sign in sign up
<<
Home , Azawakh, Basenji, Conformation (dog), Cur, Dog breed, Greyhound

Anesthesia of the

Michael H. Court

most obvious common feature of these , however, is their The s~ghthounds are an ancient group of that have been selectively bred for high-speed pursuit of prey by sight. exaggerated anatomical and physiological adaptations to high- Probably as a consequence of this selection process, these dogs speed locomotion, including lean body mass, prominent mus- have a number of idiosyncrasies that can potentially adversely culature, long limbs, and deep thorax. Today these dogs are affect their anesthetic management. These include (1) nervous bred to be racers (primarily ), lure coursers, show demeanor which can lead to stress-induced clinical complicattons, dogs, agthty dogs, obedmnce dogs, and family . Retired such as hyperthermia; (2) lean body with high racers are becoming popular as pets through the surface-area-to-volume ratto, which predisposes these dogs to efforts of local adoption agencies. All of the common, and some hypothermia dunng anesthesta; (3) hematological differences of the rarer, sighthound breeds are illustrated m Fig 1. At such as a higher packed cell volume and lower serum protein present, classification of a dog as a sighthound by either compared w~th other dog breeds which may complicate breed clubs or encyclopedias is purely subjective, based on body interpretation of preanesthetic blood work; (4) Impaired conformation similarities and current, or former, breed purpose. 3 In b~otransformation of drugs by the liver resulting m prolonged recovery from certain intravenous anesthetics, especially the near future it may be possible to more rationally group these thiopental; and increased risks of drug interactions. Safe dog breeds based on genetic relatedness (see Fig 2).4 anesthetic management of should include sedative premed~cation and appropriate use of analgesic drugs to minimize perioperative stress. Thiopental, or any other thiobarbiturate, Sighthound Idiosyncrasies and Anesthesia should not be used m these dogs. Propofol, ketamine/dtazepam A number of the idiosyncrasies of sighthounds are relevant to combinatton, and methohexital are recommended alternative intravenous anesthetics. Avoid coadministration of agents that their successful anesthenc management (Table 1) inh~bit drug biotransformatton, such as chloramphenicol. D~sposition. Much like the hot-blooded thoroughbred race- Inhalation anesthesia using isoflurane is the preferred anesthetic horse, many sighthounds are predisposed to a nervous de- maintenance technique. Core body temperature should be meanor and are at higher risk of developing stress-related monitored closely and techniques to minimize hypothermia should clinical complications, such as gastrointestinal upset and be employed both during anesthesia and into the recovery period. hyperthermia. Other contributing factors to hyperthermia Copyright © 1999 by W.B. Saunders Company include elevated environmental temperatures and post- traumatic (including postsurgical) pain. In contrast to mahg- nant hyperthermia, a rare genenc disease of muscle (see later), he sighthounds are thought to be one of the original stress-induced hyperthermia, although life-threatening, re- T groups of dogs to be selectively bred by man.1 Probably as sponds well to whole-body coohng and appropriate administra- a direct consequence, these dogs have a number of anatomical tion of sedatives and analgesics. To prevent stress-induced and physiological idiosyncrasms, which can adversely impact complications, sedative premedicants and, when indicated, anesthetic management. 2 For this reason, owners of sight- analgesic drugs are highly recommended adjuncts to anesthe- are often reluctant to allow thmr dogs to undergo sia m these ammals. routme clinical procedures that revolve general anesthesm. The On the other hand, racing greyhounds tend to be more purpose of this review is to outline the unusual characteristics comfortable than dogs in a kennel environment. The of this fascinating group of dogs and suggest appropriate tendency of these animals to sleep for long periods in the modifications of currently used anesthetic techniques to en- hospital should not be confused with depressed behavior. sure safe and effective anesthesia. Body Conformation. Compared with many other dog breeds, sighthounds are inherently lean animals with a low body-fat-to- What is a Sighthound? muscle ratio. For instance, greyhounds have been shown to average just 17% of bodyweight as fat compared with 35% in Sighthounds (aka, gazehounds, windhounds) were originally mixed-breed dogs? Although low body fat content is desirable bred to hunt prey primarily by sight, as opposed to scent. The in an athlete, it makes these animals much more susceptible to hypothermia especially during anesthesm when thermoregulatory mechanisms are suppressed. The short, thin coat of breeds like the From the Department of Pharmacology and Experimental Therapeuttcs, greyhound and , and the relatively high body-surface-area- Sackler School of Graduate Biomedical Sciences, Tufts Unlverstty, Bos- ton, MA, and the Department of Clinical Sctences, Tufts UniversW School to-volume ratio of slghthounds, can also exacerbate this effect. of Veterinary Medicine, North Grafton, MA. Hematological Differences. Sighthounds tend to have higher Supported by NIH grant K01-RR-00104. packed-cell volumes (typically 50% to 60%) and red blood cell Address reprint requests to Mtchael H. Court, BVSc, DACVA, Depart- indices, and lower serum protein (>6.5 mg/dL) and albumin ment of Pharmacology and Expenmental Therapeutics, M & V 217, 136 concentrations compared with other breeds. 67 These differ- Harrison Avenue, Boston, MA 02111. Copyright © 1999 by W.B. Saunders Company ences are seen in both fit and untrained animals and probably 1071-0949/99/1401-0005510.00/0 represent genetic adaptations to exercise: increased oxygen-

