Dr. Sheilah A Robertson BVMS (Hons), PhD, DACVAA, DECVAA, DACAW, DECAWBM (WSEL), CVA, MRCVS.

Dr. Robertson received her veterinary training at the University of Glasgow followed by training in anesthesia and a PhD at the University of Bristol. She is board certified in anesthesia and animal welfare by the respective American and European Colleges and is trained in small animal acupuncture. Her research interests include assessment of pain and use of opioids in cats and the development of anaesthetic protocols for large scale spay and neuter clinics. In 2014 she completed her graduate certificate in shelter medicine from the University of Florida. She has been a faculty member at the Western College of Veterinary Medicine, the University of Florida, Michigan State University and served as an assistant director in the Animal Welfare Division of the American Veterinary Medical Association. Currently she is the senior medical director for Lap of Love Inc, a network of veterinarians that provide hospice and in-home euthanasia services throughout the United States.

DrRobertson@LapofLove.com

Session 1

Updates in feline anesthesia and analgesia

Session 2

Anesthesia for patients with kidney disease

Managing anesthesia in patients with cardiac disease

Session 3

Anesthesia for brachycephalic breeds

Perioperative care of diabetic patients

Session 4

Anesthesia for the young and the old

Q&A

UPDATES IN FELINE ANESTHESIA AND ANALGESIA Due to several unique species specific issues cats can be challenging anesthesia and pain management patients. They may have underlying but subclinical disease (e.g. hypertrophic cardiomyopathy, HCM) and their unique metabolism requires careful choice of anesthetic and analgesic drugs. Because of their small size they are prone to hypothermia which has far reaching effects in the perioperative period. In addition, cats are easily stressed by a journey to and a stay in a veterinary clinic and this can contribute to anesthetic complications, enhance pain perception and detract from nursing care.

Feline Anesthetic Related Mortality Rates

The Confidential Enquiry into Perioperative Small Animal Fatalities (CEPSAF) study which included 79,178 cats has provided valuable information on the risks associated with anesthesia in small animals.(1, 2) The overall risk of death in dogs was 0.17%, and 0.24% in cats; in healthy dogs and cats the risks were 0.054% and 0.112% respectively. In sick dogs and cats the risks were 1.33% and 1.40% respectively. Assignment of “healthy” [ASA 1 and 2] and “sick” [ASA 3-5] status was based on the American Society of Anesthesiologist’s classification.a Most deaths occur post-operatively; in cats 61% of deaths occur during this time and especially in the first three hours after the end of anesthesia. Cardiovascular and/or respiratory causes accounted for 72% of deaths in cats. Respiratory problems were common in the post-operative period suggesting airway trauma and edema may be involved. For short procedures (< 30 minutes) intubation increased the risk of an unfavorable outcome suggesting that great care should be taken when placing an endotracheal tube in a cat. Alternatives to intubation include use of a face mask, a laryngeal mask airway or a supraglottic airway device (see below).(3)

Another reason for the higher risk in “healthy” cats may be the presence of sub-clinical cardiac disease.(4, 5) In “apparently” healthy cats, the incidence of cardiomyopathy may be as high as 15-18%. Identifying these patients without echocardiography is difficult.

Airway management

Although an endotracheal tube should always be placed if there is any doubt about maintenance of the airway, endotracheal intubation in cats is associated with an increased risk of mortality. In some cases it may be better not to intubate for short, non-head and neck procedures in otherwise healthy animals. The cat has no excess pharyngeal tissue and generally maintains a good airway without an endotracheal tube; a mask can be used to administer oxygen and inhalant anesthetics but must be of appropriate size to prevent rebreathing and should be close-fitting and well secured to prevent leakage of waste anesthetic gases.

The v-gel® (http://docsinnovent.com/products/product/cat-v-gel) is a supraglottic airway device (SGAD) and has been specifically developed for cats (and rabbits). It is easy to place and so far, appears likely to cause less damage than standard endotracheal tubes. The company website has many helpful training videos. The device comprises a tube with a distal elliptical component that has an inflatable bladder on the dorsal aspect that is used if a better seal is needed; the tip sits in the esophagus and the elliptical part sits over the larynx (Figure 1a, b). It is a practical alternative to endotracheal intubation in cats, leading to a lower incidence of upper airway discomfort after extubation compared with an endotracheal tube (cats eat sooner). The v-gel® can be inserted at a more superficial depth of anesthesia than an endotracheal tube. It

can be used for mechanical ventilation and a variety of procedures including dental work. Another advantage may be that the mucociliary tree is not damaged. However, v-gels are much more expensive than endotracheal tubes. For more information the following references are provided.(3, 6, 7)

Fluid therapy

The CEPSAF reported a four-fold increase in the odds of anesthetic death in cats given fluid therapy during anesthesia.(2) This may be a result of fluid overload in an animal whose circulating blood volume is usually under 300 ml (40-60 mls/kg compared to 80-90 mls/kg in dogs). Accurate fluid administration in the cat requires a syringe pump or controlled infusion device. A burette where enough fluid for only one hour at a time are put into the chamber is a useful safety measure.

In addition, cats with HCM (known or unknown) will not cope with excessive fluids. The American Animal Hospital Association (AAHA) and American Association of Feline Practitioners (AAFP) (8) fluid guidelines recommend 2-5 mls/kg/hour as an anesthesia maintenance rate. The guidelines and an accompanying implementation toolkit can be downloaded at: http://www.catvets.com/guidelines/practice-guidelines/fluid-therapy-guidelines

Post-anesthetic blindness (Figure 2)

Post-anesthetic blindness is a rare but well recognised complication which is noted soon after the cat regains consciousness and it may be temporary or permanent. It is thought to be associated with a hypoxic or critical cardiovascular (ischemia) event during anesthesia

A more specific cause of post anesthetic blindness (unilateral or bilateral) is now recognized because of maxillary artery occlusion when a cat’s mouth is opened widely. Case reviews of 20 cats with post-anesthetic blindness found a link between dental and endoscopy procedures where spring loaded mouth gags had been used.(9) Compared to other species, the maxillary artery which is a continuation of the external carotid is responsible for blood flow to the brain and retina in cats. The maxillary artery crosses the caudal aspect of the mandible and blood flow can be partially or completely restricted when the mouth is opened. Computer tomography, electro-retinogram and angiography studies show that spring loaded mouth gags and needle caps (42 mm) placed between the upper and lower canine teeth can alter blood flow in some cats. Smaller (20 and 30mm) plastic mouth gags had a lesser effect; these can be made from needle caps or syringe barrels.(10, 11) This evidence indicates that cat’s mouths should be opened only as far as needed for a procedure and intermittently (less than 3-5 minutes at a time) and that spring-loaded mouth gags should never be used.

Feline friendly handling - Most cats do not like being put in a carrier nor transported to a clinic. Veterinary clinics tend to be chaotic and the stimuli and smells present may be overwhelming to a cat. Inappropriate restraint and the stress of an unfamiliar environment can have a detrimental effect on cats for example distressed cats will have increased heart and respiratory rates, elevated blood pressure, elevated cortisol levels, may become anorexic and resent handling that is required for treatment purposes. As soon as the cat arrives at the clinic it is best to take it directly to a quiet and secluded area where it can wait for its pre-anesthetic evaluation. Successfully calming an injured, distressed, fearful or aggressive cat is important for a good anesthetic outcome. Excellent information is contained in the AAFP’s Feline Handling and Feline Nursing Guidelines which can be accessed at: http://www.catvets.com

The use of a synthetic fraction of feline facial pheromones in a spray formulation has been assessed for its calming effect on cats in a veterinary clinic before intravenous catheterization.(12) The cage was sprayed with facial pheromone or placebo prior to placing the cat in it. The facial pheromone had additional calming effects in cats given acepromazine and, to a lesser degree, helped to calm cats that were not given acepromazine and the authors concluded that facial pheromones help to calm cats in unfamiliar surroundings. In another study, significant increases in grooming and interest in food were found in cats exposed to facial pheromones compared with a placebo.(13) Facial pheromones also decrease stress levels during physical examination.(14)

Gabapentin is now widely used to sedate and calm cats prior to hospital visits: recommended doses are 50 - 100 mg per cat or 150 mg for a big cat, PO, 2 – 3 hours before arrival.

Hypothermia - Hypothermia occurs commonly in cats undergoing anesthesia and is linked to mortality.(15) Hypothermia leads to delayed recovery, decreased cardiac function, increased oxygen requirements during recovery and can increase blood loss and post-operative infections. Every attempt should be made to prevent heat loss in cats during anesthesia by using circulating warm water blankets, forced warm air devices and blankets made of conductive fabric in addition to avoiding cold work areas.

Metabolism – To avoid unwanted side effects in cats, their unique and limited metabolic capacity must be understood.(16) The main disparity in disposition of drugs between cats and other species can be explained by differences in drug metabolism. Many anesthetic and analgesic drugs are highly lipid-soluble drugs and must be transformed into a water-soluble form before they can be excreted. Slow metabolism of lipid soluble drugs may lead to accumulation and potentially toxic effects if dosing intervals are not adjusted. In contrast, if a metabolite has a significant role to play in the overall action of the drug, failure to produce metabolites may make the drug relatively ineffective. The liver is the major site of drug metabolism. The domestic cat seems especially sensitive to the adverse effects of drugs that require glucuronidation before elimination. This metabolic deficiency has a molecular genetic basis and pseudogenes and gene mutations linked to the glucuronidation enzymes have been identified.(17, 18)

Anesthetic Agents

Propofol (2,6-diisopropylphenol) is widely used in cats. The attractive features of propofol anesthesia include its rapid onset and offset of action. Compared to some other injectable protocols, recoveries are usually smooth and complete with no “hang over”. Cats require a higher induction dose compared to dogs when no premedicant agent is used (8.0 mg/kg versus 6.5 mg/kg), and although the total dose is decreased by sedative agents, the dose in cats is still higher.(19) In cats, recovery times after infusions that last > 30 minutes are longer than expected (20) and this may be due to decreased capacity for glucuronidation as outlined above; this is in stark contrast to dogs where infusions can be used for hours and recovery is rapid and smooth. Based on the knowledge that feline hemoglobin is susceptible to oxidative injury and that phenolic compounds are linked to this injury, Andress et al (21) studied the safety of consecutive day propofol administration in cats. By day 3, there was a significant increase in Heinz bodies, and recovery times were increased and by day 5 many some cats stopped eating. Based on this study, propofol was not recommended for repeated use at short intervals. Bley and colleagues (22) have revisited the use of repetitive propofol administration in cats that required radiation

therapy. In their study one group of cats received propofol with or without midazolam on 5 consecutive days and another group was anesthetized 12 times over a 19-day period, again using propofol or midazolam/propofol. In this study there were no clinically apparent adverse effects. The use of midazolam decreased the total amount of propofol needed for induction and maintenance by 26% and these authors concluded that propofol can be used daily for short periods.

