THE ESTIMATION OF INSPIRED ISOFLURANE CONCENTRATION IN A LOW-FLOW SYSTEM

We have examined the predictability of inspired isoflurane concentrati on during low-flow anaesthesia using a to-and-fro breathing system. Tw enty one adult patients requiring mechanical ventilation of the lungs during surgery took part in this study. Using a fresh gas flow of 21.m in(-1), the ratio of inspired isoflurane concentration to isoflurane v aporizer setting was found to be approximately 4/5th after 5 min of an aesthesia. The ratio was maintained throughout the procedure, except f or a few minutes following each change in vaporizer setting.