Brachial Plexus Block with the Nerve Stimulator:: Motor Response Characteristics at Three Sites

BACKGROUND AND OBJECTIVES: Differences in motor response patterns, minimum electrical currents, and success rates using a nerve stimulator for brachial plexus block were determined for the interscalene, supraclavicular, and axillary approaches. METHODS: Supervised, resident physicians performed 106 brachial plexus blocks. For each block, the minimum stimulating current, the strongest joint motion at the minimum current immediately before local anesthetic injection, presence or absence of other joint motion, and anesthetic success or failure were recorded. RESULTS: In the interscalene group (n = 43), strongest joint motions clustered at the shoulder (40%) and elbow (54%). In the supraclavicular group (n = 29), strongest joint motions distributed bimodally at the elbow (62%) and fingers (31%). In the axillary group (n = 34), strongest joint motions clustered at the wrist (35%) and fingers (61%). Overall, concurrent, weaker joint motion was observed in 26% (p not significant). Overall, the minimum current producing visually observable or palpable upper extremity motor responses was 0.69 +/- 0.02 mA (mean +/- SEM, range 0.2-1.5). No significant differences were found for minimum currents by site of approach, presence or absence of weaker joint motion, or success or failure of anesthesia. The overall success rate was 89%, with the rate being 91% for interscalene, 97% for supraclavicular, and 79% for axillary approaches (p not significant). Within the axillary group, elbow flexion as the strongest joint motion was a significant predictors of failure compared with other responses (p < 0.05). CONCLUSIONS: Localization of the brachial plexus with the nerve stimulator is equally effective at the interscalene, supraclavicular, and axillary sites. Current values in the range reported have no predictive value for success. Advantages of the nerve stimulator for brachial plexus block include an objective endpoint and continuous feedback.