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

Kumagai et al. provided valuable insights into the effects of postoperative peripheral nerve blocks (PNB) on the high-frequency variability index (HFVI), a surrogate for nociception monitoring. However, the analysis excluded the impact of different brachial plexus block techniques, particularly the interscalene brachial plexus block (ISB), and role of laterality in HFVI variability. ISB produces a stellate ganglion block-like effect through local anesthetic diffusion, influencing autonomic function and heart rate variability, independent of nociceptive modulation. Provided that this study included various brachial plexus block approaches, stratifying HFVI changes according to technique and laterality could enhance their clinical relevance. Right-sided ISB may have a more pronounced autonomic effect than left-sided ISB. Further research is needed to clarify these effects and optimize the interpretation of HFVI during perioperative monitoring.