To alleviate aortocaval compression, it is recommended to tilt pregnant patients into the left lateral tilt position during resuscitation. Aortocaval compression may however occur despite a lateral tilt of up to 34°, thought to be due to the relative immobility of the gravid uterus, although tilting beyond 30° is likely to lead them to slide off the bed or stretcher.

It may be more effective to tilt the patient into the full left lateral position first before returning them to the left lateral tilt position.

Positioning the parturient from supine to the left lateral tilt position (supine-to-tilt) may not effectively displace the gravid uterus, but turning from the left lateral position to the left lateral tilt position (left lateral-to-tilt) may keep the gravid uterus displaced and prevent aortocaval compression.

Fifty-one full-term parturients were randomly placed in the left lateral position, supine-to-tilt and left lateral-to-tilt positions using a Crawford wedge. Femoral vein area, femoral vein velocity, femoral artery area, pulsatility index, resistance index and right arm mean arterial blood pressure and heart rate were recorded.

Our results showed a lower mean (SD) femoral vein area (82.2 (14.9) vs 96.2 (16.4) mm(2) ), a lower pulsatility index (3.83 (1.3) vs 5.8 (2.2)), a lower resistance index (0.93 (0.06) vs 0.98 (0.57)), a higher femoral artery area (33.3 (3.8) vs 30.9 (4.4) mm(2) ) and a higher femoral vein velocity (7.9 (1.2) vs 6.1 (1.6) cm.s(-1) ) with left lateral-to-tilt when compared with supine-to-tilt (all p < 0.001).
Our results suggest that moving a full-term parturient from the full left lateral to the lateral tilt position may prevent aortocaval compression in full-term parturients more efficiently than when positioning the parturient from a supine to left lateral tilt position.

Effect of positioning from supine and left lateral positions to left lateral tilt on maternal blood flow velocities and waveforms in full-term parturients
Anaesthesia. 2012 Aug;67(8):889-93