Chemistry of halothane-enflurane mixtures applied to anesthesia

The authors obtained boiling point-composition data and vapor pressure-composition data for the halothane-enflurane system at 20 degrees C and 25 degrees C. This was used to demonstrate the existence of an azeotropic mixture of halothane and enflurane and to predict the output of an enflurane vaporizer contaminated with different amounts of halothane and a halothane vaporizer contaminated with different amounts of enflurane. The study was undertaken because the information allows a comprehensive description of the behavior of a contaminated vaporizer and the required data were not previously available. It was shown that an enflurane vaporizer contaminated with halothane delivers potentially dangerous mixtures of the two agents, whereas an enflurane-contaminated halothane vaporizer does not pose a serious problem. It was concluded that when halothane and enflurane vaporizers are mounted in series, the halothane should be downstream. It is explained why the halothane-enflurane azeotrope is unlikely to be useful clinically.