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. An animal is unlikely to die if the correct drug and dose is used. Depending on the situation, the possibility is something in the range of one in hundreds of thousands or a million. Of course there are emergency situations that would increase these odds greatly - you can't always plan surgery in the safest setting. If a dog has ruptured a liver in a car accident and is bleeding internally, then surgery is indicated immediately to stop the bleeding, but liver damage would increase your anaesthetic risk and dogs hit by a car can sometimes have a damaged heart muscle, which also greatly increases the risk of anaesthesia. But in this situation a vet would still go ahead with the surgery despite the anaesthetic risk because the animal would die without the operation. It is easy to give a statistical analysis of anaesthetic risk and these seem like rather good odds, but when that rare death does occur, it is understandably hard to accept for the owner. Maintenance of the anaesthetic in the modern age is usually done by gas. Gases are the safest way to maintain anaesthesia and only in rare circumstances do we choose to use other agents. The machine that provides gaseous anaesthetic is very heavy, and it is next to impossible to transport it and the oxygen canister that comes with it. So, if I find myself having to do surgery off site because bringing the animal to the clinic is impossible or inappropriate, I would use repeat intravenous injections. This is more dangerous; luckily, doing surgery outside an operating theatre is pretty rare in general practice. Then there is the recovery stage, which needs to be closely monitored. Animals under anaesthetic lose their ability to regulate body temperature and there is often a drop in body temperature, so adequate warmth needs to be provided. Animals sometimes struggle violently during recovery, so a confined space with no sharp corners is needed. The recovery period can be divided into immediately post-operative and a few days after. Animals can also stop breathing after surgery. You may think the animal is out of the woods within a couple of days but because of the decrease in oxygenation of the kidneys, animals that had a kidney problem to begin with can come down with kidney failure. Anaesthetics are an exercise in risk management. The best advice I can give is to defer to your veterinarian. Remember, there is often more risk from not doing the anaesthetic, so don't be put off. There are ways to decrease anaesthetic risk, such as administering pre-operative fluids and carrying out a full body blood examination, so ask questions next time your pet faces an anaesthetic. Don't worry too much because with modern anaesthetics, monitoring and procedures, it's pretty safe.
