The effects of a fluctuating Fio2 on metabolic measurements in mechanically ventilated patients

Abstract

The determination of minute oxygen consumption (Vo₂) for metabolic studies on patients using either the Beckman Metabolic Cart (MMC) or the Respiratory Monitoring System (RMS) requires a stable fractional inspired oxygen concentration (Fio₂). Measurement of Vo₂ on mechanically ventilated patients using the Bourns BEAR 1 and the Engstrom 311 and 312 was unsuccessful due to Fio₂ variations greater than the acceptable limits. The inspiratory and expiratory O₂ and CO₂ waveforms were studied using various methods of supplying source gas to the ventilators. A method using an external air/oxygen blender was found that provided a stable Fio₂ for metabolic measurements for each of the ventilators tested.