Production and characterization of impurities in isoflurane vaporizers

Unwanted substances in hydrogenated anesthetics have been reported occasionally. Raventos and Lemon and Torkelson et al. characterized the toxicity of undesirable compounds found in halothane and methoxyflurane during their industrial synthesis. Their investigations led to an awareness of the possible impurities in anesthetics and steps were taken to improve the synthesis and stabilize the halogenated anesthetics. Current commercially available anesthetics are reported to contain less than .0075% wt/wt or less than 75 ppm impurities. In a study by Sharp et al., the breakdown of halothane during closed-circuit anesthesia was examined. The degradation was found to be due to the interaction of halothane with soda lime in the filtering unit. The product of this degradation, 2-bromo-2-chloro-1,1-difluorethylene is toxic. However, toxic concentrations did not accumulate during open- or closed circuit anesthesia. In 1981 Wald described two instances of the presence of yellow 'impurities' in enflurane in an Ohio calibrated vaporizer. Wald felt that the impurities were not from the degradation of enflurane, but from a 'sulfurous' component in the vaporizer wick. In 1982 we observed a yellowish discoloration in isoflurane in an Ohio calibrated vaporizer. Preliminary studies by our laboratory found that these impurities were not 'sulfurous paper components' but were organic in nature. This report characterizes the impurities in isoflurane vaporizers, determines their origin, and performs field analyses to determine the magnitude of the problem.