Genetic differences and

anatomic factors can

contribute to variability

and complications during

anesthetic events.

Certain breed differences can lead to greater risksfor airway obstruction, increased responsiveness toanesthetic drugs, and delayed recovery, all of which

can result in increased anesthesia-related morbidity andmortality. Individual genetic variability can trigger unex-pected and adverse responses to anesthetic drugs, whichneed to be identified by good recordkeeping and consis-tent patient monitoring. Although genetic differences aretypically held responsible for prolonged recoveries andincreased drug responsiveness, true genetic sensitivity hasbeen demonstrated in only a handful of breeds, includingthe greyhound and the collie.

Because many canine breeds can suffer from cardiacdisease, both acquired and congenital, it is importantto know which patients are likely to be affected beforethe anesthetic protocol is planned. If cardiac disease issuspected, a full cardiac workup with a veterinary cardi-ologist is recommended.

C o m p l i c a t i o n s A N E S T H E S I O L O G Y

Peer Reviewed

C o N t i N u e s

Stephanie Krein, DVM, &

Lois A. Wetmore, DVM, ScD, DACVA

Tufts University

Breed-specificAnesthesia

Complications / NAVC Clinician’s Brief / March 2012 ...........................................................................................................................................................................1�

Safe andsuccessfulsedation andanesthesia canbe performedin any breed ofdog or cat withproper preoper-ative workupand appropriatepatientmonitoring.

For breed-specific anesthesia ata glance, see the Checklist onpage 20.

Comp l i c a t i o n s CONT INUED

BRACHYCEPHALIC BREEDSBrachycephalic breeds have anatomic considerations thatmay affect anesthetic outcome. Most brachycephalic breedssuffer from brachycephalic airway syndrome (BAS), which ischaracterized by stenotic nares, elongated soft palate, evertedlaryngeal saccules, and hypoplastic trachea.

Affected dogs have narrower upperairways than do dogs with normalanatomic features.1-3 Because inbrachycephalic breeds additionalairway contraction can occur withstress (ie, increased respiratoryeffort, turbulent flow), cliniciansneed to be prepared for possibleupper airway obstruction. Further-

more, brachycephalic dogs must be monitored closely afterpremedication, throughout anesthesia and the postoperativeperiod, and after extubation. An oxygen source and endotra-cheal tube should be readily available.

Many brachycephalic dogs respond well to acepromazinein conjunction with an opioid; however, the sedative doseshould be half of that used for nonbrachycephalic dogs. Fullmu-opioid agonists can be used but because they may causeexcessive respiratory depression, a reversal agent should beavailable. Dexmedetomidine should be avoided because ofthe presence of high vagal tone in these breeds. Anticholin-ergics, such as glycopyrrolate, may be used to decrease airwaysecretions and counteract high vagal tone.

Preoxygenation is recommended before dogs with BAS areinduced.2-4 Propofol or a similar short-acting drug should beused for induction and intubation should be completed asrapidly as possible. Mask inductions should be avoided,3,4

and smaller endotracheal tubes should be used.

Because brachycephalic breeds tend toward obesity, controlledor mechanical ventilation is often necessary. Most problemsassociated with mechanical ventilation occur during induc-tion and recovery, so monitoring is particularly important.

Extubation should be postponed until the patient is bright,alert, swallowing—even chewing on the endotracheal tube.4

If extubation is attempted while the patient is sedated andgroggy from anesthesia, there is increased risk for upperairway obstruction. If upper airway obstruction occurs, thepatient should be reintubated.

Brachycephalic cats should be handled with care from pre-medication to recovery and treated in a manner similar to dogs.

SIGHTHOUNDSMost breeds do nothave true sensitivitiesto anesthestics,although sighthounds(particularly the grey-hound) do havegenetic factors thatcause them to metab-olize drugs differently. Therefore, before designing an anes-thetic protocol, examination findings and blood work resultsneed to be evaluated. Sighthounds have a higher packed cellvolume and lower serum albumin concentration than domixed breeds.2,3 Sighthounds also should be evaluated forcardiac abnormalities (eg, dilated cardiomyopathy).

