Effect of lateral versus supine wedged position on development of spinal blockade and hypotension

Aortocaval compression may not be completely prevented by the supine wedged or tilted positions. It is commonly believed, however, that the unmodified full lateral position after induction of spinal anaesthesia might allow excessive spread of the block. We therefore compared baseline arterial pressures in the supine wedged, sitting, tilted and full lateral positions in 40 women who were about to undergo elective caesarean section. They were then given spinal anaesthesia in the left lateral position and randomised to be turned to the right lateral or the supine wedged position, after which speed of onset and spread of blockade to cold sensation were measured every 2 min for 10 min and mean arterial pressure and ephedrine requirement were recorded every minute for 20 min. Baseline mean arterial pressure was 9 mmHg (95% CI 3 to 14) lower in the left lateral (measured in the upper arm) than in the sitting position; those in the supine wedged and tilted positions were intermediate. Following spinal anaesthesia, hypotension (defined as a reading