed R, eds. Manual of Small Animal

Anaesthesia and Analgesia. United Kingdom: BritishSmall Animal Veterinary Association; 1999.

Short CE, ed. Principles and Practice of Veterinary Anes-

thesia. Baltimore: Williams & Wilkins; 1987.

Thurmon JC, Tranquilli WJ, Benson GJ, eds. Lumb

and Jones Veterinary Anesthesia. 3rd ed. Baltimore:Williams & Wilkins; 1996.

Tully TN, Shane SM, eds. Ratite Management, Medi-

cine, and Surgery. Malabar, FL: Krieger PublishingCo.; 1996.

302 Recommended Reading

A

Acepromazinecharacteristics of, 13, 44tspecies-specific indications

birds, 196tcats, 186t, 282tcattle, 244t, 282tdogs, 178t, 282tferret, 207t, 209thorses, 230t, 282trabbits, 209treptiles, 224tsheep, 244t, 282tswine, 258t, 282t

Acetaminophen, 166t, 171Acetylcholinesterase inhibitors,

51tAcetylpromazine.

See AcepromazineAcid-base balance, 147–148Acidosis

metabolic, 149trespiratory, 149t

Aerrane. See IsofluraneAlfentanil, 14, 46tAlkalinizing agents, 142t–143t,

146Alkalosis

metabolic, 149trespiratory, 149t

Alpha2 agonists. See also specific

drug

antagonists, 181t, 261tpain management using,

164t–165t, 168–169species-specific indications

dogs, 179treptiles, 224t

Alveolar ventilation, 81t–82tAmidate. See EtomidateAnalgesics

alpha2 agonists, 164t–165t,168–169

nonsteroidal anti-inflammatory drugs,165t–166t, 169–171

opioids, 161–168species-specific indications

camelids, 248t–249thorses, 233t–234treptiles, 225truminants, 248t–249tsmall mammals, 213t, 214t,

219swine, 262t

Anectine. See Succinylcholine

303

Index

Page references with “t” denote tables; “f” denote figures.

Anesthesiadefinition of, 1monitoring during.

See Monitoringpatient preparation for, 3–7positioning during, 154–155principles of, 2–3

Anesthesia machinecommon gas outlet, 98–99malfunction assessments, 105toperating recommendations,

105toverview of, 91–92oxygen calculations, 96, 97foxygen flush valve, 96, 98pin index safety system, 92, 93fpressure regulators, 92tanks, 91–92vaporizers, 92, 94–96

Anesthetic agents. See also specific

agent

biotransformation of, 86–87elimination of, 85–86ideal properties of, 52tinhalation. See Inhalation

agentsinjectable, 13–43, 44t–51tscheduling of, 287–288selection of, 11–12types of, 13–43

Anesthetic equipmentanesthesia machine. See Anes-

thesia machinebreathing systems, 99–103ventilators. See Ventilatorswaste gas scavenging, 103–104

Anesthetic record, 9, 10f, 113Ansed. See XylazineAnticholinergics, 44t, 175Antisedan. See AtipamezoleArrhythmias, 128tArterial blood gases, 115tArterial blood pressure.

116t–117tAspirin, 166t, 170, 196t, 213tAsystole, 276t–277tAtipamezole

general characteristics of, 14,46t

species-specific indicationsbirds, 198tcats, 282tdogs, 181t, 282thorses, 282treptiles, 224tswine, 262t, 282t

Atracurium, 14–15, 50t, 284tAtropine, 15, 44t, 207t, 209t,

224t, 270t, 282tAuriculopalpebral nerve, 62t, 66tAzaperone, 15–16, 44t, 258t, 282t

B

Barbiturates, 48t–49tBenzodiazepines, 44t–45tBeuthanasia-D. See PentobarbitalBicarbonate, 142t–143t, 147,

