The effects of carrier gas composition on the performance of the Tec 6 desflurane vaporizer

The new Tec 6 desflurane vaporizer is an electrically heated, pressurized, electromechanically coupled dual-circuit blender. We hypothesized that carrier gas viscosity should affect the electromechanical coupling of the fresh gas and vapor circuits, and that desflurane output should vary with different carrier gases. In the first portion of the study, the performance of eight vaporizers was evaluated using a constant dial setting of 10% desflurane with four different carrier gases and three different fresh gas flow rates. In the second portion of the study, the carrier gas flow rate was maintained at 1, 5, or 10 L/min, and vaporizer output was analyzed at all integer dial settings from 1% to 18%. Vaporizer output was highest when oxygen was the carrier gas and lowest when nitrous oxide was the carrier gas. This effect was accentuated at low fresh gas flow rates and correlated with carrier gas viscosity. At a flow rate of 1.0 L/min with a constant dial setting of 10%, the averaged output from vaporizers was 10.3 ± 0.66, 9.4 ± 0.58, 8.7 ± 0.52, and 8.1 ± 0.44 vol% for 100% oxygen, air, 30% oxygen plus 70% nitrous oxide, and 100% nitrous oxide, respectively. With 100% nitrous oxide as the carrier gas at a flow rate of 1.0 L/min, the vaporizer delivered 2 vol% less than the dial setting at dial settings in excess of 12%. Differences between the analyzed concentration and the dial setting were most pronounced with high concentrations of nitrous oxide at low fresh gas flow rates.