Calculation Of O2 consumption during low-flow anesthesia from tidal gas concentrations, flowmeter, and minute ventilation

Abstract

We present the principles of a new method to calculate O2 consumption (V̇O2) during low-flow anesthesia with a circle circuit when the source gas flows, end-tidal O2 concentrations and patient inspired minute ventilation are known. This method was tested in a model with simulated O2 uptake and CO2 production. The difference between calculated V̇O2 and simulated V̇O2 was 0.01 ± 0.02 L/min. A similar approach can be used to calculate uptake of inhaled anesthetics. At present, with this method, the limiting factor in precision of measurement of V̇O2 and uptake of anesthetic is the precision of measurement of gas flow and gas concentration (especially O2 concentration in end-tidal gas, FETO2) available in clinical anesthetic units. © Springer Science + Business Media, Inc. 2005.