QUANTITATIVE ASSESSMENT OF DIFFERENTIAL SENSORY BLOCKADE AFTER LUMBAREPIDURAL LIDOCAINE

A cutaneous current perception threshold (CPT) sensory testing device measures both large and small diameter sensory nerve fiber function an d may be useful in evaluating differential neural blockade. Eight subj ects received both lumbar epidural saline and lumbar epidural lidocain e. Five milliliters of normal saline was administered and the CPTs wer e measured. After the saline, 10 mt of 2% plain lidocaine was administ ered. CPTs, and sensation to touch, pinprick, and cold were subsequent ly measured. Saline had no effect on any measurements. Lidocaine cause d an increase in all CPTs at the umbilicus and the knee reaching a sta tistical significance at 5 Hz for the umbilicus only. The great toe sh owed a slight increase of the 5 Hz stimulus and no increase of the 200 0 or 250 Hz stimulus. There was a significant decrease in touch, pinpr ick, and cold sensation at the umbilicus and knee and a significant de crease in the cold sensation at the great toe. There was no effect on any measurements made at the mastoid. Epidural lidocaine resulted in a differential neural blockade as measured by a CPT monitor but not wit h crude sensory measurements.