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/m 2 , and 78.1% in patients with a CI ≥ 2.4 L/min/m 2 . 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/m 2 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/m 2 were included, while there was no improvement in CI Fick accuracy or trending ability.