272tBier block, 59tBiotransformation, 86–87Birds

anesthetic agents, 194,196t–198t

304 Index

body temperature, 5tcatheter placement, 199electrocardiographic monitor-

ing of, 200, 202, 203ffasting period, 8tfluid therapy, 146–147, 200heart rate/minute, 5tintubation of, 194, 199laboratory studies and find-

ings, 6tmonitoring guidelines, 200,

202recovery of, 202, 204respiratory rate, 5trestraint methods, 193–194

Blood. See also Plasmaintraoperative assessments,

139replacement of, 133replacement therapy, 140tvolume of, 125t, 134t

Blood pressure monitoring,116t–118t

Body temperaturemonitoring of, 191species-specific values, 5t, 125t,

191Body water, 134tBoiling point, 74, 76Brachial plexus block, 59t, 70fBreathing systems. See also Venti-

latorscircle, 99–102description of, 99gas flow rates, 100t–101tmalfunction assessments, 105tnonrebreathing, 102–103

Brevane. See MethohexitalBrevital. See MethohexitalBrietal. See MethohexitalBupivacaine, 16Buprenorphine

general characteristics of,16–17, 47t

pain management using,163t–164t, 167

species-specific indicationsdogs, 178t, 283thorses, 233t, 283treptiles, 225truminants, 248t, 283tsmall mammals, 212t, 283tswine, 262t, 283t

Butorphanolgeneral characteristics of, 17,

47tpain management using,

163t–164tspecies-specific indications

birds, 196tcats, 186t–187t, 283tcattle, 245t, 248t, 283tdogs, 178t, 180t, 283thorses, 230t, 233t, 283tllamas, 247treptiles, 225tsheep, 245t, 248t, 283tsmall mammals, 212tswine, 258t, 262t, 283t

C

C fibers, 158, 160Calcium, 271tCapnography, 121t, 123f

Index 305

Carbocaine-V. See MepivacaineCardiac compression, 275, 278Cardiopulmonary arrest,

267–268Cardiopulmonary resuscitation

condition-specific approaches,276t–277t

drugs used, 270t–274tfluid therapy, 278guidelines, 268–269intravenous access, 275postrecovery monitoring,

278–279Cardiovascular system

disorders of, 292–293inhalation agents effect, 84monitoring parameters,

115t–118tCarfentanil, 17–18, 46t, 197tCarprofen, 165t, 170, 213t, 225tCats

analgesic agents, 162t–167tblood pressure monitoring,

117tblood volume, 125tbody temperature, 5t, 125t,

191catheter placement, 189chemical restraint, 186t, 188epidural technique, 71ffasting period, 8tfluid administration rates, 137heart rate/minute, 5t, 125tinduction of, 186t–187tintubation of, 189–190laboratory studies and

findings, 6t

local anesthetic techniques,58t–61t

minute ventilation values, 125topioid use, 185, 188parenteral anesthesia of, 187tpremedication, 186trecovery of, 190–191respiratory rate, 5t, 125trestraint methods, 186t, 188sinus bradycardia in, 127tventilatory support for, 190

Cattleblood pressure monitoring,

118tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 250–251chemical restraint of,

244t–247tfasting period, 8t, 250heart rate/minute, 5t, 125tinduction of, 251intubation of, 251–252laboratory studies and find-

ings, 6tlocal anesthetic techniques,

63t–68tminute ventilation values, 125tpremedication, 244t–247t, 250respiratory rate, 5t, 125tsinus bradycardia in, 127t

Central venous pressure, 118tCesarean section, 295–296Chinchilla, 213tChloral hydrate, 18, 48t, 245t,

283tChloroprocaine, 55t

306 Index

Circle rebreathing systems,99–102

cis-Atracurium, 18–19, 50t, 284tColloid solutions, 141t–142tCommon gas outlet, 98–99Corticosteroids, 272tCow. See CattleCurare. See Tubocurarine

D

Defibrillation, 273tDehorning procedures, 66t–67tDehydration, 136tDemerol. See MeperidineDesflurane, 19, 79t–80tDetomidine, 19–20, 45t, 197t,

