Stephanie Krein, DVM, & Complications ANESTHESIOLOGY Lois A. Wetmore, DVM, ScD, DACVA Tufts University Peer Reviewed Breed-specific Anesthesia Genetic differences and ertain breed differences can lead to greater risks for airway obstruction, increased responsiveness to Safe and anatomic factors can Canesthetic drugs, and delayed recovery, all of which can result in increased anesthesia-related morbidity and successful contribute to variability mortality. Individual genetic variability can trigger unex - sedation and pected and adverse responses to anesthetic drugs, which anesthesia can and complications during need to be identified by good recordkeeping and consis - tent patient monitoring. Although genetic differences are be performed anesthetic events. typically held responsible for prolonged recoveries and in any breed of increased drug responsiveness, true genetic sensitivity has dog or cat with been demonstrated in only a handful of breeds, including the greyhound and the collie. proper preoper- ative workup Because many canine breeds can suffer from cardiac and appropriate disease, both acquired and congenital, it is important patient to know which patients are likely to be affected before the anesthetic protocol is planned. If cardiac disease is monitoring. For breed-specific anesthesia at suspected, a full cardiac workup with a veterinary cardi- a glance, see the Checklist on ologist is recommended. page 20. CoNtiNues Complications / NAVC Clinician’s Brief / March 2012 ........................................................................................................................................................................... 1 Complications CONTINUED BRACHYCEPHALIC BREEDS SIGHTHOUNDS Brachycephalic breeds have anatomic considerations that Most breeds do not may affect anesthetic outcome. Most brachycephalic breeds have true sensitivities suffer from brachycephalic airway syndrome (BAS), which is to anesthestics, characterized by stenotic nares, elongated soft palate, everted although sighthounds laryngeal saccules, and hypoplastic trachea. (particularly the grey - hound) do have Affected dogs have narrower upper genetic factors that airways than do dogs with normal cause them to metab - anatomic features. 1-3 Because in olize drugs differently. Therefore, before designing an anes - brachycephalic breeds additional thetic protocol, examination findings and blood work results airway contraction can occur with need to be evaluated. Sighthounds have a higher packed cell stress (ie, increased respiratory volume and lower serum albumin concentration than do effort, turbulent flow), clinicians mixed breeds. 2,3 Sighthounds also should be evaluated for need to be prepared for possible cardiac abnormalities (eg, dilated cardiomyopathy). upper airway obstruction. Further - more, brachycephalic dogs must be monitored closely after Because sighthounds are high-energy animals, they may expe - premedication, throughout anesthesia and the postoperative rience high levels of hospitalization stress. Acepromazine is period, and after extubation. An oxygen source and endotra - recommended for preventing stress in healthy sighthounds, cheal tube should be readily available. but some individuals may be more sensitive to its sedative effects, so a lower dose (0.02–0.03 mg/kg) is advised. 4,5 In Many brachycephalic dogs respond well to acepromazine addition, sighthounds metabolize drugs more slowly as com - in conjunction with an opioid; however, the sedative dose pared with the average dog. Thiobarbiturates should be should be half of that used for nonbrachycephalic dogs. Full avoided and other induction agents (eg, propofol, ketamine, mu-opioid agonists can be used but because they may cause etomidate) used instead. 1-3 Of note, propofol is metabolized excessive respiratory depression, a reversal agent should be more slowly in these dogs because of reduced hepatic enzy - available. Dexmedetomidine should be avoided because of matic activity, which may result in slower recovery. 4,6,7 the presence of high vagal tone in these breeds. Anticholin - ergics, such as glycopyrrolate, may be used to decrease airway Sighthounds have a low percentage of body fat (17%) com - secretions and counteract high vagal tone. pared with the average dog (35%), 6 which leaves them at risk for hypothermia during anesthetic procedures. 2,3,6 Therefore, it Preoxygenation is recommended before dogs with BAS are is important to use hot water blankets and forced-air warmers induced. 