Influence of Bag Volume on Reproducibility of Inert Gas Rebreathing Pulmonary Blood Flow Measurements in Patients with Pulmonary Diseases

Abstract

Non-invasive inert gas rebreathing (IGR) has shown promising results in the determination of pulmonary blood flow. The volume of the rebreathing bag (V bag) is proposed by the system. However, elderly patients or those with severe pulmonary disease may be unable to rebreathe this volume entirely. We evaluated the effect of adapting V bag on the reproducibility of IGR. A total of 270 valid measurements were obtained from 45 patients with obstruction (group A), restriction (group B), and in healthy controls (group C). Two measurements for each of three different V bag of 1,200, 1,700, and 2,200ml were conducted in the supine position. We found no statistically significant difference of the repeated measurements neither between the different V bag in groups A to C nor between the three groups for identical V bag. There was a weak yet significantly worse coefficient of variation between a V bag of 2,200ml in group A compared with group C with 2,200 and 1,200ml, respectively. Intraclass correlation coefficient and repeatability coefficient yielded significantly worse values in group A for a V bag of 2,200ml compared with healthy controls and lower bag volumes. No difference could be found intraclass nor interclass in groups B and C. V bag can be altered between 1,200 and 2,200ml in most situations without affecting the reproducibility. Attention has to be paid to extreme volumes in obstructive patients. Nevertheless, V bag should be chosen as large as possible and therefore has to be carefully adapted, particularly in patients with obstruction or restriction.