230t, 282tDexamethasone, 273tDextran, 141tDiazepam

cardiopulmonary resuscitationuses, 274t

general characteristics of, 20,44t, 177, 182

species-specific indicationsbirds, 196t–197tcats, 186t, 282tcattle, 244t, 282tdogs, 177, 182, 282thorses, 231t, 282trabbits, 210treptiles, 224tswine, 258t, 282t

Digital block, 60t, 72fDiprenorphine, 20–21, 47tDissociative agents, 47t–48t,

224t–225t

Dobutamine, 144t, 152, 271tDogs


117tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 183chemical restraints, 178tdiazepam administration, 177,

182epidural technique, 71ffasting period, 8theart rate/minute, 5t, 125tinduction of, 179tintubation of, 182–183laboratory studies and

findings, 6tlocal anesthetic techniques,

58t–61tminute ventilation values, 125tparenteral anesthesia of,

179t–180tpremedication of, 178trecovery of, 183respiratory rate, 5t, 125tsinus bradycardia in, 127t

Dopamine, 144t, 153, 271tDormitor. See MedetomidineDormosedan. See DetomidineDoxacurium, 50tDoxapram, 270tDuromorph. See Morphine

E

Eagles, 197tEdrophonium, 20, 51t, 284t

Index 307

Electrocardiographybird monitoring using, 200,

202, 203fdescription of, 151reptile monitoring using, 226,

228fEndotracheal intubation.

See IntubationEnd-tidal carbon dioxide,

114t–115tEnflurane, 21–22, 79t–80t, 85Ephedrine, 144t, 152, 271tEpidural anesthesia

caudal, 67t–68tcranial, 68topioids, 163t–164t, 167–168regional, 60t, 71f

Epinephrine, 144t, 270tEthrane. See EnfluraneEtodolac, 165t, 170Etomidate

for cats, 187t, 284tfor dogs, 179t, 284tgeneral characteristics of, 22,

49tEtorphine, 22–23, 46tExamination. See Physical

examinationExtracellular fluid, 134tEye lubrication, 175

F

Falcons, 197tFasting

duration of, 7species-specific recommenda-

tions, 8t, 229, 235, 250

water, 7Fentanyl

for dogs, 283tgeneral characteristics of, 23,

46tfor horses, 234tpain management using,

162t–164t, 167Ferrets

analgesic agents, 213tbody temperature, 5tcatheter placement, 206chemical restraint of,

207t–208tfasting period, 8theart rate/minute, 5tinduction of, 205–206, 208tintubation of, 206laboratory studies and

findings, 6tmonitoring of, 212premedication, 207t–208trecovery of, 212respiratory rate, 5trestraint methods, 205

Flaxedil. See GallamineFluid therapy

administration ofrates, 137, 139routes, 146–147

blood replacement, 140tbody water percentages, 134tcolloid solutions, 141t–142tcommercial fluids, 135tdescription of, 132guidelines, 133, 137, 139, 146

308 Index

infusion warmers, 137, 138fpostresuscitation, 273t–274t,

278Flumazenil, 23, 45t, 262t, 282tFlunixin meglumine, 166t, 171,

196t, 213t, 225t, 234t,249t

Fluothane. See HalothaneFoals, 233t–234t, 240Forane. See IsofluraneFurosemide, 273t

G

Gallamine, 23–24, 50tGeneral anesthesia

characteristics of, 75tdefinition of, 113monitoring parameters,

114t–119tstages of, 75t, 113

Gerbil, 213tGeriatric patients, 298–299Glycerol guaiacolate.

