In vitro study of the effect of epidural blood patch on leakage through a dural puncture.

Pressure resistance of an experimental epidural blood patch was studied in vitro. Pieces of canine lumbar dura were perforated with a 19-gauge needle (n = 12) or a 25-gauge needle (n = 6) and kept between the intercommunicating chambers of a plexiglass apparatus. One chamber (epidural side) was filled with autologous blood and the other chamber (subdural side) was filled with autologous cerebrospinal fluid. Control studies consisted of dural specimens not exposed to blood on the epidural side (19-gauge, n = 8; 25-gauge, n = 4). After 30 min, the dura was removed and placed in saline for inspection. In blood-treated specimens small sheets of coagulated blood were found attached to the epidural side of the dura, and in eight of the twelve of 19-gauge puncture experiments and one of the six of the 25-gauge puncture experiments clotted blood was visible on the subdural side. The dura was then placed back into the chamber for pressure testing 30 min or 16-18 hr later. The subdural chamber was filled with saline and air was left in the epidural chamber. Pressure (1.5, 20, 30, 40, and 50 mm Hg) was applied by injecting additional saline into the subdural chamber. Each pressure level was maintained for 5 min. Saline leaked through the perforation in all control specimens at 1.5 mm Hg pressure. Four blood-treated specimens showed some leakage at 20 mm Hg. All dura specimens perforated with a 19-gauge needle leaked at 40 mm Hg, five of them only at the lowest score rate, 1-4 drops/5 min. One blood-patched dura perforated with a 25-gauge needle did not leak until the pressure reached 50 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)