Laboratory Animal Anaesthesia

Paul Flecknell

• Publisher: Academic Press
• Year: 2015
• eBook ISBN: 9780128005781
• Edition: 4
• Topic: Medicine
• Subtopic: Pharmaceutical, Biotechnology & Healthcare Industry

Laboratory Animal Anaesthesia, Fourth Edition provides a basic guide to anaesthesia for a very diverse audience needing content, with straight-forward, structured style of writing. Updated with effects of anaesthetics in different laboratory species, including sources of dose rates will be incorporated into tabular material. New information on pain assessment and pain management will be covered, and an increased emphasis on rats and mice for anaesthesia and perioperative care. With newly revised, full color illustrations to facilitate best learning, Laboratory animal Anesthesia, Fourth Edition provides procedures, key points and invaluable advice from a well-known and respected veterinary anesthetist and scientist with over 30 years of experience in the field. - 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 - Focuses on procedures involving rats and mice used in research - Provides those with limited experience of anesthesia with the information they need to carry our procedures effectively, safely, and humanely, as well as those with more experience to continue a career with laboratory animal model research - Includes rapid, easily accessed information using tabulated summaries

Chapter 1

Basic Principles of Anaesthesia

Adequate preparations are essential to be made before attempting to anaesthetize an animal. This chapter provides an introduction to careful and safe preparation for anaesthesia. It also discusses the factors influencing the choice of a particular anaesthesia. Detailed descriptions of medical anaesthetic equipment are discussed. The single most important factor that can reduce the risks associated with anaesthesia is the use of animals of high health status. It is important to consider preparation of not only the animals to be anesthetized but also the equipment, drugs, facilities, and personnel involved in the procedure. The animal to be anaesthetized must be in good health and free from clinical disease. 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 have undergone a clinical examination to assess their state of health, their normal behaviour, and their response to humans. Species that can rapidly develop a relationship with their handler have the advantage of reducing unnecessary distress during induction and recovery from anaesthesia. 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.

Keywords

Anaesthesia; Anaesthetic equipment; Anaesthetic machine; Breathing systems; Intubation; Anaesthetic agents

To provide anaesthesia of the standard required in modern research laboratories, adequate preparations must 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 the animals that are to be anesthetized and also the equipment, drugs, facilities and personnel involved in the procedure. This section provides important background information on the process of anaesthesia. It also explains the preparation and maintenance of the equipment needed when anaesthetizing animals. It includes a description of the use of items such as anaesthetic chambers, endotracheal tubes, breathing circuits and anaesthetic machines. It also includes a brief description of the various agents used in inducing and maintaining anaesthesia.

Introduction: What is Anaesthesia and How Do We Produce it?

Anaesthesia means ‘‘loss of sensation’. This can involve loss of consciousness (general anaesthesia), or the loss of sensation can be restricted to a small area of the body (local anaesthesia). Larger body areas can be rendered anaesthetic by injecting drugs around nerve trunks, to produce regional anaesthesia. Each of these techniques can be used in laboratory animals, but general anaesthesia is the most common approach. This is because it provides a loss of awareness, as well as a loss of sensation, and so prevents any distress associated with the procedures that are to be undertaken during the anaesthetic period. It also ensures the animal remains largely immobile, produces muscle relaxation and suppresses reflex activity. General anaesthesia is produced using either injectable or inhalational agents, or a combination of the two methods. Often a single drug can be given to produce all of these required features of general anaesthesia: loss of consciousness, analgesia, suppression of reflex activity and muscle relaxation. Alternatively, a combination of agents can be given, each making a contribution to the overall effect. The advantage of this approach is that the undesirable side effects of anaesthetic agents can often be minimized. The side effects of anaesthetics are usually dose-dependent. Giving several drugs in combination, at relatively low dose rates, often has less effect on major body systems than when using a single anaesthetic agent. These combinations of agents are often administered as a single injection in small rodents. In larger species, sedatives and analgesics are usually given first, as pre-anaesthetic medication (or ‘pre-meds’), followed by other drugs to produce anaesthesia. The initial onset of anaesthesia is termed ‘induction’, and its continuation is termed ‘maintenance’. Injectable and inhalational agents can also be combined, for example with anaesthesia being induced using an injectable agent, and then the period of anaesthesia prolonged or the depth of anaesthesia increased using inhalational agents.

Local anaesthesia is produced by infiltrating tissues with local anaesthetics, or by injecting these agents around specific nerves or nerve trunks. This technique can be combined by using general anaesthetics, so that the local anaesthetic produces complete loss of sensation, and the general anaesthetic is given in a relatively low dose, to provide loss of consciousness.

The degree or depth of anaesthetic can vary, depending on the type of experimental procedures that are to be undertaken. If surgical procedures are to be carried out then pain perception must be completely suppressed. If the surgery involves relatively little trauma to tissues, then a medium plane of surgical anaesthesia may be sufficient. For more major surgery, especially if this involves traction and tearing of tissues, deep planes of surgical anaesthesia will be needed. In contrast, if anaesthesia is being induced simply to provide humane restraint while non-painful procedures are carried out, then only light anaesthesia, with little pain suppression, will be required. Different general anaesthetic agents can appear to provide similar levels of hypnosis (sleep), but the degree of analgesia produced can vary widely.

Some agents are referred to as ‘hypnotics’, rather than anaesthetics, since they produce ‘sleep’ (hypnosis) but have no specific analgesic properties. This terminology causes some confusion since, at high doses, hypnotics (e.g. tribromoethanol) produce general anaesthesia. Different anaesthetics and hypnotics act in different ways to produce their effects. Surgical planes of general anaesthesia require both loss of consciousness and loss of pain sensation, and this can be produced by agents that have both analgesic and hypnotic properties. It can also be produced by hypnotics that have no specific analgesic effects, since if a high enough dose is given, even intense pain will not be perceived, because of the very marked depression of all brain activity. However, if no specific analgesic component is provided, this may result in increased post-operative pain (see Chapter 4) because of the effects of the surgical stimuli on the nervous system. For this reason, anaesthetic protocols using hypnotics often include use of analgesic agents, such as buprenorphine.

This introductory section outlines the different anaesthetic agents available, what equipment is needed to administer them safely and effectively, what factors may influence your choice of anaesthetic, and what preparations should be made before anaesthesia. More detailed reviews of anaesthetic agents are available elsewhere (e.g. Tranquilli et al., 2013).

Anaesthetic Equipment – Preparation and Use

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 that will be needed are available and in good working order. Ensure that sufficient anaesthetic drugs and anaesthetic gases are available not just for the anticipated period of anaesthesia but also to cover unexpected additional requirements (see Appendix 2 for guidance). 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...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Preface to the Third Edition
• Preface to the Second Edition
• Preface to the First Edition
• Glossary
• List of Tables
• List of Figures
• Acknowledgements
• Introduction
• Chapter 1. Basic Principles of Anaesthesia
• Chapter 2. Managing and Monitoring Anaesthesia
• Chapter 3. Special Techniques
• Chapter 4. Analgesia and Post-Operative Care
• Chapter 5. Anaesthesia of Common Laboratory Species: Special Considerations
• Appendix 1. Recommended Techniques and Physiological Data. When No Injectable Anaesthetic Is Recommended, Inhalational Agents Should Be Used
• Appendix 2. Estimation of Required Quantities of Volatile Anaesthetics and Anaesthetic Gases
• Appendix 3. Examples of Dilutions of Anaesthetic Mixtures for Small Rodents
• Appendix 4. Manufacturers of Equipment and Other Items Illustrated or Cited in the Text
• Bibliography
• Index