TIME-COURSE IN THORACIC EPIDURAL PRESSURE MEASUREMENT

The purpose of this study was to measure thoracic epidural pressure at the time of insertion of an epidural needle. The pressure was measure d using a closed pressure measurement system after insertion of a Tuoh y needle at the T7-8 intervertebral level. This system is unique becau se it has a pressure transducer equipped with a device which regulates flow through the transducer and prevents the heparinized saline in th e system from being evacuated into the epidural space due to sudden pr essure change. As reported previously, high negative epidural pressure s, up to -60 mmHg, were observed at the moment of epidural puncture. H owever, the pressure became positive in about 30 sec in 12 of the 13 p atients, and stabilized at +3.7 +/- 3.2 mmHg (mean +/- SD) within 90 s ec. Similar results were observed when the procedure was repeated with in a few minutes to the same patients. This suggests that negative epi dural pressures at the moment of epidural puncture are artifacts induc ed by tenting of the dural membrane. Subsequent adaptation of the surr ounding tissue results in restoration of the normal positive epidural pressure.