Evaluations of the Waters MRM-6000 and Biergy VVR Closed-Circuit Indirect Calorimeters

Abstract

We evaluated the Waters MRM-6000 and Biergy VVR closed-circuit indirect calorimeters for accuracy and reproducibility of results in measuring oxygen uptake ( ${\dot{V}}_{{\text{O}}_2}$ ) and for performance during mechanical ventilation (MV). We also tested the MRM-6000 for accuracy and reproducibility in measuring carbon dioxide production ( ${\dot{V}}_{{\text{CO}}_2}$ ). METHODS: We bench tested the devices to compare their measurements with those of a model during mechanical ventilation (MV). The model included a test lung, reference spirometer, vacuum pump, flow regulator, and adult volume ventilator. Tests were conducted with tidal volumes (V_T) of 800-1600 mL at rates of 12-30 breaths/min; test-lung compliances were 0.01, 0.03, and 0.05 L/cm H2O [0.102, 0.306, and 0.510 L/kPa]; simulated ${\dot{V}}_{{\text{O}}_2}$ values were 109-844 mL/min. We also conducted clinical studies on 11 postoperative patients. RESULTS: No significant differences were found between bench-model and calorimeter ${\dot{V}}_{{\text{O}}_2}$ values for both calorimeters or between bench-model and MRM-6000 ${\dot{V}}_{{\text{CO}}_2}$ values. Good reproducibility of results was shown by a coefficient of variation of 1.5% for the MRM-6000 and 1.7% for the VVR. There were significant differences in displayed V_T compared to V_T delivered to the test lung, and individual adjustments had to be made to maintain the pretest level of mechanical ventilator support. CONCLUSIONS: The MRM-6000 and VVR calorimeters provide accurate and reproducible information during MV and perform adequately if the operator makes suitable adjustments during the test period.