Alfaxalone (Alfaxan) is a neurosteroid anesthetic which is available and labelled for use in cats (and dogs) in the USA and in most countries around the world. A previous formulation was available in the 1970’s for cats in the United Kingdom and Canada and contained alfaxalone and alfadalone, and there was also a human formulation (Althesin). It was poorly water soluble and was formulated in Cremaphor EL (castor oil); 70% of cats had swelling of the face, paws, and ears due to histamine release and some developed pulmonary edema and it was withdrawn from human market and the veterinary market.

The discovery of 2-hydroxypropyl-beta-cyclodextrin (HPCD), a molecule that is made up of oligosaccharides and has been widely used to increase the solubility of drugs allowed for the reformulation of alfaxalone without the previous side-effects.

The alfaxalone molecule is similar to progesterone but has no hormonal activity. The drug has a wide margin of safety compared to propofol. It can be given as a single induction (intravenous) bolus and can be used as an infusion without prolonged recoveries. Intramuscular and subcutaneous administration are also described in the literature, but are “off-label” in the USA.(23)

Assessment of acute pain

Validated pain scoring tools are essential for assessing pain in cats and the efficacy of analgesic interventions. The two currently validated tools are:

1. The UNESP-Botucatu Multidimensional Composite Pain Scale (UNESP-Botucatu MCPS). This is available along with examples (videos) and explanations of behaviors via a dedicated website (www.animalpain.com.br/en-us/).

2. The Glasgow Composite Measures Pain Scale-Feline (CMPS-Feline). The Glasgow tool is a simple, two- page tool that is easy and quick to use in a clinical setting.(24) The updated version of this tool is available for download at: http://www.newmetrica.com/acute-pain-measurement/ The new tool now includes assessment of facial expressions related to pain.

Analgesic Agents

Opioids are an essential component of most anesthetic protocols and historically there has been a reluctance to use opioids in cats due to fear of adverse behavioral effects. However at appropriate clinical doses euphoria and sedation usually occur and numerous research and clinical studies demonstrate that opioids can provide excellent analgesia in cats.(25) Buprenorphine is one of the most popular opioids in cats.(26) Long acting (sustained release) buprenorphine (given subcutaneously) is not FDA approved for use in cats but has been evaluated in cats undergoing ovariohysterectomy.(27) Simbadol™ b is an FDA approved

formulation of buprenorphine. It is a concentrated formulation given subcutaneously every 24 hours for up to three days.

NSAIDs

Robenacoxib is approved for use in cats 16 weeks and older for the control of post-operative pain associated with inflammation related to orthopedic surgery, ovariohysterectomy and castration, and can be given for a maximum of three days (USA label). The availability of an injectable and oral formulation increases its versatility and simplifies perioperative use. At clinical doses COX-1 inhibition is minimal and short lasting. Robenacoxib has a unique pharmacokinetic profile, with a short half-life but long residence time in target (inflamed) tissues.(28) Robenacoxib was well tolerated when given once daily for 28 days in cats with osteoarthritis, including cats with stable chronic kidney disease.(29) Note: other than a single perioperative injection any other use of meloxicam in cats is off-label in the USA.

Gabapentin is an antiepileptic drug that is also used to treat neuropathic pain. Although not a lot is known about the efficacy of this drug in cats, there are several case reports which support its use as an adjunctive drug for pain management.(30, 31) it is also widely used to calm cats prior to hospital visits (see above).

Maropitant (Cerenia)is a neurokinin-1 receptor antagonist and is an effective antiemetic in cats. It also has anesthetic sparing properties (decreased Minimum Alveolar Concentration [MAC] of inhalant agents). Whether or not it has analgesic properties is still controversial but clinical experiences suggests that it may provide visceral analgesia.

Updates in chronic pain management

New, more target therapies for the management of pain associated with degenerative joint disease in cats is an active an exciting field of study. Grapiprant (Galliprant®, Elanco US) is a prostaglandin E2 (PGE2) EP4 receptor antagonist; it is currently available for dogs and may be marketed for cats in the future. NV-02, (frunevetmab, NexVet™) is a felinized anti-Nerve Growth Factor monoclonal antibody treatment which in undergoing trials in cats.(32)

References

1. Brodbelt DC, Blissitt KJ, Hammond RA, Neath PJ, Young LE, Pfeiffer DU, et al. The risk of death: the confidential enquiry into perioperative small animal fatalities. Vet Anaesth Analg. 2008;35(5):365-73.

2. Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Risk factors for anaesthetic-related death in cats: results from the confidential enquiry into perioperative small animal fatalities (CEPSAF). British journal of anaesthesia. 2007;99(5):617-23.

3. Prasse SA, Schrack J, Wenger S, Mosing M. Clinical evaluation of the v-gel supraglottic airway device in comparison with a classical laryngeal mask and endotracheal intubation in cats during spontaneous and controlled mechanical ventilation. Vet Anaesth Analg. 2015.

4. Cote E, Manning AM, Emerson D, Laste NJ, Malakoff RL, Harpster NK. Assessment of the prevalence of heart murmurs in overtly healthy cats. J Am Vet Med Assoc. 2004;225(3):384-8.

5. Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc. 2009;234(11):1398-403.

6. van Oostrom H, Krauss MW, Sap R. A comparison between the v-gel supraglottic airway device and the cuffed endotracheal tube for airway management in spontaneously breathing cats during isoflurane anaesthesia. Vet Anaesth Analg. 2013;40(3):265-71.

7. Barletta M, Kleine SA, Quandt JE. Assessment of v-gel supraglottic airway device placement in cats performed by inexperienced veterinary students. Vet Rec. 2015;177(20):523.

8. Davis H, Jensen T, Johnson A, Knowles P, Meyer R, Rucinsky R, et al. 2013 AAHA/AAFP fluid therapy guidelines for dogs and cats. J Am Anim Hosp Assoc. 2013;49(3):149-59.

9. Stiles J, Weil AB, Packer RA, Lantz GC. Post-anesthetic cortical blindness in cats: twenty cases. Vet J. 2012;193(2):367-73.

10. Martin-Flores M, Scrivani PV, Loew E, Gleed CA, Ludders JW. Maximal and submaximal mouth opening with mouth gags in cats: implications for maxillary artery blood flow. Vet J. 2014;200(1):60-4.

11. Barton-Lamb AL, Martin-Flores M, Scrivani PV, Bezuidenhout AJ, Loew E, Erb HN, et al. Evaluation of maxillary arterial blood flow in anesthetized cats with the mouth closed and open. Vet J. 2013;196(3):325-31.

12. Kronen PW, Ludders JW, Erb HN, Moon PF, Gleed RD, Koski S. A synthetic fraction of feline facial pheromones calms but does not reduce struggling in cats before venous catheterization. Vet Anaesth Analg. 2006;33(4):258-65.

13. Griffith CA, Steigerwald ES, Buffington CA. Effects of a synthetic facial pheromone on behavior of cats. J Am Vet Med Assoc. 2000;217(8):1154-6.

14. Pereira JS, Fragoso S, Beck A, Lavigne S, Varejao AS, da Graca Pereira G. Improving the feline veterinary consultation: the usefulness of Feliway spray in reducing cats' stress. J Feline Med Surg. 2016;18(12):959-64.

15. Redondo JI, Suesta P, Gil L, Soler G, Serra I, Soler C. Retrospective study of the prevalence of postanaesthetic hypothermia in cats. Vet Rec. 2012;170(8):206.

16. Boothe DM. Drug therapy in cats: mechanisms and avoidance of adverse drug reactions. J Am Vet Med Assoc. 1990;196(8):1297-305.

17. Court M, Greenblatt D. Molecular basis for deficient acetominophen glucuronidation in cats. An interspecies comparison of enzyme kinetcis in liver microsomes. Biochem Pharmacol. 1997;53(7):1041-7.

18. Court M, Greenblatt D. Molecular genetic basis for deficient acetominophen glucuronidation by cats: UGT1A6 is a pseudogene, and evidence for reduced diversity of expressed hepatic UGT1A isoforms. Pharmacogenetics. 2000;10(4):355-69.

19. Morgan DW, Legge K. Clinical evaluation of propofol as an intravenous anaesthetic agent in cats and dogs. Vet Rec. 1989;124(2):31-3.

20. Pascoe PJ, Ilkiw JE, Frischmeyer KJ. The effect of the duration of propofol administration on recovery from anesthesia in cats. Vet Anaesth Analg. 2006;33(1):2-7.

21. Andress JL, Day TK, Day D. The effects of consecutive day propofol anesthesia on feline red blood cells. Vet Surg. 1995;24(3):277-82.

22. Bley CR, Roos M, Price J, Ruess-Melzer K, Buchholz J, Poirier V, et al. Clinical assessment of repeated propofol-associated anesthesia in cats. J Am Vet Med Assoc. 2007;231(9):1347-53.

23. Warne LN, Beths T, Whittem T, Carter JE, Bauquier SH. A review of the pharmacology and clinical application of alfaxalone in cats. Vet J. 2015;203(2):141-8.

24. Calvo G, Holden E, Reid J, Scott EM, Firth A, Bell A, et al. Development of a behaviour-based measurement tool with defined intervention level for assessing acute pain in cats. J Small Anim Pract. 2014;55(12):622-9.

25. Robertson SA. A Review of Opioids in Cats. In: Gleed RD, Ludders, J.W., editor. Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals: International Veterinary Information Service; 2007.

26. Steagall PV, Monteiro-Steagall BP, Taylor PM. A review of the studies using buprenorphine in cats. J Vet Intern Med. 2014;28(3):762-70.

27. Catbagan DL, Quimby JM, Mama KR, Rychel JK, Mich PM. Comparison of the efficacy and adverse effects of sustained-release buprenorphine hydrochloride following subcutaneous administration and buprenorphine hydrochloride following oral transmucosal administration in cats undergoing ovariohysterectomy. Am J Vet Res. 2011;72(4):461-6.

28. Giraudel JM, Toutain PL, King JN, Lees P. Differential inhibition of cyclooxygenase isoenzymes in the cat by the NSAID robenacoxib. J Vet Pharmacol Ther. 2009;32(1):31-40.