See GuaifenesinGlycopyrrolate, 24, 44t, 207t,

209t, 224t, 282tGoat

blood volume, 125tbody temperature, 5t, 125tfasting period, 8theart rate/minute, 5t, 125tlaboratory studies and

findings, 6tminute ventilation values, 125trespiratory rate, 5t, 125t

Guaifenesin, 24–25, 49t, 235,245t–246t, 260t–261t, 284t

Guinea pig, 213t

H

Halothanecardiovascular effects, 84description of, 88–89general characteristics of, 25for horses, 237physicochemical properties of,

79t–80trespiratory effects, 83

Hamster, 213tHawks, 196tHeart rate

monitoring of, 115tspecies-specific values, 5t, 125t

Hemoglobin saturation, 115tHepatic disease, 296–297Hetastarch, 141t–142tHorses

analgesic agents, 233t–234tanesthetic agents, 230t–233tblood pressure monitoring,

117tblood volume, 125tbody temperature, 5t, 125tcatheter placement, 236chemical restraint of, 230tdepth assessments, 240eye covering, 238–239fasting period, 8t, 229, 235fluid therapy, 238heart rate/minute, 5t, 125t,

240induction of, 230t–232tintubation of, 236

Index 309

Horses, cont.

laboratory studies and findings, 6t

local anesthetic techniques,62t

minute ventilation values, 125tmonitoring of, 239–240postanesthetic myopathy,

154–155premedication, 230t, 235–236recovery of, 240–241respiratory rate, 5t, 125t, 239sinus bradycardia in, 127tsupportive care, 238–239ventilatory support for, 239

Hydromorphonefor cats, 186t, 282tfor dogs, 178t, 282tgeneral characteristics of, 47tpain management using, 162t

Hypercapnia, 109Hyperthermia, malignant, 85,

265–266Hypnomidate. See EtomidateHypnovel. See MidazolamHypokalemia, 139Hypotension, 128t, 152Hypothermia

etiology of, 152fluid therapy and, 137prevention of, 152–154systemic effects, 152–153

Hypoxemia, 151

I

Infraorbital nerve, 58tInfusion warmers, 137, 138f

Inhalation agentsbiotransformation of, 86–87cardiovascular effects, 84description of, 73disadvantages of, 73elimination of, 85–86environmental exposure,

86t–87tfactors that affect, 81t–82thepatocellular injury caused

by, 84–85minimum alveolar concentra-

tion, 78, 79t–80t, 82physicochemical properties of,

74, 76quantity determination, 76,

77frequirements for, 83trespiratory effects, 82–83systemic effects of, 82–85

Inspiratory time, 108tInspiratory to expiratory ratio,

108tIntercostal nerve, 60tIntermittent positive pressure

ventilation, 104, 106Interpleural region, 60tIntracellular fluid, 134tIntraosseous cannulation,

146–147, 201fIntraval. See ThiopentalIntravenous regional anesthesia

in cats, 59tin cattle, 65tin dogs, 59tin ruminants, 65t

310 Index

Intubationgeneral considerations, 174species-specific indications and

guidelinesbirds, 194, 199cats, 189–190cattle, 250–251dogs, 182–183ferret, 206horses, 236reptiles, 223ruminants, 250–251sheep, 250–251swine, 263–264

tube placement, 174Isoflurane, 25–26, 79t–80t, 88,

194, 237Isoproterenol, 144t, 271t

K

Ketaminegeneral characteristics of, 26,

48tpain management using, 165t,

169species-specific indications

birds, 196tcats, 186t–187t, 283tdogs, 179t–180t, 283tferret, 208thorses, 230t–231t, 283trabbits, 210treptiles, 224t–225t

Ketaset. See KetamineKetoprofen, 165t–166t, 170,

214t, 234t

L

Lidocaine, 26–27, 55t, 142t, 270tLizards. See ReptilesLlamas

body temperature, 5tchemical restraint of,

246t–247tfasting period, 8theart rate/minute, 5tlaboratory studies and

findings, 6tpremedication, 246t–247trespiratory rate, 5t

Local anestheticsdescription of, 53–54mechanism of action, 54, 57pain management using, 171properties of, 55ttechniques for administering,

