An in vitro evaluation of an instrument designed to measure oxygen consumption and carbon dioxide production during mechanical ventilation

Abstract

Objective: To determine the ability of the Puritan-Bennett 7250 metabolic monitor to measure CO2 production and oxygen consumption (V̇o2) under simulated clinical conditions. Design: Anin vitrovalidation study. Setting: Laboratory of a large university medical center. Methods: Anin vitroevaluation was performed by adding precise amounts of CO2 and nitrogen to a lung model to simulate CO2 production and V̇o2. CO2 production and V̇o2 values measured by the metabolic monitor were compared with simulated values at various Fio2 values (0.21 to 0.80), levels of positive end-expiratory pressure (0 to 20 cm H2O), and flow-by mode flow rates (0 to 20 L/min). This comparison was also made at increased peak airway pressures (60 cm H2O). The effects of various concentrations of oxygen on the accuracy of the CO2 production measurements were also examined. Results: The measurements made by the instrument were within 7% of values predicted from the CO2 and nitrogen infusions. There was no effect of various oxygen concentrations on the accuracy of CO2 production measurements. Conclusion: Under thein vitroconditions tested, the metabolic monitor provided accurate measurements of V̇2 and CO2 production. (Crit Care Med 1994; 22:1995–2000)