Clinical trial of xylazine with ketamine in equine anaesthesia.

One hundred anaesthetics were administered in a clinical trial to 95 equine patients, ranging in age from nine months to 19 years and in weight from 140 to 1270 kg, undergoing a variety of surgical procedures. Acepromazine maleate premedication (0.01 to 0.03 mg per kg intramuscularly) was given to seven animals, the remainder were not premedicated. Xylazine (1.1 mg per kg) was injected intravenously over a two minute period and after a pause of two minutes ketamine (2.2 mg per kg) was injected rapidly by the same route. For 30 procedures no other anaesthetic was given but in 59 cases anaesthesia was prolonged with halothane-oxygen while in 11 additional intravenous agents were administered. Recumbency followed one-and-a-half to two minutes after completion of the ketamine injection and limb movements occurring immediately after the animal lay down gradually subsided over the next 30 to 60 seconds. On 26 occasions when no other agent was given satisfactory operating conditions were produced for a mean (+/- sd) of 20 +/- 7 minutes and on four occasions when absence of complete muscle relaxation was observed surgery was still possible. When no other agent was given the onset of recovery was abrupt but recovery was always extremely quiet; the animals stood 33 +/- 10 minutes after induction of anaesthesia and showed a remarkable absence of ataxia. A similar recovery was seen in the 56 animals receiving halothane-oxygen and all stood 28 +/- 14 minutes after disconnection from the anaesthetic system. Heart block was observed during induction of anaesthesia bu otherwise cardiovascular and respiratory parameters were well maintained. It was concluded that the xylazine-ketamine combination had advantages over other current techniques of inducing anaesthesia in horses.