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 (VO₂) 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 VO₂ and simulated VO₂ 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 VO₂ 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.