[Current Aspects of Definition and Diagnosis of Pulmonary Hypertension]

Modern gold standard of cardiac output measurement - A simplified bedside measurement of individual oxygen uptake in the cath lab

OBJECTIVES

Cardiac output (CO) measurements employing the direct Fick principle represent the gold standard in right-sided heart catheterization (RHC). The current widespread approach in hemodynamic workup however uses the indirect Fick principle with assumed values for oxygen uptake (VO₂) leading to incorrect CO values in up to 25% of patients. We have tested a contemporary breath-by-breath gas analyzer that allows precise real-time measurements of VO₂ with appropriate time and effort to serve the direct Fick principle.

METHODS

By means of a small and mobile metabolic cart assembled with widely used components of a standard spiroergometer, we performed bedside measurements of individual VO_2. In 33 unselected, consecutive patients with various indications for RHC we compared CO values derived from indirect vs. direct Fick calculations.

RESULTS

In 28 of the 33 patients, VO₂ measurements were completed with a plausible dataset within a median of 3.2 (interquartile range 2.8-6.2) min. In nine of the 28 patients, CO values based on measured VO₂ values differed by more than 20% from CO calculations based on assumed VO₂ values with value deviations scattering over a broad range in both directions (maximally +52% to minimally -46%).

CONCLUSIONS

The bedside measurement of VO₂ for gold standard CO determination is technically feasible within a few min and can thus be easily included in any RHC protocol. As modern therapy for numerus indications demand a precise upfront measurement of hemodynamics, our method might help to correctly identify patients for costly therapies.