Week 6

Your Obligation

To recognize and alleviate animal pain Many years believed pain was good to

remind the animal to avoid movementFalse belief

Uncontrolled pain leads to prolonged recovery

You are the person in with the animal and need to be able to assess pain level

Definitions IASP- International Association for the Study

of Pain Pain- unpleasant sensory and emotional

experience associated with actual or potential tissue damage, or described in terms of such damage

Nociceptor- receptor that is preferentially sensitive to a noxious stimulus3 phases- Transduction, Transmission, Modulation

Analgesia- absence of pain in response to stimulation that would normally be painful

Cont. Hyperalgesia- increased response to a

stimulus that is normally painful Peripheral sensitization- reduction in activation

threshold of peripheral nociceptors due to exposure to a # of chemical substances that arise as a result of tissue damage

Central sensitization- changes in the receptive field properties of neurons located in the spinal cord

Wind-up- produced following repeated, low-frequency input from nociceptors

Peripheral nervous system Transmission of a noxious stimulation

involves activation of specialized receptors and peripheral nerves in damaged tissue

Degree of sensitivity is directly related to density of nociceptors in that tissue (skin, joint capsule, muscle, tendon, dental pulp)

Nociceptors convert the chemical, mechanical and thermal insult into nerve impulses

Central nervous system

Pathways involved are considerably more complex than those in the periphery

Spinothalamic tract- transmits pain impulses through the spinal cord and to the brain

Axons- nerve fibers that terminate in several areas of the thalamic area of the brain and brain stem

This allows body to perceive

the aspects of the pain:

location, nature, and intensity

Problems with evaluating pain Critical before appropriate analgesic therapy

can be initiated Watch for specific behavior patterns Autonomic nervous system activates “fight

or flight” response and releases epinephrine and norepinephrine

Results in ↑HR, BP, and RR and pupil dilation

Fight or flight not specific to pain

Signs of pain and distress ↑ HR. BP, RR, pupil dilation, vocalization, and arousal

Some may have ↓HR in response to pain Behavioral signs include restlessness, ↓ appetite, not

sleeping, unusual body position, resent handling Post-op pain response: biting, scratching, or licking Know typical behavioral patterns and physical

appearance of species and breeds

Environment and nursing care Environmental factors often affect

emotional component of pain perception Keep surroundings familiar and calm Recovery areas should be quiet and

located away from high traffic Interaction with humans can help relieve

stress and anxiety Schedule tx and monitoring for less

disturbances

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Frequency of Pain Evaluation Upon admission During immediate postoperative period Every 30 minutes through critical phase Every 4-6 hours throughout

hospitalization

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Pain Scale Describes observer’s subjective opinion Describes patient’s physiological signs Should be documented in medical record Colorado State University Acute Pain Scale

pages 862-863New pain scale for dogs and catsNumerical, pictorial, and descriptive assessments

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Pain is Bad

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Pain Management Standards

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Perception Fourth phase of pain pathway

(after transduction, transmission and modulation)

Occurs in the conscious brainIs the awareness that “I hurt”

Differentiates pain from nociceptionNociception occurs even in state of unconsciousness

Occurs as anesthesia wears off; occurs as consciousness returnsGood pain management should be initiated when

pain is anticipated

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Preemptive Analgesia

Best way to treat pain is to prevent it Benefits of preventive analgesia

Reduces postprocedure analgesia requirements

Minimizes detrimental effects of painImproves handling of patientsLowers sedation or anesthetic requirementsPrevents hypersensitization at spinal cord

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“Don’t Quit Until the Pain Quits” Postoperative analgesia

3-4 days for soft tissue procedures1 week for orthopedic procedures

Pain medications sent home with patient Taper medications carefully Additional analgesia if pain persists

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Analgesic Therapy

Requires knowledge of drugs Requires anticipation of pain levels

associated with various conditions Ultimate criteria: pain relief Analgesic plan for each patient

Maximize pain controlMaintain patient on analgesic planeReduce unwanted side effects

Analgesic drugs

2 main types:Nonnarcotic NSAIDsNarcotics

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Types of Opioids Efficiency determined from specific receptors in brain

and spinal columnMu receptors

○ Sedation, analgesia, respiratory depressionKappa receptors

○ Sedation, analgesiaSigma receptors

○ Thought to be responsible for adverse effects of opioid administration

○ Dysphoria, excitement, restlessness, anxietyDelta receptors

○ Analgesia and motor disfunction

Classified as agonists or antagonists

Opioids

Narcotics Pure agonist- exert effects by only

stimulating opioid receptors (morphine) Antagonists- bind at opioid receptors and

block response; reversal agents (naloxone) Mixed agonist/antagonist- act like agonists

as some receptors and antagonists at others (butorphanol)

Narcotic effects

Minimal cardiovascular effects Bradycardia Hypotension if stimulates release of

histamine Respiratory depression Possible sedation Metabolized by liver and excreted in

urine; watch in liver disease and neonates

Narcotic agonists Morphine

All other opioids compared to itDepresses respiratory and CNSGiven IV and IM routes, can be used as a pre-

med

FentanylSynthetic, 100x potency, short duration (30-45

min)Transdermal patch- variable uptake, apply to

cats 12-16 hrs before pain and dogs 24 hours before.

