This section covers :
- What anaesthesia is
- Why we use it
- Why it is important to get it right
What does the Oxford English dictionary define anaesthesia as?
The Oxford English dictionary defines anaesthesia as a “loss of sensation”.
It can be produced either by blocking sensation to a particular region of the body (local or regional anaesthesia), or by administration of drugs that produce a loss of consciousness (general anaesthesia).
Most laboratory animals are anaesthetised using general anaesthetics, but local anaesthesia can also be useful, for example local anaesthetic cream (e.g. EMLA, Astra) can be applied to intact skin to prevent pain or discomfort associated with venepuncture.
- a loss of sensation
- a loss of pain perception
- a loss of consciousness
For what reasons may you need to anaesthetise an animal?
Laboratory animals may be anaesthetised for one or more different reasons:
- To provide immobility so the animal does not displace catheters or move during imaging procedures
- To prevent pain during experimental procedures
- To prevent distress during physical restraint
The depth of anaesthesia and the choice and dose of anaesthetic agent may vary depending upon which of these aims is to be achieved.
- To provide immobility
- To prevent pain
- To prevent distress
- To prevent infection
Why is it important to get it right?
Controlling unwanted variability is crucial to producing high quality research data. An increased variation in your data caused by use of an inappropriate anaesthetic technique, or by using a technique incorrectly may lead to an increased number of animals being required for the study.
Increased mortality from poor anaesthetic technique will also increase the numbers of animals required for the study. Carefully planned anaesthesia and pain management can help you refine your study and reduce the number of animals you use.
Refinement and reduction are two key principles of the 3Rs ethical framework.
What are the 3Rs?
The 3Rs are a widely accepted ethical framework for conducting humane and high quality animal experiments.
- Replacement - Methods which avoid or replace the use of animals.
- Reduction - Methods which reduce the number of animals used.
- Refinement - Methods which reduce to a minimum the pain and distress experienced by those animals which it is still necessary to use (after first reducing and replacing animals in your research).
Carefully planned anaesthesia is a crucial part of applying the principles of refinement and reduction to your research project.
When drafting project licences you will be asked to explain how you will address the 3Rs in your work. You need to explain why you will not use anaesthesia and analgesia if pain and distress is expected.
Is anaesthesia safe for the animal?
When we produce general anaesthesia, we depress activity in the brain and spinal cord, and this causes the animal to lose consciousness. At deeper levels of anaesthesia, the animal becomes insensible to painful stimuli.
We need to remember that other body systems, such as the heart and lungs may also be affected. Often, blood pressure falls and respiratory functions are impaired. If anaesthesia is too deep, the depression of these different body systems can be life-threatening.
To recognise when body systems are being depressed during anaesthesia, we can monitor the animal, and take measures to minimise these effects. For example we can give oxygen, or infuse fluids to support the circulation.
- During general anaesthesia, blood pressure is often increased, because of the stress caused by anaesthesia.
- During general anaesthesia, blood pressure is often unchanged from the level before anaesthesia
- During general anaesthesia, blood pressure is often depressed, because of the effects of anaesthetic agents
Please select the statement which is correct.