Posture and epidural block in pregnant women at term. Effects on arterial blood pressure and limb blood flow.

Upper and lower limb blood flow was measured in 4 fullterm pregnant women in the left lateral and supine positions before and after epidural block. Radial artery mean blood pressure was recorded in 6 full term pregnant women under the same conditions. Before epidural block there was a much greater reduction in lower limb blood flow (39-1%) than in upper limb blood flow (13-5%) when women moved from the lateral to the supine position; this was probably the result of aortic compression. Mean radial artery pressure increased slightly by 4-6% due to maternal overcompensation in the upper part of the body. After epidural block, patients in the lateral position had a mean rise in lower limb blood flow of 25% and a reduction in upper limb blood flow of 37-2%. The mean arterial pressure remained unchanged. In the supine position there was no further reduction of upper limb blood flow; this was accompanied on average by a 9% fall in mean radial arterial pressure indicating decompensation in the mother. The leg blood flow fell less, 26-9% than before epidural block. In the supine position, a greater flow to the legs, associated with a decreased mean arterial pressure, would be expected to lead to a diminution in placental perfusion, which is the probable mechanism for foetal decompensation. Therefore the supine position should be avoided with an epidural block. In other patients it would be wise not to rely upon maternal compensatory mechanisms.