A SYSTEM FOR THE CONTINUOUS MEASUREMENT OF OXYGEN UPTAKE AND CARBON DIOXIDE OUTPUT IN ARTIFICIALLY VENTILATED PATIENTS

A continuous, non-invasive system is described for measuring oxygen uptake ($V•O2$) and carbon dioxide output ($V•CO2$) in mechanically ventilated patients. Inspiratory and mixed expiratory gas samples were pumped through fine-bore tubing to a remote mass spectrometer for analysis. The expiratory flow transducer of a Siemens Servo 900B ventilator was used for expiratory flow measurement and inspiratory flow was calculated from this using the Haldane transformation. A desk-top computer calculated $V•O2$, $V•CO2$ and respiratory quotient. The system has been validated against standard methods of gas analysis and flow measurement ($V•O2$ mean difference −lOml min⁻¹: SD9.13; $V•CO2$ mean difference 8.12ml min⁻¹: SD4.66). Comparison with Douglas bag measurements in patients has been made ($V•O2$ mean difference 10.7ml min⁻¹: SD9.8; $V•CO2$ mean difference −1.07ml min⁻¹: SD4.7).