Pre$anaesthetic,preparation,!pre%anaesthetic!preparation!aims:!!

• Identify!existing!abnormalities!of!major!organ!function!• Assess!severity!of!abnormality!of!major!organ!function!• allow!for!planning!of!an!appropriate!anaesthetic!protocol!!

• include!considerations!related!to!patient!and!the!procedure!!SOAP!!

• Subjective!assessment!–!how!we!think!the!animal!is!!eg!demeanor!• Objective!assessment!–!use!measurements!eg!BP,!HR,!RR,!PR,!CRT,!temp!lab!tests!etc!• Assessment!–!make!overall!assessment!of!animal!• Plan!for!the!procedure!(pre%op,!intra%op,!post%op,!recovery)!

o Premed!o Analgesia!o Induction!agents!o Breathing!circuit!o Fluids!o Supportive!care!–!depends!on!patients!condition!what!is!needed!(eg!patient!positioning,!warmth!etc)!

!Pre%anaesthetic!patient!evaluation!

• Ask!questions!–!signalment!%!thorough!history!

! ! –!eaten!this!morning?!!%!Reason!for!anesthesia?!%!previous!anaesthetics!%!current/recent!meds!

! ! %!geriatric!patients!–!pre%anaesthetic!bloods!essential!!• Look!at!patient!–!demeanor!

%!BCS!%!breathing!pattern!%!position!%!demeanor!

• Touch!patient!–!thorough!physical!exam!!! ! –!mm!colour!

%!auscultation!of!heart!!%!identify!pulse!deficit!–!simultaneous!pulse!palpation!%!rate!and!rhythm!

• Regular?!• Regularly!irregular!or!irregularly!irregular!• Pulse!deficit!–!palpate!femoral!pulse!while!listening!to!heart!!• Pulse!strength!

%!heart!sounds!• Lub!dub!(AV!valves!close!then!aortic!and!pulmonic!valves!close)!• Murmurs!

o Systolic,!diastolic!or!continuous!o Grade!

! 1&2!–!soft!and!only!audible!at!one!location!! 3!–!soft!and!audible!at!multiple!locations!! 4!–!loud!with!no!palpable!thrill!! 5!–!loud!with!palpable!thrill!! 6!–!audible!without!stethoscope!

• Muffled!sounds?!–!pleural!effusion/pneumothroax?!• Displaced!sounds?!• Location!of!valves!

o P!–!left!ICS!2!and!3,!ventral!to!costochondral!junction!

! End!of!systole!o A!–!left!ICS!4!at!costochondral!junction!

! End!of!systole!o M!–!left!ICS!5!and!6!at!costochondral!junction!

! First!sound!in!systole!o T!–!right!ICS!3%4!at!costochondral!junction!

! Start!of!systole!%!auscultation!of!lungs!

Location!• Mid!thorax!=!tracheal!bifurcation!and!bronchial!sounds!• Caudoventral,!caudodoral!&!cranioventral!from!bifurcation=!lung!sounds!• Thoracic!inlet!=!tracheal!sounds!!Sounds!• Loudness:,muffled!sounds!=!fluid,!tissue!in!pleural!space!• Crackles,=!fluid!in!small!airways!(primary!lung!disease)!• Wheezes,=!small!airway!narrowing!(bronchitis)!• Stridor,=,insp.!wheeze!over!larynx!=!upper!airway!obstruction!• Stertor,=!insp.!snoring!=!pharyngeal!obstruction!(reverse!sneezing)!• Snapping,=!collapsing!trachea!

! **!anaesthetic!drugs!depress!CVS!function!–!must!be!at!sufficient!capacity!BEFORE!drugs!**!• Lab,tests!!

%!renal!function!%!can!push!into!renal!failure!by!anaesthetic!drugs!if!renal!function!poor!! ! %!tests!!

• BUN!–!liver!makes!urea!&!secretes!in!blood.!Kidney!removes!from!blood!• Creatinine!–!breakdown!product!of!muscle!• USG!–!concentrating!and!diluting!ability!of!kidneys! ! !

! ! %!results!–!elevated!BUN!&!creatinine!=!>!75%!of!renal!function!lost!(GFR!<!25%)!! ! %!problem!–!can!be!close!to!renal!failure!without!us!being!able!to!detect!it!and!then!!

!!!!!!!!anaesthetic!drugs!push!INTO!renal!failure!(over!75%!threshold)!! ! ! !!!%!hepatic!function!%!poor!hepatic!function!"!delayed!recovery!with!some!drugs!! ! ! ! %!tests!!

• ↑ALP!=!biliary!obstruction,!intrahepatic!cholestasis!or!infiltrative!liver!dz!• ↑ALT!=!hepatocyte!damage(very!specific!enzyme)!• ↑AST!=!may!be!hepatocyte!damage!(non!–!specific,!in!many!other!cells)!• Bilirubin!–!non!specific!for!liver!function!

! ! ! ! %!considerations!–!some!drugs!affect!test!results!!! ! ! ! ! ! %!corticosteroids!artificially!elevate!liver!enzymes!!

! !!!%!hydration!status!Tests!–!PCV,!TPP,!BUN,!serum!creatinine!

• Prerenal!azotaemia!(elevated!BUN!and!creatinine)!• Elevated!TPP!and!PCV!

! !!!%!blood!O2!carrying!capacity!!! ! %!tests!%!PCV!+!TPP!!

• Dog!PCV!=!0.37!–!0.55!• Cat!PCV!=!0.27!–!0.45!• Minimum,preanaesthetic,PCV,=,0.25,!!• PCV!<!0.25!don’t!do!any!elective!surgery!• ACP!drops!PCV!by!5!points!every!time!due!to!shift!in!body!fluids!!!

o !no!ACP!if!PCV!low!• !low!PCV!complications!–!renal!damage!(high!02!demand)!

! ! ! ! ! !!! !!!!!!!%!blindness!in!horses!and!cats!!!

! ! ! %!what!to!do!if!tests!are!not!satisfactory?!! ! ! ! %!postpone!surgery!! ! ! ! %!treat!problem!–!eg!rehydrate!