58t–68ttoxic effects of, 56t

M

M-99. See EtorphineMalignant hyperthermia, 85,

265–266Mandibular nerve, 59t, 69fMannitol, 274tMarcaine. See BupivacaineMaxillary nerve, 58t, 69fMedetomidine


pain management using,164t–165t

species-specific indicationsbirds, 197t

Index 311

Medetomidine, cont.

cats, 187t, 282tdogs, 179t–180t, 282tferret, 208t–209tswine, 258t, 282t

Meloxicam, 166tMeloxicxam, 170Mental nerve, 58t, 69fMeperidine, 27–28, 46t, 161,

162t, 282tMepivacaine, 28, 55tMetabolic acidosis, 139, 146,

149tMetabolic alkalosis, 149tMethohexital, 28–29, 48t, 283tMethoxyflurane

general characteristics of, 29nephrotoxic effects, 85physicochemical properties of,

79t–80tMetofane. See MethoxyfluraneMidazolam


species-specific indicationsbirds, 196t–197tcats, 186t, 282tdogs, 282tferret, 207trabbits, 210treptiles, 224tswine, 258t, 282t

Minimum alveolar concentra-tion, 78, 79t–80t, 82

Mivacurium, 50tMolecular weight, 76

Monitoring. See also specific species,

monitoring

capnography, 121t, 123fguidelines for, 111–113parameters assessed, 114t–119tpulse oximetry, 121t–122t,

124fMorphine


pain management using, 161,162t–164t

species-specific indicationscats, 186t, 282tdogs, 178t, 282thorses, 230t, 233t–234t,

282truminants, 248t–249t, 282tsheep, 248t–249t, 282tsmall mammals, 213tswine, 262t, 282t

Mouse, 213t

N

Nalbuphine, 30–31, 47t, 283tNalmefene


species-specific indications,181t, 283t

Nalorphine, 47tNaloxone


species-specific indicationsbirds, 198tdogs, 181t, 283t

312 Index

swine, 262t, 283tNaltrexone, 32, 47t, 198tNaproxen, 166tNarcan. See NaloxoneNembutal. See PentobarbitalNeonates, 299–300Neostigmine, 32–33, 51t, 284tNeurologic injury, 294Neuromuscular blocking agents,

49t–51tNimbex. See cis-AtracuriumNitrous oxide

diffuse hypoxia and, 88indications, 88physicochemical properties of,

79t–80tNonrebreathing systems,

102–103Nonsteroidal anti-inflammatory

drugs, 165t–166t,169–171, 213t

Norcuron. See VecuroniumNovocaine. See ProcaineNSAIDs. See Nonsteroidal anti-

inflammatory drugsNubain. See NalbuphineNumorphan. See Oxymorphone

O

Onychectomy, 61t, 72fOpioids

agonists, 167antagonists, 181t, 262tclassification of, 161dosing of, 162t–167tepidural uses, 163t–164t,

167–168

general characteristics of,46t–47t

side effects of, 161species-specific indications

cats, 185, 188dogs, 178t, 181tferrets, 213trabbits, 213tsmall mammals, 213t

types of, 162t–167tOwls, 197tOxygen flush valve, 96, 98Oxygenation

calculations regarding, 96, 97ffactors that affect, 148, 151intraoperative assessments,

148, 151Oxyhemoglobin dissociative

curve, 124fOxymorphone


pain management using,162t–163t

species-specific indicationscats, 186t, 283tdogs, 178t, 283t

P

Packed red blood cells, 140tPaCO

2. See Partial pressure ofcarbon dioxide

Paindefinition of, 157perception of, 160physiology of, 158, 160signs of, 158, 159t

Index 313

Pain, cont.

