Simultaneous measurements of cardiac output by thermodilution, esophageal Doppler, and electrical impedance in anesthetized patients.

Simultaneous intraoperative measurements of cardiac output were obtained in nine patients with transesophageal Doppler, transthoracic impedance, and pulmonary artery thermodilution techniques to evaluate the utility of the noninvasive methods. Pairs of noninvasive and thermodilution measurements were obtained 25 times with transesophageal Doppler and 58 times with transthoracic impedance. Correlation of the noninvasive measurements with thermodilution was poor, with r = 0.43 for transthoracic impedance and r = .68 for transesophageal Doppler. The average difference between the noninvasive and the thermodilution values was -0.4 +/- 1.4 L/min (mean +/- SD) and -0.1 +/- 1.6 L/min for impedance and Doppler, respectively. Changes in cardiac output at sequential time points as measured by thermodilution were predicted with 95% confidence only when a change of >4 L/min was observed by transesophageal Doppler or >8 L/min was observed by transthoracic impedance. Therefore, it is concluded that neither noninvasive technique reliably estimated cardiac output as determined by thermodilution, and neither tracked trends.