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 (VO2) and carbon dioxide output (VCO2) 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 VO2, VCO2 and respiratory quotient. The system has been validated against standard methods of gas analysis and flow measurement (VO2 mean difference -10 ml min-1: SD 9.13; VCO2 mean difference 8.12 ml min-1: SD 4.66). Comparison with Douglas bag measurements in patients has been made (VO2 mean difference 10.7 ml min-1: SD 9.8; VCO2 mean difference -1.07 ml min-1: SD 4.7).