38 ClimcalTechniques in SmallAnimalPracbce,Vo114, No 1 (February), 1999: pp 38-43 avoided in affected animals because urinary concentrating Propofol Metabolism by Liver ability is likely to be compromised. 10 Control~ctivity 9 How Can You Safely Anesthetize a Sighthound?

8 Based on the preceding discussion, examples of anesthetic X protocols that have been successfully used by this author in e- 7 X sighthounds undergoing a variety of procedures are given in E Table 2. CD 6 Sedative premedication with a drug such as acepromazine is E 5 highly recommended to reduce perioperative stress particu- o larly in animals with a nervous temperament. Minimal dosages 0 4 X X (<0.1 mg/kg body weight), however, should be used since e-E + chloramphenieol sighthounds appear to be more sensitive than other breeds, and 3 X X because acepromazine can exacerbate hypothermia. For a similar reason (stress reduction), analgesic medications should 2 X X X X be given to animals before undergoing procedures that are X 1 × likely to be painful. Thiobarbiturates should not be used for anesthetic induc- 0 tion in sighthounds for reasons described previously. Recom- ^b ..,e ^b _b ..,e ^b mended alternatives include propofol, ketamine (with diaz- epam), and methohexltal. These agents appear to be metabolized more slowly in greyhounds but nevertheless result in acceptable recoveries. Oxymorphone, hydromorphone, fen- tanyl, and etomidate are also useful for anesthetic induction, Fig 3. Breed-related differences in liver metabolism of propo- especially in animals with cardiac dysfunction, but are gener- fol and the inhibitory effect of chloramphenicol (data from ally less widely available because of expense or substance this laboratory). High-pressure liquid chromatography was abuse potential. TELAZOL (tiletamine/zolazepam mixture) is used to measure the rate of in vitro biotransformation of not recommended for use in slghthounds because of the propofol to its major metabolite (4OH-propofol) by liver microsomes from male mixed-breed, , and greyhound propensity for poor anesthetic recoveries. Inhalant anesthetic dogs (5 each) in an NADPH-regenerating incubation system. induction is a safe alternative to intravenous induction in compromised animals provided animals are sufficiently se- "porcine stress syndrome," is caused by dysfunction of the dated, or otherwise obtunded by their disease state, to avoid skeletal muscle calcium release channel probably as a result of struggling during mask application. for highly muscled animals. 14 It is therefore In most instances, animals should be intubated and anesthe- not surprising that this syndrome has been reported in sia maintained by inhalation of either halothane or isoflurane. greyhounds, 15-17 among other breeds} 8-2° At present it is not Although there is no proven advantage of one agent over known whether MH is more prevalent in some or all of the another, isoflurane would appear to be the preferred inhalant sighthound breeds; however, based on the small number of agent in sighthounds since it is metabolized to a significantly reported cases it appears to be a very infrequent complication lesser extent compared with halothane. 2z Other advantages of of anesthesia in dogs. A recent study using both m v~tro and in isoflurane include cardiovascular stability, especially in ani- vivo assays showed no difference in MH susceptibility in mals with cardiac arrhythmias, and rapid recovery. 23 In some greyhounds (n = 7) compared with mixed-breed dogs (n = 6) cases (for example, major orthopedic procedures), the slower indicating that at least there is not a ubiquitous susceptibility anesthetic recovery associated with halothane may be pre- in greyhounds.2I ferred. Clinical signs of MH include rapid increase in body tempera- Propofol can be administered by repeated intravenous - ture, muscle rigidity, tachypnea, and tachycardia. Metabolic luses, or as a constant infusion, to maintain anesthesia for short and respiratory acidosis, hypoxemia, and circulatory shock are duration, relatively noninvaslve procedures, r Combinations of also evident. Myoglobinuria and associated nephrotoxicity can propofol and a potent opioid, such as oxymorphone or be seen in severe cases. Treatment revolves normalization of fentanyl, can also be used for major surgeries for longer periods body temperature, oxygen administration, aggressive intrave- in suspected MH susceptible animals, in which inhalant nous fluid therapy and administration of dantrolene (up to 3 anesthetics are contraindicated. Such long duration infusions, mg/kg IV). Dantrolene is a specific of skeletal muscle calcium however, tend to be cost prohibitive for routine procedures. channel blocker, which is very effective in treating this There is also a higher risk of prolonged recovery with this condition if given early enough in the course of the disease. In technique compared with inhalation anesthesia, since recovery known susceptible animals, MH can be prevented during is dependent on drug elimmatlon by liver metabolism instead anesthesia by minimizing stress, avoiding known triggering of excretion through the lungs. agents and administering prophylactic dantrolene.13 Drug metabolism mhlbitors are likely to have an exaggerated Stress-induced polyuria/polydipsia ("water diabetes") is of- effect in sighthounds, since drug metabolism in these animals ten seen in racing greyhounds} These animals may be more is inherently compromised. For example, administration of prone to regurgitation of water during anesthesia. On the other chloramphenicol (50 mg/kg IV), a potent cytochrome P450 hand, prolonged periods of water deprivation should be inhibitor, to greyhounds immediately before a 2-hour infusion

