Response to "Comment on Axillary serratus anterior plane block as a novel approach to anesthetizing the intercostobrachial nerve for upper arm arteriovenous fistula creation surgery -three case reports-"

Dear Editor,

We received a Letter to the Editor under the Korean Journal of Anesthesiology titled “Comment on Axillary serratus anterior plane block as a novel approach to anesthetizing the intercostobrachial nerve for upper arm arteriovenous fistula creation surgery -three case reports-” and we would like to thank the author for his thoughtful comments [1,2]. We appreciate the opportunity to respond to and address the points raised.

The author claims that our description of the A-SAP block as “superior” and “novel” are unfounded.

First, we would like to clarify that the assertion that our described A-SAP block is the same as that used in the cadaveric study by Biswas et al. [3] is inaccurate. As discussed in our original article, Biswas et al. used a cephalad-to-caudad needle trajectory for the serratus anterior plane blocks in their cadaveric study. This approach differs fundamentally from the medial-to-lateral needle direction used in our technique. Furthermore, dye spread to the axilla was observed in only 66.6% of specimens. Indeed, this difference in needle trajectory may have contributed to the observed discrepancy, highlighting the distinct nature of the A-SAP block described in our study.

Secondly, we disagree with the assertion that describing the A-SAP block as “novel” is unfounded. Novelty encompasses not only the introduction of entirely new techniques but also the innovative application of existing approaches in new clinical contexts. Although our technique was inspired by findings from a previous cadaveric study, these authors did not describe any clinical application of the approach. In contrast, to our knowledge, our study is the first to describe and apply this technique specifically for the purpose of anesthetizing the intercostobrachial nerve (ICBN) during upper arm arteriovenous fistula (UA-AVF) creation. Therefore, we believe that referring to the A-SAP block as a novel approach in this context is justified.

Finally, we disagree with the claim that describing the A-SAP block as “superior” is unfounded. In our clinical experience, the A-SAP block has demonstrated consistently high efficacy, particularly in comparison to the pectoserratus plane block. As discussed in our original article, the combined use of a supraclavicular brachial plexus block with an ultrasound-guided pectoserratus plane block or ICBN block for UA-AVF creation resulted in approximately 30% and 20% of patients requiring further LA supplementation, respectively. This is in contrast to the 100% success rate observed thus far with the A-SAP block in the same surgical context. Although these findings are promising, we recognize that further studies are required to validate the consistency of the A-SAP block.

The author suggests that the “A-SAP” block will only confuse the clinicians as we already have many confusing nomenclatures for various similar/same techniques.

We believe that the modifications to both the approach and the technique inherent to the A-SAP block justify the assignment of a distinct name. This differentiation is important for distinguishing it from other similar techniques such as the serratus anterior plane block, which, as previously discussed, has demonstrated an inconsistent or limited spread to the axillary region. Distinct nomenclature also facilitates clearer communication in both clinical and academic contexts.

The author believes that we made contradictory statements about the direct blocking of the ICBN in the axilla.

While the ultrasound-guided ICBN block described by Magazzeni et al. [4] showed an 88% rate of complete sensory loss in the ICBN at 20 min post-injection, high-quality ultrasound images were obtained in only 20 of the 42 patients. In 13 of these patients, the nerves were poorly visualized both before and after injection, while in the remaining nine patients, the nerves only became clearly identifiable afterward. These findings support our assertion that direct ultrasound identification of the ICBN may be limited by anatomical variability, access to high-resolution ultrasounds, and patient factors such as obesity. We would like to clarify that the high clinical success rate of a nerve block does not necessarily equate to consistent or easy identification of the targeted nerve under ultrasound.

The author suggests that the infraclavicular brachial plexus block may be preferable for UA-AVF creation.

While we agree that the supraclavicular brachial plexus block does not reliably anesthetize the ICBN, we respectfully disagree that the infraclavicular approach offers consistent coverage of this nerve and do not believe that it is superior to the A-SAP block we have described. The authors cited the study by Bigeleisen and Wilson [5] to support the claim that an infraclavicular brachial plexus block can reliably anesthetize the ICBN, which reported an 87% success rate with the lateral approach. However, that study involved patients undergoing surgeries of the elbow, forearm, or hand, which do not necessarily involve ICBN distribution. Notably, sensory testing was also performed by pinching the skin distal to the axillary hair patch rather than through surgical incision. Notably, the 87% success rate reported is similar to that reported by Magazzeni et al. [4] with their ultrasound-guided ICBN block.

As outlined in our Discussion section, the ICBN gives rise to axillary branches that innervate the axilla as well as terminal branches that supply the medial aspect of the upper arm. We propose that the inconsistent blockade of the axillary branches of the ICBN, which are often inadequately targeted by ultrasound-guided ICBN blocks, may explain the occasional failure of these blocks, which tend to predominantly anesthetize only the terminal branches. Bigeleisen and Wilson [5] did not address whether the infraclavicular brachial plexus block reliably anesthetizes the axillary branches of the ICBN. The claim that the infraclavicular brachial plexus block sufficiently covers the ICBN for UA-AVF creation would be more convincingly supported by cadaveric evidence demonstrating its spread to the ICBN, or by clinical reports of successful UA-AVF surgeries performed using the infraclavicular brachial plexus block alone.

We appreciate the opportunity to clarify the differences between our A-SAP block and previously published techniques. Our original aim was to introduce a novel and clinically effective approach to achieve consistent anesthesia of the ICBN in patients undergoing UA-AVF creation. We hope that our reply will help promote further academic discussions on evolving strategies for regional anesthesia in upper limb vascular access surgery.