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To the Editor
We would like to thank Chin for his letter regarding our recent publication.1 2 We concluded that ‘paravertebral nerve blocks (PVB) are superior to erector spinae plane blocks (ESPB) for both short-term analgesia as well as opioid-sparing following non-mastectomy surgery” and Chin opined that ‘this statement is not strictly true (for the opioid)…’ We respectfully disagree as the hypothesis testing for this part of the dual primary end point demonstrated superiority of PVBs over ESPBs with a p value of 0.0043; therefore, the statement is absolutely scientifically accurate (‘true’). It is impossible to claim that ESPBs are non-inferior since PVBs were found to be superior.3 When using superiority testing and finding a statistically significant difference, it would be patently incorrect to state anything other than a superiority was found.
Chin may be suggesting that while there was a statistically significant difference, it was not a clinically meaningful difference between the two groups as the 95% CI for the group difference was within the prespecified 2 mg non-inferiority margin. However, the ‘2 mg’ of morphine equivalents noted in our statistical section was set somewhat arbitrarily as a non-inferiority margin—it was not defining the minimal clinically relevant difference. The latter value remains unknown, and unquestionably varies with the clinical situation.4 Furthermore, it would be unconventional to ignore the fact that the 95% CI excludes 0 mg, and rather—arbitrarily—emphasize that it excludes 2 mg. Regardless, we presented the results and readers will determine for themselves whether or not the difference is clinically relevant. Nevertheless, based on our results, concluding that PVB resulted in a lower opioid consumption is unquestionably an accurate statement and conclusion.
Recall that our original hypothesis was that ESPB would be non-inferior to PVB, and we were ultimately surprized by our study results. We were also somewhat disappointed by these findings as we agree with Chin that ESPB does appear to be a technically less-demanding and potentially lower-risk alternative to PVB. However, we cannot ignore the results of hypothesis testing just because we find them disappointing. Chin suggests that we should have mentioned in the abstract two secondary end points that he feels places ESPB in a more-favorable light. However, our study was prospectively powered for the primary end point and so that is the outcome measure that must be emphasized within the abstract. It would be convenient to include all secondary end points, but the maximum word count of 250 excludes this possibility; and, to cherry-pick secondary end points that suit our preferred outcome adds bias to the presentation of the study.
Chin concludes, ‘…the potential for the ESPB and other fascial plane blocks to benefit a larger number of patients with their greater reach should not be lightly dismissed (emphasis added).’ We concur, but posit that prospectively choosing the dual primary outcome of pain scores and opioid consumption, objectively testing our hypothesis, and then accurately reporting the results of that hypothesis testing is not ‘lightly dismissing’ ESPB—rather, it is the scientific method. In the history of medicine, no single trial has ever answered every question regarding an intervention, and we did not suggest as much in our manuscript. Rather, the results of our investigation will be added to the collective body of evidence currently accumulating within the published literature,5 and practitioners with their patients will decide for themselves which technique is optimal in the near-infinite variations of clinical circumstances. Until then, we believe that the results of our hypothesis testing support the conclusion stated in the abstract that, ‘PVBs provided superior analgesia and reduced opioid requirements following non-mastectomy breast surgery.’ To conclude otherwise would have placed our preconceived preferences above objective hypothesis testing and the scientific method.
Footnotes
Contributors BMI: this author helped with, literature search, manuscript preparation and review of manuscript. MCD: this author helped with, literature search, manuscript preparation and review of manuscript. MWS: this author helped with, literature search, manuscript preparation and review of manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; internally peer reviewed.