ANESTHESIA OF THE SIGHTHOUND 41 TABLE 2. Examples of Anesthetic Protocols Suitable for Use in Sighthounds

Uncomplicated Major Surgery Abdominal Orthopedic Procedure With Previous or Surgery (Long Bone Familial History Procedure Hip Radiographs (ovariohysterectomy) Fracture Repair) of MH

Premedication Acepromazme 0.05 mg/kg IM Butorphanol 0.2 mg/kg IM Morphine 1 mg/kg IM Oxymorphone 0.1 mg/kg IM Glycopyrrolate 0 01 mg/kg IM Acepromazlne 0.05 mg/kg IM Acepromaz~ne 0.05 mg/kg IM Acepromazine 0.05 mg/kg IM Glycopyrrolate 0 01 mg/kg IM Glycopyrrolate 0.01 mg/kg IM Glycepyrrolate 0.01 mg/kg IM Induction Propofol 2 to 4 mg/kg IV given Propofol 2-4 mg/kg IV given Propofol 2 to 4 mg/kg IV given Propofol 2 to 4 mg/kg IV given over 2 to 3 minutes to effect over 2 to 3 minutes to effect over 2 to 3 minutes to effect over 2 to 3 minutes to effect Intubate if risk of regurgitation and intubate and intubate Intubate and connect to oxygen or airway obstruction OR OR source, such as an anes- Ketamlne/diazepam*0.05 to Ketamlne/dlazepam* 0.05 to thetic machine that has been 0.1 mL/kg given over 2 to 3 0.1 mL/kg given over 2 to 3 flushed to remove Inhalant minutes to effect and Intu- minutes to effect and ~ntu- anesthetic bate bate OR OR Methohexltal 3 to 5 mg/kg iV Methohexital 3 to 5 mg/kg IV given over 2 to 3 minutes to g~ven over 2 to 3 minutes to effect (give initial 1/2 dose effect (gwe initial 1/2 dose more rapidly to avoid excite- more rapidly to avoid excite- ment) and intubate ment) and intubate Maintenance Propofol 0.1 to 0 4 mg/kg/min Isoflurane/oxygen Isoflurane/oxygen Propofol 0.1 to 0.4 mg/kg/mm as a constant IV infusion or as a constant IV infusion or 0 5 to 1 mg/kg as incre- 0.5 to 1 mg/kg as incre- mental IV boluses every 3 to mental IV boluses every 3-5 5 minutes minutes Analgesia Not usually needed Buprenorphlne 0 01 mg/kg IV Epldural morphine 0 1 to 0.2 Additional boluses of oxymor- after induction and thereafter mg/kg using preservative- phone 0.1 mg/kg IV as as needed (generally every 4 free 1 mg/mL preparation. needed (generally every 30 to 6 hours) For hind limb procedures, to 60 minutes) 50% of the volume of mor- phine can be replaced with 0.5% preservative-free bup~vIcainefor complete analgesia.

