Anaesthesia of sheep with a combination of ketamine- guaifenesin (with and without fentanyl), nitrous oxide and halothane.

: The concept of combined anaesthesia, the centrally-acting muscle relaxant guaifenesin (My 301) in a 5% solution with ketamine (and/or fentanyl) in addition to the inhalation of nitrous oxide and halothane is based upon the principle of "balanced anaesthesia". Guaifenesin amplifies the effect of several anaesthetics, which complement one another, allowing the dosage to be decreased and thereby reducing the cardiovascular stress. To induce anaesthesia, the combination of a cataleptic anaesthetic (ketamine = Ketanest, Ketolar) and a centrally acting skeletal muscle relaxant (guaifenesin = Myolaxin, My 301) is used. Because of the risk of aspiration the animal should be intubated as soon as possible. Anaesthesia will be prolonged by the carrier gas nitrous oxide (65%, weakly analgesic)/oxygen (65%), low concentrations of halothane (1.0 to 0.6 to 0.4%, weakly hypnotic and analgesic) and by a continuous drip infusion of 5% guaifenesin (relaxing, mild analgesic and sedative). The effect of all the other anaesthetics is increased by guaifenesin. To increase the analgesia and to control the cardiovascular parameters the additional injection of ketamine or fentanyl is recommended. The recovery period is short and the general condition is good both after a lengthy anaesthesia of 9 hours (n = 32) and after anaesthesia of 2 hours. No significant adverse effects on the cardiovascular system were detected.