Narcotic agonists Hydromorphone

6-7x more potentSynthetic, 4-6 hr durationUsed more commonly than Oxy

Oxymorphone10-15x more potentSynthetic, 2-4 hr duration

EpiduralsMany of these and the local anesthetics can be

administered via epidural

Mixed agonist/antagonists Butorphanol (Torbutrol)

Synthetic, stronger agonist, weak antagonistUsed commonly as perioperative analgesiaUsed as antiemetic for chemo

Buprenorphine (Buprenex)300x potencyUsed for post-op pain transmucosalCan be absorbed through mm when given PO

Antagonists

NaloxoneAntagonizes all opiate receptorsLess effective for reversal of buprenorphine

NaltrexoneSimilar to Naloxone but longer acting and

administered orally

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Tramadol For moderate pain Synthetic drug Opioid-like analgesic effects Fewer side effects than with opioids Oral route of administration Suitable for long-term at-home management

Cancer patientsProblem osteoarthritis casesPostoperative prolonged pain

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NSAIDs Precautions for Patients Normal blood pressure Normal renal function Normal liver function No bleeding abnormalities No evidence or concern for gastric

ulceration No dosing of other NSAIDs,

corticosteroids, or aspirin

NSAIDs Nonsteroidal anti-inflammatory drugs Exert analgesic effects in the peripheral

tissues by blocking production of prostaglandins

Inflammation begins with local tissue injury Vasoactive substances produce pain, heat

and swelling NSAIDs control pain by inhibiting

cyclooxygenase, leads to production of prostaglandins

Salicylate analgesics

Aspirin Bismuth subsalicylate Effective in relieving pain associated with

peripheral inflammation: muscle and joint disease

Absorbed through GI tract, metabolized by liver, excreted by kidneys

Absorbed into synovial fluid, peritoneal fluid, milk, saliva, and placental membranes

Propionic acid derivatives Carprofen (______)

Inhibits COX2 but doesn’t totally aviod COX1

Used for musculoskeletal and acute pain

Deracoxib (______)More focused on COX2 compared to

RimadylUsed same as Rimadyl

Naproxen (Naxen)Nonselective and used for musculoskeletal

Propionic acid derivatives Ibuprofen

Nonselective, not as safe

Ketoprofen (Ketofen)Nonselective, used in large and small

animal

Etodolac (EtoGesic)Nonselective , used in large and small

animal

Fenamic acids Meclofenamic acid

Inhibits cyclooxygenase and blocks cell surface receptors from prostaglandins

Musculoskeletal painSide effects: V and D, GI ulceration

Flunixin MeglumineAnalgesic and antipyretic activityBlocks production of prostaglandinsUsed for DJD that is unresponsive to other

NSAIDsCan cause GI ulceration and bleeding

Oxicans

MeloxicamControl of pain and inflammation associated

with osteoarthritisTx in dogs and cats

Pyrazolone derivative

PhenylbutazoneAnalgesic, anti-inflammatory and antipyretic

propertiesTx in dogsPainful arthritis and skeletal muscle disease

Tx of GI ulceration

SucralfateMixes with mucous and forms a band aid

H2 blockersCimetidine (Tagamet), ranitidine(Zantac), famotadine (Pepcid)

Tranquilizers

Psychotropic drug Provide sedation and some muscle

relaxation and anxiolysis Tranquilizers provide no analgesia and

that it is inappropriate to use these drugs alone for postoperative pain control

Alpha2-Adrenergic agonists Xylazine

Binds to alpha2 receptors in CNS causing sedative and analgesic effects

Effects may be reversed with antagonists: yohimbine, atipamezole, tolazoline, or idazoxan

Can be used for analgesia in small animals however medetomidine works better

Others include: Domitor, Dexdomitor

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“Kitty Magic”

Most common use of α2-agonists in cats

General anesthetic for minor procedures Anesthetic before gas anesthetic for

more advanced procedures Components

An α2-agonist

An opioid (commonly buprenorphine)Ketamine

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MLK Combination

Administered as a CRI Infusion combination

Morphine ○ An opioid

Lidocaine ○ A local anesthetic

Ketamine ○ Provides optimal analgesia○ Prevents wind-up

Corticosteroids

Dampen the fire of inflammation but doesn’t eliminate the cause of it

Can cause impairment of wound healing and mask underlying diseases

Should not be used with NSAIDs due to ↑ risk of GI ulceration

Includes: cortisone, hydrocortisone, prednisone, prednisolone

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Local Anesthetics Mode of action: disrupt neural transmission Routes of administration

