Maternal cerebral hemodynamics in the supine hypotensive syndrome.

Cerebral hemodynamics were studied in eight nonpregnant women and 24 women in late pregnancy by internal carotid artery velocimetry with a 3.5-MHz continuous-wave Doppler system. Criteria for supine hypotensive syndrome were a mean blood pressure decrease of 15 mmHg and a 2-minute sustained increase in pulse of 20 beats per minute under postural change from the left lateral to supine position. Nonpregnant and normal pregnant controls not meeting these two criteria displayed decreases of 22.9 and 21.7%, respectively, in time-averaged mean peak velocity (mean velocity) in the supine position compared with the left lateral position. Five subjects with subclinical supine hypotensive syndrome who met one of the above criteria showed a 37.0% decrease in internal carotid artery mean velocity in the supine position. Two patients with supine hypotensive syndrome could not tolerate the supine position for more than 6 minutes, at which time internal carotid artery mean velocity fell below 10 cm/second, reverse flow was observed, and they complained of dizziness, nausea, and syncope. Internal carotid artery mean velocity in all women showed no change in the sitting position compared with the left lateral position. These results indicate that the supine position should be avoided in late pregnancy, especially by women with cerebrovascular complications.