29. King JN, King S, Budsberg SC, Lascelles BD, Bienhoff SE, Roycroft LM, et al. Clinical safety of robenacoxib in feline osteoarthritis: results of a randomized, blinded, placebo-controlled clinical trial. J Feline Med Surg. 2015.

30. Lorenz ND, Comerford EJ, Iff I. Long-term use of gabapentin for musculoskeletal disease and trauma in three cats. J Feline Med Surg. 2012;15(6):507-12.

31. Steagall PV, Monteiro-Steagall BP. Multimodal analgesia for perioperative pain in three cats. J Feline Med Surg. 2013.

32. Gearing DP, Huebner M, Virtue ER, Knight K, Hansen P, Lascelles BD, et al. In Vitro and In Vivo Characterization of a Fully Felinized Therapeutic Anti-Nerve Growth Factor Monoclonal Antibody for the Treatment of Pain in Cats. J Vet Intern Med. 2016;30(4):1129-37.

a http://www.asahq.org

b Simbadol ™ (buprenorphine injection), Zoetis, Florham Park, New Jersey

Figure 1a, b. A feline supraglottic airway device ready for use, and secured in place.

Figure 1a

Figure 1b

Figure 2. A cat with central blindness following a long dental procedure with a spring-loaded mouth gag in place.

ANESTHESIA FOR PATIENTS WITH KIDNEY DISEASE Kidney disease can be divided into two main categories: acute kidney injury (AKI) and chronic kidney disease (CKD). AKI develops over hours or days and may be a result of toxicities, sepsis or acute urinary obstruction; these are high risk anesthesia patients and should be stabilized as much as possible before sedation or anesthesia. CKD which is more commonly encountered is the focus of this discussion.

CKD is a structural or functional disease of one or both kidneys which has been present for an extended period (weeks, months or years). CKD is progressive and irreversible and currently there are no effective treatments that significantly slow the disease process. This is predominately a disease of older animals and the prevalence increases with age and one of the most common diseases seen in veterinary practice. Recent studies suggest it is more common than previously thought in cats across all age groups.(1) There may be a known underlying disease process that initiates renal damage but in most cases an inciting cause cannot be identified. There are several hallmark changes that aid in the diagnosis of CKD and staging is recommended. The International Renal Interest Society (IRIS) uses renal function tests, proteinuria and blood pressure to stage the disease in cats and dogs on a scale of 1 to 4 (www.iris-kidney.com). This approach allows for individualized treatment at each stage.

The functions of the kidneys include excretion of metabolic waste products, regulation of blood volume, extracellular blood volume, acid-base balance and red blood cell production; therefore disease can have far reaching effects. The kidneys have the ability to maintain these functions even as nephrons become damaged; azotemia does not become apparent until 60-70% of the functional kidney tissue is damaged. A dog or cat may present with no obvious clinical signs of renal disease and may have normal blood work yet have only a small percentage of functional kidney tissue left: when these patients are challenged by anesthesia they make be “tipped” over into renal failure.

Abnormalities that will affect anesthesia in dogs and cats with known CKD include an elevated blood urea nitrogen, elevated creatinine, and hypoproteinemia; the latter is relevant as many anesthetic drugs are protein bound. Electrolyte abnormalities may be present with potassium (high or low) being highly relevant to anesthetic management. Metabolic acidosis, hypertension, anemia and dehydration may be present and some patients may experience nausea and vomiting. Other co-morbidities, for example diabetes mellitus and degenerative joint disease / osteoarthritis may be present, and in older patients the consequences of ageing and their impact on anesthetic management must also be considered.

These patients may require anesthesia for many reasons, e.g. planned dental and orthopedic procedures or in an emergency situation such as trauma. In addition to considering the effects of anesthesia on renal function, the impact of surgery must also be appreciated; surgical stimulus results in catecholamine, renin, arginine vasopressin (AVP) and aldosterone release leading to increased renal vascular resistance and decreased renal blood flow (RBF) and glomerular filtration rate (GFR). Similar responses are elicited by pain and fear. These responses can be significantly ameliorated by low stress handling and good analgesic protocols. Laparoscopic surgery increase intra-abdominal pressure resulting in direct venous compression, decreased cardiac output and increases in renin, aldosterone and AVP sufficient to cause oliguria in human patients.(2)

The kidneys receive 20-25% of the cardiac output and have a high oxygen consumption rate (higher than the brain on a per gram basis). General anesthesia commonly results in decreased cardiac output, hypotension (Mean Arterial (MAP) Pressure < 60 mmHg or Systolic Arterial Pressure (SAP) < 90 mmHg); in one report 22% of dogs and 33% of cats were hypotensive during elective procedures.(3) Renal blood flow and GFR are directly related; in normal healthy patients GFR is stable over a wide range of systemic blood pressure (mean arterial pressure of 80-180 mmHg) due to renal autoregulation. However, autoregulation may be different in the face of disease and hypotension should always be addressed.

There is no single recommended anesthetic protocol for dogs and cats with CKD; each one will require an individualized approach, however some suggestions can be made.(4) Goals of anesthetic management include maintaining normotension, isovolemia and good cardiac output to maintain perfusion of vital organs.

Patients with CKD should be stabilized as much as possible prior to surgery; this is possible when the procedure is elective but even in an emergency situation spending time prior to anesthesia to correct as many abnormalities as possible is time well spent. It is important to ensure patients are adequately hydrated and this may require intravenous fluid administration prior to anesthesia. If nausea and vomiting are present these will contribute to dehydration and are very unpleasant; anti-nausea and / or anti-emetic drugs such as ondansetron or maropitant may be indicated. Normal serum potassium should be < 5.5 mEq/L and must be checked as hyperkalemia can be life threatening. Hyperkalemia causes altered cardiac excitability, automaticity and conduction and can result in cardiac arrest; it may be tolerated in the awake non-medicated patient but the additional disruption of homeostasis caused by anesthesia puts the patient at greater risk of adverse cardiac events. If the patient is dehydrated, lactated Ringers solution is indicated and may be all that is required as fluid therapy will dilute serum potassium, correct fluid deficits and cardiovascular function and enhance renal perfusion and excretion. Metabolic acidosis enhances hyperkalemia and should be corrected; this may also respond to rehydration. Regular insulin (0.5-1.0 U/kg) and dextrose (1-2 g per unit of insulin) can be used to rapidly decrease serum potassium. In an emergency 10% calcium gluconate (0.5-1.0 mg/kg IV) can be given to protect the heart until other measures are put in place to decrease serum potassium.

If anemia is present it is usually long standing and well tolerated; however if bleeding is expected and the hematocrit is < 20% or Hb is < 7 g/dl transfusion should be considered. Pre-oxygenation via face mask is recommended.(5)

Decreasing stress, fear and pain are important and can be achieved with sedatives, tranquillizers, analgesics and low stress handling techniques.

A baseline blood pressure should be measured prior to anesthesia; CKD patients may be hypertensive and renal autoregulation may be altered (shifted to a higher range); in these patients a drop in blood pressure that would be tolerated by healthy patients may result in a significant decrease in RBF.

Acepromazine can be used if hypovolemia has been corrected. Low doses (0.01-0.02 mg/kg) are usually adequate and avoid the potential hypotension secondary to vasodilation seen with higher doses. There is some data in dogs suggesting acepromazine may offer renal protection.(6) Alpha2-adrenergic agents should be avoided as their effects on the kidney are unpredictable.(7) Benzodiazepines (diazepam and midazolam) have minimal renal and

cardiovascular effects; however their effects on behavior when given as a premedicant are unpredictable and some animals become excited. Benzodiazepines are idea for co-administration at induction to reduce the dose of induction agent (e.g. propofol). Opioids should be incorporated and even for non-painful diagnostic procedures they are valuable because of their sedating properties, minimal cardiovascular effects and anesthetic sparing effects.

Injectable induction agents should be used; mask induction with inhalant agents is stressful and also requires a “large dose” which will cause cardiovascular depression. Propofol and alfaxalone are good choices. Ketamine will stimulate sympathetic activity and is not a “first-line” drug in these patients. The dose of induction agent will be decreased if co-administered with a benzodiazepine.

Although isoflurane is less metabolized that sevoflurane this is a theoretical advantage. Anesthetic sparing techniques should be used (e.g. opioids, local anesthetic blocks) to minimize the cardiorespiratory depressant effects of inhalant agents.

Intraoperative use of “low dose dopamine” infusion is no longer advocated and has not been shown to provide renal protection; however inotropes may be used to support cardiac output. Some CKD patients may benefit from mannitol induced diuresis;(4, 7) and suggested doses are 0.5-1.0 g/kg over 20 minutes.

Intraoperative monitoring is routine but should focus on blood pressure and if hyperkalemia is a concern the ECG should be closely monitored.

Non-steroidal anti-inflammatory use:

Animals with stable CKD may be receiving NSAIDs. CKD and DJD are common diseases of older cats: one study reported that their co-prevalence may be as high as 68%.(1) There are reports on the use of both meloxicam and robenacoxib in this category of patient.(8-10) In cats with normal or reduced renal function GFR is not dependent on renal prostaglandins. However in volume depleted dogs and cats NSAIDs have an adverse effect on GFR because in this scenario, renal function depends on intact cyclooxygenase activity and release of vasodilatory prostaglandins.(11) In these patients it is important to ensure they are properly hydrated and to monitor blood pressure closely and act quickly if hypotension or acute blood loss occurs.

CKD patients may be challenging to anesthetize but with careful planning they can be well managed without further renal insult if the pathophysiology of the disease and the effects of anesthetic drugs on the kidney are understood.

References

1. Marino CL, Lascelles BD, Vaden SL, Gruen ME, Marks SL. Prevalence and classification of chronic kidney disease in cats randomly selected from four age groups and in cats recruited for degenerative joint disease studies. J Feline Med Surg. 2014;16(6):465-72.

2. Morgan G, Mikhali M, Murray M. Renal Physiology and Anesthesia. In: Morgan G, Mikhail M, Murray M, editors. Clinical Anesthesia. 4th ed. Columbus: McGraw-Hill medical; 2005. p. 662-78.

3. Gordon AM, Wagner AE. Anesthesia-related hypotension in small animal practice. Veterinary Medicine. 2005;In Press.

4. Bednarski R, Grimm K, Harvey R, Lukasik VM, Penn WS, Sargent B, et al. AAHA anesthesia guidelines for dogs and cats. J Am Anim Hosp Assoc. 2011;47(6):377-85.

