Many cases have been reported indicating that postspinal headache can be relieved immediately by an epiduralinjection of saline: also autologous blood has recently been used successfully instead of saline. C.S.F. changes in 20 cases were observed in the support of the concept; that a continuous leakage in association with hypovolemia and hypotension of C.S.F is the primary cause of postspinal headache. Subarachnoid pressure increased immediately with Xylocaine injection into lumbar epidural space. A spinal needle was inserted into the subarachnoid space at the level Ll-L2 and opening pressure of C.S.F. was read, epidural Tuohy needle was inserted at the 4~5. Twenty-five ml of Xylocaine was injected into epidural space and C.S.F. pressure changes were observed. This procedure was performed on 10 patients in lateral position and another 10 patients were tested in the sitting position.

Sitting position:

Condition / Pressure rise

Highest pressure change / 350 mm H₂O

Lowest pressure change / 60 mm H₂O

Average pressure change / 191 mm H₂O

Average opening pressure / 369 mm H₂O

Horizontal position:

Highest pressure change / 290 mm H₂O

Lowest pressure change / 40 mm H₂O

Average pressure change / 142 mm H₂O

Average opening pressure / 165 mm H₂O

These pressure changes responded almost simultaneously as xylocaine was injected. The immediate relief of postspinal headache by injecting fluid into epidural space is simultaneous with the increase of C.S.F. pressure. In summary, the direct cause of postspinal headache is probably hypotension of C.S.F. pressure resulting from continuous leakage from spinal tap.