Felis ISSN 2398-2950

Analgesia: overview

Contributor(s): John Dodam, Jo Murrell, Polly Taylor

Introduction

  • One of the primary duties of the veterinarian is to relieve pain and suffering.
  • Pain is subjective and difficult to define. The International Association for the Study of Pain (1979) defined pain as 'an unpleasant sensory and emotional experience associated with actual or potential tissue damage' (abridged).
  • As pain is subjective it is impossible to prove that animals feel pain although as all mammals have the same basic physiological structure it is reasonable to assume that the perception of pain is broadly similar across species. Clinical observation confirms this hypothesis.

Recognition and assessment of pain

  • Purring does not indicate that a cat is comfortable and free of pain. As a complex semi-automatic response to being handled this behavior may persist in the presence of injuries which would be acutely painful in a human subject.

Acute, severe pain

  • Cats in acute, severe pain will generally show some or all of the following:
    • Vocalization during the painful stimulus or when the animal is being handled. The tone used is often of a higher pitch than when the cat is merely protesting at being handled.
    • Guarding behavior when the painful area is touched or manipulated.
    • Aggressive behavior, hissing, growling, again particularly when the animal is disturbed.
    • Panting, open mouth breathing.
    • Self mutilation.

Chronic pain

  • Chronic or less severe pain produces more insidious changes in the cat's behavior and may be a challenge to detect:
    • Hiding away, often in dark quiet places or the corner of a kennel.
    • Inappetence or anorexia.
    • Reduced interaction with owners or other pets in the household.
    • Reduction in grooming behavior.
    • Musculo-skeletal pain may be manifested as lameness, stiff gait or difficulty in standing or sitting.

Physiological changes

  • The following alterations may be expected in animals in pain:
    • Increased pulse rate.
    • Rapid shallow respiration unless the painful area is involved in respiratory movements in which case suppression of those movements may occur.
    • Hypertension Hypertension.
    • Changes in hormonal balance consistent with stress.

Pain scoring

  • An attempt to quantify the degree of pain Pain: assessment is useful in:
    • Giving a guide as to when intervention with analgesics is desirable.
    • Providing a more objective assessment on which the efficacy of analgesia can be based.
    • Determining when repeat doses of analgesics are necessary.
  • A possible method of producing pain scores in cats involves assessing:
    • Degree to which the cat is exhibiting normal social and grooming behaviors.
    • The presence or degree of absence of a normal appetite.
    • Vocalization patterns in response to handling and manipulation of the painful area.
  • These parameters can each be awarded numerical values of:
    • Normal - 0.
    • Slightly abnormal, eg will only eat favorite foods - 1.
    • Moderately abnormal, eg will only eat favorite/highly palatable food with encouragement or hand feeding - 2.
    • Severely abnormal, eg anorexia - 3.
  • When the values for social/grooming behavior, appetite and vocalization are added together an overall score of between 0 and 9 is obtained. A suggested level for intervention with analgesics is a score of 4-5.

Use of analgesics

  • Control of acute pain:
    • Post-trauma.
    • Post-surgical.
    • Acute medical cases.
  • Control of chronic pain:
    • Musculo-skeletal.
    • Analgesia is most effective in the postoperative period when it is in full effect before the animal regains conciousness and is aware of any pain. This means that the timing of analgesic administration requires some thought, bearing in mind:
      • Duration of effect of analgesic components of premedication.
      • Time required for onset of action of any analgesics to be administered.
      • Residual analgesic effects of some anesthetic agents.
    • In combination with sedative drugs to produce neuroleptanalgesia, profound sedation for some minor procedures.
    • As part of a balanced anesthetic technique, reducing the amount of potent general anesthetic agent required, thereby reducing the side effects of high doses of such agents, eg respiratory and cardiovascular system depression.

Analgesic drugs

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Miscellaneous analgesics

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Acupuncture

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Aids to analgesia

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Hansen B (2008) Analgesia for the critically ill dog or cat: an updateVet Clin North Am Small Anim Pract 38, 1353-1363 PubMed.
  • Robertson S A (2005) Managing pain in feline patients. Vet Clin North Am Small Anim Pract35, 129-146 PubMed.
  • Johnson C (1999) Chemical restraint in the dog and cat. In Practice 21, 111-118.
  • Taylor P M (1985) Analgesia in the dog and cat. In Practice 7, 5-13.

Other sources of information

  • Hall L W & Taylor P M (1994) Eds Anaesthesia of the Cat. London: Bailliere Tindall. pp112-113, 116-118, 120-128. ISBN 0 7020 1665 9
  • Nolan A M (1989) Analgesia. In: Manual of Anaesthesia for Small Animal Practice. Ed A D R Hilbery. Cheltenham: British Small Animal Veterinary Association. pp33-38. ISBN 0 905214 09 9.


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