5. McNally EM, Robertson SA, Pablo LS. Comparison of time to desaturation between preoxygenated and nonpreoxygenated dogs following sedation with acepromazine maleate and morphine and induction of anesthesia with propofol. Am J Vet Res. 2009;70(11):1333-8.

6. Bostrom I, Nyman G, Kampa N, Haggstrom J, Lord P. Effects of acepromazine on renal function in anesthetized dogs. Am J Vet Res. 2003;64(5):590-8.

7. Schroeder C. Renal Disease. In: Snyder L, Johnson R, editors. Canine and Feline Anesthesia and Co-exisiting Disease. Ames, Iowa: Wiley Blackwell; 2015. p. 116-28.

8. Gowan RA, Baral RM, Lingard AE, Catt MJ, Stansen W, Johnston L, et al. A retrospective analysis of the effects of meloxicam on the longevity of aged cats with and without overt chronic kidney disease. J Feline Med Surg. 2012.

9. Gowan RA, Lingard AE, Johnston L, Stansen W, Brown SA, Malik R. Retrospective case-control study of the effects of long-term dosing with meloxicam on renal function in aged cats with degenerative joint disease. J Feline Med Surg. 2011;13(10):752-61.

10. King JN, King S, Budsberg SC, Lascelles BD, Bienhoff SE, Roycroft LM, et al. Clinical safety of robenacoxib in feline osteoarthritis: results of a randomized, blinded, placebo-controlled clinical trial. J Feline Med Surg. 2015.

11. Surdyk KK, Brown CA, Brown SA. Evaluation of glomerular filtration rate in cats with reduced renal mass and administered meloxicam and acetylsalicylic acid. Am J Vet Res. 2013;74(4):648-51.

MANAGING ANESTHESIA IN PATIENTS WITH CARDIAC DISEASE “Heart disease” in dogs and cats comes in a lot of different versions and even if a specific diagnosis is made, each patient is different depending on the severity of their disease and how well they have compensated for it. The primary problem may be electrical in origin (e.g. atrio-ventricular conduction blocks and ventricular tachycardia) mechanical (e.g. mitral insufficiency and pulmonic stenosis) or related to myocardial disease (dilated cardiomyopathy or hypertrophic cardiomyopathy). Each abnormality presents different challenges and requires a different anesthetic approach. The dog or cat may undergo anesthesia so that the defect can be repaired (e.g. correction of a patent ductus arteriosus), or it may have some degree of heart failure (e.g. mitral regurgitation) but require anesthesia for a dental procedure. In many cases it is possible to stabilize the patient prior to anesthesia (e.g. treat pulmonary edema and improved contractility in cases of congestive heart failure). Assigning a risk factor (e.g. using the American Society of Anesthesiologist’s physical status classification system)(1) (Table 1) is recommended and the risks related to anesthesia should be discussed with the owner.

Table 1: American Society of Anesthesiologist’s physical status classification system

ASA Classification Definition

ASA I A normal healthy patient

ASA II A patient with mild systemic disease

ASA III A patient with severe systemic disease

ASA IV A patient with severe systemic disease that is a constant threat to life

ASA V A moribund patient who is not expected to survive without the operation

When developing a plan for a patient with heart disease, it is a good idea to remind yourself of the heart’s primary function and how a normal healthy heart works, then consider what is different about your patient and how you will avoid further compromise. Some basic physiologic equations are always worth remembering.(2)

The most important function of the heart is to continuously deliver oxygen to tissues and this depends on adequate carriage of oxygen by hemoglobin and a functional cardiovascular system:

Oxygen delivery (DO2) = cardiac output (CO) x oxygen content (CaO2)

DO2 is the milliliters (mls) of oxygen delivered per minute, cardiac output is a product of stroke

volume (SV; mls per beat) and heart rate (HR; beats per minute) and is the millliters of blood ejected per minute. Stroke volume depends on preload (venous return to the heart), afterload (resistance to systolic ejection) and contractility (inotropy or strength of contraction). Preload is an important concept: in a healthy heart an increase in preload will increase SV (Frank-Starling Law of the heart), but an unhealthy heart does not respond in the same way. A major determinant of preload is circulating blood volume and an adequate preload is required to

produce a good CO. However, when dealing with a failing heart there is a fine balance; an increased fluid load will increase the myocardial workload to a point that may not be sustainable, resulting in a negative effect on CO. Until recently fluid administration rates during anesthesia were not evidence based and have been, in most cases, excessively high especially in cats. Accurate delivery of appropriate fluid rates is essential in the face of cardiac disease; excellent guidelines for perioperative fluid administration have been provided by the American Animal Hospital Association and American Association of Feline Practitioners.(3) These are available along with an accompanying implementation toolkit for download at:

www.catvets.com/guidelines/practice-guidelines/fluid-therapy-guidelines

www.aaha.org/professional/resources/fluid_therapy_guidelines_abstract.aspx

Oxygen content is the mls of blood carried per dL of blood:

Oxygen content (CaO2) = Hemoglobin concentration (Hb) x 1.34 x oxygen saturation of hemoglobin (SaO2) + 0.003 x partial pressure of oxygen dissolved in blood (PaO2)

Measuring blood pressure is easy to do in clinical practice but it is important to know that this is a reflection of CO and systemic vascular resistance (SVR; dynes.s.cm-5). SVR is a measure of the degree of vasodilation or vasoconstriction. Mean Arterial Pressure (MAP) is important for tissue and organ perfusion:

Mean Arterial Pressure = CO x SVR

A MAP of > 60 mmHg or a systolic arterial pressure of > 90 mmHg have historically been the numbers to aim for to ensure adequate oxygen delivery. Note however that MAP may be a “good number” but a low CO and high SVR may be present and perfusion may not be adequate. For this reason it is important to use several different parameters when monitoring the anesthetized patient including blood pressure, mucus membrane color, warmth of the periphery (toes, feet, tongue) and urine production.

From these equations it becomes clear that many variables can be affected by disease processes or can be manipulated by the anesthesiologist.

Table 2: Examples of common causes of changes in cardiovascular variables

BRADYCARDIA TACHYCARDIA VASODILATION DECREASED PRELOAD

DECREASED CONTRACTILITY

Hypothermia

Opioids

Vagal stimulation

Β-blocking drugs

Fear

Ketamine

Anticholinergics

Sepsis

Hypercapnia

Isoflurane

Sevoflurane

Propofol

Alfaxalone

Dehydration

Hemorrhage

Vasodilation

IPPV*

Isoflurane

Sevoflurane

Propofol

Alfaxalone

* Intermittent Positive Pressure Ventilation

General Principles

If the patient is receiving cardiac medications these should not be stopped prior to anesthesia. Reducing stress is a high priority in patients with cardiac disease as catecholamine release will result in vasoconstriction (increased systemic vascular resistance), tachycardia and increased myocardial oxygen demands. Stress can be decreased by judicious use of sedatives, tranquilizers, opioids and correct handling and restraint. Due to decreased cardiac reserve and intolerance to hypoxemia pre-oxygenation for 3 minutes, using a face mask, is recommended to increase the time taken to desaturation.(4) So-called “anesthetic sparing” techniques should be embraced: induction agents and inhalant anesthetics can have profound cardiorespiratory depressant effects so their use should be reduced as much as possible by good premedication protocols, preemptive analgesia, supplemental infusions during procedures (e.g. opioids) and the use of loco-regional anesthesia. Co-induction is a technique where one drug is used to decrease the requirements of another; for example the induction dose of propofol can be significantly reduced by using drugs with minimal negative cardiovascular effects such as midazolam or diazepam (0.25 mg/kg IV), or with fentanyl (2-5 microg/kg). Induction drugs should also be given slowly and to effect. Of the induction drugs available, etomidate has the least effect on cardiac function but is expensive and not readily available. Mask induction with inhalant agents cannot be recommended due to the stress this causes and the high dose of inhalant agent required to achieve unconsciousness; this technique has been documented to significantly increase mortality in dogs.(5) Preventing and treating hypothermia is also important in these patients; hypothermia causes bradycardia that is not responsive to anticholinergic drugs, decreases cardiac contractility, increases viscosity of blood, increases bleeding and during rewarming, shivering dramatically increases oxygen requirements. Patients should receive supplemental oxygen until they are normothermic.

Positive inotropes may be required to maintain contractility and cardiac output. Dopamine and dobutamine are the most commonly used drugs. Both must be diluted and administered accurately using a syringe pump. In cats a study demonstrated that dopamine, dobutamine, phenylephrine and epinephrine all increase cardiac output but dopamine had the most beneficial effects.(6)

Armed with knowledge of the basic principles outlined above a plan can be devised for most animals even with complex cardiac diseases. The basic principles should be applied to all patients undergoing anesthesia. A common disease of the cat is discussed in more detail below.

Feline hypertrophic cardiomyopathy (HCM)

HCM is a common disease in cats. Several studies suggest that approximately 15-18% of all cats are affected.(7, 8) The challenge of this disease is that apparently healthy young cats may be affected and it is subclinical until they are challenged by anesthesia. Auscultating a heart murmur does not necessarily mean a cat has functional cardiac disease and 50% of cats with HCM do not have a murmur. Echocardiography is required for diagnosis therefore we often anesthetize a cat with HCM thinking it is normal. Affected cats have a thickened and stiff left ventricle which fails to relax normally and a decreased internal ventricular volume. In some cases there is left ventricular outflow obstruction. The goals of anesthesia are to maintain a normal heart rate and avoid tachycardia, maintain preload, increase afterload and avoid increased myocardial contractility. Ketamine should be avoided as it causes tachycardia, increased contractility and myocardial oxygen demand. Acepromazine can cause vasodilation

and worsen outflow obstruction. Opioids should be utilized and bradycardia is beneficial. Alpha2-agonists have been shown to decrease left ventricular outflow obstruction in cats with this specific abnormality.(9) Induction should be with a benzodiazepine plus propofol or alfaxalone. The maintenance requirements for inhalant agents can be minimized by using opioid infusions (e.g. fentanyl).

References

1. Bednarski R, Grimm K, Harvey R, Lukasik VM, Penn WS, Sargent B, et al. AAHA anesthesia guidelines for dogs and cats. J Am Anim Hosp Assoc. 2011;47(6):377-85.

2. Congdon JM. Cardiovascular disease. In: Snyder LBC, Johnson RA, editors. Canine and Feline Anesthesia and Co-Existing Disease. Ames, Iowa: Wiley Blackwell; 2015.

