Distribution of evoked paraesthesiae and effectiveness of brachial plexus block.

The distribution of paraesthesiae evoked by a low power nerve stimulator during performance of supraclavicular brachial plexus block was studied in 120 patients. Evoked paraesthesiae in the distribution of the median nerve was associated with a significant improvement in effectiveness of the block when compared with evoked paraesthesiae in the ulnar and radial distributions. A possible explanation for this finding is proposed.