Anaesthesia, Analgesia

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Anaesthesia, Analgesia Peri-operative Care

• Belinda Farnfield BVSc PhD CertVA MRCVS

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Introduction

• Where laboratory animals are used for scientific
  procedures, must always ensure that pain,
  suffering and distress are minimised
• Provision of high quality anaesthesia, analgesia
  peri-operative care is a very important way of
  doing this

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Anaesthesia definition

• State of controllable, reversible insensibility
  in which sensory perception and motor responses
  are both depressed

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Anaesthesia three aims

• Analgesia
• Abolition of pain perception
• Humane restraint
• Muscle relaxation and suppression of reflexes

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Analgesia

• Vital to eliminate perception of pain so that
  procedures can be carried out humanely

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Humane restraint

• Restraint / immobilisation needed so that
  procedures may be carried out safely with a
  minimum of distress
• For most species and procedures a general
  anaesthetic where the animal loses consciousness
• Local anaesthesia may be appropriate for some
  species / procedures where the animal can be
  restrained humanely fully awake or sedated eg
  farm animals

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Muscle relaxation and elimination of reflex
responses

• Eg to prevent muscle spasm and allow manipulation
  for surgery

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Anaesthesia achieving these aims

• A single anaesthetic drug may be able to produce
  analgesia, loss of consciousness, muscle
  relaxation reflex suppression
• Often more than one drug is needed
• Now recognised that many anaesthetic agents are
  able to provide loss of consciousness and muscle
  relaxation/ reflex suppression but are poor
  analgesics

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Analgesia, pain and wind-up of the central
nervous system

• Pain
• Conscious perception of a noxious stimulus
• Analgesia
• Temporary abolition or diminution of pain
  perception
• Wind-up
• During general anaesthesia although the animal is
  unconscious and as such unable to perceive pain,
  noxious stimuli wind-up the central nervous
  system
• Nerve pathways not usually involved in pain
  transmission are recruited to transmit pain
• Once the animal is awake, more difficult to
  abolish pain perception

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Preventing wind-up

• Provide analgesia before any painful stimuli
  occur
• For every anaesthetic drug or drug combination
  you plan to use, assess what degree of analgesia
  is likely
• Supplement with specific analgesic drugs as
  necessary