ANAESTHESIA IN SIGHTHOUNDS

This is a précis of an article & a paper written by Dr John Dillinger DVM. Indiana USA that I put together for an EEAC magazine in 1999.

I am indebted to Wendy Cross (Deerhounds) for an article that she wrote for HCEA in regard to problems that she had encountered over the years concerning general anaesthetics in her deerhounds. Wendy kindly sent to me  at that time, Dr Dillinger's veterinary paper as several Afghan Hound owners had expressed concern in regard to the recovery period with anaesthesia in their hounds for a variety of procedures.

With grateful thanks to the author & Barbara Heidenreich DVM Ontario, who had sent to Wendy the original veterinary  paper, for allowing further  readership amongst the Afghan Hound fraternity of the information contained in this paper.

During the Renaissance period, Paracelus, a Swiss born physician, first put forward the idea that poisons, substances that HARM, are not almost intrinsically different from medicines that HELP. His ideas, radical at that time, are now widely accepted.

Almost ANY SUBSTANCE can be harmful OR beneficial, dependent on the circumstances and how much is given. As often as not, the only difference between a compound being harmful in one instance and beneficial in another is the amount (dose) given.

These concepts are ESSENTIAL in the understanding of ANAESTHETICS.

Anaesthesia is a state in which the patient loses its ability to feel pain.

Local anaesthesia means pain is blocked only in a localised area.

General anaesthesia means pain is blocked everywhere.

In everyday use, general anaesthesia has come to mean not only loss of ability to feel pain but also.

1. NUMBNESS. loss of all feeling.

2. UNCONCIOUSNESS .loss of awareness.

3 IMMOBILISATION.......paralysis and

4. MUSCLE RELAXATION. The loss of muscle tone.

Opium and related narcotic alkaloids from plants or alcohol, in the form of fermented beverages, were the first anaesthetics.

Gas anaesthesia began in the mid-1880s with the discovery of ether and the effects of nitrous oxide but it was not until cyclopropane was introduced as a human anaesthetic in 1934 that true inhalation anaesthesia found favour. The injectable anaesthesia also began in the 1930s decade when physicians & veterinary surgeons started using pentobarbital. A variety of other gas and injectable agents have subsequently been developed.

Today so called “Balanced Anaesthesia”, using a combination of BOTH agents is the NORMAL for many procedures both in man & in dogs.

In today’s veterinary medicine, many combinations of anaesthetic agents and techniques are available and new ones continue to be developed. Each will have its advantages and disadvantages.

Which one your vet  may use for a particular patient will depend on  a multitude of factors; agents and equipment available; the reasons for the anaesthetic (Xray; minor /major surgical procedure; caesarean section to name but a few); the patient’s age; health factors & BREED.

Vets will commonly use injectable agents for short term anaesthesia (10 minutes or so).

An advantage of  some of these, such as Droperidol, is that the action of the drug can be rendered reversible once the procedure has been completed so that a hound can be awakened immediately. Costs of such drugs are usually high.

Another option for a short procedure is to give the hound a gas agent such as Isoflurane by face mask until it is  anaethetised deeply enough for whatever procedure is intended. Isoflurin’s main advantage is that the patient can be awakened rapidly, as soon as the mask is removed the hound wakes up.

Still another option for a short procedure, such as suturing a wound, is the use of a local anaesthetic, however this will only work if the dog is co-operative, a calm dog who will remain still whilst a wound is clipped, debrided and sutured.

During the past two decades, the trend for a long tem anaesthetic has been away from using the injectables alone, but towards “Balanced Anaesthesia” in which the patient is lightly anaethetised with an injectable agent and maintained throughout the procedure on a gas anaesthesia.

BREED as been mentioned as a factor affecting choice of anaesthetic.

SIGHTHOUNDS have been selected over centuries for speed and stamina, they are often referred to as the “CANINE ATHLETES”. They differ anatomically and physiologically from other breeds.

Sighthounds in general are lean.

An average mixed breed dog has 35o/o of body fat.

The average Greyhound has 17o/o.

Reduced body fat affects anaesthesia in at least two ways.

1. LESS FAT means less  insulation so any Sighthound is more prone to HYPOTHERMIA (low body temperature) whilst under GA.. This tendancy is aggravated in the larger sighthound by their high area to body mass ratio, which causes them to cool off more rapidly.

Hypothermia is especially common in anaesthetised Whippets; Greyhounds; Ibizan Hounds; Pharaoh Hounds and Salukis. their short coats provide NO body insulation.

