AN IN-VITRO EVALUATION OF AN INSTRUMENT DESIGNED TO MEASURE OXYGEN-CONSUMPTION AND CARBON-DIOXIDE PRODUCTION DURING MECHANICAL VENTILATION

Objective: To determine the ability of the Puritan-Bennett 7250 metabo lic monitor to measure CO2 production and oxygen consump tion (($) ove r circle Vo(2)) under simulated clinical conditions. Design: An in vit ro validation study. Setting: Laboratory of a large university medical center. Methods: An in vitro evaluation was performed by adding preci se amounts of CO2 and nitrogen to a lung model to simulate CO2 product ion and ($) over circle Vo(2). CO2 production and ($) over circle Vo(2 ) values measured by the metabolic monitor were compared with simulate d 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 p ressures (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 va lues predicted from the CO2 and nitrogen infusions. There was no effec t of various oxygen concentrations on the accuracy of CO2 production m easurements. Conclusion: Under the in vitro conditions tested, the met abolic monitor provided accurate measurements of Vo(2) and CO2 product ion.