3. Davis H, Jensen T, Johnson A, Knowles P, Meyer R, Rucinsky R, et al. 2013 AAHA/AAFP fluid therapy guidelines for dogs and cats. J Am Anim Hosp Assoc. 2013;49(3):149-59.

4. McNally EM, Robertson SA, Pablo LS. Comparison of time to desaturation between preoxygenated and nonpreoxygenated dogs following sedation with acepromazine maleate and morphine and induction of anesthesia with propofol. Am J Vet Res. 2009;70(11):1333-8.

5. Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Results of the confidential enquiry into perioperative small animal fatalities regarding risk factors for anesthetic-related death in dogs. J Am Vet Med Assoc. 2008;233(7):1096-104.

6. Pascoe PJ, Ilkiw JE, Pypendop BH. Effects of increasing infusion rates of dopamine, dobutamine, epinephrine, and phenylephrine in healthy anesthetized cats. Am J Vet Res. 2006;67(9):1491-9.

7. Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc. 2009;234(11):1398-403.

8. Cote E, Manning AM, Emerson D, Laste NJ, Malakoff RL, Harpster NK. Assessment of the prevalence of heart murmurs in overtly healthy cats. J Am Vet Med Assoc. 2004;225(3):384-8.

9. Lamont LA, Bulmer BJ, Sisson DD, Grimm KA, Tranquilli WJ. Doppler echocardiographic effects of medetomidine on dynamic left ventricular outflow tract obstruction in cats. J Am Vet Med Assoc. 2002;221(9):1276-81.

ANESTHESIA FOR BRACHYCEPHALIC BREEDS In the United States, the top 10 American Kennel Club most popular breeds list features two brachycephalic breeds (Table 1), the Bulldog (English or British) and the French Bulldog and recent reports from the United Kingdom suggest that the French Bulldog is set to become the most popular dog, overtaking the Labrador retriever for the first time in 30 years, with a 47% increase in registrations between 2015 and 2016. Brachycephalic cats are also popular including the Himalayan and Persian breeds.

Table 1. AKC MOST POPULAR BREEDS 2016

Rank Breed 1 Labrador retriever 2 German Shepperd Dog 3 Golden Retriever 4 Bulldog 5 Beagle 6 French Bulldog

So, like it or not we are all anesthetizing a lot of brachycephalic breeds and this is unlikely to change any time soon. These breeds have a multitude of health issues and their welfare should be a concern to veterinarians and the public (1, 2), however many owners consider their pet’s clinical signs as “normal” which makes efforts to improve the health and welfare of these breeds a challenge.(3)

Problems seen in Bulldogs include but are not limited to breathlessness, respiratory distress, inability to whelp normally (> 80% require a C-section), skin diseases, eye problems, osteoarthritis, heat stress (brachycephalic dogs have the highest mortality rate during air transportation and many airlines now refuse to transport them) and pulmonic stenosis.

Upper respiratory tract disease known as brachycephalic airway obstruction syndrome (BAOS) has been described in the Pekinese, Pugs, Bulldogs, and Boxers. Airway obstruction results from stenotic nares, elongated soft palate (Figure 1), redundant pharyngeal folds, as well as secondary changes, including everted laryngeal saccules (Figure 2), laryngeal collapse and aspiration pneumonia. Compared to dolichocephalic dogs brachycephalic dogs have lower arterial oxygen concentration (PaO2), higher carbon dioxide values (PaCO2), elevated packed cell volumes and hypertension.(4) Other problems reported are hypoplastic tracheas (Figure 3), partial collapse of the left main stem bronchi, epiglottic cysts and laryngeal granulomas.(5) In addition many brachycephalic dogs are obese (Figure 4) which adds another layer of problems to everyday living and when they require anesthesia including left ventricular hypertrophy, further hypertension and hypoxemia, altered requirements for anesthetic drugs, increased anesthetic mortality, additional risk of heat stress, and exaggerated inflammatory responses after surgery or following trauma.(6-9)

The welfare of these dogs is an active area of discussion in the veterinary profession and since the documentary film “Pedigree Dogs Exposed”a attempts to change the situation have come into effect at least in some countries but progress has been slow.

Reasons for anesthesia

There are many reasons for anesthesia in brachycephalic breeds; it may to surgically ameliorate BAOS by shortening the soft palate, enlarging the nares and removing everted laryngeal saccules, to perform a C-section or to perform an orthopedic procedure. Regardless several key steps are required for a good outcome.

1. Keeping the patient calm – this may require sedation or someone sitting with the dog and using low-stress handling techniques.

2. Vomiting and aspiration are more likely in brachycephalic than non-brachycephalic breeds. Avoid opioids associated with vomiting (morphine, hydromorphone). Pre-anesthetic use of maropitant is recommended.

3. Gastroesophageal reflux (GER) is common – maropitant has no effect on GER therefore cisapride or metoclopramide should be considered. After intubation and at the end of the procedure the esophagus should be suctioned.

4. IV catheter placement may be challenging. Use of a tourniquet and applying topical anesthetic cream (e.g. a prilocaine/lidocaine eutectic mixture) over the site 15 minutes prior to placement can increase the success rate on the first attempt.

5. Pre-oxygenation; in healthy dogs 3 minutes of 100% oxygen administered by facemask prior to induction of anesthesia increases the mean time to desaturation from approximately 70 seconds to 300 seconds.(10) During intubation a red-rubber catheter or the end of the anesthesia circuit can be used to direct oxygen into the airway.

6. Being prepared to intubate: Use a long flat bladed laryngoscope (Miller) and have several sizes of endotracheal tubes (ETT) smaller than the one you anticipate using available; even in a 30 kg Bulldog the largest ETT that can be placed may be a size 5 mm one!

7. Be prepared to provide intermittent positive pressure ventilation, especially if placed in dorsal recumbency; this can be performed by hand (but ties up a person full time) or a mechanical ventilator.

8. Monitoring: End-tidal CO2 (capnography), SaO2 (pulse oximeter), body temperature (rectal and esophageal) and blood pressure are all recommended.

9. Monitor body temperature closely as overheating is a real risk. 10. If airway surgery is performed with a laser make sure all safety procedures are followed;

the endotracheal tube can remain in place but must be shielded (e.g. use 3M aluminum tape to wrap the tube) to prevent an airway fire.

11. If airway surgery is performed dexamethasone SP 0.25 -0.5 mg/kg IV is recommended and if given, NSAID cannot be used.

12. Recovery: these patients should be observed closely during and for at least 3 hours after the end of anesthesia. After extubation be prepared to re-anesthetize and reintubate if there are problems (stridor, cyanosis etc.) Figure 5.

13. After extubation, supplement with oxygen by facemask for 3-5 minutes then challenge the patient by monitoring with a pulse oximeter for at least 5 minutes after they are breathing room air.

Anesthetic protocols

Premedication: acepromazine (0.01-0.03 mg/kg) plus an opioid such as butorphanol (minor procedures or for diagnostic non-surgical procedures), buprenorphine or methadone; these

opioids do not cause vomiting. If hydromorphone or morphine are used, give maropitant at least 45 minutes prior to administration. Dexmedetomidine is reversible and the sedative effects are dose related; however vomiting is possible so again, maropitant or ondansetron is recommended.

Induction: oxygen should be administered by face mask for 3 minutes before giving intravenous induction agents (with the face mask kept in place until it is time to intubate). Propofol or alfaxalone co-administered with midazolam or diazepam are excellent choices. Propofol and alfaxalone can cause apnea unless administered slowly (over 60 seconds). Giving 1-2 mg/kg of lidocaine IV 1-5 minutes prior to intubation will obtund the gag / cough reflex and improve intubation conditions.(11, 12) Ketamine can be used (with a benzodiazepine) but the gag reflex is maintained and may make intubation more challenging. On a mg/kg basis obese animals need significantly less induction agent therefore always give them slowly and to effect.(6)

Maintenance: isoflurane or sevoflurane are suitable maintenance agents.

Take-home message

Brachycephalic breeds have a higher risk of anesthetic related morbidity and mortality and require careful planning and changes in routine management, however the outcome can be good.

Figure 1. Elongated soft palate

Figure 2. Everted laryngeal saccules in a Bulldog presented with acute respiratory distress

Figure 3. lateral thoracic radiograph showing a Bulldog with a hypoplastic trachea.

Figure 4. In addition to airway issues many Bulldogs are obese.

Figure 5. Be prepared to anaesthetize and reintubate if there are problems after extubation.

References

a. http://topdocumentaryfilms.com/pedigree-dogs-exposed/ 1. Schlueter C, Budras KD, Ludewig E, Mayrhofer E, Koenig HE, Walter A, et al.

Brachycephalic feline noses: CT and anatomical study of the relationship between head conformation and the nasolacrimal drainage system. J Feline Med Surg. 2009;11(11):891-900.

2. Beausoleil NJ, Mellor DJ. Introducing breathlessness as a significant animal welfare issue. N Z Vet J. 2015;63(1):44-51.

3. Packer RMA, Hendricks A, Burn CC. Do dog owners perceive the clinical signs related to conformational inherited disorders as "normal" for the breed? A potential constraint to improving canine animal wlefare. . Animal Welfare. 2012;21(S1):81-93.

4. Hoareau GL, Jourdan G, Mellema M, Verwaerde P. Evaluation of arterial blood gases and arterial blood pressures in brachycephalic dogs. J Vet Intern Med. 2012;26(4):897-904.

5. Bernaerts F, Talavera J, Leemans J, Hamaide A, Claeys S, Kirschvink N, et al. Description of original endoscopic findings and respiratory functional assessment using barometric whole-body plethysmography in dogs suffering from brachycephalic airway obstruction syndrome. Vet J. 2010;183(1):95-102.

6. Boveri S, Brearley JC, Dugdale AH. The effect of body condition on propofol requirement in dogs. Vet Anaesth Analg. 2013;40(5):449-54.

7. Adolphe JL, Silver TI, Childs H, Drew MD, Weber LP. Short-term obesity results in detrimental metabolic and cardiovascular changes that may not be reversed with weight loss in an obese dog model. Br J Nutr. 2014;112(4):647-56.

8. Love L, Cline MG. Perioperative physiology and pharmacology in the obese small animal patient. Vet Anaesth Analg. 2015;42(2):119-32.

9. Mosing M, German AJ, Holden SL, MacFarlane P, Biourge V, Morris PJ, et al. Oxygenation and ventilation characteristics in obese sedated dogs before and after weight loss: a clinical trial. Vet J. 2013;198(2):367-71.

