Measurement of breath-by-breath gas exchange during general anaesthesia using a single pneumotachograph

A breath-by-breath gas exchange measurement system using a single pneumotachograph suitable for use during general anaesthesia is described. The system's accuracy has been assessed by a combination of error sensitivity analysis, laboratory testing of the component measurements used to calculate gas exchange and measurements on volunteers and patients. The system is shown to have a mean accuracy of +/- 2.6 ml breath-1 for VCO2 measurements, +/- 7.12 ml breath-1 for VO2 and +/- 5.55 ml breath-1 for VN2O measurement. The application of a lung gas stores correction using argon improved between breath variability by 50%.