Accurate Fick cardiac output estimation: direct and simultaneous oxygen consumption measurement is imperative in heart failure

Background: Estimated oxygen consumption (VO2) values may compromise the accuracy of the Fick method for predicting cardiac output (CO) during a right heart catheterization (RHC). We aimed to compare VO2 measured in the hemodynamic laboratory (HL) with those measured on the ward or estimated, and to compare derived CO values with that obtained by thermodilution (TD) in people with severe heart failure (HF). Methods and results: In this prospective observational study, VO2 was measured breath-by-breath in the HL and in the ward (within 24h of RHC), or estimated using formulas. CO was calculated from both estimated and measured VO2 and assessed by TD. Eighty individuals with HF (69.6 ± 8.3 years; 74% male) were included. Significant differences were found between HL-measured VO2 (247 ± 55 mL/min), ward-measured VO2 (267 ± 74 mL/min), and the estimated values (Bergstra: 287 ± 33; Dehmer: 234 ± 24; LaFarge: 163 ± 11 mL/min). CO calculated from HL-measured VO2 (5.03 ± 1.51 L/min) differed from CO based on ward-measured VO2 (5.46 ± 1.93 L/min), estimated VO2 (Bergstra: 5.85 ± 1.38; Dehmer: 4.77 ± 1.12; LaFarge: 3.34 ± 0.80 L/min), and by TD (3.65 ± 1.22 L/min). Measured and estimated VO2 values showed moderate association (r values range: 0.479-0.526). CO calculated from HL-measured VO2 showed higher association (r values range: 0.708-0.765) with CO calculated from ward-measured VO2 and estimated VO2. The agreement between HL and ward-measured VO2 was moderate, with a concordance correlation coefficient of 0.48 (0.31;0.62). Conclusions: In people with severe HF undergoing RHC, VO2 must be directly measured in the HL, rather than on the ward or estimated.