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.