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

Abstract

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.