Laboratory Animal Anaesthesia

Paul Flecknell

• Publisher: Academic Press
• Year: 2009
• ISBN:
  9780080918990
• Edition: 3
• Topic: Medicine
• Subtopic: Pharmacology

Laboratory Animal Anesthesia looks at recent significant developments in anesthetic practices in laboratory experiments involving animals. It also provides information about basic standards for proper use of anesthesia. In addition, it examines the equipment and different anesthetic agents that are used in performing an experiment on animals. The book also discusses the profound effects of anesthesia on the physiological aspect of the animals' body systems, such as hypothermia and respiratory depression. The book addresses the proper management and care that should be provided for the animals that undergo anesthesia. Furthermore, it covers different anesthetic procedures that should be used on various kinds of small animals intended for laboratory experiments. The main goal of this book is to provide information about the different anesthetic agents used in experiments, and the proper standards to follow when using anesthetics on lab animals.• New edition provides new information on anesthesia and analgesia, and has an extensively revised and updated bibliography• Provides a balanced consideration of the needs of scientific research and the welfare of laboratory animals• Written by a veterinary anesthetist and scientist with over 30 years' experience in the field, and who is actively engaged in research in this area• Provides rapid, easily accessed information using tabulated summaries• Provides those with limited experience of anesthesia with the information they need to carry our procedures effectively, safely, and humanely• Provides sufficient depth for the more experienced anesthetist moving to this field

Chapter 1. Preparing for Anaesthesia

Safe and effective anaesthesia requires careful preparation. Anaesthetic and monitoring equipment must be checked carefully to ensure they are in good working order and that any item that would come in contact with the animal has been cleaned and disinfected. It is also important to make sure that sufficient supplies of drugs and anaesthetic gases are available to meet both planned and emergency use. The animals to be anaesthetized should normally be allowed to acclimatize to the research facility. They should also have undergo a clinical examination to assess their state of health and their normal behaviour and response to humans.

To provide anaesthesia of the standard required in modern research laboratories, it is essential that adequate preparations be made before attempting to anaesthetize an animal. Good pre-operative care will reduce the incidence of many of the complications that can occur during anaesthesia, and thorough preparation of facilities and equipment contributes to the smooth running of a research protocol. It is important to consider preparation of not only the animals to be anaesthetized but also the equipment, drugs, facilities and personnel involved in the procedure.

Anaesthetic Equipment and Anaesthetic Drugs

The factors influencing the choice of a particular anaesthetic are discussed in more detail later, but irrespective of the agent or combination of agents selected, it is important to establish that all the items of equipment are necessary are available and in good working order. Ensure that sufficient anaesthetic drugs and anaesthetic gases have been provided not just for the anticipated period of anaesthesia but also to cover unexpected additional requirements (see Appendix 2 for calculations of inhaled anaesthetics). Check the expiry date of all drugs, and ensure they have been properly stored. For clear drugs stored in uncoloured glass bottles, check for unexpected turbidity or colour changes. In addition to the anaesthetic agents, drugs needed for coping with emergencies must also be readily available (see Chapter 4).

If an anaesthetic trolley is to be used to deliver an volatile anaesthetics or oxygen, then it is essential to check them carefully before use. A simple pre-use checklist for anaesthetic machines is given in Table 1.1. Anaesthetic machines appear complex, but their underlying design and operation is very simple. Most machines comprise a compressed gas source that, after pressure reduction, is passed through a flow meter and an anaesthetic vaporizer, and delivers anaesthetic gases to the animal through a breathing system. If using an unfamiliar machine, ask a colleague who has used the apparatus or the equipment supplier to provide a demonstration. Very detailed descriptions of medical anaesthetic equipment are available (Davey and Diba, 2005). An excellent description of anaesthetic equipment together with animations to illustrate breathing circuits can be found at http://www.asevet.com/resources/index.htm

Table 1.1 Pre-anaesthetic Checks of Anaesthetic Equipment.

These checks should be routine procedures since they will minimise the occurrence of anaesthetic accidents which could result in the death of the animal.

• Is only one oxygen cylinder marked as ‘in use’ and the other full? • Check that the valve on the cylinder in use is opened fully to provide a free flow of gas (the reading on the pressure dial on an oxygen cylinder gives a reasonable indication as to how much oxygen it contains, Appendix 2). • Check that the cylinders are full and properly attached to the anaesthetic machine; ensure the flow meters are functioning correctly by opening the cylinder valves and the needle valves that control the flow of gas through the flow meters. The bobbins should rotate when gas is flowing (most are marked with a small white dot to assist in assessing this). The gas flow rate is measured from the top of the bobbin. Turn off the gas flow using the needle valve and check that the bobbin sinks smoothly back to zero and is not sticking and giving a false high gas flow rate. • Check that the emergency oxygen button is functioning correctly. • If a volatile anaesthetic is to be used, check that the vaporizer has been filled and that the control dial moves smoothly over the entire range of possible settings. If using a machine with several vaporizers, check that the correct one has been selected. • If the anaesthetic machine has a built-in circle-type absorber, ensure that this is switched out of circuit (usually marked ‘open’) if the absorber is not to be used. Check that soda lime is not exhausted (indicated by a colour change from pink to white or white to violet). • Attach the circuit which will be used to the anaesthetic machine, turn on the oxygen supply and check the circuit for leaks by occluding the patient end of the tubing and fully closing any valves. Open the valves to check they are not sticking. • If a mechanical ventilator is to be used, switch it on and observe it for a few respiratory cycles. If possible, check the tidal volume that is being delivered with a respirometer. • Run through the manufacturer’s recommended pre-use check on any monitoring equipment.

Compressed Gas Source

Gas is either supplied from cylinders on the anaesthetic machine or piped using hoses from larger cylinders. If using hoses, the pressure reducing valve (see below) should be fitted to the large cylinder so that gas at lower pressure is supplied through the hose. The mounts for the hoses or cylinders have small pins located in corresponding holes in the cylinders to ensure that the correct gas (e.g. oxygen or nitrous oxide) is attached (Fig. 1.1). Cylinders are also colour coded (oxygen cylinders are green in the USA and black with a white shoulder in the UK; nitrous oxide cylinders are blue). A small metal and neoprene seal (Bodok seal) ensures a gas-tight fit between the cylinder and the mount block (Fig. 1.1). Under no circumstances should oil or grease be used around the seal because the pressurized gases give off heat as they are released from the cylinder and may cause explosions if oil is used. A pressure gauge (Fig. 1.2) indicates that gas is available. Oxygen cylinders contain oxygen under pressure, and the pressure gauge gradually fal...