This week: The perils of anaesthetics
An anaesthetic is one of the few procedures that always has an element of the unknown and a definite degree of danger. What an anaesthetic basically breaks down to is a semi-controlled coma, where the patient is expected neither to feel nor react to any painful procedure, but still wake up predictably. It usually brings any vet to full alertness, as at any time something can go wrong.
I am going to demystify what occurs when an anaesthetic is given. Whenever there is a negative reaction to an anaesthetic, the first thing that comes up in the client's mind is: has too much anaesthetic agent been used? The answer is rarely so simple.
The procedure can usually be broken down into three stages - induction, maintenance and recovery. The induction stage generally means the use of an anaesthetic agent, usually delivered by injection, that knocks the patient out enough to place a plastic tube down the airways through which anaesthetic gas can be delivered to keep the animal anaesthetised.
The choice and dose of anaesthetic used as an induction agent is usually very well defined. So, if a dog is pregnant and having difficulties in giving birth and a Caesarean section needs to be performed, then we would automatically select a safe anaesthetic for the mother that has a minimal effect on the puppies or kittens. The weight of the dog pretty much defines the dose of anaesthetic.
The best induction agents are given straight into a vein or through a gas mask. In some situations in which our patients are too scared to be handled, such as with a feral cat or a stressed stray dog with a tendency to bite, we may use more risky drugs that can be given anywhere in any muscle.
The most dangerous anaesthetic of all in common use is that employed in dart guns. These are solely used by wildlife vets and the anaesthetic is so potent that a small dart dipped superficially in the anaesthetic agent can knock down a multi-tonne elephant. Not surprisingly, we don't use it in small-animal practice.