The coated  hounds, Deerhounds: Afghan Hound & the Borzoi, their coats may reduce their risk of hypothermia BUT it is  still a good idea to cover such anaesthetised hounds with warm blankets, keep them off cold surfaces and to avoid giving such hounds refrigerated intravenous fluids.

The second way  reduced body fat affects anaesthesia has to do with how commonly used injectables (called ultra short acting barbiturates) work.

These will include a variety of agents  ie Pentothal: Brevetal: such are widely used for procedures such as taking of Xrays; suturing wounds because they produce anaesthesia that begins fast & only lasts for a short time. Once injected, such agents rapidly leave the bloodstream to enter the brain, where they are active. However they also rapidly leave the bloodstream to accumulate in fat tissue where they are not active. As the concentration in the blood falls, these ultra shots leave the brain and return to the bloodstream, eventually ending up in body fat.

When the concentration level in the brain falls below a certain level, the patient wakes up. Over several hours, the concentration levels continue falling but more slowly, as the ultra short agent seeps out of the fat and is metabolized by the liver.

These types of injectables affect SIGHTHOUNDS in a different way to other breeds.

The SIGHTHOUND having less body fat means blood & brain concentrations remain HIGHER for LONGER so that the SIGHTHOUND stays UNCONSCIOUS LONGER.

The liver in the SIGHTHOUND metabolises this type of anaesthetic agent more SLOWLY, so as the anaesthetic agent seeps out of the fat, the blood concentration can remain HIGH enough to keep the hound groggy and uncoordinated for HOURS (even DAYS)….Who has not seen this at some stage with an AFGHAN HOUND following even some minor procedures if you have been involved with our breed over the past 20/30 years?....but this does not mean that such agents should not be used on these  breeds, it just means LOWER DOSES should be used & a longer recovery period anticipated.

Compared to other breeds, the SIGHTHOUNDS have larger hearts in proportion to their body weight, this is genetic, nothing to do with exercise or conditioning.

SIGHTHOUNDS pump more blood with each single heart beat, pump it more forcefully, and have a greater elasticity within their arteries to accommodate this. They also have MORE red blood cells per millilitre of blood, this means that they are able to deliver more oxygen faster to their muscles. Such cardiovascular adaptations should actually reduce the risks in anaesthesia.

SIGHTHOUNDS livers metabolise some substances including barbiturate anaesthesia, such as Pentothal more SLOWLY, with small doses this should NOT present a problem but with a LARGER dose being administered or in a hound with a liver that is NOT functioning as efficiently as it should (Age may come into this equation) prolonged barbiturate metabolism can lead to prolonged unconsciousness  and a slow rocky road to recovery with lots of struggling.

There is evidence that dogs recovering from barbiturate anaesthesia begin to feel PAIN long before they are fully conscious and co-ordinated. Some vets have approaches that avoid the barbiturates altogether, certainly prudent in a hound with any evidence of liver damage, by using pre-medication type drugs and then immediately maintaining anaesthesia with the gas agents.

Blood tests run routinely prior to ANY general anaesthetic procedure should be considered a NORMAL ROUTINE practice to detect any specific abnormalities such as liver and kidney disfunction, anaemia, dehydration, infection or potential clotting problems that may NOT be apparent from physical/clinical assessment.

THE BOTTOM LINE.

The development of anaesthetic agents and techniques over the last two decades has made anaesthetics easier and safer and reliable in ALL animal species, including man. There are and always will be risks involved and occasionally patients will die. However many more would die without diagnostic and surgical procedures anaesthesia makes possible.

SIGHTHOUNDS gained their reputation for being at a greater risk from anaesthetics than other breeds during the period when the injectable barbiturates were the main anaesthetic agents that vets used. SIGHTHOUNDS DO react to barbiturates differently but now days BALANCED ANAESTHESIA uses such lower doses of such barbiturates or avoids their use altogether. In addition the action of injectable narcotic anaesthetics can be reversed as soon as anaesthesia is no longer needed.

Gas anaesthetics give a much finer control over anaesthetic depths and allow for a rapid recovery.

Isoflurine gas allows anaesthesia to be induced by a face mask, avoiding the injectable agents completely.

Do not weigh up the risks  of  anaesthesia for  your hound based on opinions formed in the past. Discuss your anxieties with your vet. Anaesthetics are a lot safer today than they were even 20 years ago.

Sylvia Evans.

1999

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