The enhancement of sensory blockade by clonidine selectively added to mepivacaine after midhumeral block

Clonidine added to local anesthetics results in an increased duration of an esthesia or analgesia after brachial plexus block. We investigated the effe ct of selective application of clonidine to the median and musculocutaneous nerves during midhumeral block, a technique allowing selective nerve block s with the use of different local anesthetics. Initially, 58 patients sched uled for hand surgery were prospectively enrolled to receive a midhumeral b lock. These patients were randomly allocated into two groups. The Control g roup (n = 28) received 10 mL of plain mepivacaine 1.5% for each nerve (medi an, musculocutaneous, ulnar, and radial). The Clonidine group (n = 30) rece ived 10 mL of plain mepivacaine 1.5% for each nerve, but the median and mus culocutaneous nerves also received a dose of 50 mug clonidine. One patient in the Control group and two patients in the Clonidine group with a failed block were therefore excluded from the analysis. The onset time of surgical anesthesia was recorded. The durations of sensory and motor blocks were ch ecked every 15 min. The plasma mepivacaine concentration was analyzed from 10 patients in each group. Onset times for complete sensory block were simi lar between the two groups. Adding 50 mug clonidine to the median and muscu locutaneous nerves resulted in a significant increase in the duration of se nsory block in these nerves (P < 0.0001). Recovery of motor block was not d ifferent between the two groups. No significant difference was found betwee n the two groups in the mean plasma mepivacaine concentration.