Equipment
Before anaesthetising an animal:
- Check that all of the equipment that you need is readily available and functioning correctly. This may include heating pads (which should be set up and turned on 15-30 minutes in advance to check that they reach the required temperature, monitoring equipment, and an anaesthetic machine.
- Check the anaesthetic machine and breathing system.
- Check that any drugs or equipment needed for dealing with anaesthetic emergencies are readily available.
- Check that the equipment you will need in the post-anaesthetic or post-operative period, such as incubators or heated cabinets, special bedding and special foodstuffs are available and ready to use.
Personnel
Check that your assistants or co-workers have been properly briefed about the research protocol and are familiar with the equipment and techniques to be used. Ensure that they are aware of the time for which they are required, including attendance for post-operative observation and care, which may be outside the normal working day. If the tasks they will undertake will require authorisation (eg with a Personal licence in the UK, and prior assessment of competency), make sure this has all been undertaken.
Animals
Acclimatising the animal
Animals should be obtained at least 7 and preferably 14 days before their intended use in any research procedure, so that an appropriate period is allowed for acclimatisation to their new environment. Requirements vary in different establishments, and you should check on local practices. During this period the metabolic and hormonal changes caused by the stress of transportation will return to normal, and the animal can be monitored for any signs of ill health (Conour et al, 20061, Montonye et al, 20182). Animal care staff and research workers will have the opportunity to familiarise themselves with the behaviour and characteristics of the particular group of animals, and body weight, growth rate and food and water consumption can be recorded. This information is invaluable if animals are intended to recover from anaesthesia after undergoing a surgical procedure. Many of the pain assessment schemes that are under development rely on knowledge of these variables, and it is important that such information is obtained and recorded. Even when planning non-recovery procedures, an assessment of food and water intake or growth rate will provide some reassurance that the animal is in a normal physiological state.
Acclimatisation of species that can rapidly develop a relationship with their handler (e.g. dogs, cats and pigs) has the advantage of reducing avoidable distress during induction and recovery from anaesthesia. Regular handling of most species, including small rodents, will habituate the animals to the procedure. Consequently, the animals will be easier to restrain and more co-operative, and induction of anaesthesia will be safer for both the animals and the staff involved.
If animals are to be housed singly after a surgical procedure, it is preferable to acclimatise them to this environment beforehand. This will allow them to adapt to the stress of social isolation and therefore be better able to cope with the stress of anaesthesia and surgery. It will also allow assessment of their normal behaviour when housed singly.
Assessing the animal’s health
The single most important factor that can reduce the risks associated with anaesthesia is the use of animals of high health status. Most small laboratory species are now free from disease agents, but should still be examined to assess that they are in good health. Larger species, such as farm animals, may not have been purpose bred for research, and may have inapparent infections that could complicate anaesthesia or cause problems in the recovery period. It may be advisable to ask your facility veterinarian for assistance in assessing the health of any animal that is to be anaesthetised. If the animal is intended to recover from the procedure, then it is good practice to start a clinical monitoring sheet, to record these initial observations, and other information such as the animal’s body weight. It is helpful to monitor body weight and, if practicable, food and water intake for a few days pre-operatively. This will allow assessment that the intake is normal and will be of use in monitoring the post-operative recovery of the animal.
In some cases, it may be necessary to anaesthetise animals that are known to be in poor health, for example when a disease condition has been deliberately induced as part of the program of research. These animals may be at much greater risk during anaesthesia, and it is often advisable to discuss how this may influence the choice of anaesthetic, and the monitoring techniques, with your facility veterinarian.
Whatever the health status of the animal, a general clinical examination should be carried out before induction of anaesthesia. Although you may not be very familiar with signs of disease or ill health in animals, you should become very familiar with the behaviour and appearance of normal animals. If there is any deviation from normal, further advice can be sought from experienced animal technicians and veterinarians. The presence of discharges from the eyes or nose, matting of the fur around these regions or soiling of the perianal region with faeces requires further investigation. If the overall appearance of the animal is abnormal or any of the clinical signs mentioned is present, anaesthesia should be delayed until expert advice is obtained. Detailed descriptions of how to assess the health of animals can be found in the Pain and Distress eModule
Pre-operative fasting
Anaesthesia can result in nausea and vomiting so some animals should be fasted before surgery. Vomiting or regurgitation during the onset or recovery from anaesthesia can have serious consequences, as the protective coughing reflexes that are present when an animal is fully conscious may have been lost. This can result in material being inhaled into the lungs, causing severe pneumonia.
Non-human primates, dogs, cats and ferrets may vomit on the induction of anaesthesia, or during recovery, so it is advisable to withhold food for 12–16 hours, and water for 3–4 hours before induction of anaesthesia. Small rodents and rabbits do not vomit so there is generally no need to withhold food or water prior to anaesthesia. Withholding food from small rodents for prolonged periods can be detrimental as it can predispose to hypoglycaemia, and in rabbits and guinea pigs withholding food can lead to the development of gastrointestinal disorders in the post-operative period. Problems are most unlikely to be encountered when allowing free access to both food and water until immediately prior to anaesthesia in both rodents and rabbits. In guinea pigs, small quantities of food are often found in the mouth, but this is not due to regurgitation of stomach contents. Sheep and other ruminants regurgitate and withholding food may not reduce this.
References
- Conour, Laura A., Kathleen A. Murray, and Marilyn J. Brown. “Preparation of animals for research—issues to consider for rodents and rabbits.” ILAR journal 47, no. 4 (2006): 283-293.
- Montonye, Dan R., Aaron C. Ericsson, Susheel B. Busi, Cathleen Lutz, Keegan Wardwell, and Craig L. Franklin. “Acclimation and Institutionalization of the Mouse Microbiota Following Transportation.” Frontiers in Microbiology 9 (2018).