Integrated electromyographic measurement of abdominal motor blockade during bupivacaine epidural anesthesia for lower abdominal and pelvic surgery

The onset and regression of abdominal motor blockade was monitored with integrated electromyography in eighteen patients undergoing pelvic or lower abdominal surgery during lumbar epidural anesthesia using 0.75% bupivacaine with 1:200,000 epinephrine. The integrated electromyograph (EMG) was measured at the T-6, T-8, T-10 and T-12 dermatomes during a standardized head-raising test before anesthesia and at fixed time intervals thereafter for a minimum of four hours. Simultaneous measurements were made of abdominal sensory block (analgesia to Allis forceps pinch expressed in dermatomes) and lower limb motor blockade (Bromage scale). Motor block at a given dermatome level was defined as reduction of the integrated EMG amplitude to less than 20% of control. Mean maximum level of sensory block was T-4.2 +/- 0.6 (SEM) mean maximum level of motor block was T-8.8 +/- 0.5. The mean motor sensory differential varied between 4.5 +/- 0.6 and 5.3 +/- 0.9 segments over the 4-hr study period. Mean time to maximum abdominal sensory block was 28 +/- 3 min, and maximum abdominal motor block was 29 +/- 6 min. Mean time to two-segment regression of abdominal motor block was 94 +/- 18 min and to two-segment regression of abdominal sensory block, was 150 +/- 18 min.