Background This prospective, randomized, observer-blinded study compared 3 combinations of volume and concentration using the same total dose of lidocaine for ultrasound-guided infraclavicular block.

Methods Ninety patients were randomized to 1 of 3 combinations of volume and concentration for lidocaine: (1) 52.5 mL of lidocaine 1%, (2) 35 mL of lidocaine 1.5%, and (3) 26.25 mL of lidocaine 2%. In all 3 groups, the total dose administered (525 mg) was the same. In addition, epinephrine 5 fg/mL was used in all subjects. The main outcome variable was onset time. The performance time, number of needle passes, block-related pain scores, success rate (surgical anesthesia), and the incidence of vascular puncture and paresthesia were also recorded. The total anesthesia-related time was defined as the sum of the performance and onset times.

Results The onset times, which were 18.8 ± 5.6 minutes (95% confidence interval [CI], 16.4–21.1 minutes), 20.7 ± 7.0 minutes (95% CI, 18.0–23.5 minutes), and 21.7 ± 6.0 minutes (95% CI, 19.1–24.2 minutes) for the 1%, 1.5%, and 2% groups, respectively, were not statistically different.

Furthermore, the performance times (4.4–4.7 minutes), total anesthesia-related times (23.7–26.3 minutes), and rates of surgical anesthesia (90.0%–96.7%) were comparable among the 3 groups. The number of needle passes and procedural discomfort, as well as the incidence of paresthesia and vascular puncture, were also similar. There were minor differences in the patterns of block for individual nerves. In terms of sensory block, compared with the 2% group, more patients in the 1.5% group displayed a complete block of the ulnar and radial nerves at 10 and 20 minutes, respectively. In terms of motor block, the 2% group yielded the lowest of rate of complete block of the musculocutaneous nerve from 15 minutes onward.

Conclusions Using an identical dose (525 mg) of adrenalized lidocaine for ultrasound-guided infraclavicular block, we found no differences in onset time among 3 commonly used concentrations (1%, 1.5%, and 2%). Further studies are required to determine the optimal combination of volume and concentration of lidocaine for other ultrasound-guided approaches to the brachial plexus.