Supraclavicular vs Infraclavicular vs Axillary Blocks

Study Summary

This study shows that the time to readiness for surgery (or anesthesia-related time) was similar for three commonly-used, ultrasound (US)-guided, approaches to the brachial plexus: the supraclavicular (SCB), infraclavicular (ICB), and axillary (AXB) blocks. Success rates were also equivalent between the three groups. The fact that over 80% of the blocks were done by inexperienced operators increases the generalizability of the results.

Methods

120 patients were recruited and randomized to one of 3 groups, to receive either an US-guided supraclavicular (SCB), infraclavicular (ICB), or axillary (AXB) block.
A multi-frequency (5-10 MHz) linear probe and portable ultrasound unit with compound imaging capability (Sonosite Micromaxx) were used for all blocks. A 17G Tuohy needle was used for all blocks, and a perineural catheter was inserted after injection of 35 mL of lidocaine 1.5%; however the effectiveness of the catheter was not examined in this study.
In the SCB approach, local anesthetic (LA) injection was performed at the junction of the first rib and axillary artery. In the ICB approach, LA injection was performed posterior to the axillary artery. In the AXB approach, LA was injected separately around the musculocutaneous nerve, and then in a perivascular distribution around the axillary artery.

Results

Anesthesia-related time (block performance time + onset time of surgical anesthesia) was the primary outcome. There was no difference between groups (SCB 23.1 ± 8.6 min, ICB 23.9 ± 9.2 min, AXB 25.5 ± 7.7 min). The AXB was associated with a (statistically) significantly longer needling and performance time, but this difference was not clinically significant (needling time: SCB 294 ± 114 sec, ICB 331 ± 251 sec, AXB 442 ± 131 sec; performance time: SCB 6.0 ± 2.1 min, 6.2 ± 4.5 min, AXB 8.5 ± 2.3 min).
Block success was defined in terms of a composite score of sensory and motor blockade at 30 minutes, and required at least 14 out of a possible 16 points. There was no significant difference between groups (SCB 92.5%, ICB 92.5%, AXB 90.0%).
Block-related pain scores, the incidence of vascular puncture and paresthesia were similar between groups; however significantly more patients receiving a SCB developed a Horner's syndrome (SCB 37.5%, ICB 5%, AXB 0%).

Comments

This is a useful study because it involved multiple operators, the majority of whom were inexperienced (defined as less than 60 blocks performed), and also because it utilized relatively simple US-guided techniques with easily reproducible endpoints. The similar success rates suggests that any of these three techniques are a suitable choice for anesthesia of the distal upper limb; although it should be noted that the study was not powered to detect a difference in this outcome. The AXB was associated with more needle passes, and a longer needling and performance time; this is not unexpected given the technique itself. What is notable is that it did not significantly prolong the time to readiness for surgery, nor did it increase the block-associated pain scores.

In our opinion, the main considerations for choosing one of these blocks over the other two relates to other factors that may hinder ease of block performance, and the adverse effects that may accompany the block. It can be difficult to visualize the brachial plexus in the SCB approach in individuals who have short necks, pronounced concavity of the supraclavicular fossa, or both. The ICB approach is relatively difficult in individuals with a thick chest wall (although the use of a curved low-frequency probe may help). In these instances, the AXB approach may be the best choice. The AXB is also the best choice if the risks of phrenic nerve palsy and Horner's syndrome are to be avoided. It is possible that the ICB and SCB approaches may provide better anaesthesia for surgery on the elbow, compared to the AXB, although this has not been formally studied.