Interscalene block with a nerve stimulator: a deltoid motor response is a satisfactory endpoint for successful block

The interscalene brachial plexus block (ISB) is an effective and well-established anesthetic technique for shoulder surgery. Using nerve stimulation as an aid in block placement, a motor response (twitch) in the biceps or a more distal upper limb muscle has been recommended to indicate accurate needle placement. Our clinical experience, as well as anatomic reasoning, suggests that a deltoid twitch may be just as effective as one in the biceps for predicting successful block. This prospective clinical study was undertaken to compare a deltoid with a biceps twitch with respect to onset and success of motor block.

A total of 160 patients scheduled for shoulder surgery were studied prospectively. Interscalene blocks were performed using neurostimulation according to our standard technique. Twitches of the deltoid or biceps or both, whichever appeared first, were accepted and used as the endpoint for needle placement and injection of local anesthetic. Motor block success, i.e., patient inability to lift the arm against gravity, and minutes to motor block onset were recorded.

There was 1 failed motor block in the deltoid group and none in the other groups (not a statistically significant difference). When the same local anesthetic was used, there were no statistically significant differences in onset times between the biceps, deltoid, or biceps/deltoid groups.

A deltoid twitch is as effective as a biceps twitch in determining accurate needle placement for ISB and in predicting successful motor block. Acceptance of a deltoid twitch during ISB eliminates the need for further probing and may translate into better patient acceptance and in a smaller risk of needle-induced nerve damage.