Influence of cerebrospinal fluid on epidural pressure.

The pressure in the epidural space was measured with a water manometer in 40 women receiving elective epidural for pain relief in labour, and in three patients who were undergoing lumbar puncture. Injection of a small volume of fluid in the epidural space produced a positive pressure in all subjects, with a mean of 14 cmH2O (range 6.5-20 cmH2O). Pressure varied with posture, respiration, cough and jugular venous compression. The variations in pressure agreed closely with those reported for cerebrospinal fluid (CSF) pressure. It is suggested that in the lumbar region the dura fills the vertebral canal and is both compressible and expansile. When fluid is injected into the epidural space, the dura acts as a movable membrane and pressures on either side of it tend to equalise. Measurement of epidural pressure may provide a less traumatic way of estimating CSF pressure than traditional methods.