A system for the continuous measurement of oxygen uptake and carbon dioxide output in artificially ventilated patients

Abstract

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). © 1983 The Macmillan Press Ltd.