VPT 321: Veterinary Neuropharmacology (2+1) copy 1

PRE-ANAESTHETIC MEDICATION

• Use of drugs prior to anaesthesia - to have smooth and safe induction of anaesthesia and to establish balanced anaesthesia.
• Merits of preanaesthetic medication:
• Alleviate or minimize pain
• Allay apprehension
• Facilitate handling
• Minimize undesirable reflex actions
• Supplement general anaesthesia - decrease dose of anaesthetic and add extra analgesia and sedation
• Minimize events in recovery

Major classes of drugs used as preanaesthetics

• Tranquilizer – sedatives: Acepromazine,Chlorpromazine,Promethazine, Diazepam, Midazolam, Droperidol, Azaperone
• Hypnotic sedatives : Pentobarbital, Chloral hydrate
• Opioid analgesics : Morphine, Pethidine, Fentanyl, Pentazocine
• α₂ agonists : Xylazine, Detomidine
• Dissociatives : Ketamine
• Cholinolytics : Atropine, Glycopyrrolate (these agents inhibits the secretory activity of salivary glands that may help in prevention of regurgitation)

Complications of preanaesthetics

• Opioids: respiratory depression, hypotension
• Atropine: Mydriatic 
• α₂ agonists : cardiac depression

Preanaesthetic agents may potentiate  anaesthetic toxicity and prolong the recovery 

Neuroleptic  analgesia

• A combination of neuroleptics (benzodiazepines, butyrophenones or phenothiazines) + opioids derivatives
• At lower doses – produce preanaesthetic effect 
• At higher doses - Neuroleptic analgesia which is enough depression to cause surgical anaesthesia
• Popular combinations: Fentanyl + Droperidol ,Fentanyl + Fluanisone, Etorphine+ Acepromazine