Epidural space pressures during pregnancy.

The epidural space pressure in the lumbar region was monitored and recorded in 21 full term pregnant patients, before and during labour and 6-12 hours postpartum, in different positions. The pre-labour epidural pressure was found to be above atmospheric in all patients, being highest when supine, and lowest in the lateral position. Three patients with twin pregnancy showed a greater rise in epidural space pressure in the supine position even with the use of lateral tilt, compared with patients with single fetus pregnancy. It is suggested that the epidural space pressure in the full term pregnant patient is closely related to the degree of inferior vena caval obstruction imposed by the gravid uterus. It is also suggested that when the patient is aware of a uterine contraction, the synchronous rise of the epidural space pressure with the contraction is a result of reflex increase in abdominal muscle tone. With established epidural block, and the parturient unaware of a contraction, such a rise was minimal, and was replaced by a drop in pressure in patients with a single fetus who developed loss of muscle power. The magnitude of the drop in the epidural space pressure immediately after delivery was found to be related to the duration of labour and to the mode of delivery. Epidural pressures measured 6-12 hours after delivery were comparable in all patients.