10. McNally EM, Robertson SA, Pablo LS. Comparison of time to desaturation between preoxygenated and nonpreoxygenated dogs following sedation with acepromazine maleate and morphine and induction of anesthesia with propofol. Am J Vet Res. 2009;70(11):1333-8.

11. Panti A, Cafrita IC, Clark L. Effect of intravenous lidocaine on cough response to endotracheal intubation in propofol-anaesthetized dogs. Vet Anaesth Analg. 2016;43(4):405-11.

12. Thompson KR, Rioja E. Effects of intravenous and topical laryngeal lidocaine on heart rate, mean arterial pressure and cough response to endotracheal intubation in dogs. Vet Anaesth Analg. 2016;43(4):371-8.

Suggested reading

Dr. Stuart Clark-Price, Anesthesia Tips for the Obese Patient: Ask the Expert, NAVC Clinician’s Brief, February 2010

Dr. Jonathan Miller and Dr. Kristi Gannon, Perioperative Management of Brachycephalic Dogs, Ask the Expert (surgery), Clinicians Brief, April 2015. [cliniciansbrief.com]

Dr. Heidi Phillips, Brachycephalic Syndrome, Veterinary Team Brief, September 2016 [veterinaryteambrief.com]

Tasha McNerney, Top 3 Tips for Intubating Brachycephalic Dog Breeds, Veterinary Team Brief, April 2016. [veterinaryteambrief.com]

Tasha McNerney, Anesthetic Considerations in Brachycephalic Dogs, Veterinary Team Brief, March 2017. [veterinaryteambrief.com]

PERIOPERATIVE CARE OF DIABETIC PATIENTS Diabetes mellitus (DM) in dogs and cats is a treatable condition but requires a committed owner and veterinarian and long term stabilization can be challenging. The risk of developing this disease is increasing as obesity rates in pets rises.

A DM patient may require anesthesia for reasons related (e.g. phacoemulsification cataract surgery) or unrelated (e.g. endoscopy, mass removal, GI foreign body removal) to the disease. Other comorbidities may be present including but not limited to obesity, autonomic neuropathy, hepatic lipidosis, hyperadrenocorticism and infections (e.g. urinary tract). Regardless of the type of DM (1 or 2), chronic hyperglycemia leads to damage to the kidney, eye, heart and vasculature all resulting in an increased anesthetic risk. Electrolyte disturbances, especially a high or low blood potassium is an additional concern. If a procedure is elective, any patent with ketoacidosis should be stabilized. Some dogs with DM may be receiving medication to control hypertension (often vasodilators), which can result in hypotension during anesthesia especially with high vaporizer settings of inhalant anesthetics. The focus of the rest of this discussion is on anesthesia for non-ketoacidotic patients.

There are no “set” protocols for insulin administration to diabetic patients on the day of surgery; Kronen and colleagues randomly assigned dogs to receive 25% or 100% of their normal insulin dose on the morning of surgery and concluded that “the administration of a full dose of insulin is only marginally advantageous for reducing glucose to normal (70-120 mg/dL) after anesthesia but neither dose consistently induced glycemic values in an acceptable range (70-200 mg/dL)”.(1)

A single blood glucose result in a cat can be difficult to interpret because stress related hyperglycemia is so common in this species. A stressful event in any cat may result in blood glucose values of between 180 and 270 mg/dL for 3 to 4 hours. For this reason at-home results or the results of a fructosamine test (in dogs) can provide valuable information. In dogs, the fructosamine concentration reflects the average blood glucose concentration in the previous 1-2 weeks so provides information on glycemic control.

Another common question is “how long should dogs and cats be fasted prior to surgery?”, this is now an area of debate for all anesthesia patients, not just those with DM. A small (≤ half the daily ration) meal of canned food 3 hours before anesthesia results in a higher pH of gastric contents and no significant difference in gastric volume compared to dogs fasted for 10 hours.(2)

This strategy may reduce gastroesophageal reflux and the less acidic gastric contents are less likely to lead to esophageal damage and is what this author recommends. The owner can feed to dog or cat early in the morning, but if there is a history of motion sickness, oral maropitant can be dispensed to be given at the same time.

Diabetic patients should be scheduled for first thing in the morning, so that they can, if possible, be sent home the same day – this allows them to resume their normal routine and especially for cats, will reduce stress. Dogs with diabetic induced cataracts require special handling due to their vision impairment. Signs should be posted on the cage or kennel door that the dog is blind and it is important to speak and maintain physical contact with these patients when working with them. As for all patients, low-stress and fear-free handling techniques should be used.

Patient preparation, premedication, induction and maintenance of anesthesia

The following (Table 1) table gives recommendations for insulin administration on the morning of surgery.

Table 1. Insulin administration on the morning of surgery:

Blood glucose mg/dL Blood glucose mmol/l Action < 145 < 8 No insulin

145-270 8-15 Give half of the regular dose of insulin

> 270 > 15 Give full insulin dose To convert mg/dL to mmol divide by 18, to convert mmol/l to mg/dL multiply by 18

A main goal of anesthesia of DM patients is a smooth but rapid recovery and resumption of feeding soon after surgery.

As soon as the patient arrives and the physical examination has been completed, maropitant (if not already given by the owner- see above) is an excellent strategy. Maropitant decreases the time to resumption of voluntary food intake and food consumption in the first 24 hours (in dogs given morphine), decreases the risk of vomiting, and is anesthetic sparing.

Short acting and / or reversible drugs are preferred; however alpha2 -adrenergic agonist drugs (dexmedetomidine) should be avoided because they exacerbate hyperglycemia by inhibiting the release of insulin. In a patient that is easy to manage, an intravenous catheter can be placed without sedation. Diabetic patients are immunosuppressed and more prone to infection therefore great care is required when placing IV catheters – an aseptic rather than “clean” placement is essential, and if things do not go as planned IV catheters may be required for > 24 hours compared to the usual 3-4 hours after routine anesthetic and surgical procedures. Wipe injection ports with alcohol every time they are to be used. After anesthesia induction, a second catheter should be placed so that one is for fluid administration and one is dedicated to blood sampling – ideally there is one in a forelimb and one in a hindlimb and both should be easy to access. If dextrose containing fluids are administered that IV line / catheter site can no longer be relied upon for sampling even if blood is drawn back before taking the sample.

During anesthesia diabetic dogs are significantly more likely to suffer from moderate to severe hypotension (mean arterial pressure < 54 mmHg) than non-diabetic dogs. This may be explained by hypovolemia secondary to hyperglycemia resulting in osmotic diuresis.(3)

Glycosuria usually occurs in dogs when blood glucose is > 200 mg/ dl and >250 mg/dL in cats. Because many DM patients are hypovolemic starting fluids prior to anesthesia can be valuable and may help prevent episodes of severe hypotension.

Suitable premedicant agents include opioids and benzodiazepines. Midazolam but not diazepam can be given IM, and both drugs are reversible with flumazenil. An excellent way to utilize benzodiazepines as part of the anesthetic protocol is a co-induction drugs (see below). If possible avoid intramuscular administration of emetogenic opioids such as morphine and hydromorphone; unless maropitant has been given. However these opioids rarely cause vomiting if given slowly IV. Buprenorphine, butorphanol and methadone are unlikely to result in vomiting regardless of route of administration. It is much more difficult to recognize or quantify nausea in dogs and cats and clinical signs can be subtle (e.g. lip licking), but in humans most opioids can result in nausea and unwillingness to eat after anesthesia. Maropitant is a good

anti-emetic but not a good anti-nausea drug therefore ondansetron is a drug worth considering in DM patients.

Low doses (0.01-0.025 mg/kg) of acepromazine can be used if hypovolemia is controlled; this drug has anti-emetic properties and is anesthetic sparing (significant decrease in inhalant anesthetic requirements).

Suitable induction drugs include propofol and alfaxalone as both are short acting. Using diazepam or midazolam as a co-induction agent will reduce the dose of propofol and alfaxalone and result in excellent muscle relaxation; one way to do this is to give ¼ of the calculated dose of propofol or alfaxalone, followed 30 seconds later with diazepam or midazolam at 0.25 mg/kg; reassess the patient and often within 30 seconds intubation is possible; if not give another small dose of the chosen induction agent. Ketamine can induce hyperglycemia in rodent models of diabetes, but not in normal rats.(4) This may be more of a theoretical rather than a clinical concern and if a ketamine/benzodiazepine induction is appropriate it should be used and if a constant rate infusion (CRI) of ketamine was indicated in a diabetic patient (as part of a multimodal analgesic plan) it should also be used.

Choice of maintenance agent includes sevoflurane or isoflurane. Inhalant agents cause vasodilation, respiratory and cardiovascular depression therefore anesthetic sparing techniques are encouraged and will greatly reduce the incidence of hypotension. A CRI of lidocaine can be used in dogs to provide additional analgesia and decrease inhalant anesthetic requirements but are not recommended in cats due to severe cardiovascular depression.(5) Fentanyl infusions can be used in dogs and cats to decrease inhalant anesthetic requirements and to provide analgesia. Whenever possible utilize local anesthetic techniques to decrease anesthetic requirements and to improve patient comfort post-operatively. This can range for using intraperitoneal bupivacaine for abdominal procedures to sciatic and femoral nerve blocks for stifle surgery.

Frequency of blood glucose sampling will depend on the actual starting blood glucose and how labile or sick the patient is, but testing every 30-60 minutes is recommended. All blood glucose monitors should be calibrated and validated or designed for use in dogs and cats and ideally the same one is used for the patient for every sample. It should be noted that some hand-held glucometers designed for humans are inaccurate especially at the low end of their scale. The optimal target for BG in dogs and cats in the perioperative period is unknown but maintaining a BG between 150 and 250 mg/dL is suggested. If dextrose is given it should be diluted to a 1-5% solution by adding 50% dextrose to an isotonic fluid (e.g. lactated Ringers solution), or using commercially available solutions (e.g. 5% dextrose); 50% dextrose will cause phlebitis if given through a small bore peripheral catheter.

Management of severe changes in blood glucose

Blood glucose mg/dL Blood glucose mmol/l Action

Hypoglycemia < 54 < 3 0.25-0.5 g/kg glucose as slow IV bolus. Stop when BG reaches 250-300 mg/dL

BG between 300 and 540

> 6 and < 30 Give half the patients’ normal insulin dose SC

Hyperglycemia > 540 > 30

Give normal insulin protocol SC Or, start an infusion of regular insulin at 0.025-0.05 U kg/hour

SC = subcutaneous.

