Background: When performing a supraclavicular brachial plexus block (SCB) under ultrasound (US) guidance, the needle may approach the nerves in-plane with the US beam from 1 of 2 directions relative to the transducer, lateral-to-medial (lateral) or medial-to-lateral (medial). We aimed to compare the rates of sensory and motor block of the 4 major peripheral nerves of the upper extremity following a lateral or medial needle approach for US-guided SCB.

Methods: Eighty adult patients undergoing US-guided SCB for elective hand, wrist, forearm, or elbow procedures were randomized to either a lateral or medial needle approach. A 30-mL local anesthetic admixture (1:1 lidocaine 2%-bupivacaine 0.5% with 1:200,000 epinephrine) was injected to all patients. Sensory and motor function was assessed by a blinded observer at predetermined intervals. The primary outcome was the rate of sensory block in the distribution of the ulnar nerve measured 20 mins after block performance.

Results: Seventy-two patients were included in the final analysis. Patient characteristics were similar between groups. The rate of ulnar nerve sensory block at 20 mins was 63% in the lateral group and 62% in the medial group (P = 0.81). The rate of ulnar nerve sensory block at 30 mins increased to 89% in the lateral and 84% in the medial group (P = 0.96). The rates of both sensory and motor block in the distributions of the median, radial, and musculocutaneous nerves were high and did not differ between groups at any measured time interval. The block performance time and the postoperative pain scores were similar between the 2 groups. Complications were minor and transient and did not differ between groups.

Conclusions: The rates of sensory and motor block of all 4 major peripheral nerves of the upper extremity did not differ at any time following a lateral compared with medial needle approach for US-guided SCB. Regardless of needle approach, the rate of ulnar nerve sensory block was less compared with the other peripheral nerves following US-guided SCB.