Successful interscalene block with a nerve stimulator may also result after a pectoralis major motor response

Interscalene block of the brachial plexus is a well-established anesthetic and analgesia technique for shoulder surgery. The endpoint for successful block using the nerve stimulator has been described by previous authors as a bicep motor response (twitch) and recently by a deltoid motor response. This retrospective observational case study of regular clinical practice examined the efficacy of using the pectoralis major motor response as an endpoint for a successful block.

A total of 120 patients who were scheduled for elective ambulatory shoulder surgery were retrospectively studied. All interscalene blocks were performed with aid of a nerve stimulator. Patients were categorized into 3 groups of 40 patients. Group 1 (biceps twitch), group 2 (deltoid twitch), and group 3 (pectoralis major twitch) were compared on success of the block. This retrospective study was conducted by reviewing interscalene block data sheets from the last 40 patients consecutively receiving interscalene block from either a bicep, deltoid, or pectoralis major motor response. A successful block was defined by the inability of the patient to raise their arm against gravity 20 minutes after injection of the local anesthetic.

Pectoralis major motor response as an endpoint for local anesthetic injection was examined. Of 40 patients studied in this group, 38/40 were judged successful. This was comparable to the success rate in biceps (38/40 successful) and deltoid groups (37/40 successful).

This retrospective observational case study of regular clinical practice suggests that a pectoralis major motor response can be a satisfactory endpoint for interscalene block.