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 anesthesia or analgesia after brachial plexus block. We investigated the effect of selective application of clonidine to the median and musculocutaneous nerves during midhumeral block, a technique allowing selective nerve blocks with the use of different local anesthetics. Initially, 58 patients scheduled for hand surgery were prospectively enrolled to receive a midhumeral block. These patients were randomly allocated into two groups. The Control group (n = 28) received 10 mL of plain mepivacaine 1.5% for each nerve (median, musculocutaneous, ulnar, and radial). The Clonidine group (n = 30) received 10 mL of plain mepivacaine 1.5% for each nerve, but the median and musculocutaneous 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 checked every 15 min. The plasma mepivacaine concentration was analyzed from 10 patients in each group. Onset times for complete sensory block were similar between the two groups. Adding 50 mug clonidine to the median and musculocutaneous nerves resulted in a significant increase in the duration of sensory block in these nerves (P < 0.0001). Recovery of motor block was not different between the two groups. No significant difference was found between the two groups in the mean plasma mepivacaine concentration.