Continuous cardiac output determination using transtracheal Doppler: initial results in humans.

Transtracheal Doppler, a procedure developed in the authors' laboratory, provides an estimate of cardiac output in endotracheally intubated dogs. The present study reports initial results in humans with a Doppler probe incorporated into an endotracheal tube. The system was first calibrated by empirically determining phi, the angle of the ultrasound beam with respect to the blood velocity vector. For a best least squares fit for phi, aortic diameters can be calibrated over a range of 22-37 mm. The calibration was then tested in a separate group of patients using the same empirically derived angle to calculate cardiac outputs. The transtracheal Doppler cardiac outputs show good correlation with those obtained by thermodilution over a range of cardiac outputs, 2.69-8.62 1/min, R2 = 0.835.