Authors’ reply to “Umbrella over erector spinae plane block: wide coverage, narrow clarity”

TO THE EDITOR

We are grateful for the thoughtful considerations raised by Dr. Mistry and Nair [1] regarding our umbrella review [2], which highlight several points that warrant further discussion.

Regarding the comparator strategy, we agree that comparing erector spinae plane block (ESPB) to a placebo does not establish superiority over other regional techniques, nor does it inform best practice nor guidelines for a given procedure [3]. However, this was a deliberate methodological choice: establishing whether ESPB confers any benefit over an inactive control is a necessary prerequisite before meaningful comparative effectiveness conclusions can be drawn. This question is, in fact, less trivial than it may appear—particularly given the ongoing debate surrounding the mechanism of action of the ESP block, which remains incompletely understood. A prospectively registered overview with active comparators, and where feasible a network meta-analysis, would be the logical next step.

The correspondents flag that at least one included SRMA pooled trials with non-placebo comparators. This was transparently declared in Table 1, but we wish to clarify further: Wu et al. [4] included local wound infiltration as one of its comparators alongside sham block and no block. We were aware of this at the time of inclusion; the decision to retain the study was based on the fact that the majority of its trials used placebo or no-block controls, and excluding it entirely would have discarded a substantial body of relevant primary data. Wu et al. [4] included 25 studies, comprising 873 patients in the ESP block group and 874 in the control group. However, only three studies used wound infiltration as the comparator, representing just 8% of the overall study population, with 73 patients in each group. However, we acknowledge that this introduces a degree of comparator heterogeneity that readers should bear in mind.

On the clinical magnitude of effects, the MME reduction of 8.70–18.69 mg over 24 hours is statistically robust and consistent across all eight SRMAs reporting this outcome. We deliberately refrained from applying MCID thresholds dogmatically: in well-structured perioperative analgesic protocols, both groups are not expected to experience significant pain, compressing detectable differences by design. That said, if one wishes to engage with the MCID framework, the observed reduction should be interpreted in relation to the commonly cited threshold of 10 mg MME and its corresponding confidence interval [5]. More importantly, we recognize that opioid consumption is not itself a patient-centered outcome—a patient does not directly perceive a difference in milligrams spared, however it is known that opioid-sparing strategies have important benefits on the actual patients [6]. Future syntheses should therefore prioritize outcomes that more directly reflect patient experience, such as time to pain relief, opioid-related complications, and validated quality-of-recovery instruments.

Finally, we fully acknowledge that high heterogeneity across nearly all outcomes, combined with a corrected covered area of 24%, represents a meaningful limitation. This overlap reduces the statistical independence of SR-level estimates, which is precisely why we refrained from pooling SR-level results directly and instead presented findings descriptively using modified forest plots. The absence of meta-regression reflects a genuine constraint of the umbrella review format: when included SRMAs do not report the moderator variables needed for such analyses, cross-SR regression is not feasible. The correspondents’ suggestions regarding standardized ESPB technique reporting, uniform outcome definitions, consistent opioid conversion metrics, and predefined subgroup analyses are well-taken, and we hope our review can serve as a methodological reference point for future work.

We thank the correspondents for reinforcing several of our stated limitations and for clearly articulating the path forward.