Anesthesia

Anesthesia for Scottish Deerhounds

by John Dillberger, DVM, PhD

Reprinted from the March/April 2023 issue of The Claymore.

A one-page sheet that summarizes the key points in this article and is intended specifically for veterinarians can be found here. Feel free to print it and hand it to your own practitioner. 

When I began practice in 1979, sighthounds were considered different than other breeds when it came to anesthesia.  They often needed a lower dose of anesthetic agent, took longer to recover from anesthesia, and had episodes of struggling and excitement during recovery.  Veterinarians attributed these differences to either the lean sighthound body type (less body fat) or some unknown difference in how a sighthound’s body cleared the anesthetic agents commonly used at the time.  

In the decades since, new anesthetic agents and practices have made sighthound anesthesia safer.  Also, researchers have discovered heritable/genetic differences that affect how anesthetic agents (and other drugs) are cleared from a dog’s body.  These genetic differences help explain why some dogs react differently than others to anesthesia.  Genetic tests for these differences are just over the horizon.  

This month, I review what owners and veterinarians should consider when planning to anesthetize a Deerhound.  While I cannot avoid naming specific anesthetic agents, I have tried to keep my explanations free of medical jargon and easy to follow.  That said, don’t worry if your eyes glaze over by the second page.  A 1-page sheet that summarizes the key points in this article and is intended specifically for veterinarians can be found here. Feel free to print that page and hand it to your own practitioner. 

What is anesthesia?

Anesthesia is the process of reversibly rendering a Deerhound unconscious, immobile, relaxed, and pain-free.  It is used to facilitate a diagnostic procedure like getting an X-ray or passing an endoscope down the esophagus, or to allow a surgical procedure.  The process of anesthesia can be divided into five phases:

  1. Pre-anesthesia.  During this phase, the Deerhound is evaluated and tested for anything that might affect anesthesia risk or the choice of anesthetic agent(s).  In non-emergency situations, this can be done days or weeks before anesthesia.
  2. Pre-medication.  During this phase, drugs may be given to relieve anxiety or pain.
  3. Induction.  During this phase, fast- and short-acting injectable anesthetic agents are given to rapidly render a Deerhound unconscious.  These agents may give enough time to do a very short procedure.  But for a longer procedure, the induction phase provides enough time to place a tube into the dog’s windpipe (called an endotracheal tube) through which a gas anesthetic agent is administered.
  4. Maintenance.  During this phase, gas anesthesia and/or injectable agents are used to keep the Deerhound unconscious, immobile, relaxed, and pain-free while maintaining good blood circulation.  
  5. Recovery.  During this phase, the administration of gas anesthesia is stopped so that the Deerhound can regain consciousness and mobility.  Drugs may be given to counteract some that were used during the maintenance phase.  If the dog has undergone surgery, then drugs will continue to be given to manage pain.

Pre-anesthesia Considerations

Before anesthetizing a Deerhound, a veterinarian will have at least 4 questions.

Does the dog have normal heart, liver, and kidney function? 

An issue with heart, liver, or kidney function may influence which drugs and anesthetic agents the veterinarian chooses to use.  Heart function can be evaluated by ultrasound examination (an echocardiogram), electrocardiographic (ECG) evaluation, and/or auscultation with a stethoscope.  Ideally, a Deerhound will have had an echocardiogram to check for heart disease/defects some weeks before surgery.  Liver and kidney function are evaluated through blood tests and sometimes also by urinalysis.

Has the dog been anesthetized previously and, if so, then how did the experience go?  

If a Deerhound has been anesthetized before, then the veterinarian will want to know if the dog had an unexpected or dangerous event during anesthesia.  For example, did the dog have an episode where its heart rate or blood pressure dropped dangerously low?  Did it have an unexpected rise in body temperature (called hyperthermia)?  Was recovery from anesthesia unexpectedly slow or rocky?

Is the dog likely to become excessively excited, anxious, nervous, or stressed by an upcoming veterinary visit for anesthesia?  

For a Deerhound that is stressed by a veterinary visit, the veterinarian may prescribe a sedative or tranquilizer that the owner can give before the dog leaves home and/or administer such a drug as soon as the dog arrives.  Commonly used sedative/tranquilizer drugs are Gabapentin, Acepromazine, and Trazodone.  

Trazodone should NOT be used in Deerhounds that have experienced slow recovery from anesthesia in the past or that genetic testing shows to be at risk for Slow Drug Metabolism.

Has the dog been tested for genetic variants associated with a condition called Slow Drug Metabolism?

