Comparison of transesophageal echocardiographic, fick, and thermodilution cardiac output in critically ill patients

Abstract

Purpose: Recent observations have highlighted errors in the thermodilution technique of measuring cardiac output. Thus, cardiac output measurements using transesophageal echocardiography and the Fick method were compared with simultaneous thermodilution measurements. Methods: In 13 mechanically ventilated critically ill patients, cardiac output was determined simultaneously using (1) transesophageal echocardiography (CO TEE), (2) the Fick method (CO FICK), and (3) thermodilution (CO TD) immediately before and after a rapid infusion of 500 mL of saline. Left ventricular end-diastolic and end-systolic areas were measured using the transesophageal echocardiographic transgastric short axis view, and CO TEE was calculated from the corresponding volumes. Absolute cardiac output values and the changes from before to after saline infusion (ΔCO) were compared using analysis of variance, linear regression, and the Bland and Altman method. Results: There were no significant differences between CO TEE (8.0 ± 3.4), CO FICK (8.4 ± 3.3), and CO TD (8.3 ± 3.0) or between ΔCO TEE, ΔCO FCK, and ΔCO TD using analysis of variance. However, correlations between CO TEE and CO TD ( r 2 = 0.46; P < .00001), CO FICK and CO TD ( r 2 = 0.46; P < .00001), and CO TEE and CO FICK ( r 2 = 0.42; P < .00001) were only moderately good. Using the method of Bland and Altman, the mean difference (±2 standard deviations) between CO TEE and CO TD was 0.3 ± 4.3 L/min, between CO FICK and CO TD was −1.0 ± 3.8 L/min, and between CO TEE and CO FICK was 0.6 ± 5.6 L/min, whereas the difference between ΔCO TEE and ΔCO TD was 0% ± 26%, between ΔCO FICK and ΔCO TD was 9% ± 46%, and between ΔCO TEE and ΔCO FICK was 8% ± 39%. Conclusions: There are substantial differences in cardiac output as measured by these three methods, best demonstrated using the method of Bland and Altman. The variability of cardiac output and its derivatives (eg, oxygen delivery) should be borne in mind when making clinical decisions on individual patients.