Effects of maternal postural change from supine to left-lateral on tocolysis, maternal cardiac function and pulsatility index of uterine artery.

In order to prove the usefulness of the left-lateral position (l-lat.) in preventing the cardiovascular complications associated with ritodrine, twenty-nine patients having preterm labor were employed as the subjects of this study. Before and during the administration of ritodrine, the cardiac function was recorded by impedance cardiography. (1) When ritodrine was administered in the supine position, SV and CO first increased but eventually tended to decrease. When the position was changed to the l-lat. after SV and CO had almost returned to the preadministration level, HR decreased and SV and CO increased in 70% (10/14) of the patients. However, in patients showing no change in HR in the supine position, the cardiac function did not change either. (2) The magnitude of the changes in cardiac function accompanying the postural change during ritodrine administration was compared with that observed before administration. The decrease in HR and the increase in SV due to the postural change to the l-lat. were larger during ritodrine administration than before administration. The l-lat. position is recommended as a means for preventing the side effects accompanying ritodrine administration. This study also indicated the possibility that the inferior vena cava may be more strongly compressed in the supine position by the relaxed gravid uterus.