! ! ! ! %!adjust!anaesthetic!protocol!–!don’t!use!drugs!eliminated!through!kidney/liver!! ! ! ! ! ! ! !!!!!!!!!!%!increase!monitoring!and!supportive!care!!

Min!tests!for!healthy!patient!w/!elective!surgery!• PE!=!body!temp,!thoracic!auscultation!(heart!and!lungs),!pulse!palpation,!MM!colour!+!CRT!• Lab!tests!=!PCV,!TPP,!BUN,!USG!• Rarely!done!• Many!believe!this!is!not!needed!

!Min!tests!for!old/ill!patients!!

• PE!=!body!temp,!thoracic!auscultation!(heart!and!lungs),!pulse!palpation,!MM!colour!+!CRT!• PCV,!TPP,!albumin,!kidneys!(BUN,!creatinine,!USG),!liver!(ALP,!ALT),!electrolytes!(Na,!Cl,!K,!Ca)!• Can!do!extra!tests!if!needed!–!U/S,!xray,!urinalysis,!CBC!

!!Advantages!of!pre!anaesthetic!lab!tests!

• Provide!reference!for!intra%!and!post%!anaesthetic!tests!• Indicate!unexpected!abnormalities!• Optimise!anaesthetic!outcome!but!allowing!us!to!address!underlying!issues!

!Physical,status,ASA!score!=!american!society!of!anaesthesiologists!! %!est.!of!patients!physical!status!(bases!on!Hx,!PE!and!tests)!indicates,likelihood,of,anaesthetic,complications,! %!ASA!≠!anaesthetic!risk!! %!ASA!contributes!to!anaesthetic!risk!! %!scale!!!%!1"5!!! ! %!1=!lowest,!no!observable!dz!! ! %!2!=!small!abnormalities!in!lab!tests!indicate!mild!subclinical!dz!

! Doesn’t!affect!normal!activity!! Eg!obesity,!pregnancy,!neonates,!geriatrics!

! ! %!3!=!moderate!systemic!dz!that!interferes!with!day%today!activity!(often!geriatrics)!• Normal!activity!limited!but!not!incapacitating!dz!• Eg!anaemia,!uraemia,!pneumonia,!hepatic!dz,!electrolyte!imbalances,!diabtetes!

! ! %!4!=!life!threatening!disease,!will!not!survive!without!intervention.!!• Disease!is!incapacitating!• Avoid!elective!procedures!• Eg!GDV,!equine!acute!colic,!trauma,!haemorrhage,!pneumothorax!

! ! %!5!=!moribund!patient!with!little!chance!of!survival!with!or!without!surgery!• Eg!head!trauma,!severe!trauma!

! ! %!E!=!emergency!–!can!be!any!score!as!no!time!to!be!fasted,!stabilised,!&!PE,!Hx!and!tests!not!done!! %!can!increase!physical!status!by!fixing!some!problems!eg!rehydrate,!change!drugs!etc!!Anaesthetic!risk!=!Physical!status!class(ASA)!+!degree!of!invasiveness!of!procedure!+!skill!of!anaesthetist!and!surgeon!!!!!!!!!!!!

Premedication,of,dogs,and,cats,!Advantages!

• Calms!patients!!• good!for!handling!%!catheterisation,!clipping!etc!• Decreases!dose!requirements!for!induction!and!maintenance!agents!!• Provides!pre%op!analgesia!• Reduces!vomiting!• Improves!recovery!• Reduces!vagally!or!stress!mediated!CV!responses!(decreases!autonomic!reflexes)!

!Disadvantages!

• Time!required!to!wait!for!effect!–!must!wait!short!time!to!do!surgery!• Delayed!recovery!–!not!always!a!bad!thing,!enables!a!smoother!recovery!• Extra!cost!(negligible)!

!Premeds!–!can!use!drugs!off!label!(few!drugs!registered!in!animals!eg!buprenorphine!&!morphine)!

• Anticholinergics!! %!atropine!–!advantages!–!prevents!vagally!induced!arrhythmias!by!decreasing!vagal!tone!! ! ! ! ! %!bradycardia,!bradyarrhythmia!! ! ! ! ! %!causes!for!increased!vagal!tone!

o Drugs!–!opiods,!alpha!2!agonists,!anaesthetics!o Vagal!reflexes!%!viscera!manipulation/eye!surgery!o hypothermia!

! ! ! ! %!dries!up!saliva!and!other!secretions!!%!eg!cats!v.!small!airways!so!v.!good!to!dry!up!resp!secretions!%!makes!intubation!easier!

! ! ! ! ! %!increases!HR!! ! ! ! ! ! %!improves!BP!and!prevents!hypotension!!

! ! !!!!%!disadvantages!–!may!cause!tachycardia!(by!inhibiting!vagal!tone)!! ! ! ! ! %!as!HR!always!high!can’t!use!as!an!indicator!of!anaesthetic!depth!! ! ! ! %!may!reduce!GIT!motility!"!ileus!! ! ! ! ! %!horses!v.!sensitive!and!can!get!colic!even!from!eyedrops!!! ! ! ! %!causes!bladder!contraction!! ! ! ! %!can!cause!bradycardia/2nd!degree!heart!block!at!low!doses!(paradoxical)!! ! ! ! %!causes!pupilary!dilation!%!mydriasis!(can’t!assess!depth)!! ! ! ! %!paralyses!ciliary!muscles!! ! ! ! %!Increases!intraocular!pressure!!! ! %!contraindications!–!hyperthyroidism!! ! ! ! %!tachycardia/arrhythmias!! ! ! ! %!Hypertrophic!cardiomyopathies!(heart!reserve!already!low)!! ! ! ! %!perforating!eye!injuries!! ! ! ! %!glaucoma!!! ! %!route!of!admin!–!IV,!IM,!SQ!! ! %!onset!of!action!–!15%20!mins!after!IM!and!SQ!! ! %!duration!of!action!~!1!hour!!! %!glycopyrrolate!–!similar!to!atropine!! ! ! %!doesn’t!increase!HR!as!high!as!atropine!