*An equal volume mixture of ketamlne (100 mg/mL) and diazepam (5 mg/mL).

of propofol increased recovery time to standing from approxi- 4. Vlla C, Savolainen P, Maldonado J, et al: Multiple and ancient origins mately 1 hour (without chloramphenicol) to nearly 10 hours. 2. of the domestic dog. Science 276:1687-1689, 1997 Concomitant use of drugs that are known to inhibit drug 5. Sams R, Muir W, Detra R, et al: Comparative pharmacoklnetlcs and anesthetic effects of methohexltal, pentobarbital, thiamylal and thlo- biotransformation with intravenous anesthetm agents should pental in greyhound and non-greyhound mixed-breed dogs Am J Vet therefore be avoided in sighthounds. Other than chlorampheni- Res 46 1677-1683, 1985 col, examples of such drugs include H2 antagonists (clmeti- 6. Robinson E, Sams R, Muir W Barbiturate anesthesia in greyhound dine, ranitidine), the macrolide anubiotics (erythromycm) and and mixed-breed dogs: Comparative cardiopulmonary effects, anes- the azole antifungals (ketoconazole, itraconazole). thetic effects, and recovery rates Am J Vet Res 47:2105-2112, 1986 7. Robertson S, Johnston S, Beemsterboer J: Cardlopulmonary, anes- [n addition to routme anesthetm monitoring, close attention thetic and postanesthetm effects of intravenous infusions of propofol should be given to core body temperature because of the in greyhounds and non-greyhounds. Am J Vet Res 53:1027-1032, propensity for hypothermia in sighthounds. Hypothermia 1992 depresses bodily functions and prolongs the duration of 8. Began J" Factors affecting duration of thlopentone anesthesia in dogs, recovery from anesthesia. ~5 Adequate insulation to reduce w~th particular reference to greyhounds. Proc Assoc Veterinary body heat loss and supplemental heat sources such as a Anaesthetists of Great Britain and , 1970, 18-24 (abstr) 9. Sams R Muir W: Effects of phenobarbital on thiopental pharmacoki- recirculating warm water blanket or a forced warm air blanket netics m greyhounds. Am J Vet Res 49:245-249, 1988 should be provided. The rate of cooling of an animal under 10. Ilkiw J, Sampson D, Cutler D: Thiopentone sodium in the greyhound. anesthesia is also determined in large part by environmental Proc 2nd Internat Congress on Veterinary Anesthesia, Davis, CA temperature. 26 The ambient temperature of the procedural area 1985, 118-119 (abstr) should therefore be maintained at a maximal value that is 11. Zoran D, Rledesel D, Dyer D. Pharmacoklnetlcs of propofol m mixed-breed dogs and greyhounds. Am J Vet Res 54"755-760, 1993 compatible with personnel comfort. Likewise animals should 12, Bernard~ G: Longevity and morbidity in the Insh Wolfhound in the be recovered in a warm area and body temperature monitored United States--1966 to 1986. Report to the Club of until values return to normal. Amenca. c/- G Bernardl, P O Box 275, Edwardsville,IL, USA, 62025 1988 13. Nelson T: Malignant hyperthermla in dogs. JAVMA 198.989-994, 1991 14. Nelson T: SR function in mahgnant hyperthermla. Cell Calcium References 9:257-285, 1988 15. Bagshaw R, Cox R, Knight D, et al: Malignant hyperthermla in a 1, Hart E: Encyclopedia of dog breeds. Neptune City, NJ: TFH Publlca- greyhound. JAVMA 172:61-62 1978 hens, 1975 16. Kirmayer A, Khde A, Purvance J: Malignant hyperthermla in a dog 2, Smith C: Veterinarians probe greyhound idiosyncrasies. JAVMA Case report and rewew of the syndrome. JAVMA 185'978-982, 1984 206:1689-1693, 1995 17. Leary S, Manning P, Bache R, et al: Recurrent malignant hyperther- 3. American , New York, NY m~a in a greyhound. JAVMA 182:521-522, 1983

