SOME ACTIONS OF HALOTHANE AND ETHER IN BLED DOGS

A method is described of bleeding dogs under anaesthesia withethylene (79 per cent) and oxygen (21 per cent) to an arbitrarylevel of hypotension. Arterial blood oxygen saturations remainednormal while the hyperventilation of the animals in responseto haemorrhage was unimpaired. In dogs rendered hypotensiveby 30-50 per cent reductions of their circulating blood volume,halothane caused a fall, and di-ethyl ether a rise in the arterialblood pressure, heart rate and respiratory minute volume. Venouspressure fell further on administration of halothane. Acuteexperiments in dogs bled to a mean blood pressure of 50 mm Hgdid not distinguish a lethal effect of halothane due to itshypotensive action. Increasing the severity of the bleedingprocedure demonstrated the lethal effect of impairing the hyperventilationwith halothane in air which caused marked arterial desaturation.Survival experiments might demonstrate a deleterious effectof halothane due to its hypotensive action in severe haemorrhagewhen compared with ether anaesthesia. Preliminary survival experimentsare reported. ^*Present address: University College Hospital, London, W.C.I.