!–!not!great!for!emergencies!where!HR!critically!low!! ! ! %!doesn’t!cross!BBB!(atopine!does)!–!i.e.!won’t!work!in!OP!poisoning!!! ! ! %!doesn’t!cross!blood%placental!barrier!(atopine!does)!–!not!harmful!to!neonates!! ! ! %!longer!duration!of!action!~!4!hours!

• Tranquilizers!! %!phenothiazines!! ! %!ACP!–!block!dopamine!in!CNS!and!α!%receptors!in!peripheral!tissues!(reduces!vasomotor!tone)!

!–!advantages!–!dose!dependant!sedation!

! ! ! ! !!!!!!!%!long!duration!of!effects!(lasts!through!procedure!and!recovery)!! ! ! ! !!!!!!!%!antiarrhythmic!! ! ! ! !!!!!!!%!antiemetic!! ! ! ! !!!!!!!%!antihistaminic!! ! ! ! !!!!!!!%!calming!effects!–!antidopaminergic!effects!and!depressing!RAS!! ! ! ! !!!!!!%!potentiates!analgesics!eg!opiods!! ! ! ! !!!!!!!%!reduces!mortality!risks!during!&!after!surgery!(slow!sedated!recovery)!!! ! ! %!disadvantages!–!dose!dependant!decrease!in!BP!

%!Ad!can’t!work!to!cause!vasoconstriction!(α%1!receptors!blocked)!! ! ! ! ! %!may!lower!seizure!threshold!!

–!don’t!use!if!seizure!Hx!or!brain!disease!! ! ! ! ! %!decreases!BP!(due!to!vasodilation)!! ! ! ! ! %!exacerbates!hypothermia!(due!to!vasodilation)!%!keep!patient!warm!!! ! ! ! ! %!aggression?!–!usually!oral!doses!!, , , , , $,provide,no,analgesia,–,MUST,be,used,with,analgesic,eg,opiods!!! ! ! %!contraindications!–!hypovolaemia!! ! ! ! ! %!hx!of!seizures!! ! ! ! ! %!boxers!–!have!idiopathic!reactions!! ! ! ! ! ! %!causes!hypotension!and!bradycardia!! ! ! ! ! %!advanced!liver!disease!–!metabolised!by!liver!!! ! ! %!route!of!admin!–!IV,!IM,!SQ!! ! ! %!onset!of!action!–!30!mins!! ! ! %!duration!of!action!–!2%4!hours!!! %!benzodiazepines!! ! %!diazepam!(brand!name!=!pamlin)!! ! ! %!action!–!potentiate!GABA!and!glycine!(inhibitory!CNS!NTR’s)!!! ! ! %!advantages/indications!! ! ! ! ! %!sedative!! ! ! ! ! %!muscle!relaxant!%!works!with!anaesthetic!drugs!! ! ! ! ! %!!potentiates!CNS!!and!muscle!relaxing!effects!of!anaesthetic!drugs!! ! ! ! ! %!anticonvulsant!%!treats!seizures!! ! ! ! ! %!stimulates!appetite!in!cats!! ! ! ! ! %!no!CVS!effects!–!can!use!if!hypovolaemic!! ! ! ! ! %!reversal!agent!–!flumazenil!(BZ!antagonist)!!! ! ! %!disadvantages!–**!unreliable!sedative**!! ! ! ! ! ! %!may!get!sedation!or!excitation!in!healthy!patients!if!used!alone!! ! ! ! ! %!may!change!behaviour!in!cats!–!aggression!and!axiety!! ! ! ! ! %!IM!injections!painful!–!propylene!glycol!solvent!! ! ! ! ! %!IM!and!SQ!absorption!unreliable!(esp!SQ)!, , , , , $,provide,no,analgesia,–,MUST,be,used,with,analgesic,eg,opiods,! ! ! !! ! ! %!onset!of!action!IV!–!1%2!min!! ! ! %!duration!of!action!–!20!–!30!mins!!! ! %!midazolam!–!advantages!–!similar!to!diazepam!! ! ! ! ! !!!!!%!water!soluble!–!good!for!IM!and!SQ!injections!as!well!as!IV!! ! ! %!duration!of!action!–!30!mins!• Opiods!–!AVOID!COMBINATIONS!OF!OPIODS!–!effects!unreliable!

o Pure!agonists!%!bind!to!one!or!more!receptor!type!and!activate!it!o Partial!agonists!%!bind!to!one!or!more!receptor!type,!but!once!bound!will!activate!some!and!occupy!

others!without!activating!them!

o Agonists/Antagonists!%!bind!to!more!than!one!receptor!type.!Activate!one!type!of!receptor!and!inhibit/reverse!the!action!of!an!agonists!specific!for!the!other!receptor!

o Agonists/antagonists!and!partial!agonists!! “ceiling!effect”!%!less!effective!analgesics!than!pure!agonists!!! can!reverse/block!effects!of!agonists!

!! %!Receptors!affected!! –!Mu!–!sedations,!analgesia,!resp!depression,!bradycardia,!!! ! ! ! ! hypothermia/hyperthermia,!dependence/tolerance,!euphoria,!! !! ! ! ! reduced!GIT!motility,!antitussive!

! ! ! ! %!kappa!–!analgesia,!sedation,!dysphoria,!antitussive!! ! ! ! %!delta!–!dependence,!analgesia!

!

! %!opiods!%!advantanges!–!analgesia!%!sedation!%!few!CVS!effects!

%!antitussive!%!!reversible!(naloxone,!temgesic)!%!effects!are!dose!dependant!

! %!disadvantages!!o histamine!release!(decrease!BP!due!to!vasodilation)!o bradycardia!o hypothermia!o panting!o resp!depression!(worse!when!mixing!drugs)!

! !tachypnoea!+!resp!depression!with!methadone!o git!hypermotility!–!initial!defecation!"!constipation!

o excitation/dysphoria!o dependence!o tolerance!o emesis!–!morphine!only!

! do!not!use!in!animals!where!vomiting!is!going!to!be!BAD!!

