Instrumentation for monitoring gas exchange and metabolic rate in critically ill patients

Abstract

In the critically ill patient the monitoring of oxygen consumption (Vo2) and carbon dioxide production (Vco2) can identify abnormalities in tissue perfusion and metabolism. A patient's metabolic utilization can be calculated by indirect calorimetry, once Vo2 and Vco2 are measured. This paper evaluates a compact instrument designed for monitoring Vo2 and Vco2 in the critically ill adult. Accuracy was measured under controlled laboratory conditions using oxygen-enriched air, PEEP, and intermittent mandatory ventilation (IMV). Accuracy averaged 1.3% for Vo2 and 0.9% for Vco2 when room air was used. Accuracy was 11.7% for Vo2 and 6.8% for Vco2 when 80% oxygen was used. PEEP of 30 cm H2O had little effect on accuracy. IMV at 2 breath/min (room air) resulted in an accuracy of 4.0% and 4.1% for Vo2 and Vco2, respectively.