42 COURT Fig 1. Examples of sight- dog breeds, includ- ing Afghan (A), Italian grey- hound (B), (C), greyhound (D), Irish - hound (E), (F), pharoah hound (G), whip- pet (H), (I), (J), (K), and Scottish - hound (L). Other sight- hound breeds that may be encountered less fre- quently include American greyhound, Australian kan- garoo dog, , Cen- tral Asian tazi, chart polski, cirneco dell'etna, galgo Es- pagnol, , Magya agar, ramphur hound, Rus- sian highland hound, , and . Photos cour- tesy of the American Ken- nel Club. 3 carrying capacity and decreased blood viscosity. Importantly, short-term anesthesia. However, almost 30 years ago it was these normal values should be born in mind when interpretmg recognized that greyhounds tended to recover much more preanesthetic laboratory tests to avoid misdiagnosis or missed slowly from the effects of these drugs compared with other dog diagnosis of such conditions as anemia, hypoprotenemia, or breeds, e Such a prolonged anesthetic recovery is characterized hemoconcentration. It is also possible, although unproven, by a protracted drunken state interspersed with periods of that lower serum albumin concentrations m sighthounds may delirium, vocalizauon, and violent struggling during which result in an exaggerated effect of drugs that are highly protein there is significant risk of self-injury.6 In some animals, bound. complete recovery can take more than 8 hours compared with Drug Hypersensitivity. Thiobarbiturates, such as thiopental the usual 1 to 2 hours in mixed-breed dogs. and thiamylal,* are commonly used in dogs for intravenous Recovery from thlobarbiturate anesthesia in dogs occurs by induction prior to gas anesthesia or for maintenance of redistribution of the drug from brain to muscle and fat with concomitant elimination of the drug from the body by liver *Thlamylal is currently unavailable in the USA because of manufacturing metabolism. 9 Slowed recovery in greyhounds was imtially problems, Future avaMlablhtyJs uncertain at present. attributed to the lean body conformation of these animals