! %!Opiods!(natural)!–!Morphine!–!Mu!agonist!! ! ! ! ! %!good!analgesia!! ! ! ! ! %!moderate!to!good!sedation!! ! ! ! ! %!long!duration!(2%6!hrs)!!! %!Opiate!–!semi%synthetic!–!Buprenorphine!–!partial!Mu!agonist!!! ! ! ! ! ! ! %!v.!high!affinity!for!Mu!receptors!! ! ! ! ! ! ! %!can’t!ever!get!full!effect!–!limited!analgesia!! ! ! ! ! ! ! %!can!partly!antagonise!effects!of!pure!mu!agonists!! ! ! ! ! ! %!moderate!analgesia!! ! ! ! ! ! %!moderate!sedation!! ! ! ! ! ! %!long!duration!of!action!(2%12!hours)!!! ! ! ! %!butorphanol!%!Kappa!agonist!&!Mu!antagonist!! ! ! ! ! ! ! %!can!antagonise!effects!of!pure!mu!agonists!! ! ! ! ! ! %!moderate!analgesia!(not!first!drug!if!big!procedure)!! ! ! ! ! ! %!moderate!sedation!! ! ! ! ! ! %!moderate!duration!(0.5%2!hrs)!! ! ! ! %!naloxone!%!Mu!antagonist!(antagonises!Mu!agonists)!,! ! ! ! %!methadone!%!Mu!agonist!! ! ! ! ! ! %!good!analgesia!

! ! ! ! ! ! %!moderate!"!good!sedation!! ! ! ! ! ! %!long!duration!(2%6!hrs)!! ! ! !! ! %!synthetic!–!pethidine!%!Mu!agonist!! ! ! ! ! %!mild!analgesia!(not!used!often)!! ! ! ! ! %!mild!sedation!! ! ! ! ! %!short!duration!(0.5!%!3)!!! !!!! ! !!!!!%!Fentanyl!%!Mu!agonist!! ! ! ! !!!!!!!!!%!short!duration!(0.5!–!1)!!!! ! %!cat!vs!dog!–!metabolism,!pharmacokinetics!and!response!different!to!dogs!

%!can’t!just!give!cat!dose!for!small!dog!! ! ! %!adverse!CNS!effects!to!morphine!more!pronounced!in!cats!(agitiation!&!excitation)!! ! ! %!hyperthermia!more!common!! ! ! %!buprenorphine!and!methadone!more!reliable!than!morphine!! ! ! **adjust!dose!and!dose!intervals!to!minimise!drug!accumulation**!!! NB:!only!methadone!and!butorphanol!registered!for!animal!use!–!all!others!used!off!label!!• Alpha%2!agonists!! %!xylazine!! %!medetomidine!! ! %!action!–!stimulate!pre%!and!post%synaptic!alpha%2!andreno%receptors!in!CNS!and!peripheral!tissues!! ! %!advantages!–!reversal!agent!–!don’t!reverse!when!premed!(removes!analgesia)!! ! ! ! ! !!!!!!!!!!!%!alpha%2!antagonist!! ! ! ! ! !!!!!!!!!!!%!example!–!atipamezole!! ! ! ! ! ! ! ! %!reverses!sedation!and!analgesia!! ! ! ! ! ! ! ! ! %!don’t!reverse!for!painful!procedures!!! ! ! ! ! ! ! ! %!partially!reverses!bradycardia!! ! ! ! %!far!more!potent!than!xylazine!! ! ! ! %!muscle!relaxation!! ! ! ! %!dose!dependant!sedation!

%!α2:!α1!ratio!very!high!(>10!x!xylazine)!! %!increased!sedation!but!also!increased!CVS!effects!

! ! ! ! ! %!rapid!onset!! ! ! ! %!strong!analgesia!!! ! %!disadvantages!–!hypertension!(vasoconstriction)!followed!by!hypotension!as!it!wears!off!! ! ! ! %!pronounced!bradycardia!(due!to!sedative!effect!intense!vasoconstriction!–!!! ! ! ! !!!HR!slows!to!decrease!workload!against!vascular!resistance)!! ! ! ! ! %!+/%!1st!or!2nd!degree!heart!block!! ! ! ! ! %!reduces!CO!! ! ! ! ! %!prolonged!‘arm%brain!circulation!time’!in!combo!with!vasoconstriction!! ! ! ! %!poor!peripheral!tissue!perfusion!(due!to!vasoconstriction)!! ! ! ! %!respiratory!depression!–!larger!doses!! ! ! ! %!be!careful!not!to!overdose!induction/maintenance!agent!

–!vasoconstriction!slows!onset!of!drugs!–!don’t!give!more!too!quickly!!!%!xylazine!only!!! %!vomiting!! %!increased!mortality!risk!in!dogs!

! %!dysrhythmmias!! ! %!indications!–!premed!–!only!in!healthy!dogs!! ! ! ! ! %!can!combine!with!opiods!! ! ! !!!!!!!!!%!sedation!for!non%invasive!procedures!(eg!imaging)!

!!!!!!!!!%!analgesia!

,,,,,,,,,$,healthy,young,animals,only,!

! ! %!contraindications!–!old!animals! !! ! ! ! %!sick!animals!esp!CVS!dz!! ! ! ! %!no!xylazine!in!dogs!at!ALL,!only!medetomidine!!! ! %!duration!of!action!! ! ! %!xylazine!%!20%40!mins!! ! ! %!medetomidine!–!40%90!mins!!• Combinations!!, $,tranquilizer,+,opiod,! ! Effect!=!neuroleptanalgesia!=!hypnosis!+!analgesia!! ! Examples!–!morphine/methadone!+!ACP!! ! ! %!butorphanol!+!ACP!! ! ! %!buprenorphine!+!ACP!! ! ! %!methadonembutorphanol!+!medteomidine!! ! ! %!methadone/morphine!+!midazolam/diazepam!–!less!reliable!sedation!! ! ! ! ! ! ! ! ! %!good!for!old!debilitated!patients!! ! ! %!fentanyl!+!midazolam/diazepam!–!less!reliable!sedation!! ! ! ! ! ! ! ! %!good!for!old!debilitated!patients!!! ! !advantages!–!analgesia!AND!sedation!! ! ! ! %!improved!sedation!at!lower!dose!than!tranquilizer!alone!! ! ! ! %!improved!analgesia!! ! ! ! %!improved!recovery!! ! ! ! %!doses!adjustable!for!more/less!sedation!and!analgesia!! ! ! ! %!good!for!chemical!restraint!!! ! Disadvantages!