Slow Drug Metabolism is a condition that is well documented in Greyhounds and also occurs in Deerhounds.  A dog with Slow Drug Metabolism will clear some anesthetic agents more slowly than normal.  As a consequence, the dog will wake up more slowly and may even have episodes of flailing and excitement while recovering from anesthesia.  The latter is more likely to occur with a group of injectable anesthetic agents called barbiturates (not used much now) or with Ketamine than with Propofol, a newer injectable anesthetic.  

Dr. Court’s laboratory has evidence that Slow Drug Metabolism is partly due to variant forms of two genes named CYP2B11-H3 and POR-H3, which code for enzymes that break down anesthetic drugs. These variants are most common in Greyhounds and Deerhounds.  Genetic testing is not available commercially, but it can be done through Dr. Court.  

Dr. Court would like a DNA sample from any dog that has a slow recovery from anesthesia.  For information and a cheek swab test kit, email his lab.

Pre-medication Phase Considerations

The drugs most often used in sighthounds during this phase are Acepromazine, Hydromorphone, and Butorphanol. 

Acepromazine is a tranquilizer/sedative that can be used to calm nervous dogs.  It is available as a pill that an owner can give the dog before a veterinary visit.  The dose level should be the lowest needed to effectively calm the dog.  Even if the owner has given the dog acepromazine before the visit, an additional dose of acepromazine can be given by injection at the clinic, if necessary; however, the total dose of acepromazine should not exceed 3 mg.  

Hydromorphone and Butorphanol are opioid drugs that provide not only sedation but also pain relief.  They may be used before a procedure that might be painful.  Either can be used with or instead of Acepromazine.  That said, butorphanol alone, without co-administration of a sedative/tranquilizer like Acepromazine, has been associated with mild hyperthermia in susceptible dogs.

Trazodone is sometimes used in the pre-medication phase; however, it can cause a problem for dogs at risk for Slow Anesthetic Drug Metabolism, as previously noted. 

Induction and Maintenance Phases Considerations

During the induction phase, a drug or combination of drugs is given to cause rapid unconsciousness.  The induction agents used today are typically very short-acting and allow only enough time for the placement of an endotracheal tube to administer gas anesthetic or to do a very short procedure.  

Propofol is the most-used drug for anesthesia induction of sighthounds.  An excitement phase can occasionally occur with propofol induction in Deerhounds, but this doesn’t outweigh propofol’s superiority to other drugs in many other ways.  Propofol is fast-acting and safe, and recovery is short and rarely violent.  Propofol is metabolized so rapidly that it makes an excellent induction agent even for Caesarean-sections, where the intent is to minimize the effects in puppies.  

Alfaxalone is a newer anesthetic agent that has proven safe and effective in sighthounds.  It can be used instead of propofol.  However, since Alfaxalone is new, some veterinarians may be less familiar with its use.

Drugs to AVOID using to induce anesthesia in Deerhounds are:

  * Ketamine and Thiobarbiturates (such as thiopental), which can result in slow recovery from anesthesia in dogs at risk for Slow Anesthetic Drug Metabolism.  

  * Co-administration of Ketamine + Diazepam or Tiletamine + Zolazepam (Telazol), as both combinations can cause hyperthermia in susceptible dogs.

  
* Butorphanol without co-administration of a sedative, as this has been associated with mild hyperthermia in susceptible dogs.

During the maintenance phase, one or more anesthetic agents are given to keep the dog unconscious for as long as necessary.  Continuous administration of a gas anesthetic through an endotracheal tube is the maintenance technique of choice nowadays because anesthesia can be easily controlled, the depth of anesthesia can be quickly adjusted by changing the flow rate of the gas, and recovery is rapid when gas administration ends. 

During the maintenance phase of anesthesia, a dog should be carefully monitored for signs of pain, distress, a change in body temperature, or inadequate circulation.  Among the serious events that can affect Deerhounds during the maintenance phase, two deserve mention:  anesthesia-/stress-related hyperthermia and anesthesia-related hyperkalemia. 

Anesthesia-/Stress-related hyperthermia

Hyperthermia is synonymous with fever and means an elevated body temperature.  Deerhounds can develop hyperthermia during either the maintenance or recovery phase of anesthesia.  Hyperthermia most often occurs when anesthesia is used in conjunction with a surgical procedure.  An affected dog will have a rapid increase in body temperature to more than 105°F, which will trigger panting and cause the mucous membranes to take on a deep red color. Treatment includes rapid cooling, intravenous fluid administration, and other measures that vary with the situation. 

Anesthesia-/stress-related hyperthermia is different from a condition known as malignant hyperthermia, which is an increase in body temperate that is invariably fatal. To date, all reported cases of anesthesia-/stress-related hyperthermia in Deerhounds, if recognized early, have responded to appropriate cooling. One Deerhound responded to administration of Dantrolene, a muscle relaxant used to treat malignant hyperthermia. 

