Agreement of an inert gas rebreathing device with thermodilution and the direct oxygen Fick method in measurement of pulmonary blood flow.

Abstract

Inert gas rebreathing is a well established method for the non-invasive measurement of pulmonary blood flow. We tested the agreement in measurement of pulmonary blood flow (Qt rb) by a new inert soluble gas rebreathing device, the Innocor (Innovision, Copenhagen), with bolus thermodilution (Qt td) and the direct oxygen Fick (Qt Fick) method.9 patients pre- and post-cardiac surgery were recruited resulting in 20 sets of measurements overall. Arterial and mixed venous blood samples were collected simultaneously with a thermodilution measurement and rebreathing manoeuvre to measure both V*O2 and effective pulmonary capillary blood flow.Mean bias (95% confidence limits) was: Qt rb - Qt td 0.01 (+/- 0.42) L/min; Qt rb - Qt Fick + 0.34 (+/-0.59) L/min. The standard deviation of the difference between paired measurements was: Qt td - Qt rb +/- 0.89 L/min; Qt Fick - Qt rb +/- 1.26 L/min.Acceptable overall agreement between the Innocor and these reference standards was demonstrated.