− Compounds!CVS!effects!eg!ACP!=!vasodilation!&!opiod!=!bradycardia!− Opiod!side!effects!

! Emesis!! Panting!! Defecation!followed!by!constipation!

!! %!dissociatives,+,benzodiazepines,! ! Examples!–!ketamine!(anaesthetic)!+!diazepam/midazolam!! ! ! %!tiletamine!+!zolzaepam!(zoletil)!!!! ! Advantages!! –!dose!dependant!sedation!+!muscle!relaxation!! ! ! ! %!analgesia!! ! ! ! %!rapid!onset!! ! ! ! %!good!for!young,!healthy,!aggressive!cat!restraint!! ! ! ! %!aggressive!dog!restraint!!! ! Disadvantages!–!increased!salivation!"!airway!obstruction!! ! ! ! %!ketamine!alone!"!rigid!muscles!+!seizures!! ! ! ! %!rough!recovery!! ! ! ! %!benzodiazepines!=!renal!elimination!of!active!form!"!renal!failure!esp!in!!old!cats!!!!! ! Contraindications!

− Dogs!other!than!aggressive/unmanageable!dogs!− Cats!w/!renal!insufficiency/renal!failure!− Cats!w/!hyperthyroidism!

!! %!pre%prepared!combinations!! ! Examples!–!BAA!–!butorphanol!+!ACP!+!atropine!! ! ! %!MAA!–!morphine/methadone!+!ACP!+!atropine!! ! ! %!BAG!–!butorphanol!+!ACP!+!glycopyrrolate!!! ! Advantages!–!mid%range!sedation!and!analgesia!! ! ! !!!!!!!!!%!anticholinergic!effects!–!prevents!autonomic!responses!! ! ! !!!!!!!!%!neuroleptanalgesia!benefits!

! ! ! !!!!!!!!!%!!analgesia!AND!sedation!! ! ! !!!!!!!!!%!improved!sedation!at!lower!dose!than!tranquilizer!alone!! ! ! !!!!!!!!!%!improved!analgesia!! ! ! !!!!!!!!!%!improved!recovery!! ! ! !!!!!!!!!%!doses!adjustable!for!more/less!sedation!and!analgesia!! ! ! !!!!!!!!!%!good!for!chemical!restraint!

! ! ! !!!!!!!!!%!ACP!=!anticholingeric!prevention!of!autonomic!reflexes!!! ! Contraindications!–!old/young/sick!patients!(ASA!>3)!! ! ! ! !!!!%!v.!painful!procedures!! !! %!premeds!for!cats!

! ! %!ASA!1!and!2!–!zoletil!+!ACP!+!butorphanol/buprenorphine/methadone!! ! ! ! %!ketamine!+!ACP!+!buprenorphine!! ! ! ! %!medetomidine!+!methadone/buprenorphine/butorphanol!! ! %!ASA!>!2!–!ACP!+!methadone/buprenorphine/butorphanol!

!summary!

− Analgesia!+!sedation!=!ok!to!use!alone!for!premed!for!painful!procedures!!o Opiods!o Alpha!2!agonists!

− Sedation!only!(no!analgesia)!–!don’t!use!alone!for!premed!for!painful!procedures!o Benzodiazipines!–!xylazine,!medetomidine!o Phenothiazines!%!ACP!

!Choosing!pre%med!!

• Analgesia!level!required!%!high!pain!level/more!invasive!procedure!=!stronger!analgesia!• Sedation!level!required!

• Temperament!of!patient!• Procedure!being!conducted!

• Patient!status!–!ASA!level!+!pre%op!SOAP!assessment!• Route!of!admin!–!crazy!animals!don’t!want!to!do!IV,!difficult!to!get!vein!in!dehydrated/fat!animals!• If!in!doubt!–!middle!of!suggested!dose!range!!

!!!!!!!!!!Route!of!admin!

• IV!–!immediate!onset,!reliable!effects!!!!!!%!rapid!peak!effect!!!!!!%!reliably!short!duration!!!!!!%!need!patient!compliance!–!no!point!man%handling!and!stressing!them!out!

!• IM!–!variably!delayed!onset!(5%30!mins!depending!on!drug)!

!!!!!!%!peak!effect!less!pronounced!than!IV!!!!!!!%!peak!effect!depends!on!%!tissue!blood!supply!! ! ! !!!!!!!!%!drug!absorption!! ! ! !!!!!!!!%!!drug!metabolism!!!!!!!%!painful!admin!!!!!!!%!prolonged!duration!of!action!!

• SQ!–!unpredictable!delayed!onset!!!!!!!%!less!pronounced!effect!than!IV!and!IM!!!!!!!%!peak!effect!depends!on!%!tissue!blood!supply!! ! ! !!!!!!!!!%!drug!absorption!! ! ! !!!!!!!!!%!!drug!metabolism!!!!!!!%!prolonged!duration!of!action!!

!

,,After!pre%med!–!leave!patient!alone!top!relax!and!let!drug!work!! ! %!keep!warm!!!!NB:!increased!mortality!risk!when!using!medetomidine!in!cats!and!BZ!+!opiod!combo!in!dogs!or!cats!! Using!ACP!in!dogs!and!cats!or!medetomidine!in!dogs!DECREASES!mortality!risk!compared!to!no!pre%med!!!!!!!!!!!!!!!

Induction,of,Anaesthesia,!Routes!!inhalation,induction,

%!administer!via!mask!or!induction!chamber!%!advantages/indications!! %!no!hepatic!or!renal!metabolism!needed!to!regain!consciousness!! ! %!good!for!hepatic/renal!insufficiency!! %!lots!of!O2!provided!during!induction!! %!great!for!really!sick!patients!or!fractious!animals!! %!“reversible”!!%!disadvantages!! %!rough!induction!%!slow!induction!! ! ! %!healthy!animals!struggle!against!mask!and!odour!! ! ! %!healthy!animals!become!initially!excitable!before!induction!! %!exposes!nurses!and!vets!to!induction!gases!

