Ultrasound-Guided Supraclavicular vs Infraclavicular Blocks

Study Summary

This article attempts to answer the important question of which ultrasound (US)-guided block to choose for surgery of the elbow / forearm / hand by comparing two popular techniques: supraclavicular (SCB) versus infraclavicular block (ICB). The strengths of this study include diversity of operator experience (residents as well as staff anesthesiologists), and a detailed assessment of both efficacy and adverse outcomes. It is important to interpret the results (better success and faster onset of sensory block with ICB) in the context of the details of the block techniques used. It is possible that the efficacy of the SCB may have been different if a variant of the technique (e.g. the "corner pocket" technique) had been used.

Methods

The authors recruited 120 patients having surgery of the elbow /forearm/hand and randomized them to receive either an US-guided supraclavicular (SCB) or infraclavicular block (ICB). A 0.5ml/kg volume of a local anesthetic (LA) mixture of 50:50 ropivacaine 0.75% and mepivacaine 2% was injected in all patients.

The supraclavicular block was performed as follows: coronal oblique probe orientation, in-plane needle advancement, and injection of the first half of the LA mixture superficial to the plexus, and the remainder injected so as to achieve circumferential spread around visible nerves.

The infraclavicular block was performed as follows: parasagittal probe orientation, in-plane needle advancement, and injection of the first half of the LA mixture posterior to the axillary artery, and the remainder injected to achieve a U-shaped LA spread. The nerves themselves were not specifically targeted.

Surgical readiness or block success was defined as analgesia or anesthesia to pinch in all 5 nerves distal to the elbow (median, ulnar, radial, musculocutaneous, medial brachial cutaneous nerves).

Results

ICB resulted in significantly greater block success (93% vs 78%, p = 0.017). There was also a statistically significant difference in block onset time (ICB 19.0 min vs SCB 22.7 min, p = 0.003) although this is not clinically significant. Block performance times were similar (ICB 5.0 min vs SCB 5.7 min)

There were more adverse effects in the SCB group: paraesthesiae/pain on injection (37% vs 13%, p = 0.003), Horner's syndrome (29% vs 0%, p < 0.0001), suspected diaphragmatic palsy (12% vs 0%, p < 0.0001).

Comments

The authors are to be commended for producing a study that involved operators with a range of experience, including supervised residents (although it would have been helpful to know the number and distribution of operators involved). This makes the results more applicable to a non-expert practitioner trying to decide between one block or another.

However the relatively low success rates observed with the supraclavicular block are not congruent with results reported in other studies (1,2,3). Reasons for this include operator bias in favor of the ICB (this was discussed by the authors), and the fact that the technique used here may not have been the optimal one. Our experience indicates that it can be difficult to visualize the inferior trunk of the brachial plexus in the supraclavicular approach, and this leads to the ulnar nerve being missed in a disproportionate number of patients, as it was in this study. Our solution to this is to perform a "corner pocket" technique, in which the majority of the local anesthetic solution is injected deep to the plexus at the "corner" between the subclavian artery and the first rib (3). We postulate that this may produce better block success than the technique described in this study, in which the initial injection was performed superficial to the plexus. This has also been observed by other authors (4), and may explain why a similar study comparing US-guided SCB, ICB and axillary block failed to show any significant difference in block success (5).

The higher incidence of adverse outcomes is worthy of note, and of further study in a large number of patients. Given the high incidence of block success that is achievable with most US-guided approaches, the risk of adverse effects may prove to be the deciding factor in choosing which block to perform.

References

1. Perlas A, Lobo G, Lo N et al. Ultrasound-guided supraclavicular block - outcome of 510 consecutive cases. Reg Anesth Pain Med 2009;34:171-176.
2. Arcand G, Williams SR, Chouinard P, et al. Ultrasound-guided infraclavicular versus supraclavicular block. Anesth Analg 2005;101:886-90.
3. Soares LG, Brull R, Lai J, Chan VW. Eight ball, corner pocket: the optimal needle position for ultrasound-guided supraclavicular block. Reg Anesth Pain Med 2007;32:94-5.
4. Tran de QH, Munoz L, Russo G, Finlayson RJ. A trick shot to the corner pocket. Reg Anesth Pain Med 2008; 33: 503-4.
5. Tran de QH, Russo G, Munoz L, Zaouter C, Finlayson RJ. A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks. Reg Anesth Pain Med 2009; 34: 366-71.