Thermodilution vs Estimated Fick Cardiac Output Measurement in Clinical Practice An Analysis of Mortality From the Veterans Affairs Clinical Assessment, Reporting, and Tracking (VA CART) Program and Vanderbilt University

IMPORTANCE Thermodilution (Td) and estimated oxygen uptake Fick (eFick) methods are widely used to measure cardiac output (CO). They are often used interchangeably to make critical clinical decisions, yet few studies have compared these approaches as applied in medical practice. OBJECTIVES To assess agreement between Td and eFick CO and to compare how well these methods predict mortality. DESIGN, SETTING, AND PARTICIPANTS This investigation was a retrospective cohort study with up to 1 year of follow-up. The study used data from the Veterans Affairs Clinical Assessment, Reporting, and Tracking (VA CART) program. The findings were corroborated in a cohort of patients cared for at Vanderbilt University, an academic referral center. Participants were more than 15 000 adults who underwent right heart catheterization, including 12 232 in the Veterans Affairs cohort between October 1, 2007, and September 30, 2013, and 3391 in the Vanderbilt cohort between January 1, 1998, and December 31, 2014. EXPOSURES A single cardiac catheterization was performed on each patient with CO estimated by both Td and eFick methods. Cardiac output was indexed to body surface area (cardiac index [Cl]) for all analyses. MAIN OUTCOMES AND MEASURES All-cause mortality over 90 days and 1 year after catheterization. RESULTS Among 12 232 VA patients (mean [SD] age, 66.4 [9.9] years; 3.3% female) who underwent right heart catheterization in this cohort study, Td and eFick Cl estimates correlated modestly (r = 0.65). There was minimal mean difference (eFick minus Td = -0.02 L/min/m(2), or -0.4%) but wide 95% limits of agreement between methods (-1.3 to 1.3 L/min/m2, or -50.1% to 49.4%). Estimates differed by greater than 20% for 38.1% of patients. Low Td Cl (<2.2 L/min/m(2) compared with normal Cl of 2.2-4.0 L/min/m(2)) more strongly predicted mortality than low eFick Cl at 90 days (Td hazard ratio [HR], 1.71; 95% Cl, 1.47-1.99; chi(2) = 49.5 vs eFick HR, 1.42; 95% Cl, 1.22-1.64; chi(2) = 20.7) and 1 year (Td HR, 1.53; 95% Cl, 1.39-1.69; chi(2) = 71.5 vs eFick HR, 1.35; 1.22-1.49; chi(2) = 35.2). Patients with a normal Cl by both methods had 12.3% 1-year mortality. There was no significant additional risk for patients with a normal Td Cl but a low eFick Cl (12.9%, P = .51), whereas a low Td Cl but normal eFick Cl was associated with higher mortality (15.4%, P = .001). The results from the Vanderbilt cohort were similar in the context of a more balanced sex distribution (46.6% female). CONCLUSIONS AND RELEVANCE There is only modest agreement between Td and eFick Cl estimates. Thermodilution Cl better predicts mortality and should be favored over eFick in clinical practice.