To the Editor:
We read with great interest the noninferiority trial by Auyong et al.1 We greatly appreciate the authors for their novel technique, the anterior suprascapular nerve block. They have shown that it provides noninferior analgesia compared to that of interscalene block, and at the same time preserves vital capacity and has lower incidence of Horner syndrome.
Our question is: when the anterior suprascapular block, which did not target the superior trunk, offers a noninferior analgesia to interscalene (targeting the roots and trunks), how did the supraclavicular block targeting the superior and middle trunk not offer a noninferior analgesia? As per the authors, for supraclavicular block, a large volume of local anesthetic is required as the cross-sectional area of the brachial plexus increases at the supraclavicular level. This could have been a good explanation if the brachial plexus divisions were targeted, but the authors had targeted the superior and middle trunk in the supraclavicular group. When 15 ml volume of local anesthetic was deposited at the suprascapular nerve, laterally away from superior trunk had spread and blocked the axillary and subscapular nerves, arising from the posterior division of superior trunk (in the anterior suprascapular group), how did the same volume of local anesthetic that was deposited directly on the superior trunk (in the supraclavicular group) not block them?
In table 2 of Auyong et al. (PACU Pain and Opioid Consumption—Interscalene, Supraclavicular, and Anterior Suprascapular), all values in all the three groups have SD more than the mean. For example, the average postoperative numerical rating scale score at 60 min postsurgery (scored from 0 to 10) in the interscalene group, has mean ± SD of 2.1 ± 2.6, which implies the values ranges from −0.5 to 4.7 (2.1 to 2.6 is equal to −0.5 to 2.1 + 2.6 = 4.7). Logically pain score and opioid consumption cannot be represented negatively when the minimum score is zero. When the SD is more than the mean while analyzing data which is nonnegative (pain score, opioid consumption), it implies nonnormal or skewed distribution. The primary outcome of this trial is pain in the postanesthesia care unit and one-way ANOVA has been applied. For the ANOVA to be applied, the data has to be of normal distribution. If data collected is of nonnormal distribution, the recommendation is to use the median as a measure of central tendency and the interquartile range as a measure of dispersion.2
We would like to get clarification from the authors as to whether the data collected for pain scores at 60 min postsurgery was of nonnormal distribution and skewed, and whether application of mean as measure of central tendency in such nonnormal distribution has hindered the supraclavicular group to meet the noninferiority criteria in comparison to the interscalene group.
The authors declare no competing interests.