Oxygen consumption measurement: agreement between the closed-circuit PhysioFlex anesthesia machine and the Deltatrac II indirect calorimeter.

Abstract

We designed this study to ascertain whether, for the purpose of clinical interpretation, the direct measurement of O(2) consumption with the PhysioFlex closed-circuit anesthesia machine and with the Deltatrac II indirect calorimeter are interchangeable. Oxygen consumption was measured using the two instruments successively in critically-ill, mechanically-ventilated patients. Measurements were recorded as the mean of 10 consecutive, minute-by-minute, stable readings. The degree of agreement between the measurements obtained with the two systems was estimated using Bland-Altman analysis and the intraclass correlation coefficient. Forty-four pairs of measurements made in 21 patients were analyzed, yielding a mean bias of 6.32 mL/min and limits of agreement of 40.28 and -27.63 mL/min. The intraclass correlation coefficient was 0.95, and the 95% confidence interval ranged from 0.91 to 0.97. The measurement of O(2) consumption obtained with the PhysioFlex anesthesia machine is interchangeable with that obtained by indirect calorimetry. The PhysioFlex anesthesia machine (Dräger Inc., Lübeck, Germany) is a closed circuit anesthesia delivery device. The oxygen delivered by this device to maintain a steady-state inspired oxygen concentration is therefore a measure of the patient's oxygen consumption. This study was designed to evaluate the accuracy of the PhysioFlex for measuring oxygen consumption by comparing it with an established technology (Deltatrac II Calorimeter) for making this measurement.