Topical Local infiltration Circumferential ring block Dental nerve block Intraarticular (joint space) Epidural nerve block Transdermal Intravenous

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Topical Route of Administration Application to skin or mucosa

Soaked gauze pads, creams, or jelliesApply 20-30 minutes direct contact timeDesensitization at application site

Reduces pain associated with minor proceduresWound suturing, venipuncture, arterial puncture,

nasal cannulization, and urinary catherization

Solutions usedLidocaine, bupivacaine, tetracaine, and/or

ephinephrine

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Circumferential Ring Block

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Dental Nerve Block

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Intraarticular Block

A local anesthetic Also effective in reducing joint pain

Use of morphine

Injection directly into joint space Smooth plane of anesthesia maintained

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Epidural Nerve Block

Analgesia to caudal half of body Sedative effects kept to a minimum Injection made at lumbosacral space

Opioids (morphine, fentanyl)And/or local anesthetics (lidocaine,

bupivacaine)

Epidural catheters for long-term administration

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Transdermal Anesthetics

Lidocaine transdermal patchWidely accepted in humansUse in veterinary medicine is being tested

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Intravenous Administration Manages variety of pain states

Visceral pain○ Pancreatitis○ Parvovirus

Extensive nerve damage○ Limb amputation

Effective administration by CRILidocaine as sole agentLidocaine in conjunction with other analgesics

Local Anesthetics All inhibit nerve conduction via sodium

channel blockade. Bupivacaine hydrochloride (Marcaine)

Inhibits nerve conductionStronger and longer acting than lidocaine

○ 15-20 minutes, lasts 6-8 hours.Commonly used for declaws and tooth extractions

Mepivacaine (Carbocaine-V)Shorter acting and not as potent as BupivacaineLonger acting but equal potency to lidocaine

Local Anesthetics

LidocaineAlso is an antiarrhythmic commonly used for

ventricular arrhythmiasUsed in horses for GI motility after ileusUsed as local block for small mass removals

or suturing skin wounds without anethesiaTakes effect in 3-5 minutes and is effective

for 60-90 minutes.“-caine” at the end of a word means it blocks

a nerve.

Tx of pain in dogs and cats 1st step- recognizing behavioral and

physiologic signs Good nursing care is critical Always watch for side effects of any

drugs being administered Know if pain is chronic or acute Know Hx of animal being treated

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Why Is Large Animal Pain Not Treated? 1- “Animals don’t feel pain” 2- “Animals don’t show pain” 3- “Limited number of analgesic drugs

available for farm animals” 4- “Owners or producers won’t pay for

analgesia”

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Pain in Large Animals

Strong tendency to hide pain until severe

Consequences of painDecreased food intakeWeight lossDecreased milk production

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Signs of Pain in Large Animals Stop eating Appear lethargic Stand with hunched back (ruminants) Stretch out in abnormal posture (horses) Grind teeth (horses) “Dog sit” (foals)

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Treating Pain in Large Animals NSAIDs

Therapeutic analgesic due to effect on inflammation Safe Easy to administer: IV, IM, SQ, PO, or transdermal Inexpensive Long lasting Should be paired with more potent short-acting drugs

Commonly used NSAIDs Phenylbutazone (“bute”) Flunixin meglumine (“Banamin”)

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Treating Pain in Large Animals Opioids

Primarily for acute medical or surgical painVaried responses from various receptorsMay cause excitement in farm animals; use in

conjunction with sedative.Administration by IV, IM, SQ, transdermal,

epidural, intraarticular, and CRI

Commonly used opioidsButorphanol is most commonMorphine, buprenorphine, fentanyl

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Treating Pain in Large Animals α2-agonists

Used more commonly in large animals, than smallWide variation in species’ response

○ Pigs most resistant and require high dosages for sedation

○ Horses next in sensitivity○ Cattle, sheep, and goats are most sensitive

Considered a sedative, but provide pain reliefOften combined with opioids for painful proceduresCommon α2-agonists:

○ Detomidine, Xylazine, Medetomidine

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Treating Pain in Large Animals Local anesthetic agents

Most effective of analgesic drugs Least expensive of analgesic drugsBlock transmission of painful impulsesAdministration by IV as a CRI

Commonly used anesthetic agentsLidocaine, bupivacaine

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Horse-specific Information Receive better analgesic treatment

Treated as “companion” animalsAre generally performance animalsBecome violent when in acute painDo not have absolute economic value

NSAIDs for chronic and acute pain Opioids used more commonly in horses

for intraoperative and postoperative pain and for medical pain

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Analgesia for Food-producing Animals

Cows, sheep, and goats are least likely large animals to receive analgesia because of narrow profit margin

Difficult to regulate analgesia when many procedures are done by producers and not by veterinarians

Strict regulations regarding use of many drugs in meat and milk-producing animals

Oral drugs slowly absorbed, or inactivated in rumen