Relationship between different motor responses evoked by nerve stimulator and efficacy of radial nerve block during brachial plexus block

Objective To investigate the relationship between different motor responses evoked by nerve stimulator and efficacy of radial nerve block during brachial plexus block in patients. Methods One hundred and twenty ASA I or II patients aged 18-60 yr scheduled for hand, wrist or forearm surgery were randomly allocated into 2 groups ( n = 60 each) . The triple-injection axillary brachial plexus block was performed under the guidance of peripheral nerve stimulator. The mixture of 1% lidocaine and 0.33% ropivacaine was injected around the musculocutaneous nerve (S ml) and median nerve (10 ml) . When forearm extension in group I and the wrist and finger extension in group II were evoked, 20 ml of the mixture mentioned above was injected around the radial nerve. Sensory blocks of musculocutaneous and median nerves, sensory and motor blocks of the proximal or distal branches of the radial nerve were assessed at 5-min intervals in 30 min after the injection was completed. The time to perform the block and number of locating the radial nerve were recorded. Results The success rate of complete sensory block was significantly higher, the success rate of sensory and motor blocks of the distal branches of the radial nerve was significantly higher, the time to perform the block was significantly longer, and the localization of the radial nerve was more difficult in group II than in group I ( P < 0.05 or 0.01). Conclusion The wrist and finger extension evoked by peripheral nerve stimulator predicts better efficacy than forearm extension in triple-injection axillary brachial plexus block with 20 ml mixture of 1 % lidocaine and 0.33 % ropivacaine. Key words: Brachial plexus;  Nerve block;  Radial nerve;  Electric stimulation