A comparison between the transthoracic electrical impedance method and the direct Fick and the dye dilution methods for cardiac output measurements in man.

In fourteen patients referred for preoperative evaluation of heart disease we compared the transthoracic electrical impedance method to the direct Fick (four patients) and dye dilution methods (ten patients) for estimation of cardiac output. On statistical analysis of paired differences we found no reliable agreement between the absolute impedance values and the reference methods. The reproducibility was, however, acceptable, and the coefficient of variation for impedance cardiac output was 7.8%, and for impedance stroke volume 7.6%. Our conclusion is that in patients with advanced heart disease cardiac output cannot be determined with accuracy with the impedance cardiographic method. In clinical practice this must be considered so important, that we hesitate to use the method for monitoring cardiac output in critically ill patients even if the reproducibility for individual changes is acceptable.