Accumulation of thymol in halothane vaporizers.

Thymol may accumulate in halothane vaporizers and influence their accuracy. We determined the thymol concentration in residual liquid halothane of 28 vaporizers in regular use. Two halothane samples were brownish, probably due to a long exposure to light and irregular drainage. Irregularly drained vaporizers contained higher thymol concentrations than those drained weekly (p less than 0.05). The highest individual thymol concentration was 19 times that found in fresh halothane. Halothane vapour concentration deviated most from setting in Fluotec Mark II vaporizers, but this did not correlate with thymol concentrations in halothane liquid. The need for weekly drainage and regular service of halothane vaporizers is stressed.