2-4 Propofol or a similar short-acting drug should be during the perioperative period. used for induction and intubation should be completed as rapidly as possible. Mask inductions should be avoided, 3,4 and smaller endotracheal tubes should be used. Boxers of UK Lineage Because brachycephalic breeds tend toward obesity, controlled On rare occasions, individual or mechanical ventilation is often necessary. Most problems variability can result in a sub - associated with mechanical ventilation occur during induc - population within a breed tion and recovery, so monitoring is particularly important. that responds differently to anesthetics. An example can Extubation should be postponed until the patient is bright, be seen in boxers from the alert, swallowing—even chewing on the endotracheal tube. 4 UK. In this subpopulation, If extubation is attempted while the patient is sedated and acepromazine often causes groggy from anesthesia, there is increased risk for upper severe bradycardia, hypoten - airway obstruction. If upper airway obstruction occurs, the sion, and collapse, so a patient should be reintubated. reduced dose of acepro - mazine (0.01 –0.025 mg/kg) is recommended. 2,4 Brachycephalic cats should be handled with care from pre - Because there are no published reports describing simi - medication to recovery and treated in a manner similar to dogs. lar effects in US-bred boxers, standard doses of acepro - mazine are typically routine in the US subpopulation. BAs = brachycephalic airway syndrome 1 ........................................................................................................................................................................... NAVC Clinician’s Brief / March 2012 / Complications HERDING BREEDS TOY BREEDS The effect of certain anesthetic Because of their size, drugs on herding dogs (eg, toy breeds can present collie, border collie, Australian unique challenges. shepherd, Shetland sheepdog) Obtaining an accurate is somewhat controversial. weight and using the However, these breeds have a appropriate dose of high prevalence (eg, up to 75% anesthetic drug are in collies in the United States) essential. Monitoring for genetic mutation in the during surgery likewise is important. In small ABCB1 (formerly MDR1 ) patients, Doppler blood pressure measurement gene. 8,9 ABCB1 encodes has been more accurate than oscillometric mon - P-glycoprotein, an adenosine itoring; in addition, it provides an auditory triphosphate–driven pump sound to monitor heart rate and rhythm. that is an integral component of the blood –brain barrier and Toy breeds have a greater body surface area– GIANT BREEDS provides protection from toxic to–body mass ratio and higher metabolic rate, Giant breeds often respond profoundly drug accumulation in body flu - which can lead to lower body temperatures and to normal therapeutic doses of seda - ids, such as cerebrospinal fluid hypoglycemia. 1 It is important to support nor - tives, such as acepromazine. In this (CSF). 10 In the collie and mal body temperature during anesthesia, moni - patient population, it is important to other herding breeds, this tor blood glucose levels, and apply adequate either reduce the dose of acepromazine genetic mutation results in a supplementation as indicated. 3 (0.01–0.025 mg/kg) or calculate the defective pump that allows a dose based on lean body mass or surface select group of drugs to accu - area and not the actual body weight. 2,3 mulate within the brain. Acepromazine and opioids, 9 particularly butorphanol, are DOBERMAN PINSCHER members of this drug group, Genetic variation is also noted in Doberman pinschers. In addition and their accumulation in CSF to a predilection for developing dilated cardiomyopathy, these dogs may cause marked sedation can have von Willebrand disease, which impairs normal clotting. It and respiratory depression. is important to evaluate the coagulation status of these patients When using these agents in before surgery. susceptible breeds, the dose should be decreased by 25% If von Willebrand disease is suspected, desmopressin (also known and patients closely monitored as DDAVP) given before surgery promotes von Willebrand factor for side effects. 5,9 secretion 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 should be given to cyclooxygenase (COX)-2–selective drugs. CLOSING REMARKS Although it is important to be aware of breed-related anesthetic differences, the primary consideration is the individual patient and tailoring the anesthetic protocol accordingly. With proper perioperative workup and appropriate patient monitoring, safe and successful sedation and anesthesia can be performed in any breed of dog or cat. Patient monitoring should begin with premedication and end only after the patient has been extubated and is normothermic, stable, and alert. CoNtiNues See Aids & Resources , back page, for references