Felis ISSN 2398-2950

Therapeutics: anesthesia and analgesia

Contributor(s): Kyle Braund, Hill J, Lauren Trepanier

Sedatives

  • Produce calmness, drowsiness, and indifference to the surroundings (tranquilizers produce calmness with less drowsiness).
  • Included in pre-anesthetic medication   →   reduce dose of general anesthetic.
  • Used for restraint, behavior modification, facilitate handling and transport, allow positioning for radiography.
  • Administer before animal becomes upset otherwise may need increased dose.
  • Deep sedation requires monitoring - same as general anesthesia.
  • Administer in combination with analgesic if procedure too painful to be controlled by sedation alone.

Phenothiazines

  • Neuroleptics with wide range of activity. (Dopamine receptor antagonists, alpha-adrenoceptor antagonists, muscarinic receptor antagonists (weak), 5-HT receptor antagonists).
  • Acepromazine  Acepromazine maleate  :
    • Mild to moderate sedation, no analgesia.
    • Variable effect and unpredictable, with oral administration.
    • IV or IM administration preferred.
    • High doses may   →   excitement.
      Lowers the threshold for seizure activity - avoid in epileptics.
    • Can increase sedation with concurrent administration of opioid analgesic.
      Alpha-adrenoceptor antagonist action will cause hypotension, particularly in hypovolemic patients. Use conservative dosage IV and monitor pulse, heart rate, and blood pressure.

Butyrophenones

  • Major tranquilizers, dopamine receptor antagonists.

Alpha-2-adrenoceptor stimulants

  • Marked sedative, muscle relaxant and analgesic properties   Analgesia: alpha-2 agonist  .
  • Initial hypertension with marked bradycardia at moderate doses followed by normo- to slight hypotension and bradycardia mediated by a central action.
  • Also hyperglycemia and polyuria.
  • Medetomidine hydrochloride  Medetomidine  : more potent than xylazine and more alpha-2-adrenoceptor specific than xylazine. Licensed solely or in combination as a sedative or premedicant. In general, concomitant administration of atropine should be avoided.
  • Atipamezole  Atipamezole  used as reversal agent.
  • Xylazine  Xylazine  : for minor procedures, to facilitate handling and premedicant; induces vomiting in cats; administer with atropine to reduce salivation and bradycardia - controversial, if give with atropine the hypertensive effect will be more marked.
    Avoid in animals with cardiovascular disease or in poor general health - care is advised in animal with pre-existing hepatic or renal disease.

Benzodiazepines

  • Useful premedicants in elderly, debilitated animals or with risk of epileptiform seizures (epileptic patient, myelography).
  • In intensive care where invasive monitoring required.
  • IV administration in normal animal may   →   excitation.
  • Respiratory depression may require ventilatory support in debilitated animals.
  • Combined with fentanyl   Fentanyl (parenteral)  or morphine   Morphine      →   profound sedation, minimal disturbance to cardiovascular system, smaller doses of induction agent.
  • Diazepam*   Diazepam  : available in oil-based or emulsion preparations.
  • Midazolam*   Midazolam  : shorter acting and less sedative.

Sedative antagonists

  • Atipamezole  Atipamezole  : licensed to reverse medetomidine, but also reverses xylazine.

Analgesics

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Opioid antagonists

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Anesthetics

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Modifiers of neuromuscular transmission

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Drugs for euthanasia

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.
  • Johnson C (1999)Chemical restraint in the dog and cat. In Practice21, 111-118.
  • Karas A Z (1999)Sedation and chemical restraint in the dog and cat. Clin Tech Small Anim Pract14(1), 15-26.

Other sources of information

  • Plumb D C (1999)Veterinary Drug Handbook.3rd edn. Iowa State University Press, Ames Iowa.


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