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

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 (COTEE), (2) the Fick method (COFICK), and (3) thermodilution (COTD) 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 COTEE was calculated from the corresponding volumes. Absolute cardiac output values and the changes from before to after saline infusion (Delta CO) were compared using analysis of variance, linear regression, and the Bland and Altman method. Results: There were no significant differences between COTEE (8.0 +/- 3.4), COFICK (8.4 +/- 3.3), and COTD (8.3 +/- 3.0) or between Delta COTEE, Delta COFICK, and Delta COTD using analysis of variance. However, correlations between COTEE and COTD (r(2) = 0.46; P < .000D1), COFICK and COTD (r(2) = 0.46; P < .00001), and COTEE and COFICK (r(2) = 0.42; P < .00001) were only moderately good. Using the method of Bland and Altman, the mean difference (+/-2 standard deviations) between COTEE and COTD was 0.3 +/- 4.3 L/min, between COFICK and COTD was -1.0 +/- 3.8 L/min, and between COTEE and COFICK was 0.6 +/- 5.6 L/min, whereas the difference between Delta COTEE and Delta COTD was 0% +/- 26%, between Delta COFICK and Delta COTD was 9% +/- 46%, and between Delta COTEE and Delta COFICK 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 leg, oxygen delivery) should be borne in mind when making clinical decisions on individual patients. Copyright (C) 1996 by W.B. Saunders Company.