%!requires!anaesthetic!machine! !!

! Mask!induction!!! ! %!process!–!apply!well!fitting!mask!

%!administer!O2!only!–!preoxygenation!+!enable!acclimatisation!to!mask!! ! ! !%!gradually!increase!conc!of!agent!starting!at!low!setting!! ! ! ! %!start!at!1%!on!vaporiser!and!slowly!increase!by!0.5%!every!12%30!secs!! ! ! ! %!safer!! ! ! ! %!animal!less!likely!to!smell!agent!and!not!want!to!breathe!! ! ! %!continuously!check!patient!until!deep!enough!to!intubate!! ! ! %!intubate!! ! ! %!adjust!oxygen!and!vaporiser!to!suit!breathing!circuit!and!patient!! ! ! %!monitor!patient!!! ! %!agents!–!isoflurane,!sevoflurane!!

!Advantages/indications!

• little!metabolism!required!for!regaining!of!consciousness!!

o primarily!eliminated!via!pulmonary!ventilation!• Oxygen!given!with!induction!drug!• Suitable!in!severely!ill!patients!

• “Retrievable”!–!can!monitor!and!adjust!depth!easily!!Disadvantages/contraindications!

• slow!induction!• Struggling!against!mask!"stress,

o Pungent!odour!of!agent!may!cause!struggling!

• Air!pollution!and!operator!exposure!• Unsuitable!for!most!patients!• Anaesthesia!machine!required!

• Relatively!high!dose!of!anaestheic!required!to!enable!intubation!• Relatively!high!vaporizer!setting!required!for!subsequent!maintenance!of!analgesia!as!no!

parenteral!anaesthetics!present!• Only!safer!compared!to!parenteral!induction!in!moribund!patients!

!!

! Chamber!induction!!! %!mechanism!–!inlet!=!O2!and!anaesthetic!gas!! ! %!outlet!"!scavenger!tube!!!!!!!!%!process!

1. Flow!high!conc!of!inhalant!(max!vaporiser!setting)!+!O2!into!chamber!

2. Observe!patient!closely!3. Remove!from!chamber!once!anaesthetised!sufficiently!to!handle!4. Assess!anaesthetic!depth!5. Intubate!(can!increase!anaesthetic!depth!by!administering!anaesthetic!via!mask)!!

! %!advantages!–!no!patient!restraint!needed!! ! ! %!good!for!intractable!(can!NOT!handle)!small!animals!! %!disadvantages!–!rough!induction!! ! ! %!nurses!and!vets!exposed!to!anaesthetic!gases!! ! ! %!not!used!for!any!manageable!patient!!

!parenteral,induction,(IV,,IM),

IV,induction,! Advantages!

• Immediate!onset!of!action!• Peak!effects!rapid!

o Can!titrate!to!effect!• Short!duration!of!actions!as!lower!dose!required!

!Disadvantages!

• Require!IV!catheter!placement!(don’t!do!“off!the!needle”!induction)!• Need!dose!calculation!and!adjustment!

!Desirable!characteristics!of!an!agent!

%!Smooth!induction!(smoother!with!premed)!! Rapid!loss!of!consciousness!! Muscle!relaxation!! Short!duration!of!action!! Minimal!CV!depression!

!!NB:!can!use!parenteral!anaesthetic!agents!for!short!surgical!procedures!by!topping!up!animal!Common!agents!

o Thiopental!o Action!–!mimic!GABA!"!prolonged!Cl%!ion!channels!opening!o dose!=!10%15!mg/kg!after!premed!o need!venous!access!

! tissue!toxic!if!injected!outside!vein!o must!dilute!to!2.5%5%!at!time!of!admin!o admin!–!¼%!½!increments!over!10%20!secs,!wait!30!secs!and!repeat!if!needed!

! arm"brain!circulation!takes!20!secs!o Not!redistributed!into!fat,!into!muscle!o T!½!%!8!hours!!!

o Do!not!top!up!or!infuse!(long!T!½!"!accumulation)!o contraindications!!

! severe!liver!dz!(long!T!½!as!can’t!be!metabolised!by!liver)!! pre%existing!cardiac!arrhythmias!–!can!CAUSE!arrhythmias!! advanced!cardiac!dz!(heart!has!poor!contractility)!! c%section!(can!affect!foetus)!! ASA!>3!(physical!health!status)!–!want!smooth!recovery!in!these!animals,!have!many!

other!drugs!that!can!interact!w/!drug!! Emaciated!patients!–!no!muscle!for!thiopental!redistribution!(long!recovery),! Greyhounds,and,all,sight,hounds!!,–!missing!enzyme!in!liver!to!metabolise!

thiopental!so!it!accumulates!if!you!top!it!up!and!have!very!delayed!recovery!and!may!not!wake!up!at!all,

!o Alfaxalone!

o Dose!=!2%3!mg/kg!(after!premed)!o Admin!–!½!total!dose!over!slow!injection!(60!secs),!additional!¼!increments!if!needed!

%!slow!admin!avoids!overdose!as!alfaxalone!has!slow!blood%brain!equilibrium!o T!½!=!25!mins!o Contraindications!–!none!known!

!o Propofol!=!only!white!drug!given!IV!

o Dose!=!4%6!mg/kg!(after!premed)!o Mode!of!action!

o Mimics!GABA!"!prolonged!Cl%!ion!channel!opening!time!o Na!channel!blocker!

!o Made!with!many!solvents!

! Propofol!non!water%soluble,!mixed!with!oil%water!emulsion!! Can!promote!bacterial!growth!(should!use!bottle!within!24hrs!after!opening)!! Can!cause!immune!reaction!! Can!cause!pancreatitis!–!solvents!have!oils!and!fats!in!them!

!o T!½!=!30%60!mins!o Contraindications!

