Disagreement in cardiac output measurements between fourth-generation FloTrac and critical care ultrasonography in patients with circulatory shock: a prospective observational study

Background: Cardiac output measurements may inform diagnosis and provide guidance of therapeutic interventions in patients with hemodynamic instability. The FloTrac algorithm uses uncalibrated arterial pressure waveform analysis to estimate cardiac output. Recently, a new version of the algorithm has been developed. The aim was to assess the agreement between FloTrac and routinely performed cardiac output measurements obtained by critical care ultrasonography in patients with circulatory shock. Methods: A prospective observational study was performed in a tertiary hospital from June 2016 to January 2017. Adult critically ill patients with circulatory shock were eligible for inclusion. Cardiac output was measured simultaneously using FloTrac with a fourth-generation algorithm (COAP) and critical care ultrasonography (COCCUS). The strength of linear correlation of both methods was determined by the Pearson coefficient. Bland-Altman plot and four-quadrant plot were used to track agreement and trending ability. Result: Eighty-nine paired cardiac output measurements were performed in 17 patients during their first 24h of admittance. COAP and COCCUS had strong positive linear correlation (r(2)=0.60, p<0.001). Bias of COAP and COCCUS was 0.2 L min(-1) (95% CI - 0.2 to 0.6) with limits of agreement of - 3.6 L min(-1) (95% CI -4.3 to -2.9) to 4.0 L min(-1) (95% CI 3.3 to 4.7). The percentage error was 65.6% (95% CI 53.2 to 77.3). Concordance rate was 64.4%. Conclusions: In critically ill patients with circulatory shock, there was disagreement and clinically unacceptable trending ability between values of cardiac output obtained by uncalibrated arterial pressure waveform analysis and critical care ultrasonography.