treatment ofalpha2 agonists, 164t–165t,

168–169local anesthesia, 171nonsteroidal anti-

inflammatory drugs,165t–166t, 169–171

opioids, 161–168regional anesthesia, 171

Pancuronium, 33–34, 50t, 284tParavertebral techniques,

63t–65tPartial pressure of carbon

dioxide, 106, 109Partial pressure of oxygen, 124fPatient preparations, 3–7Pavulon. See PancuroniumPeak inspiratory pressure, 108tPentazocine, 34, 47t, 283tPenthrane. See MethoxyfluranePentobarbital, 34–35, 48t, 283tPentothal. See ThiopentalPeterson eye block, 65tPethidine. See MeperidinePhenobarbital, 35Phenylbutazone, 166t, 234t, 249tPhysical examination

laboratory studies and findings, 6t

parameters assessed, 3, 5tpreprocedural, 3species-specific findings, 5t

Physical status, 4tPig. See SwinePin index safety system, 92, 93f

Piroxicam, 166tPlasma. See also Blood

replacement therapy, 141tvolume assessments, 134t

Pontocaine. See TetracainePositioning, 154–155Postanesthetic myopathy,

154–155Pregnancy, 295–296Premature ventricular

contractions, 128t, 151Premedication agents, 12,

44t–48tPressure regulators, 92Procaine, 36, 55tPromace. See AcepromazinePropofol

cardiopulmonary resuscitationuses, 274t


species-specific indicationscats, 187t, 283tdogs, 179t, 182, 283tferret, 208trabbits, 210treptiles, 225t

Prostigmine. See NeostigminePulse oximetry, 121t–122t, 124fPulse rate, 115t–116tPulseless electrical activity, 277tPyridostigmine, 37, 51t, 284t

R

Rabbitsanalgesic agents, 213tblood volume, 125t

314 Index

body temperature, 5t, 125tcatheter placement, 215chemical restraint of,

209t–210tfasting period, 8theart rate/minute, 5t, 125timmobility reflex of, 212induction of, 210t, 216–217laboratory studies and

findings, 6tminute ventilation values, 125tmonitoring of, 217–218premedication, 209t–210t, 215premedication of, 209t–210trespiratory rate, 5t, 125trestraint methods, 212, 215

Rapifen. See AlfentanilRapinovet. See PropofolRat, 213tRecord keeping, 9, 10f, 113Recovery, anesthetic

birds, 202, 204cats, 190–191dog, 183ferret, 212horses, 240–241reptiles, 227ruminants, 253swine, 266

Regional anesthesiain cats, 59tin cattle, 65tin dogs, 59tpain management using, 171in ruminants, 65t

Regonol. See Pyridostigmine

Renal disease, 297Reptiles

anesthetic agents, 224t–225tfluid therapy, 226induction of, 222–223intubation of, 223monitoring of, 226–227recovery of, 227restraint methods, 221–222ventilatory support, 226

Respiratory acidosis, 149tRespiratory alkalosis, 149tRespiratory rate

decreased, 126t–127tmonitoring of, 114t–115tspecies-specific values, 5t, 125t

Respiratory systemdisorders of, 293–294inhalation agents effect, 82–83

Revex. See NalmefeneRevivon. See DiprenorphineRobinul. See GlycopyrrolateRocuronium, 50tRomazicon. See FlumazenilRomifidine, 37–38, 45t, 282tRompun. See XylazineRuminants


118tcatheter placement, 250–251cattle. See Cattlechemical restraint of,

244t–247tfasting period, 250induction of, 251

Index 315

Ruminants, cont.

intubation of, 251–252llamas. See Llamaspositioning of, 253premedication, 244t–247t, 250recovery of, 253sheep. See Sheepsinus bradycardia in, 127t

S

Scoline. See SuccinylcholineSedivet. See RomifidineSevoflurane, 38, 79t–80t, 85, 89,

194, 237Sheep

blood volume, 125tbody temperature, 5tcatheter placement, 250–251chemical restraint of,

244t–245tfasting period, 8t, 250heart rate/minute, 5t, 125tinduction of, 251intubation of, 251–252laboratory studies and find-

ings, 6tminute ventilation values, 125tpremedication, 244t–245t, 250respiratory rate, 5t, 125t