Intraoperative hypotension

As already discussed this is more common in diabetic than non-diabetic patients. It can be ameliorated by starting IV fluids prior to anesthesia, using anesthetic sparing techniques but may still occur and require treatment. The first step would be to assess anesthetic depth and turn down the vaporizer setting if possible. If a bolus if IV fluids results in an increase in blood pressure, volume depletion is likely the cause, and the fluid rate can be increased. However this is not recommended in the face of cardiac disease. Colloids (e.g. hydroxyethyl starch, [Hetastarch, 6% Hetastarch in 0.9% Sodium Chloride Injection]) may be required. Other strategies are to give positive inotropes (dopamine or dobutamine), or a mixed alpha and beta agonist drug such as ephedrine; dopamine and dobutamine must be given as an infusion but ephedrine can be given as a single bolus.

Post-anesthetic care

If there is a delay in recover check:

1. the temperature (if cold start active warming) 2. check blood glucose, if low administer dextrose (as above)

If neither of the above are the problem, reverse anesthetic drugs such as benzodiazepines. If this still does not result in recovery, opioids can be reversed but if surgery has been performed this should be done very slowly with dilute naloxone (1:10 dilution to achieve 0.04 mg/ml), or using butorphanol to reverse a pure opioid agonist – with either technique stop administration as soon as the dog or cat becomes aware.

As soon as the dog or cat can maintain sternal recumbency unaided a small amount of food can be offered; ideally this should be its normal food (ask the owner what that is and if you do not stock it have them bring some with them). It is also good to know what the pet’s favorite treat is as that may be required to coax them to start eating. Returning to normal feeding and schedule of insulin administration should be achievable within 24 hours.

Check list for diabetic patients

� Pre-anesthetic glucose value � Pre-anesthetic electrolytes

� 2 IV catheters – placed aseptically � Glucometer � 50% dextrose � 0.9% saline � LRS � Insulin

References

1. Kronen PWM, Moon-Massat PF, Ludders JW, Gleed RD, Kern TJ, Randolph J, et al. Comparison of two insulin protocols for diabetic dogs undergoing cataract surgery. Veterinary Anaesthesia and Analgesia. 2001;28:146-55.

2. Savvas I, Rallis T, Raptopoulos D. The effect of pre-anaesthetic fasting time and type of food on gastric content volume and acidity in dogs. Vet Anaesth Analg. 2009;36(6):539-46.

3. Oliver JA, Clark L, Corletto F, Gould DJ. A comparison of anesthetic complications between diabetic and nondiabetic dogs undergoing phacoemulsification cataract surgery: a retrospective study. Vet Ophthalmol. 2010;13(4):244-50.

4. Chen H, Li L, Xia H. Diabetes alters the blood glucose response to ketamine in streptozotocin-diabetic rats. Int J Clin Exp Med. 2015;8(7):11347-51.

5. Pypendop BH, Ilkiw JE. The effects of intravenous lidocaine administration on the minimum alveolar concentration of isoflurane in cats. Anesth Analg. 2005;100(1):97-101.

Recommended reading

Dr. Khursheed Mama, Anesthesia for pancreatic disease, Clinician’s Brief, June 2013.

Dr. Dana L. Clarke and Dr. Deborah C. Silverstein, Blood Glucose Monitors, Clinician’s Brief, June 2010.

American Animal Hospital Association 2010 Diabetes Management Guidelines for Dogs and Cats. https://www.aaha.org/professional/resources/diabetes_management.aspx

ANESTHESIA FOR THE YOUNG AND THE OLD Anesthesia for dogs and cats at either end of the age spectrum deserves special attention. Pediatric and senior patients have unique physiology and are less robust than when adolescents or in their prime. The unique needs of dogs and cats at different life stages have led to the publication of several excellent resources:

• The AAFP-AAHA Feline Life Stages Guidelines: o available at: https://www.aahanet.org

• The AAFP Senior Care Guidelines: o available at: http://catvets.com

• The AAHA Senior Care Guidelines for Dogs and Cats: o Available at: https://www.aahanet.org

The International Veterinary Senior Care Society (http://ivscs.org) is another resource for information about senior animals and is aimed at veterinarians, veterinary teams and owners. Senior pets may make up 30% of the patients seen by veterinarians and many of these may require anesthesia for a variety of reasons including dental procedures which are recommended on a frequent basis in this population. Many animals undergoing elective neutering at an early age and these patients require special handling to ensure a good outcome.

For the purposes of this talk a pediatric kitten or puppy is less than 6 months of age. Cats tend to age more uniformly and a senior cat is between 11 and 14 years of age and a geriatric cat is between 15 and 25 years of age. Breeds of dogs age at different rates therefore dogs can be considered “senior” when they have reached 75% of their expected life span.

Anesthetic mortality related to age and size

The Confidential Enquiry into Perioperative Small Animal Fatalities (CEPSAF) study which included 79,178 cats has provided valuable information on the risks associated with anesthesia in small animals. Senior dogs (> 12 years) are at a significantly higher risk (7 times more likely to die than dogs in the 6 month to 8-year-old range) when they undergo anesthesia. This risk is still real when other confounding factors such as ASA physical statusa are accounted for.(1, 2) As with dogs, older cats carry a higher anesthetic risk – cats older than 12 years are twice as likely to die compared to cats aged 6 months to 5 years and this increased risk was independent from their ASA status.(3).

Small size rather than actual young age also increases anesthetic related mortality; cats that weigh less than 2 kg are high risk cases (odds ratio of 15.7 – i.e. over 15 times more likely to die than cats weighing between 2-6 kg) and dogs < 5kg are at increased risk of anesthetic related deaths (8 times more likely to die than dogs that weigh between 5 and 15kg.[1,2,3]

Pediatric animals

Their small size and large surface area to body weight ratio and lack of body fat makes young animals susceptible to hypothermia. Their small size also makes intravenous access challenging. Monitoring vital signs can also be difficult. Cardiac output in young animals is predominantly heart rate dependent as they have little ability to alter stroke volume. One of the most common causes of bradycardia is hypothermia. Sympathetic innervation to the heart is

immature early in life but parasympathetic innervation is mature and they are less able to compensate for fluid losses or hemorrhage. Oxygen requirements are high and this age group is at an increased risk for hypoxemia especially if they become cold then shiver during recovery because shivering can dramatically increase oxygen requirements. Their ability to metabolize some drugs may be limited due to immature hepatic enzyme systems. Glycogen stores are very limited therefore hypoglycemia is another threat they face.

Data from animal and human neonates clearly demonstrate that inadequate pain management in early life alters neurodevelopment and pain thresholds with negative effects that are long lasting and influence pain experiences later in life.(4) (5)

Tips for pediatric anesthesia:

• Do not fast if still on an all milk diet • Fast for < 2 hours if on solid food • Give 50% dextrose or corn syrup (e.g. Karo syrup) prior to anesthesia • Weigh accurately • Dilute drugs to ensure accuracy of dosing • Use insulin syringes to measure drug volumes accurately • Use short acting or reversible drugs, for example:

o Diazepam and midazolam o Opioids o Dexmedetomidine

• Use analgesic agents preemptively • Monitor heart rate – a Doppler probe placed over the heart works well • Monitor SpO2 (pulse oximeter) • Treat bradycardia • Prevent hypothermia

o Avoid cold scrub solutions and excessive wetting o Pre-warm neonates in the waiting area (cover with blankets, use heating

pads and forced warm air devices • Minimize anesthesia time

Senior and geriatric animals

Although geriatric patients may belong in a specific “age-bracket” there is a wide variation in their health status. A sub-classification of the geriatric population has been suggested.(6) This includes healthy patients, those with subclinical organ dysfunction and those with overt conditions.

Age related and disease related changes in organ function and body composition can impact on the pharmacokinetics (absorption, distribution, metabolism and elimination) of drugs and dose and dosing intervals may require adjustment in geriatric patients. Organ dysfunction may or may not be measurable. In many cases significant decreases in renal and hepatic function can exist yet this will not be reflected by running routine hematology and chemistry tests.

Cardiac disease can also have a silent presence; a patient may have no detectable heart murmur or history of exercise intolerance yet echocardiography may show evidence of decreased cardiac function; not enough to cause overt disease, but enough to cause concern with some of the agents used for anesthesia and sedation.

When we give a drug we are looking for a pharmacodynamic effect and in geriatric patients this may be different due to changes in body composition (e.g. decreased lean body mass), drug receptors and neurotransmitters.(7) Age and disease related changes in pharmacokinetics and pharmacodynamics can result in adverse effects unless the clinician individualizes each anesthetic and analgesic plan.

Geriatric animals may respond poorly to changes in their environment and many have clinical signs suggestive of cognitive dysfunction (see Benaryeh 2015 under suggested reading). Faced with a hospitalization, or extensive in-patient treatments, some of these animals seem to “give up” within moments of being in a strange environment. This might be something as mild as refusing to interact with caretakers, but could also result in more serious issues such as refusal to eat, or drink water. Encourage caregivers to bring in and leave familiar toys or blankets which are often a comfort to any animal, but especially to older animals. Keeping the hospital stay as short as possible will be beneficial; when possible schedule these patients first thing in the morning so that they can be discharged on the same day.

The most important age-related changes in cardiac function is older animals are decreased ventricular compliance and cardiac reserve. This renders older animals less tolerant of acute changes in intravascular volume – both fluid loss and fluid overload. Older patients have a decreased respiratory reserve. Vital capacity is reduced, the chest wall and lungs become less compliant and anatomic dead space increases making them more susceptible to hypoxia and hypercapnia. With a decrease in respiratory reserve, older animals may rapidly become hypoxic in the immediate post-induction period before they are intubated. For this reason, pre-oxygenation is recommended in older patients.(8) As animals age, renal blood flow decreases as does glomerular filtration rate and the number of functional glomeruli. Older animals may have underlying renal pathology which is well compensated for until they are stressed in the perioperative period (fasting, fluid deprivation, and hypotension) therefore overt post-anesthetic renal failure is a concern. These patients may be administered non-steroidal anti-inflammatory drugs (NSAIDs) for chronic pain or be given these for the acute pain associated with surgical procedures. These drugs block prostaglandin production which is important for maintaining renal blood flow during periods of hypotension. If an NSAID is used in the peri-anesthetic period, great care must be taken to prevent, recognize and treat hypotension and to maintain normal fluid balance and organ perfusion.

