• Motoi Kumagai, Naoto Yamada, Masahiro Wakimoto, Shohei Ogawa, Sho Watanabe, Kotaro Sato, and Kenji S Suzuki.
• Department of Anesthesiology, School of Medicine, Iwate Medical University Hospital, 2-1-1 Idai-dori, Yahaba-cho, Japan. bear@kxd.biglobe.ne.jp.
• J Clin Monit Comput. 2025 Jan 29.

PurposeThe analgesia nociception index (ANI), also referred to as the high frequency variability index (HFVI), is reported to be an objective measure of nociception. This study investigated changes in ANI after peripheral nerve blocks (PNB) under general anesthesia. Understanding these changes could enhance assessment of PNB efficacy before emergence from general anesthesia.MethodsThis study enrolled 30 patients undergoing elective upper limb surgery. After surgery, median and maximum ANI values were recorded during two periods: a 5-minute period before PNB and a 20-minute period after PNB. The numeric rating scale (NRS) for pain was assessed twice: immediately after emergence from general anesthesia (N1) and the maximum pain experienced by the following morning after PNB effects subsided (N2). The difference in ANI before and after PNB was tested using the Wilcoxon signed-rank test. Statistical significance was set at P < 0.05.ResultsThe ANI significantly increased after PNB in both the median (pre vs. post PNB value: 53.5 [44.0-68.0] vs. 59.0 [47.0-78.3], median [interquartile range]; P < 0.05) and maximum values (64.0 [56.3-79.5] vs. 74.5 [61.5-85.3]; P < 0.01). Secondary analysis revealed that significant ANI increases in both median (48.0 [42.3-66.5] vs. 61.0 [50.0-76.5]; P < 0.01) and maximum values (58.5 [50.3-75.3] vs. 76.0 [71.8-83.5]; P < 0.01) in the 18 cases with N2 ≥ 4 whereas no statistical differences were observed in the 12 cases with N2 < 4.ConclusionThe increased ANI value after PNB under propofol anesthesia may be a valuable indicator for assessing PNB efficacy.Trial Registration NumberUMIN000050334.Date Of RegistrationFebruary 28, 2023.© 2025. The Author(s).

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