Dogs that experience anesthesia-/stress-related hyperthermia are often very anxious before being anesthetized. According to a Greyhound medicine expert (Dr. Guillermo Couto), hyperthermia often can be prevented by judicious use of sedatives before a triggering event (veterinary visit), as well as taking other steps to minimize stress.  While we still have a lot to learn about hyperthermia, the current recommendation is that an owner of a Deerhound that experiences a lot of stress during a veterinary visit or has had a previous hyperthermic event should consider administering an anti-anxiety drug such as gabapentin to the dog before leaving home.  In addition, body temperature should be monitored closely during and following anesthesia and other stressful events. 

Since not all Deerhounds are susceptible to anesthesia-/stress-related hyperthermia, a genetic predisposition has been suspected. With support from the SDCA, Dr. Court has identified a variant of the RYR1 gene in dogs with a history of stress-related hyperthermia.  This variant appears to be a milder form of a variant that causes malignant hyperthermia in dogs.  

Dr. Court would like a DNA sample from any dog that has anesthesia- or stress-related hyperthermia.  For information and a cheek swab test kit, please email his lab.

To date, Dr. Court has studied eight Deerhounds and one Greyhound with anesthesia-related hyperthermia.  In this small series of cases, the following are true:

  1. Most hyperthermic dogs had received Diazepam/Ketamine or Telazol.  One had received Butorphanol.
  2. Anesthetic agents that have been used without problems in these dogs include the injectable agents dexmedetomidine, propofol, alfaxalone and the gas anesthetic isoflurane.
  3. One of the dogs developed hyperthermia (105°F) during anesthesia that decreased by recovery; most other dogs developed hyperthermia during recovery.  Hyperthermia in one dog was not detected until it had returned home the evening of surgery (107°F). However, it was mildly elevated at discharge (103°F).
  4. Agitation and anxiety are frequently mentioned during anesthetic recovery.

Anesthesia-associated hyperkalemia

Hyperkalemia means a higher-than-normal blood potassium concentration.  Anesthesia-related hyperkalemia has not been reported in a Deerhound.  However, a series of cases in Greyhounds and a single case in a Rottweiler have been reported.  Since Deerhounds and Greyhounds share several anesthesia-related issues, and Deerhounds have died during anesthesia of unconfirmed cause, it is worth keeping this possibility in mind.  

Anesthesia-related hyperkalemia is typically noticed as a slow heart rate without another common cause (deep anesthesia, dexmedetomidine use).  If the dog is on a heart monitor, then characteristic changes in the ECG waveform may be observed.  Hyperkalemia can be confirmed by measuring the potassium concentration in the blood.  Treatment involves administration of insulin, which directly lowers blood potassium concentration, along with administration of glucose-containing intravenous fluid to prevent an insulin-related decrease in blood sugar. 

If you have a Deerhound that experiences anesthesia-related hyperkalemia, then please contact the SDCA Health & Genetics Committee or email Dr. Court.

Recovery Phase Considerations

When anesthesia is discontinued, a Deerhound should be moved to a well-padded recovery area with someone designated to sit by the dog’s side as it wakes up.  Body temperature should be monitored often, as most reported cases of hyperthermia in Deerhounds have occurred during recovery.  Heart rate and rhythm also should be monitored, as arrhythmias can occur after anesthesia.  Blood circulation should be monitored, not only by way of mucous membrane color (which should be pale pink and not red, white, grey, blue, or purple) but also by evaluating capillary refill.  Capillary refill is easy to check by pressing your finger on the dog’s gum for a few seconds and then removing your finger.  Your finger will leave a blanched white area.  If it takes longer than 2 seconds for the color to return, then circulation is not adequate. 

Sometimes a dog recovering from anesthesia will be briefly aroused by a noise of light and struggle or try to stand.  Hence, the padding…

The endotracheal tube should be left in place until the swallow reflex returns.  If the dog has slept for awhile before wakening, it may be able to stand and walk immediately.  If not, then the dog should be attended by a calm individual who can stroke and reassure it.  Sometimes the dog’s owner can be that person, unless they are too nervous to be good attendants.  

If the dog is struggling to stand, confinement to a run, cage or ex-pen might be necessary. Depending upon the procedure, release to the owner and home can be accomplished as soon as the dog is steady on its feet.

Treatment for slow anesthetic recovery is simple supportive care.  The dog should be kept warm with blankets and maybe a warm water mattress or bottle(s).  The dog should be kept hydrated by administering intravenous fluids.  The dog should be on appropriate bedding, and its position should be changed periodically to avoid pressure sores and pooling of blood.

With Appreciation

Dr. Michael Court, Dr. Betty Stephenson, and the SDCA’s Health Research Liaison, Miranda Levin, contributed extensively to this article, both in content and review time.