! Hypovolaemia!or!hypotension!–!exacerbates!hypotension!! Advanced!cardiac!dz!(heart!has!poor!contractility)!! Bradycardia!(sick!sinus!syndrome)!! Consecutive!days!in!cats!"!methaemoglobinaemia!(not!in!dogs)!! Disease!where!hypotension!is!poorly!tolerated!

!o Ketamine!+!benzodiazepines!(following!pre%med!)!

o Mode!of!action!–!NMDA!antagonist!–!Na+,!K+!and!Ca+!channel!blockers!o Dose!=!10!mg/kg!+!diazepam/midazolam!0.2%0.5!mg/kg!o Cause!rigidity!or!relaxation!o Administration!–!¼!of!ketamine!dose!followed!by!¼!or!½!dose!of!diazepam,!wait!30!secs,!!

! ! repeat!if!required!!! OR! %!¼!of!total!volume!(ketamine!+!diazepam),!wait!30!secs,!repeat!if!required!!!

o T!½!=!2%3!hours!o Effects!of!ketamine!alone!

o Unconsciousness!o Some!analgesia!o Poor!muscle!relaxation!–!muscle!rigidity!o Rough!recovery!if!used!alone!due!to!hallucinogenic!effects!

o Contraindications!(less!important!if!used!with!diazepam)!! ↑!intraocular!pressure!(causes!↑!CNS!activity!and!↑!intracranial!pressure)!! ↑!intracranial!pressure!! Seizuring!animals!–!any!anaesthetic!induction!agent!can!cause!CNS!

abnormalities!eg!seizures!! Cats!with!renal!dz!or!urinary!obstruction!

! Cats!eliminate!Ketamine!as!active!metabolite!through!kidney!! Dogs!do!NOT,!they!metabolise!it!to!inactive!form!

! C%section!! Heart!Dz!–!Ketamine!increases!HR!and!contractility!

! %!esp!HCM!or!other!dz’s!with!high!sympathetic!tone!already!! Do!not!top!up!or!infuse!(long!T!½!"!accumulation)!

!Considerations!to!choosing!safe!induction!agent!

• Mortality!rate!for!that!drug!o Highest!in!mask!induction!

!• Adverse!effects!in!cardiopulmonary!system!

o All!induction!drugs!!! decrease!blood!oxygenation!(due!to!resp!depression)!! apnoea!possible!! increase!HR!and!therefore!CO!(CO!=!HR!x!SV)!! can!cause!cardiac!dysrhythmias!(unknown!whether!alfaxolone!does!this)!! adverse!effects!are!dose!dependant!

• minimise!dose!by!using!premed!and!doing!a!SLOW!step%wise!injection!so!you!don’t!overdose!

• dose!and!speed!of!admin!determine!strength!of!cardiopulmonary!effects!• decrease!O2!and!increaseCO2!!

o Ketamine!(a!LOT!)!and!Thiopental!increase!BP!o Propofol!and!alfaxolone!cause!vasodilation!"!decreases!BP!o Minimise!cardiopulmonary!effects!of!induction!agents!when!used!as!premed!

!• Speed!of!elimination!

• Rapid!elimination!=!better!recovery!• Cumulative!drugs!=!poor!recovery!if!topped!up!during!surgery!or!induction!dose!too!large!

!• Toxic!dose!

!• Therapeutic!index!=!LD50/AD50!(anaesthetic!dose!in!50%!of!animals)!

o ↑TI!=!safer!o Alfaxalone!>!ketamine!>!propofol!>!thiopental!

!• Recovery!

o Smooth!vs!rough!(quality)!o Quick!vs!slow!o Propofol!=!fastest!and!best!quality!recovery!in!small!animals!o Ketamine!and!alfaxolone!=!fast!recovery!with!poor!quality!o Thiopental!=!slow!recovery!with!poor!quality!o Horses!–!v.!important!as!can!injure!themselves!

! Ketamine!most!popular!choice!as!has!a!good!recovery!in!horses!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!Redistribution!"equilibration"!eventual!elimination!!!!!!!!!!!!!!!!!!

! At!time!of!recovery!most!of!anaesthetic!agent!is!still!stored!in!muscle!! Recovery!due!to!redistribution!and!metabolism!"!elimination!! Initial!recovery!due!to!redistribution!later!follow!by!elimination!

!Half,life,,

• Alfaxalone!(25!mins)!<!propofol!(30%60!mins)!<!ketamine!(2%3!hrs)!<!thiopental!(8!hrs)!• Determines!time!of!complete!recovery!

! Short!T!½!=!short!time!to!complete!recovery!! NOT!time!to!regaining!consciousness!

• This!is!similar!between!all!anaesthetics!• Redistribution!and!metabolism!remove!anaesthetic!from!CNS!so!animal!wakes!up!• Animal!can!be!awake!but!have!high!levels!of!drug!in!its!body!–!ie!not!complete!recovery!!

• Determines!slope!of!metabolic!curve!(steeper!w/!short!T!½)!• Determines!amount!of!drug!still!in!body!at!time!of!regaining!consciousness!• Anaesthetics!with!long!T1/2!are!not!suitable!for!continuous!top!up!or!infusion!

! thiopentone!accumulates!and!has!VERY!slow!recovery!! Propofol!has!v!short!T1/2!so!can!top!up!or!infuse!

!!Price,–!alfaxolone!>!propofol!>!ketamine!>!thiopental!

!Maximising,anaesthetic,induction,safety,

• premeds!–!ACP!–!reduces!negative!!cardiopulmonary!effects!far!more!than!medetomidine!! ! %!enables!lower!dose!of!induction!agent!

• calculate!dose!(don’t!just!have!a!stab)!• check!patient!immediately!prior!to!induction!(subjective!and!objective!assessment!of!premed)!

• correct!bradycardia!if!using!propfol!or!alfaxalone!• correct!pulse!quality!by!administering!10!ml/kg!fluids!IV!rapidly!

• pre%oxygenate!administer!O2!via!mask!• creates!oxygen!reservoir!to!delay!onset!of!hypoxaemia!due!to!apnoea/intubation!problems!• induction!not!as!rushed!to!get!to!intubation!• all!agents!can!cause!hypoventilation!

