Uteroplacental haemodynamics during spinal anaesthesia for caesarean section with two types of uterine displacement.

The effects of two types of uterine displacement, on uterine and umbilical artery blood flow waveforms were investigated in 22 healthy parturients undergoing elective caesarean section. Displacement was accomplished with either a wedge under the right hip or a mechanical displacer plus 5 degrees left lateral tilt of the operating table. The first 14 patients were assigned randomly into one of the two displacement methods and the left (underlying) uterine and umbilical artery blood flow waveforms were recorded. In a further 8 patients the displacer was used and flow velocity waveforms for both the right and left uterine arteries and the umbilical artery were recorded. Arterial resistance was expressed in terms of the pulsatility index (PI). There were no significant changes in Doppler velocimetry recordings after preloading in either group, but blood flow velocity waveform indices for the underlying left uterine artery increased significantly (P < 0.001) following spinal anaesthesia when the mechanical device was used. This finding indicates increased vascular resistance in the left uterine artery and is probably due to mechanical compression. A wedge as a method for displacing the gravid uterus seems preferable since its use had no effect on the blood flow indices. The unaltered umbilical artery index values in the groups suggest a great tolerance of minor changes in maternal uterine circulation on the part of the fetus.