Background and Objectives. Paresthesia is widely considered a useful indicator for locating components of the brachial plexus using the axillary approach. While establishing axillary brachial plexus blocks, the authors attempted to correlate the area of paresthesia with the effectiveness of the sensory block.

Methods. Axillary brachial plexus blocks were established in 222 consecutive adult patients scheduled for elective surgery of the hand or forearm. After paresthesia was elicited in the distribution of one of the three terminal nerves of the hand (median, radial, or ulnar nerve), 30 mL 1.5% mepivacaine without epinephrine was injected after advancing an indwelling catheter. Sensory block of each terminal nerve was assessed 20 minutes after the injection.

Results. The median and radial nerves were blocked with the highest reliability (87% and 93%, respectively) after paresthesia was elicited in the areas supplied by the corresponding nerves. The ulnar nerve was blocked most reliably (>85%) after the elicitation of paresthesia in its area of distribution as well as when no paresthesia was induced. The most reliable block of the musculocutaneous nerve (72%) was achieved after paresthesia was induced in the area supplied by the median nerve.

Conclusion. Eliciting paresthesia at the nerve supplying the area of a planned surgical incision is a reliable determinant of successful axillary brachial plexus block.