ANESTHESIA OF THE SIGHTHOUND 39 Prototypical Dog Breeds (Canisfamiliaris) Metris-optimae lntermedius Leineri Inostranzewi 1 /X 1 /X Fig 2. Origin of the mod- sheepdogsPersian )~~E?;~ :.rEeg~plt~~cte~ .2]sian ern dog breeds from four prototypical dog breeds ( metris-optimae, interme- dius, leineri, and inostran- zewi) as proposed more % s'es than 25 years ago by Hart 1 based on fossil evidence, geographic derivation and conformational similarities. A recent study by Vila et al 4 indicates that there are in fact four genetically dis- Shepherd dogs tinct groups of modern do- ~.~ Pointers & mestic dog. However, this study also showed that the ~ ievers origins of individual dog breeds were probably much more diverse than is depicted in this illustra- ~ Large herding breeds tion. resulting in delayed re&stribuuon of the drug. 8 Although this times m greyhounds to equal that of mixed-breed dogs) A may contribute m part, recent pharmacokinetic studies lnd> number of other intravenous anesthetics, including propofol cate that this problem primarily results from breed-related and methohexital, also appear to be cleared more slowly in differences in drug metabolism.5,~° Specifically, it was shown greyhounds although not as severely as are the thiobarbitu- that greyhounds have significantly lower hepatic clearance of rates. 5,r,ll Recent in wtro studies of differences in thmbarbiturates compared with mixed-breed dogs. In addition, drug metabolism m this laboratory confirm these findings and the rate of ehminatmn of thiobarbiturates was nonhnear in additionally indicate that this defect is associated with reduced greyhounds suggesting that enzymatic clearance processes activity of a specific hepauc cytochrome P450 enzyme (Fig 3). were saturated. In support of this, inductmn of hepatic The molecular genetic basis for this reduced activity is - enzymes by administration of phenobarbital reduced recovery rently under investigation. At this time it is not known whether all greyhounds or, for TABLE 1. Characteristics of Sighthounds That may Affect that matter, which sighthound breeds are affected. Anecdotal Anesthetic Management evidence of uncomplicated use of thiobarblturates in grey- Charactenstics Clinical Consequences Management hounds by some practitioners mdmates that there are differ- ences between individual animals probably related to genetic Nervous temperament Easilystressed Ensure adequate seda- factors and previous drug exposure. It has also been suggested tion and analgesia Stress hyperthermla Reduce core tempera- that some nonsighthound breeds of dog, including colhes and ture soft-coated wheaton , have a similar anesthetic sensitiv- Administer intravenous ity. Although this has yet to be substantiated, it is possible that fluids, sedatives,and analgesmsas these breeds may share a common ancestry and genetic needed anomaly with the sighthounds (Fig 2). The most prudent Low fat-to-muscle ratio Susceptibleto hypo- Provide adequate insu- strategy at this time ts to avoid using thiobarbiturates in all High surface-area-to- thermla lation and supple- volume ratio mental warmth, such sighthounds. Suitable ahernauve anesthetic agents are dis- as recirculatinghot cussed later in this review. water blanket or Disease Susceptibility. There are a number of diseases that forced hot air heater Impaired hverdrug Slowed recoveryfrom Avoidusingthiobarbltu- appear to be more prevalent in certain slghthound breeds that metabolism some intravenous rates (thiopentalor are worthy of discussion. anesthetics thlamylal) The large sighthound breeds, especially the Irish wolfhound Induce anesthesiaw~th propofol, ketamine/ appear to have a relatively high incidence of dtlatative cardio- dlazepam or metho- myopathy.~ZBecause of the substantial risks of general anesthe- hex~tal sta with thxs &sease, these ammals should be routinely Drug interactionsmore Avoidcoadmm~stratlon hkely of drugs that Inhibit screened for signs of cardiac dysfunction including exercise drug blotransforma- intolerance, cough, elevated resting heart rate, weak pulses or tlon such as chloram- heart murmur. phenlcol, erythro- mycm, cimetidine, Malignant hyperthermia (MH) is a rare but life-threatening ran~t~dme,ketocona- genetic disorder of skeletal muscle in humans, pigs, dogs, cats, zole, and itracona- and horses that is triggered by anesthetic agents, primarily the zole volaule inhalants, and stress.13 The defect in the pig, also called

40 COURT 18. Rand J, O'Bnen P: Exerc~se-mduced malignant hypertherm~a in an 23. Seeler D, Dodman N, Norman W, et al: Recommended techniques in English springer . JAVMA 190:1013-1014, 1987 small animal anaesthesia. IV. Anaesthesia and cardiac dtsease. Br 19. Sawyer D: Malignant hyperthermia. JAVMA 179:341-344, 1981 VetJ 144"108-122, 1988 20. Short C, Paddleford R: Malignant hyperthermla in the dog. Anesthesi- 24. Mandsager R, Clarke C, Shawley R, et al: Effects of chloramphenicol on infusion pharmacokmetics of propofol in greyhounds. Am J Vet Res ology 39:462-463, 1973 56:95-99.1995 21. Cosgrove S, Eisele P, Martucci R, et al Evaluation of greyhound 26. Dodman N, Seeler D, Court M: Recommended techniques in small susceptibility to malignant hyperthermia using halothane-succinylcho- animal anaesthesia: An update. Br Vet J 140:505-516, 1984 line anesthesia and caffeine-halothane muscle contractures. Lab 26. Frank S, Beattle C, Chnstopherson R, et al: Epidural versus general Anim Sc142:482-485, 1992 anesthesia, ambient operating room temperature, and patient age as 22. Holaday D Fiserova-Bergerova V, Latto I, et al: Resistance of predictors of inadvertent hypothermla Anesthesiology 77:252-257, isoflurane to blotransformat~on in man. Anesthesiology 43:1975 1992

ANESTHESIA OF THE SIGHTHOUND 43