Evaluation of five small turbine-type respirometers used in adult anesthesia

The purpose of this study was to determine the accuracy of five rotating vane or turbine-type respirometers--fdE Magtrak Respiratory Monitor, fdE Haloscale Standard Wright Respirometer, Micro-Medical Pocket Monitor II, and Ohmeda 5400 and 5410 Volume Monitors--which are marketed as suitable for measuring expired gas volume in anesthetized adult patients.

The devices were tested for accuracy at simulated minute ventilations ranging from 2.4 to 15 L/min with three gas mixtures: air, air saturated with water vapor, and N2O/O2 (70:30).

In the usual range for adult minute ventilation during general anesthesia with intermittent positive-pressure ventilation (5-12 L/min), all devices were on average accurate to within 12%. At the lowest minute volume readings (2.4 L/min) all devices except the Pocket Monitor tended to have low readings. No significant differences in readings were introduced by either saturation with water vapor or introduction of 70% N2O, except with ventilation below 4 L/min with both Ohmeda respirometers.

All monitors showed reasonable clinical accuracy in the usual adult minute ventilation range during general anesthesia with intermittent positive-pressure ventilation (> 5 L/min) when used to measure air, water vapor-saturated air, or N2O/O2 mixtures.