Evaluation of an Isoflurane Vaporizer

Abstract

The delivery performance of two Fortec vaporizers for isoflurane in oxygen (O2) was evaluated. Isoflurane concentration was measured at a constant O2 flow rate (from 0.75 to 15 L/min) as the vaporizer dial setting was changed over the range of 0% to 5%. At vaporizer dial settings of 2% or less the average delivered isoflurane concentration differed from dial settings by less than 0.25 vol% at all O2 flows. At dial settings of 3% or greater delivered concentrations were greater than dial settings at O2 flows less than 4 L/min and at O2 flow greater than 4 L/min delivered were less than dialed concentrations. Time-related reductions in delivered concentrations were most evident at dial settings of 3% or greater and O2 flow rates greater than 6 L/min. Increasing the environmental temperature to 30 degrees C or decreasing it to 15 degrees C increased or decreased, respectively, vaporized output when compared with conditions at 22 degrees C. Little or no effect on vaporizer output was noted with simulated positive pressure ventilation up to a breathing circuit pressure of 25 torr. We conclude the Fortec vaporizer is as efficient in delivering isoflurane in O2 as previous reports have shown the Fluotec Mark III to be in its delivery of halothane.