Continuous Peripheral Nerve Blocks and Alternative Regional Analgesic Modalities: Clarification Regarding Relative Superiority

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I would like to thank Drs Soffin and YaDeau for their discerning editorial addressing a review article I recently authored, “Continuous Peripheral Nerve Blocks: An Update of the Published Evidence and Comparison with Novel, Alternative Analgesic Modalities.”1,2 I found the editorial both thoughtful and insightful but would like to clarify my article’s meaning with respect to an important statement made within the editorial: “Here, Ilfeld reviews 4 alternatives to CPNB for extended analgesia and concludes that in each case, the catheter is likely superior [emphasis added].”
Regarding adjuvants added to single-injection local anesthetic-based peripheral nerve blocks, the review article noted that “…no adjuvant given by any route of administration has been shown to reliably extend analgesia even one full day.” The conclusion was not that continuous peripheral nerve blockade (CPNB) was likely superior, but that: “The two techniques do not, in fact, “compete”; but, are rather complementary, depending upon the desired duration of block effects [emphasis added].”
Concerning liposome bupivacaine, the editorial stated that “based on the data from several RCTs, that liposomal bupivacaine is probably not even equivalent to plain bupivacaine for analgesia after TKA, much less superior to CPNB.” The review article noted that there is little evidence that liposome bupivacaine infiltrated into the surgical wound is superior to bupivacaine HCl—especially for knee arthroplasty—but this is different than claiming “liposomal bupivacaine is probably not even equivalent [emphasis added]” to bupivacaine HCl. Failure to demonstrate superiority is not the same as demonstrating inferiority as the editorial suggested. It is also important to differentiate liposome bupivacaine surgical wound infiltration (on-label use) and use in a peripheral nerve block (off-label use). The review article noted that “…liposome bupivacaine in a femoral nerve block produced over 72 hours of analgesia with an incomplete motor block in healthy volunteers, and demonstrated analgesic activity for up to 72 hours versus placebo in subjects following total knee arthroplasty (albeit extraordinarily minimal analgesic differences following 24 hours).” In addition, “recently-published data from one RCT strongly suggests that liposome bupivacaine within a single-injection subcostal TAP [transversus abdominis plane] block provides statistically and clinically superior analgesia to bupivacaine HCl up to 3 days following robotic assisted hysterectomy.” While further research is required to draw comparisons, there was no conclusion stated that CPNB is likely superior to liposome bupivacaine used as part of a peripheral nerve block.
Regarding cryoneurolysis, the editorial noted that “…this technique is still in its infancy, and there are insufficient data regarding safety, efficacy, and direct comparisons with CPNB.” This statement is accurate for application to postoperative pain (ultrasound-guided, percutaneous cryoanalgesia has been used to treat chronic pain states for decades), but a lack of data does not suggest the likely superiority of CPNB. I can only speculate given the current lack of published research, but cryoneurolysis will probably be applicable to only a small subset of surgical procedures considering that it induces a complete sensory, motor, and proprioception block lasting for multiple weeks or months.3 However, in cases amenable to such a block, it will most likely prove superior to CPNB due to its relative potency and duration.
Finally, concerning percutaneous peripheral nerve stimulation, the editorial stated that “…there is probably no practical advantage when the method of placement is compared with CPNB…” However, the review article specified that “Leads function optimally when inserted 0.5–3.0 cm from a target peripheral nerve, negating the importance of location within a particular facial plane.” For this reason, accurately inserting a percutaneous lead is—at least in my experience—demonstrably easier to both master and successfully achieve compared with a perineural catheter.
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