Because sighthounds are high-energy animals, they may expe-rience high levels of hospitalization stress. Acepromazine isrecommended for preventing stress in healthy sighthounds,but some individuals may be more sensitive to its sedativeeffects, so a lower dose (0.02–0.03 mg/kg) is advised.4,5 Inaddition, sighthounds metabolize drugs more slowly as com-pared with the average dog. Thiobarbiturates should beavoided and other induction agents (eg, propofol, ketamine,etomidate) used instead.1-3 Of note, propofol is metabolizedmore slowly in these dogs because of reduced hepatic enzy-matic activity, which may result in slower recovery.4,6,7

Sighthounds have a low percentage of body fat (17%) com-pared with the average dog (35%),6 which leaves them at riskfor hypothermia during anesthetic procedures.2,3,6 Therefore, itis important to use hot water blankets and forced-air warmersduring the perioperative period.

BAs = brachycephalic airway syndrome

Boxers of UK LineageOn rare occasions, individualvariability can result in a sub-population within a breedthat responds differently toanesthetics. An example canbe seen in boxers from theUK. In this subpopulation,acepromazine often causessevere bradycardia, hypoten-sion, and collapse, so areduced dose of acepro-

mazine (0.01–0.025 mg/kg) is recommended.2,4

Because there are no published reports describing simi-lar effects in US-bred boxers, standard doses of acepro-mazine are typically routine in the US subpopulation.

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HERDING BREEDSThe effect of certain anestheticdrugs on herding dogs (eg,collie, border collie, Australianshepherd, Shetland sheepdog)is somewhat controversial.However, these breeds have ahigh prevalence (eg, up to 75%in collies in the United States)for genetic mutation in theABCB1 (formerlyMDR1)gene.8,9 ABCB1 encodesP-glycoprotein, an adenosinetriphosphate–driven pumpthat is an integral componentof the blood–brain barrier andprovides protection from toxicdrug accumulation in body flu-ids, such as cerebrospinal fluid(CSF).10 In the collie andother herding breeds, thisgenetic mutation results in adefective pump that allows aselect group of drugs to accu-mulate within the brain.Acepromazine and opioids,particularly butorphanol,9 aremembers of this drug group,and their accumulation in CSFmay cause marked sedationand respiratory depression.When using these agents insusceptible breeds, the doseshould be decreased by 25%and patients closely monitoredfor side effects.5,9

TOY BREEDSBecause of their size,toy breeds can presentunique challenges.Obtaining an accurateweight and using theappropriate dose ofanesthetic drug areessential. Monitoring

during surgery likewise is important. In smallpatients, Doppler blood pressure measurementhas been more accurate than oscillometric mon-itoring; in addition, it provides an auditorysound to monitor heart rate and rhythm.

Toy breeds have a greater body surface area–to–body mass ratio and higher metabolic rate,which can lead to lower body temperatures andhypoglycemia.1 It is important to support nor-mal body temperature during anesthesia, moni-tor blood glucose levels, and apply adequatesupplementation as indicated.3

GIANT BREEDSGiant breeds often respond profoundlyto normal therapeutic doses of seda-tives, such as acepromazine. In thispatient population, it is important toeither reduce the dose of acepromazine(0.01–0.025 mg/kg) or calculate thedose based on lean body mass or surfacearea and not the actual body weight.2,3

DOBERMAN PINSCHERGenetic variation is also noted in Doberman pinschers. In additionto a predilection for developing dilated cardiomyopathy, these dogscan have von Willebrand disease, which impairs normal clotting. Itis important to evaluate the coagulation status of these patientsbefore surgery.

If von Willebrand disease is suspected, desmopressin (also knownas DDAVP) given before surgery promotes von Willebrand factorsecretion from endothelial storage sites.3

In this patient population, the use of NSAIDs is somewhat controversial and other anal-gesic options should be explored. If NSAIDs must be administered, preference shouldbe given to cyclooxygenase (COX)-2–selective drugs.

