The effects of sampling site on the two-dimensional echo-Doppler determination of cardiac output

Cardiac output was measured by two-dimensional echocardiographic Doppler technique in 55 adult patients in the intensive care unit. Doppler cardiac output determinations were measured from four sites (suprasternal long axis of the ascending aorta, suprasternal long axis of the descending aortic, apical left ventricular outflow tract, and parasternal long axis of the main pulmonary artery) and were compared to cardiac output determined by thermodilution for a total of 101 observations (r = 0.84). Mean cardiac output was 5.3 L/min (range 1.8 to 9.5 L/min) by Doppler technique and 5.1 L/min (range 1.6 to 8.9 L/min) as measured by thermodilution. Correlation of Doppler cardiac output with thermodilution cardiac output gave r values of 0.85, 0.83, 0.90, and 0.81 from the ascending aorta, descending aorta, left ventricular outflow tract, and pulmonary artery, respectively. Averaging of data in patients in whom more than one determination was possible resulted in improved correlation (r = 0.94). Thus, cardiac output can be measured with reasonable accuracy by Doppler from a variety of sampling sites and averaging of data from more than one site may improve these results.