Objectives. The purpose of this study was to check the precision of the Drager vaporizer model 19.3 when filled with three different preparations of isoflurane. Methods. Six Drager vaporizers model 19.3 calibrated with forene were filled with forene (Abbott), isoflurane (Lilly) and isoflurane (Pharmacia); gas output was measured by infrared absorption (Irina, Drager) at vaporizer settings of 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 and 5.0 vol%, starting with a fresh gas flow of 2 l/min followed by 4, 6 and 12 l/min. Thus each of the three isoflurane preparations was checked in six different vaporizers and with four different fresh gas flows. Results. Within the concentration range used in clinical practice there was no significant difference in the delivery of the three isoflurane preparations. Each of the six vaporizers produced a controllable acid predictable concentration of the three preparations. Conclusion. Vaporizers of Drager type 19.n calibrated with forene deliver the same predictable concentration of the volatile anaesthetic when filled with isoflurane from Lilly or isoflurane from Pharmacia instead of forene and may be used without impairment in patient safety. In addition, no specific calibration with one of the new isoflurane preparations is required.
