Anesthetic drugs: A review and what's new (Proceedings)

Anesthetic drugs: A review and what's new (Proceedings)

Apr 01, 2009

• There is no single best way to anesthetize dogs and cats, making it imperative to be familiar with a variety of different anesthetic drugs and techniques. As a general rule when putting together an anesthetic plan, it is best to use relatively low doses of several different drugs (termed balanced anesthesia) rather than a large dose of a single drug to decrease unwanted side effects.

Drug selection should depend on

• Patient's physical status, temperament, type of procedure being performed (including length), present or anticipated pain, familiarity of anesthetic drugs, availability of equipment and personnel, cost of drugs

Sedative and tranquilizers

• Used for sedation, restraint, to reduce the amount of inhalant needed, to decrease vomiting, to increase muscle relaxation and to smooth out recovery

• Benzodiazepines

o General characteristics

• Sedation and neuroleptanalgesia (when given with an opioid), paradoxical excitement when given alone, decreases inhibition (licking, sniffing, biting, jumping off of table), anticonvulsant, minimal cardiovascular and respiratory depressant, reversible with flumazanil at 0.08 mg/kg IM, NO ANALGESIA

o Diazepam (0.1-0.2 mg/kg; IV only)

• Not compatible with other drugs because it is based in propylene glycol (can mix with ketamine only), not a reliable sedative when given alone, may cause dysphoria and/or aggression in cats

o Midazolam (0.1-0.2 mg/kg; SQ, IM, IV; duration of action 1-2 hours)

• Water soluble, not a reliable sedative in young dogs and cats, great sedation seen in rabbits, ferrets and some birds (doses vary)

• Phenothiazines

o Acepromazine (0.01-0.1 mg/kg- start low, you can always add more if needed)

• Profound sedation (dose dependent)

• Long onset of action (can take 15 minutes) and long duration of action

• Neuroleptic (when combined with an opioid)


• Anti-emetic

• Negative cardiovascular side effects (dose dependent)

• Vasodilation, hypotension, direct cardiac depression

• Use with care (or not at all) in sick or debilitated animals

• Alpha-2 agonists (1 mcg/kg up to 10 mcg/kg SQ, IM, IV; duration of action ~ 90 min dose dependent)

o Dexmedetomidine

• Dose dependent sedation with some analgesia

• Reversible

• Peripheral vasoconstriction (pale mucous membranes, cold extremities)

• Bradycardia

• Treatment with anticholenergics not always recommended (causes increase in myocardial work)

• Increase urine production

• Vomiting

• Some animals refractory to drug

• Pre-existing stress, fear, anxiety, pain

• Co-administer with opioid and put in quiet area

• Can take up to 30 min to take effect!

• Effects tend to be more variable than with domitor

• Go low IV especially when coupling with opioid- you can always add more!

• 2-3 mcg/kg IV, 5-7 mcg/kg IM (opioids smooth sedation and decrease necessary dose)