Validation of a compact system for measuring gas exchange

Abstract

Measuring gas exchange in critically ill patients can provide valuable information on their nutritional status and energy expenditure. Several semiautomated machines are available for measuring oxygen consumption (VO2) and carbon dioxide production (VCO2). This study evaluated, under controlled laboratory conditions, a Gould 9000 IV prototype designed for use with mechanically ventilated patients. Various VO2 and VCO2 values were simulated at different combinations of frequency, tidal volume, minute ventilation, and inspired oxygen fraction (FIO2). Variations in frequency, tidal volume, and minute ventilation had no significant effect on the measured VO2 and VCO2, but FIO2 had a dramatic effect on the accuracy of VO2. Errors in measured VO2 were 2.6%, 3.5%, 5.9%, and 16.9% at FIO2 values of 0.22, 0.40, 0.60, and 0.80, respectively. Addition of a dead space to the spirometer dump port (to prevent room-air contamination) corrected a larger error initially found. The accuracy of VCO2 was +/- 2.6%.