A prospective, randomized, double-blind comparison of ultrasound-guided axillary brachial plexus blocks using 2 versus 4 injections.

INTRODUCTION: In this prospective, randomized, double-blind study, we compared the effectiveness and time efficiency of perioperative axillary blocks performed via 2 different techniques, 1 involving 2 and the other 4 separate skin punctures.

METHODS: One hundred twenty patients undergoing upper limb surgery were randomized to receive either (1) an axillary brachial plexus block involving 2 injections, with 30 mL local anesthetic injected posterior to the axillary artery (with redirection, as needed, to achieve circumferential spread), plus 10 mL local anesthetic to the musculocutaneous nerve, guided by ultrasound (group 1, n = 56); or (2) 4 separate 10-mL injections to the median, ulnar, radial, and musculocutaneous nerves, using a combined ultrasound and neurostimulation technique (group 2, n = 58). All patients received 40 mL of 0.5% ropivacaine with 1:400,000 epinephrine. The primary outcome was the success rate of the block, defined as anesthesia adequate for surgery. Secondary outcomes were the time to administer the block, time to the onset of motor-sensory block, time to surgical readiness, and incidence of adverse events.

RESULTS: The 2-injection technique was slightly faster to administer (8 vs 11 minutes, P = 0.003). The mean nerve block score was slightly higher for the 4-injection group at the 10-, 15-, 20-, and 30-minute time points, but the cumulative percentages of blocks having taken effect were not significantly different over these time points, at 0.0%, 5.4%, 12.5%, and 37.5% among those who had received a 2-injection block versus 6.9%, 10.4%, 19.0%, and 48.3%, respectively, with the 4-injection block (P = 0.20). There was no difference in the percentage of patients with complete block by 30 minutes (32.1% vs 37.5%, P = 0.55) or in final block success rates (89.3% vs 87.9%, P = 0.99).

CONCLUSIONS: An ultrasound-guided 2-injection axillary block may be as effective as, and more time efficient than, a 4-injection technique.