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™ (CIFT) or derived by the Fick equation (CIFick) using E-CAiOVX (enables continuous monitoring of oxygen consumption) with that measured by thermodilution (CITD) in patients with off-pump coronary artery bypass surgery. Twenty-two patients undergoing elective off-pump coronary artery bypass surgery were included. CIFT and CIFick 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 (CITD 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, CIFT and CIFick showed percentage errors of 49.5% and 78.6%, respectively, compared with CITD. Subgroup analysis showed a percentage error between COFT and COTD 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 CIFT and 66.7% for CIFick in datasets where CITD ≥ 2.4 L/min/m2 before and after phenylephrine administration were included. CIFT and CIFick had wide limits of agreement with CITD, and were below acceptable limits for tracking phenylephrine-induced CI changes. However, subgroup analysis showed improved accuracy and trending ability of CIFT when only points where CITD ≥ 2.4 L/min/m2 were included, while there was no improvement in CIFick accuracy or trending ability.