Design and validation of an automatic metabolic monitor

A self-calibrating fully automatic instrument for the measurement of oxygen consumption, carbon dioxide production and the respiratory quotient of mechanically ventilated patients has been developed. The instrument is based on commercially available conventional oxygen and carbon dioxide gas analysers and a domestic natural gas volumetric flow meter. The distribution of the different gas flows, i.e. calibration gases, the inspiratory mixture sample and the expiratory mixture sample, are controlled by in inexpensive microprocessor, which also performs the necessary calculations. The accuracy of the instrument has been validated by bench tests. The present prototype has been in use for over 3000 h without major failures.