Brain mass decreases with age as a result of neuronal loss, cerebral blood flow declines and the quantity of neurotransmitters is reduced. Specific age-related changes indicative of neurodegeneration similar to those seen in aged people have been identified in the brain, brainstem and spinal cord of cats.(9, 10) Although the exact reasons are unclear older humans have decreased anesthetic requirements and this is best documented with the inhalant agents;(11) and has also been demonstrated in dogs.(12, 13) Because of the documented decrease in anesthetic requirements in older patients the depth of anesthesia must be closely monitored by assessing jaw tone, general muscle tone and eye position.

Age can cause changes in drug concentration at the site of action and also alter drug action per se. Some of these changes are related to altered body composition, blood flow and organ perfusion and some are a result of altered metabolism and excretion and changes in the number and density of receptors in target organs. Advanced age can result in unpredictable

drug effects therefore careful choice and administration is the key to a good outcome. It is prudent to choose drugs that are reversible, can be given “to effect” and have a short duration of action.

As with all patients a complete history and physical examination are mandatory. Clinical findings will dictate which pre-anesthetic blood work and tests are undertaken. In humans there are no agreed or mandated laboratory tests based solely upon age.(14) A compete blood count and chemistry plus a urine analysis is generally warranted in this patient population both for evaluation of major body systems and as a baseline for comparison at a later time.

One of the most commonly made mistakes when anesthetizing older patients is to depend primarily on inhalant agents and avoid premedicant agents in the misunderstanding that inhalant agents are somehow “safer”. Sedation is recommended to decrease anxiety and fear that lead to increased catecholamine release which predisposes the animal to cardiac arrhythmias, peripheral vasoconstriction, increased cardiac work and decreased tissue perfusion. Acepromazine is not contraindicated in geriatric patients although dose requirements (on an mg/kg basis) may be decreased. Acepromazine is an anti-emetic and anti-arrhythmic but one of its most important properties is its anesthetic sparing effect.(15) Two studies have examined the effects of acepromazine on systemic blood pressure and glomerular filtration rate (GFR) measured by scintigraphy in dogs.(16, 17) Acepromazine appears to protect renal function, at least in normal dogs despite a decrease in blood pressure. Acepromazine combined with butorphanol provided excellent sedation and dogs required minimal restraint for the nuclear scintigraphy procedure and glomerular filtration rate was no different after sedation compared to measurements obtained from the same dogs without sedation despite a decrease in systolic, diastolic and mean blood pressure.(16) In the same study, diazepam and ketamine resulted in significant increases in heart rate and blood pressure but resulted in a lower GFR compared to the acepromazine/butorphanol combination. Preserving renal blood flow and GFR is especially important in older patients who may have decreased renal reserve or are receiving non-steroidal anti-inflammatory medication for acute or chronic pain.

Benzodiazepines such as midazolam and diazepam produce more reliable sedation in older patients than in younger ones. For premedication, midazolam has an advantage over diazepam because it can be given intramuscularly. These drugs are also reversible with flumazenil should an adverse event occur. Opioids produce sedation and provide analgesia and should be a part of all anesthetic protocols. In dogs opioids are significantly anesthetic sparing but this effect is less in cats.

Ketamine causes an increase in heart rate and blood pressure which may be detrimental to some older patients. Ketamine used at induction or at recovery offers some additional analgesic benefits.(18) In the face of hypovolemia, ketamine supported cardiovascular function and did not impair tissue oxygenation.(19) The pros and cons of ketamine in each individual must be considered before it is used. Propofol can be titrated slowly “to effect” without causing excitement and when used after premedication the dose required for induction is significantly reduced. When preceded by intravenous diazepam or midazolam, induction is smooth and again the dose can be reduced. It is important to avoid large doses of propofol as it can result in hypotension. Propofol is rapidly metabolized even in patients with poor liver function(20, 21) and recovery is rapid and complete with no “hang over”. Etomidate has minimal cardiopulmonary depressant effects and in aged dogs and cats with cardiac disease or in the face of fluid losses, but is expensive and not commonly available.(22)

For all but the shortest procedures inhalant agents are most commonly used for maintenance of anesthesia. All inhalant agents are potent cardio-respiratory depressant agents making the use of anesthetic sparing drugs and techniques important. Intra-operative infusions such as opioids and low doses of ketamine reduce inhalant agent requirements and provide additional analgesia. Lidocaine infusions can be used in dogs(23) but not cats.(24) The use of locoregional techniques (e.g. epidurals, specific nerve blocks) are extremely beneficial in older patients as they decrease anesthetic requirements and improve post-operative comfort.

Most anesthetic deaths occur in the first three hours of the recovery period, likely because this is a time when physiological support is withdrawn; for example animals go from breathing 100% oxygen to room air at a time when their requirements for oxygen may increase if they are cold and shivering. This is especially detrimental in older patients with reduced cardiac and respiratory reserves. For these reasons, supplemental oxygen should be given until animals are normothermic and thermal support should be provided. At this time all patients should be assessed for pain in addition to other vital signs.

Although our very young and very old patients may be “more delicate” and challenging to anesthetize, with careful assessment and choice of anesthetic protocols a good outcome should be the rule and not the exception.

References

a. American Society of Anesthesiologists physical status classification: http://www.asahq.org

1. Brodbelt DC, Blissitt KJ, Hammond RA, Neath PJ, Young LE, Pfeiffer DU, et al. The risk of death: the confidential enquiry into perioperative small animal fatalities. Vet Anaesth Analg. 2008;35(5):365-73.

2. Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Results of the confidential enquiry into perioperative small animal fatalities regarding risk factors for anesthetic-related death in dogs. J Am Vet Med Assoc. 2008;233(7):1096-104.

3. Brodbelt DC, Pfeiffer DU, Young LE, Wood JL. Risk factors for anaesthetic-related death in cats: results from the confidential enquiry into perioperative small animal fatalities (CEPSAF). British journal of anaesthesia. 2007;99(5):617-23.

4. Brondani JT, Luna SP, Marcello GC, Padovani CR. Perioperative administration of vedaprofen, tramadol or their combination does not interfere with platelet aggregation, bleeding time and biochemical variables in cats. J Feline Med Surg. 2009;11(6):503-9.

5. Allegaert K, Tibboel D, van den Anker J. Pharmacological treatment of neonatal pain: In search of a new equipoise. Semin Fetal Neonatal Med. 2013;18(1):42-7.

6. Kukanich B. Geriatric veterinary pharmacology. Vet Clin North Am Small Anim Pract. 2012;42(4):631-42, v.

7. Landsberg GM, Denenberg S, Araujo JA. Cognitive dysfunction in cats: a syndrome we used to dismiss as 'old age'. J Feline Med Surg. 2010;12(11):837-48.

8. McNally EM, Robertson SA, Pablo LS. Comparison of time to desaturation between preoxygenated and nonpreoxygenated dogs following sedation with acepromazine maleate and morphine and induction of anesthesia with propofol. Am J Vet Res. 2009;70(11):1333-8.

9. Zhang JH, Sampogna S, Morales FR, Chase MH. Age-related ultrastructural changes in hypocretinergic terminals in the brainstem and spinal cord of cats. Neurosci Lett. 2005;373(3):171-4.

10. Gunn-Moore DA, McVee J, Bradshaw JM, Pearson GR, Head E, Gunn-Moore FJ. Ageing changes in cat brains demonstrated by beta-amyloid and AT8-immunoreactive phosphorylated tau deposits. J Feline Med Surg. 2006;8(4):234-42.

11. Nickalls RW, Mapleson WW. Age-related iso-MAC charts for isoflurane, sevoflurane and desflurane in man. British journal of anaesthesia. 2003;91(2):170-4.

12. Yamashita K, Iwasaki Y, Umar MA, Itami T. Effect of age on minimum alveolar concentration (MAC) of sevoflurane in dogs. J Vet Med Sci. 2009;71(11):1509-12.

13. Magnusson KR, Scanga C, Wagner AE, Dunlop C. Changes in anesthetic sensitivity and glutamate receptors in the aging canine brain. J Gerontol A Biol Sci Med Sci. 2000;55(9):B448-54.

14. John AD, Sieber FE. Age associated issues: geriatrics. Anesthesiol Clin North America. 2004;22(1):45-58.

15. Heard DJ, Webb AI, Daniels RT. Effect of acepromazine on the anesthetic requirement of halothane in the dog. Am J Vet Res. 1986;47(10):2113-5.

16. Newell SM, Ko JC, Ginn PE, Heaton-Jones TG, Hyatt DA, Cardwell AL, et al. Effects of three sedative protocols on glomerular filtration rate in clinically normal dogs. Am J Vet Res. 1997;58(5):446-50.

17. Bostrom I, Nyman G, Kampa N, Haggstrom J, Lord P. Effects of acepromazine on renal function in anesthetized dogs. Am J Vet Res. 2003;64(5):590-8.

18. Slingsby LS, Waterman-Pearson AE. The post-operative analgesic effects of ketamine after canine ovariohysterectomy--a comparison between pre- or post-operative administration. Res Vet Sci. 2000;69(2):147-52.

19. Haskins SC, Patz JD. Ketamine in hypovolemic dogs. Critical care medicine. 1990;18(6):625-9.

20. Servin F, Cockshott ID, Farinotti R, Haberer JP, Winckler C, Desmonts JM. Pharmacokinetics of propofol infusions in patients with cirrhosis. British journal of anaesthesia. 1990;65(2):177-83.

21. Servin F, Desmonts JM, Haberer JP, Cockshott ID, Plummer GF, Farinotti R. Pharmacokinetics and protein binding of propofol in patients with cirrhosis. Anesthesiology. 1988;69(6):887-91.

22. Pascoe PJ, Ilkiw JE, Haskins SC, Patz JD. Cardiopulmonary effects of etomidate in hypovolemic dogs. Am J Vet Res. 1992;53(11):2178-82.

23. Valverde A, Doherty TJ, Hernandez J, Davies W. Effect of lidocaine on the minimum alveolar concentration of isoflurane in dogs. Vet Anaesth Analg. 2004;31(4):264-71.

24. Pypendop BH, Ilkiw JE. Assessment of the hemodynamic effects of lidocaine administered IV in isoflurane-anesthetized cats. Am J Vet Res. 2005;66(4):661-8.

Suggested reading

Benaryeh, B. (2015) Cognitive Dysfunction: Overview. Veterinary Team Brief, Nov/Dec. Available at http://www.veterinaryteambrief.com/clinical‐suite/cognitivedysfunction/overview.