[Intraoperative cardiac output monitoring by the transtracheal Doppler method]

We investigated the cardiac output measured with a transtracheal doppler (TTD) tube in surgical patients and evaluated its usefulness during operations. This tube was located at the point where maximum velocity of blood flow was obtained in the ascending aorta. At this point the cross-sectional area of the ascending aorta was calculated and the cardiac output was obtained by multiplying this area with average blood flow velocity which had been ultrasonically determined. The cardiac output by the TTD method was compared with that of the thermodilution method in 10 patients. The results with both groups showed a direct linear correlation. We obtained the following linear equation: TTD C.O. = 0.61 Thermo C.O. + 1.3 C.O.: cardiac output. The direct correlation coefficient proved to be 0.85 at a risk factor of 0.01. The result suggests that this non-invasive TTD method is easily available and useful in monitoring the intraoperative cardiac output.