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 VO2. 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.

Cardiac Output Determination in Precapillary Pulmonary Hypertension: A Systematic Review

<b><i>Background:</i></b> Cardiac output determination is essential in precapillary pulmonary hypertension. While direct Fick is the gold standard, thermodilution is commonly used as the reference method. Moving to noninvasive methods would be highly beneficial for patients, avoiding repetitive invasive assessments. This systematic review followed 3 objectives: (1) assessing the validity of indirect Fick and thermodilution in precapillary pulmonary hypertension, (2) assessing the interchangeability of noninvasive cardiac output measurement methods against reference methods in precapillary pulmonary hypertension, and (3) detecting methodological heterogeneity in the included studies. <b><i>Methods:</i></b> We systematically reviewed the literature using medical databases and following PRISMA guidelines. We included articles comparing an invasive or noninvasive cardiac output measurement method with thermodilution or direct Fick in precapillary pulmonary hypertension patients. Cutoffs of limits of agreement and percentage error derived from the Bland and Altman graph were used to accept interchangeability. To study methodological heterogeneity, we extracted 9 quality criteria from all studies. <b><i>Results:</i></b> Eleven studies were included. None reached the suggested interchangeability criteria. The median number of the 9 assessed quality criteria was 2 with interquartile range (0–4). <b><i>Conclusions:</i></b> Further studies evaluating the reliability of thermodilution and the consequences of its use in precapillary pulmonary hypertension patients are necessary. No evidence supports the use of indirect Fick in precapillary pulmonary hypertension. The studied noninvasive methods could not be considered interchangeable with invasive methods. A robust methodology should be used to draw sensible conclusions.