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AFGHANS ARE US -HEALTH
ANAESTHESIA IN SIGHTHOUNDS
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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 - 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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