Effects of mild Trendelenburg on central hemodynamics and internal jugular vein velocity, cross-sectional area, and flow.

Despite widespread use of the Trendelenburg position, its autotransfusion effect remains controversial. Additionally, its adverse effect on cerebral circulation is not generally appreciated. The effects of a 10 degrees head-down tilt on central hemodynamics and flow through the internal jugular vein (IJV) were examined in ten healthy volunteers. Left ventricular end-diastolic volume (LVEDV) and cardiac output (CO) were calculated from two-dimensional echocardiograms. IJV velocity and cross-sectional area were determined by the pulsed Doppler system. Measurements were made with the subjects in the supine position and at 1 minute and 10 minutes after tilting. A significant increase (16%) in CO followed by the increase in LVEDV was observed at 1 minute after tilting, although these changes disappeared after 10 minutes of tilting. Mean arterial pressure at the heart level did not change during the maneuver. The IJV velocity decreased whereas the IJV cross-sectional area increased at 1 minute after tilting, but both factors returned to control level at 10 minutes after tilting. As a result, calculated IJV blood flow was unchanged throughout the period of tilt. Therefore, the mild trendelenburg position produces a transient autotransfusion effect in normovolemic patients. Our data also suggest that the Trendelenburg produces no adverse effect on cerebral circulation in patients with normal cerebral autoregulation.