General information on anaesthetic monitoring
When an animal has to have surgery, there are different ways to eliminate pain. Depending on the operation, local anaesthetic may suffice or a general anaesthetic may be needed. This can be a drug injected into muscle or vein or inhaled through a mask. The choice of a suitable drug depends on the duration and type of operation and on the patient’s fitness. Every general anaesthetic – even when given perfectly – is associated with a certain risk. Good anaesthetic monitoring minimises this risk.
Anaesthetic monitoring stages in animals
Before the operation
Anaesthetic monitoring includes prior clarification of certain questions:
- How old and fit is the animal? A general anaesthetic always affects the circulation to a greater or less degree, depending on the drug used.
- The exact weight is recorded and height is estimated to calculate the correct dose of the anaesthetic. Animals with a lot of fat are given different doses than very fit and muscular animals.
- Are there known allergies or intolerances for certain drugs?
- Are there chronic diseases that have nothing to do with the reason for surgery? For instance, chronic kidney or liver disease can alter the metabolism of an anaesthetic drug. Or certain drugs must not be used because they would stress the already diseased organs too much. It is also important for the vet to know if the animal has haemophilia, a blood clotting disorder. If the operation is performed anyway, it may be useful to have stored blood available in case too much blood is lost.
By the way, animals should ideally be fasting when they are given a general anaesthetic, which is not always possible with emergency surgery. Many anaesthetics cause nausea. If the animal then vomits, the vomited food can be inhaled or can choke the animal, which must be prevented as far as possible. For small animals such as rabbits or guinea pigs, this does not apply so much. Their gastrointestinal tract does not cope as well with periods of fasting as that of carnivores such as dogs and cats, so they may eat at least hay until shortly before the operation.
During the operation
While the animal is under anaesthetic, the veterinary surgeon checks various parameters regularly. These include the pulse and respiration, blood pressure, body temperature and blood oxygen saturation. The concentration of carbon dioxide (CO2) in the exhaled air is also measured. These parameters give a good overview of how the animal is doing. Well-equipped veterinary practices and hospitals have ultramodern technology for this purpose, which show an overview of all the parameters on a screen.
Knowing the situation of the animal’s circulation helps to avoid anaesthetic incidents. For instance, if the oxygen supply drops, the animal will also be ventilated artificially or the oxygen concentration in the inspired air will be increased. The heart rate may possibly decrease also, which can be a sign that the anaesthetic is too deep. The volume of anaesthetic gas that is inhaled is then reduced. The depth of anaesthesia is also checked regularly and the veterinary surgeon uses the function of certain reflexes to do this. The animal should not have any pain but at the same time it should not be so deeply anaesthetised that its vital functions such as respiration and heartbeat are impaired too greatly.
After the operation
Animals are still watched closely after the operation until they are awake and active again. The animal should be breathing regularly and is kept warm until it wakes up fully. Since every anaesthetic also affects the circulation, there can be a drop in body temperature, which should be avoided particularly in debilitated animals. It is usually given a pain killer appropriate to the operation so that it does not feel any major pain after it wakes up. With some operations, slight pain is desirable, however, so that the animal does not overdo things. They should eat again only after they have woken up fully so as to avoid choking.