The accuracy and trending ability of cardiac index measured by the fourth-generation FloTrac/Vigileo system™ and the Fick method in cardiac surgery patients

To compare the accuracy and trending ability of the cardiac index (CI) measured by FloTrac/Vigileo™ (CI_FT) or derived by the Fick equation (CI_Fick) using E-CAiOVX (enables continuous monitoring of oxygen consumption) with that measured by thermodilution (CI_TD) in patients with off-pump coronary artery bypass surgery. Twenty-two patients undergoing elective off-pump coronary artery bypass surgery were included. CI_FT and CI_Fick were determined simultaneously at six time-points during off-pump coronary artery bypass surgery. At each time-point, phenylephrine (50 µg) was administered to increase systematic vascular resistance, with CI measured before and after administration (CI_TD used as reference method). Agreement of each method was evaluated by Bland–Altman analysis, while trending ability was evaluated by four-quadrant plot analysis and polar plot analysis. By Bland–Altman analysis, CI_FT and CI_Fick showed percentage errors of 49.5% and 78.6%, respectively, compared with CI_TD. Subgroup analysis showed a percentage error between CO_FT and CO_TD of 28.9% in patients with a CI ≥ 2.4 L/min/m², and 78.1% in patients with a CI ≥ 2.4 L/min/m². The concordance rate of four-quadrant plot analysis was 93.3% for CI_FT and 66.7% for CI_Fick in datasets where CI_TD ≥ 2.4 L/min/m² before and after phenylephrine administration were included. CI_FT and CI_Fick had wide limits of agreement with CI_TD, and were below acceptable limits for tracking phenylephrine-induced CI changes. However, subgroup analysis showed improved accuracy and trending ability of CI_FT when only points where CI_TD ≥ 2.4 L/min/m² were included, while there was no improvement in CI_Fick accuracy or trending ability.