[Quantitative assessment of differential nerve block during lumbar epidural anesthesia]

The study was performed to evaluate differential neural blockade during lumbar epidural anesthesia with a cutaneous current perception threshold (CPT) sensory testing device. Fourteen patients undergoing elective gynecological surgery received 10 ml of 2% lidocaine through an epidural catheter inserted at the L 1/2 interspace. CPTs at 2000, 250, and 5 Hz stimulation and sensation to light touch, temperature, and pinprick at ipsilateral dermatomes V, Th 9, and L 2 were measured before and every 5 min, until 60 min after the epidural lidocaine. The epidural block caused a significant increase in all CPTs at dermatome L 2 and in CPTs at 250 and 5 Hz at Th 9. Touch sensation at Th 9 was intact during the study period in 12 patients, most of whom lost sensation to the other stimulus: 12 patients did not respond to the cold stimulus and 10 patients to the pinprick. At L 2, sensory block to light touch, temperature, and pinprick was found in 11, 14, and 14 patients, respectively. There was no effect on any measurements made at V. In conclusion, epidural lidocaine results in a differential neural blockade as measured with CPT testing. Since the 2000-Hz stimulus detect abnormalities that correlate with large fiber functioning, it is suggested that loss of touch sensation is associated with effects of epidural lidocaine on large fibers.