Canis ISSN: 2398-2942

Therapeutics: anesthesia/analgesia

Contributor(s): Kyle Braund, Lauren Trepanier

Sedatives

  • Produce calmness, drowsiness, and indifference to the surroundings (tranquillizers 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 dosages IV and monitor pulse, heart rate, and blood pressure.

Butyrophenones

  • Major tranquilizers, dopamine receptor antagonists.
  • Fluanisone Fentanyl (parenteral) (in combination with fentanyl). Not used in the US.

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, concomitant use of atropine should be avoided.
  • Atipamezole Atipamezole used as reversing agent.
  • Xylazine Xylazine : for minor procedures, to facilitate handling and premedicant; administer with atropine to reduce salivation and bradycardia - controversial, if give with atropine the hypertensive effect will be more marked.
    Avoid in animals in congestive heart failure or suffering from circulatory disturbances.

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 or morphine → profound sedation, minimal disturbance to cardiovascular system, smaller doses of induction agent.
  • DiazepamDiazepam : available in oil-based or emulsion preparations.
  • MidazolamMidazolam : shorter acting and less sedative.

Sedative antagonists

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

Opioid analgesics

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General anesthetics

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Modifiers of neuromuscular transmission

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Local anesthetics

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Drugs for euthanasia

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.
  • Dewey C W et al(2004)Zonisamide therapy for refractory idiopathic epilepsy in dogs. JAAHA40(4) 285-291PubMed.
  • 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.
  • Venugopalan C S et al(1998)Sedative and analgesic effects of medetomidine in Beagle dogs infected and uninfected with heartworm. Vet Res Commun22(2), 97-106.

Other sources of information

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


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