The action of the halothane-diethyl ether azeotropic mixture on experimental animals.

MANY mixtures of volatile anaesthetics have been -used in the past with some success, but they are difficult to handle in the modern anaesthetic apparatus. Because of the differences in the boiling points of the components of these mixtures, they volatilize at different rates and therefore it is almost impossible to know their concentration in the anaesthetic mixture administered to the patient. This difficulty can be overcome by the use of several vaporizers, each rilled with a different agent, and the anaesthetist can regulate the composition of the anaesthetic mixtures by controlling the output of each vaporizer. Another way to solve this problem is by the use of azeotropic mixtures of volatile anaesthetics. An azeotropic mixture is defined as a mixture of two or more liquids distilling over in a certain ratio at a constant boiling temperature. Hudon and his collaborators (1958) have found that an azeotrope is formed when 2 vols. of halothane are mixed with 1 vol. of diethyl ether; this mixture has a boiling point of 51.5 °C and gives out vapours containing halothane and ether in the proportion of 2 : 1 . These authors have investigated the anaesthetic action of this azeotrope in more than 1,000 cases and have compared its action with the effects of halothane observed in over 3,000 cases. They claim that its effect, although very similar to that of halothane, has the following advantages: (1) It produces an increase in the respiratory minute volume during induction and maintenance of anaesthesia. (2) It causes less hypotension and less frequent cardiac irregularities than halothane. (3) It is easier to control, and it has a larger margin of safety than halothane. After reading Hudon's observations, we thought 46 that it would be interesting to see if these claims could be confirmed in experimental animals. In the experiments described below, therefore, we compared the effects of the azeotrope with those of halothane.