This report documents the validity of clinical measurements of oxygen comsumption (V̇(O2)) and carbon dioxide production (V̇(CO2)) made with a new metabolic gas monitor (MGM) suitable for use in critically ill patients receiving mechanical ventilatory support. Paired samples of inspired and expired gases were obtained, and exhaled minute volume was measured in 12 patients receiving supplemental oxygen, intermittent mandatory ventilation, and PEEP. Gas volume was measured with a calibrated spirometer and oxygen and CO2 fractions were measured by mass spectrometry. Measured and derived values were compared to those obtained from the MGM connected in series with the ventilator circuit. There were no statistically significant differences between values obtained from the mass spectrometer/spirometer vs. the MGM in exhaled volume (8.60 ± 3.81 vs. 8.58 ± 3.72 [SD] L/min), fraction of inspired oxygen (0.451 ± 0.011 vs 0.452 ± 0.010), fraction of expired oxygen (0.413 ± 0.013 vs. 0.415 ± 0.012), V̇(O2) (290 ± 113 vs. 275 ± 88 ml/min), V̇(CO2) (245 ± 95 vs. 247 ± 96 ml/min), or respiratory quotient (0.85 ± 0.14 vs. 0.88 ± 0.08). The fraction of expired CO2 measured by the MGM was significantly greater (0.034 ± 0.006 vs. 0.035 ± 0.006; p < .001) than that measured by mass spectrometer/spirometer. Twelve additional patients were studied to compare metabolic measurements made on 45% oxygen with those made at other fraction of inspired oxygen values. There was no significant difference between values measured on 45% oxygen and those measured on 30% to 50% oxygen. These data suggest that when a proper interface is obtained between the patient, ventilator, and device, the MGM will yield clinically valid determinations of V̇(O2) and V̇(CO2) in critically ill patients receiving supplemental oxygen PEEP, and mechanical ventilation.
ASJC Scopus subject areas
- Critical Care and Intensive Care Medicine