Single vs Triple-Injection Ultrasound-Guided Infraclavicular Block

Study Summary

The authors enrolled 100 patients undergoing surgery of the distal upper arm under regional anesthesia alone. Blocks were performed under ultrasound-guidance without neurostimulation, using a 20G Tuohy needle and a 5-12 MHz linear high-frequency ultrasound probe. The needle was inserted in-plane in a cephalad to caudad direction, and patients were randomized to one of two groups. In group S, the needle was positioned at the posterior aspect of the axillary artery (with elicitation of a fascial click) and 30 mls of 1.5% mepivacaine was injected in a single bolus. In group T, 10 mls of 1.5% mepivacaine was injected at each of three locations: lateral, posterior and medial aspects of the axillary artery. Patients were subsequently assessed at 5 minute intervals for complete loss of cold sensation in the ulnar, median, radial and musculocutaneous dermatomes.

The primary outcome was complete loss of cold sensation in all 4 dermatomes at 15 minutes post-block. The incidence of this was similar between groups S and T (84% vs 78%), and remained similar up to 30 minutes post block. Block performance time was shorter in group S, and this difference was statistically but not clinically significant (2 vs 3 minutes). There were no other significant differences between the two groups.

It is important to note though, that because the block success rate at 15 minutes was higher than that assumed in their power analysis, the study is actually underpowered to detect any difference in the primary outcome between the two techniques. Detection of a 15% difference, given the observed success rate of 78% in group T, would require at least 150 patients per group.

Notwithstanding this, the findings are consistent with our clinical observation that U-shaped local anesthetic spread posterior to the axillary artery is an appropriate endpoint for an ultrasound-guided infraclavicular block is; visualization and targeting of individual cords is not necessary for block success. The study further suggests that there is no benefit with regards to rapidity of onset, and that the single-injection technique is easier to perform (as reflected by the shorter block performance time). At this time therefore, we support the authors' conclusion that the single-injection technique described is the preferred approach to ultrasound-guided infraclavicular block.