The vapour pressure-composition diagram for halothane-methoxyflurane and its relevance to cross-contamination

Abstract

A cross-contaminated anaesthetic agent forms a binary liquid mixture with its contaminant. Since it was thought possible that the behaviour of contaminated vaporizers could be predicted from a knowledge of the vapour pressure-composition diagram for the binary liquid mixture, the diagram for a typical system was determined. The technique used was to allow a suitable mixture of agents to equilibrate, measure their combined vapour pressure, and determine the liquid and vapour compositions by infrared analysis. A vacuum line suitable for the vapour pressure measurements is described. The vapour pressure-composition diagram for halothane-methoxyflurane was found to be ideal both at 20 and 25ºC. This finding is used to account for some results reported in the literature concerning cross-contamination between halothane and methoxyflurane.