Assessment of vaporizer performance in low-flow and closed-circuit anesthesia.

The performance of five of the most commonly used halothane vaporizers and three enflurane vaporizers was tested under conditions encountered in low-flow and closed-circuit anesthesia. Anesthetic gas concentrations were measured continuously with a mass spectrometer connected to a circle system. The results indicated that all of the units tested, except the Fluotec Mark II, may be adapted for use in low-flow or closed-circuit anesthesia to provide accurate amounts of potent inhalation anesthetics. One should be aware, however, that the concentration of nitrous oxide affects vaporizer output, that changes in output occur during positive-pressure ventilation, and that the output of some of the vaporizers may increase when a change from high flow to low flow is made. It is also strongly recommended that upstream oxygen flushing be abandoned in the practice of low-flow or closed-circuit anesthesia.