Sinus bradycardia, 127tSinus tachycardia, 128tSmall mammals

ferret. See Ferretguidelines regarding, 218–219rabbit. See Rabbit

Snakes. See ReptilesSolubility coefficient, 78

Solu-Delta-Cortef, 272tSolu-Medrol, 272tSpecific gravity, 76Stiglyn. See NeostigmineStresnil. See AzaperoneSublimaze. See FentanylSuccinylcholine, 38–39, 51tSucostrin. See SuccinylcholineSufenta. See SufentanilSufentanil, 38, 46tSupportive care

acid-base balance, 147–148,149t

adjunctive drugs, 151–152fluid therapy. See Fluid therapyintraoperative, 131–132oxygenation, 148, 151preoperative, 131

Suprane. See DesfluraneSupraorbital nerve, 62tSwine

analgesic agents, 262tblood pressure monitoring,

118tblood volume, 125tbody temperature, 5t, 125t, 265catheter placement, 264chemical restraint of, 258tfasting period, 8t, 256heart rate/minute, 5t, 125tinduction of, 256, 258t–261tintubation of, 263–264laboratory studies and

findings, 6tmalignant hyperthermia in,

265–266

316 Index

minute ventilation values, 125tmonitoring of, 264–265premedication, 258trecovery of, 266respiratory rate, 5t, 125trestraint methods, 255–256

T

Tachycardia, 128t, 151, 159t, 276tTachypnea, 126t, 159tTalwin. See PentazocineTelazol


species-specific indicationsbirds, 196tcats, 187t, 283tdogs, 179t, 283tferret, 208thorses, 283trabbits, 210t

Temgesic. See BuprenorphineTensilon. See EdrophoniumTetracaine, 55tThiopental

characteristics of, 39–40, 48tspecies-specific indications

cats, 186t, 283tdogs, 179t, 182, 283tferret, 208truminants, 245t, 283tswine, 260t, 283t

Tidal volume, 108t, 114tTolazoline


species-specific indications,181t, 261t, 282t

Torbugesic. See ButorphanolTorbutrol. See ButorphanolTotal body water, 134tTracrium. See AtracuriumTrauma, 291–292Trexonil. See NaltrexoneTrigeminal nerve, 58t, 69fTromethamine organic amine

buffer, 143tTubocurarine, 41, 50tTurtles. See Reptiles

U

Ultrane. See SevofluraneUrinary output assessments, 118t

V

Valium. See DiazepamVapor pressure, 74Vaporizers, 92, 94–96Vecuronium, 41–42, 50t, 284tVentilators

indications, 104, 106–107malfunction assessments, 106tpressure-cycled, 107settings, 108tspecies-specific support

cats, 190horses, 239reptiles, 226

volume-cycled, 107–108Ventricular arrhythmias, 128t,

151Ventricular fibrillation, 276tVersed. See Midazolam

Index 317

Vetalar. See KetamineVetergesic. See Buprenorphine

W

Waste gas exposureminimization methods, 87tscavenging systems, 103–104,

106tside effects of, 86t

Water withholding, 7Wildnil. See Carfentanil

X

Xylazinegeneral characteristics of, 42,

45tpain management using,

164t–165tspecies-specific indications

cats, 187t, 282tcattle, 244t, 246t, 282tdogs, 179t–180t, 282t

ferret, 208t–209thorses, 230t, 282tllamas, 246trabbits, 210treptiles, 224truminants, 244tsheep, 244t, 246t, 282tswine, 258t–260t, 282t

Xylocaine. See Lidocaine

Y

Yohimbine (Yobine)general characteristics of, 43,

45tspecies-specific indications

birds, 196t, 198tcats, 282tdogs, 181t, 282thorses, 282tsheep, 282tswine, 261t, 282t

318 Index

veterinary anesthesia

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