Reply to: Pulse oximeter perfusion index for assessment of brachial plexus block: a holy grail or a design fail?

Editor—We thank Daoud for his interest in our study¹ and are pleased to address the two concerns raised in his letter.²

Concerning the first query raised in the comment, it appears that Daoud has misunderstood our findings, and confused between ‘blocked and unblocked limbs’ and ‘successful and failed blocks’. When we performed our area under receiver operating characteristic (AUROC) analysis, we had two groups: failed block (n=7) and successful block (n=70), as presented in figure 1. In table 2 we presented blocked limb (n=70) and unblocked limb (n=70). The values of perfusion index (PI) in the unblocked limb (mentioned in table 2) are distinctly different from the values in the failed blocks (presented in figure 1). We have only 7 failed blocks in our study and their PI values at 10 min were {3.2, 2.1, 3.3, 2.6, 2.7, 2.9, 2.6, and 2.1}. Thus, our cut-off value which is 3.3 will not miss any failed blocks.

Regarding the second query, Student’s t-test and Mann-Whitney U-test are used for comparison of single measurements and not repeated measures; thus, it was not appropriate to use these tests for analysis of PI in our study.³

We do agree that the answer to the question raised is that using our threshold value or both PI and PI ratio in predicting successful supraclavicular block might not be the holy grail.

Declaration of interest

None declared.

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