CLOSING REMARKSAlthough it is important to be aware of breed-related anesthetic differences, the primaryconsideration is the individual patient and tailoring the anesthetic protocol accordingly.With proper perioperative workup and appropriate patient monitoring, safe and successfulsedation and anesthesia can be performed in any breed of dog or cat. Patient monitoringshould begin with premedication and end only after the patient has been extubated and isnormothermic, stable, and alert.

See Aids & Resources, back page, for references & suggested reading.

CsF = cerebrospinal fluid, CoX = cyclooxygenase

Complications / NAVC Clinician’s Brief / March 2012 ...........................................................................................................................................................................1�

C o N t i N u e s

Comp l i c a t i o n s C O N T I N U E D

Classification Problem Checklist of Actions

CHECKLIST Anesthesia-Related Problems by Breed

BRACHYCEPHALIC BREEDS(eg, bulldog, pug, Boston terrier,boxer, Cavalier King Charlesspaniel, Pekingese)

SIGHTHOUNDS (eg, greyhound,whippet, Italian greyhound,Afghan hound, Borzoi, Irishwolfhound, Saluki)

HERDING BREEDS (eg, collie,Shetland sheepdog, Australianshepherd, border collie)

TOY BREEDS (eg, shih tzu,Pomeranian, Chihuahua,Pekingese, Brussels griffon, toyfox terrier, Affenpinscher)

GIANT BREEDS (eg, Newfound-land, Great Pyrenees, SaintBernard)

DOBERMAN PINSCHER

BOXER of UK lineage only

Brachycephalic airway syndrome; increasedrespiratory effort; potential for upper air-way obstruction

Delayed metabolism, increased responsive-ness to acepromazine; possible delayedrecovery from propofol; lower body fatpercentage; hypothermia; high-stresshyperthermia

ABCB1 mutation causes defect in P-glyco-protein pump, resulting in accumulation ofcertain drugs in CSF, followed by excessivesedation/respiratory depression

Hypothermia from large body surface arearelative to body size; difficulty monitoring;hypoglycemia

Profound response to sedatives

Predilection for dilated cardiomyopathy,von Willebrand disease

Acepromazine-induced vagal response;marked hypotension, bradycardia; boxercardiomyopathy

� Avoid excessive sedation� Avoid α2-agonists� Administer acepromazine at half dose� Preoxygenate� Use short-acting induction agent� Use appropriately sized endotracheal tubes� Extubate after patient is sitting up, vigorously

chewing, bright, alert

� Use low-dose acepromazine (0.02–0.03 mg/kg)� Administer propofol slowly, only to effect� Avoid thiopental & barbiturates� Avoid patient contact with cold tables� Use forced-air warmers, hot water blankets as

needed� Treat stress/pain-induced hyperthermia with

anxiolytics, whole-body cooling, analgesics

� Reduce butorphanol dose by 25%� Reduce acepromazine dose by 25%� Monitor carefully after sedationNote: Morphine not proven P-glycoprotein substrate, butdose may need to be reduced

� Use forced-air warmers, hot water blankets, warm IVfluids, warm fluid bags around breathing tubes asneeded

� Avoid patient contact with cold tables� Perform intraoperative Doppler imaging, along with

routine monitoring (ECG, pulse oximetry, temperature)� Monitor blood glucose concentration; supplement as

needed

� Administer acepromazine or α2-agonists at half dose� Dose IM drugs based on lean body mass

� Evaluate coagulation status� If von Willebrand disease suspected, administer

desmopressinNote: NSAID use controversial (if necessary, give COX-2–selective drug)

� Reduce acepromazine dose (0.01–0.025 mg/kg); avoidα2-agonists

� Use anticholinergic drug with acepromazine unlessheart disease present

� Give IV fluids, supportive care

20 ...........................................................................................................................................................................NAVC Clinician’s Brief / March 2012 / Complications

CsF = cerebrospinal fluid, CoX = cyclooxygenase