Comparisons of cardiac output in supine and lateral positions.

Cardiac output was measured by thermodilution in 51 adult postcardiac surgical patients using three positions, supine, right lateral, and left lateral, each with 20 degrees backrest elevation. Measurements were taken 4 to 24 hours (M = 10.58) after surgery. Mean cardiac output was significantly different in the three positions, p = .03. This difference resulted from changes in stroke volume, p = .004, rather than changes in heart rate, p = .12. The largest variation occurred between cardiac outputs measured in the supine position and those measured in the left lateral position. Patients at greatest risk for variations in cardiac output with lateral postural change were those with a cardiac index less than 2.3 L/min/m2, those in whom the time elapsed since surgery was less than 12 hours, and those receiving either vasoactive drugs or mechanical ventilation. These results suggest that nurses need to measure cardiac output using a supine position to control for physiological changes that may occur with lateral postural change.