Simultaneous cardiac output measurements by transtracheal Doppler, electromagnetic flow meter, and thermodilution during various hemodynamic states in pigs.

The transtracheal Doppler (TTD) method of cardiac output (CO) measurement was compared with thermodilution (TDL) and aortic electromagnetic flow meter (EFM). Simultaneous CO measurements with the three methods were obtained during various hemodynamic states in eight pigs. Cardiac output ranged from 1 to 3 L/min during the study. For 128 measurements, the mean difference +/- SD between TTD-TDL and TTD-EFM measurements was -0.037 +/- 0.24 L/min and -0.055 +/- 0.23 L/min, respectively. TDL-EFM mean difference +/- SD was -0.017 +/- 0.15 L/min. The limits of the agreement between TTD and the reference methods were 0.4 to -0.5 L/min. The limits of agreement between the reference methods were 0.3 to -0.3 L/min. Regression analysis yielded TTD = 0.383 + 0.779 TDL (r = 0.86); TTD = 0.351 + 0.788 EFM (r = 0.87); TDL = 0.077 + 0.95 EFM (r = 0.95). Only a change greater than 0.6 L/min in TTD CO could predict with 95% confidence a change in TDL or EFM CO. These results suggest that, in the CO range of this study, the TTD method does not accurately reproduce the CO measurements obtained by TDL or EFM.