The reliability of noninvasive cardiac output measurement using the inert gas rebreathing method in patients with advanced heart failure.

BACKGROUND Impaired cardiac output (CO) is a key element of heart failure (HF). So far, there has been no simple, reliable, inexpensive and non-invasive CO measurement method feasible for clinical practice. Not a single diagnostic test has been elaborated to diagnose and monitor HF. The aim of the study was the evaluation of the reliability of a new, non-invasive CO measurement device utilizing an inert gas rebreathing technique and an infrared photoacoustic gas analyzer, in comparison with standard invasive methods. METHODS In 21 patients with advanced HF (NYHA classes III and IV) undergoing cardiac catheterization as a routine hemodynamic evaluation before heart transplantation, CO measurements with the tested non-invasive method were carried out during invasive examination. RESULTS CO measured by the inert gas rebreathing technique (CO(RB)), according to the statistical Bland-Altman method, was, on average, 0.1 L/min higher than that determined by thermodilution (CO(TD)) and 0.006 L/min higher than the CO determined by the Fick formula (CO(Fick)). This magnitude of difference equals 2.8% of CO(TD) and 0.15% of CO(Fick) values. The limits of agreement between CO(RB) and CO(TD) were +/- 1.4 L/min, and between CO(RB) and CO(Fick) +/- 1.3 L/min. In the subgroup with atrial fibrillation, the mean difference between tested and reference methods (0.3 +/- 1.0 L/min for both CO(TD) and CO(Fick)) was higher than in the sinus rhythm subgroup (0.06 +/- 1.5 L/min for CO(TD) and 0.08 +/- 1.5 for CO(Fick)). CONCLUSIONS CO measurement with the inert gas rebreathing method utilizing an infrared photoacoustic gas analyzer seems reliable enough to be employed in clinical practice. Being non-invasive, it may well be used for repeated determinations in patients with HF.