Response to comments on "Effect of postoperative peripheral nerve blocks on the analgesia nociception index under propofol anesthesia: an observational study.".

Tanaka et al. suggested that the increase in high-frequency variability index (HFVI) after peripheral nerve block (PNB) may result from autonomic effects mediated by the stellate ganglion block when an interscalene brachial plexus block (ISB) is performed. To investigate this, we analyzed patients receiving PNB with (ISB group; n = 8) or without ISB (non-ISB group; n = 22). HFVI increased significantly in both groups to a similar extent. These findings suggest that ISB's direct autonomic influence on HFVI is minimal. Additionally, laterality effects could not be assessed due to limited cases. We conclude that HFVI elevation is more likely due to PNB's analgesic effects rather than ISB's autonomic influence. Further studies are needed to confirm these findings.