• administer!via!IV!catheter!• slow!injection!–!enables!lower!dose!as!you!can!correctly!estimate!depth!of!anaesthesia!

!Choosing!induction!agents!based!on:!

! Safety!–!CVS!stability,!high!TI,!non!non%drug!related!adverse!effects!o ketamine,!propofol,!alfaxolone,!thiopental!

! quick!and!smooth!recovery!o !propofol!

! patient!type!o ASA!physical!status!1!&!2!–!any!anaesthetic!agent!o ASA!physical!status!3!&!4!%!alfaxolone!and!propofol!(short!T!½!and!good!recovery)!

! Do!NOT!use!thiopental!or!ketamine!! Cost!–!thiopental!&!ketamine!+!diazepam!

!,,,,,,,,,IM,induction,! No!premed!given!usually!! Advantages!–!no!venous!access!needed!–!if!veins!can’t!be!found!(fat!or!very!small)!! ! ! ! ! ! %!v.!difficult!animals!! ! ! ! ! ! %!v.!Small!animals!! Disadvantages!–!slow!onset!! ! ! ! %!titration!to!effect!is!difficult!

! ! ! ! %!overdosing!or!underdosing!v.!easy!as!you!may!think!you!didn’t!give!enough!! ! ! %!effects!less!predictable!–!fat!animals!have!variable!uptake!and!distribution!!! ! ! ! !! ! !!!%!peak!effects!depend!on!–!tissue!blood!supply!! ! ! ! ! ! ! ! ! !!!!!!%!drug!absorption!and!metabolism! !! ! ! %!prolonged!recovery!!!! Dosing!–!must!give!2!X!IV!dose!!! IM!Agents!%!ketamine!+!BZ!! ! ! %!diazepam!v.!poorly!absorbed.!Unpredictable!IM,!don’t!give!S/c!! ! ! %!midazolam!=!water!soluble!"!much!better!! ! %!alfaxalone!! ! %!don’t!use!propofol!! ! %!can’t!given!thiopental!any!way!but!IV!!!!! IM!protocols!in!CATS!

• ACP!+!ketamine!!• Diazepam!+!ketamine!!• Midazolam!+!ketamine!• Zoletil!!• Medetomiding!+!ketamine!!

! IM!protocols!in!DOGS!(much!less!common!• Zoletil!

Anesthetic,maintenance,!Methods,

! Top!up!induction!agent!–!less!smooth!! Inhalational!gases!

!o ET!tube!

! Advantages!• Secure!patent!airway!!• Minimum!pollution!of!gases!–!inspired!by!nurses!and!vets!• Protection!of!airway!–!minimal!risk!of!aspiration!• Minimum!dead!space!(equipment!dead!space!and!anatomical!dead!space)!

! ! %!dead!space!=!inhaled!and!exhaled!air!is!mixed!!• Artificial!ventilation!easily!possible!(squeeze!bag)!• Reduced!airway!resistance!%!easier!through!tube!than!through!nose!

! ! ! ! %!much,less,work,involved,in,respiration!for!the!animal,,,

! Features!!–!cuff!(balloon)!–!seals!airway!!! %!!PVC!=!better!as!has!high%volume!low!pressure!in!balloon!!! %!rubber!–!inflexible,!becomes!brittle!and!has!low!volume,!high!pressure!in!balloon!!! %!diameter!and!length!indicated!on!side!!! %!murphy’s!eye!–!part!where!air!travels!through!!! %!pilot!balloon!–!had!one!way!valve!!! ! ! %!enable!inflation!and!deflation!of!cuff!with!syringe!!

!!

• Placement!o Knowledge!of!anatomy!of!larynx!o Choose!correct!size!and!length!–!tip!of!nose!to!point!of!shoulder!

! ! ! ! %!ET!adapter!just!infront!of!incisors!(not!inside!mouth!)!! ! ! ! %!ET!cuff!just!caudal!to!larynx!and!cranial!to!thoracic!inlet!! ! ! ! %!palpate!trachea!for!estimation!of!ET!diameter!! ! ! ! %!too!long!=!more!dead!space!=!rebreathing!of!CO2!

o Adequate!anaesthetic!depth!o Patient!in!sternal!recumbency!with!assistant!to!position!correctly!o Proper!laryngeal!visualisation!%!Laryngoscope!enables!abnormality!identification!and!!

! ! ! ! correct!positioning!!! ! ! ! %!should!not!go!into!larynx!!!! ! ! ! %!push!tip!of!scope!downwards!onto!base!on!tongue!to!!! ! ! ! depress!epiglottis!!!!

o Unforced!ET!placement!! ! %!curve!of!tube!pointing!ventrally!! ! %!sit!between!vocal!cords!and!gently!manouveure!like!a!cork%screw!

%!slowly!rotate!ET!tube!in!ONE!DIRECTION!ONLY!–!not!back!and!forth!!!%!causes!for!difficult!placement!! ! %!inadequate!anaesthetic!depth!! ! %!ET!tube!size!too!big!! ! %!animal!not!positioned!properly!by!assistant!

! ! %!cats!more!difficult!–!everything’s!smaller!! ! ! ! !!!!!!!!%!larynx!further!back!in!oral!cavity!! ! ! ! !!!!!!!!%!sensitive!larynx!"!layngospasm!unless!local!anaesthetic!!

!!!!!!!!used!(0.2!ml!of!lignocaine)!o Proper!cuff!inflation!

! Too!much!=!tracheal!damage%!pressure!on!tracheal!mucosa!compromises!!vascular!supply!!and!causes!mucosal!necrosis!!

! ! ! ! %!can!rupture!trachea!esp!in!cats!! Too!little!=!anaesthetic!gases!and!oxygen!escape!!! Process! %!connect!ET!tube!to!breathing!circuit!with!vaporiser!off!but!O2!on!

%!close!relief!valve!! ! %!assistant!squeezes!rebreathing!bag!to!20!cm!H20!for!2!secs!! ! %!listen!for!air!escaping!from!patients!lungs!! ! %!assistant!squeezes!bag!you!inflate!cuff!slowly!! ! %!inflate!until!no!air!is!escaping!! ! %!start!vapouriser!