Evaluation of Surgical Pleth Index and Analgesia Nociception Index as surrogate pain measures in conscious postoperative patients: an observational study


We evaluated the performance of the Surgical Plethysmographic Index (SPI) and the Analgesia Nociception Index (ANI) as surrogate pain measures and determined their respective cut-off values for detecting pain in conscious postoperative patients. In total, 192 patients after elective surgery were enrolled. Baseline SPI and ANI data were acquired for 10 min in the operating room prior to surgery when the patients rated their pain as 0 on the numerical rating scale (NRS). Upon arrival in the post-anaesthesia care unit (PACU) after surgery, SPI and ANI data were recorded for 10 min. The means of the recorded data at OR and PACU were defined as the values representing baseline and postoperative pain, respectively. SPI and ANI data obtained from 189 patients were analysed, who were anesthetized with propofol (n = 149) or sevoflurane (n = 40). Remifentanil was continuously infused intraoperatively in all patients. The values of SPI and ANI were significantly different in conscious patients without (NRS = 0) and with pain (NRS > 0). The areas under the receiver operating curves for SPI and ANI were 0.73 (P < 0.0001) and 0.67 (P < 0.0001), respectively. The cut-off values for SPI and ANI in predicting postoperative pain were 44 (sensitivity: 84%, specificity: 53%) and 63 (sensitivity: 52%, specificity: 82%), respectively, which are different from those suggested by their respective manufacturers for use in intraoperative state under general anaesthesia. The cut-off values of SPI and ANI for detecting pain were similar regardless of the type of anesthesia.

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Fig. 1



Analgesia Nociception Index




Heartbeat interval


Heart rate variability


Numerical Rating Scale


Operating room


Patient-controlled analgesia


Post-anaesthesia care unit


Photo-plethysmographic amplitude


Receiver operating curve


Surgical Plethysmographic Index




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We thank Dr Joon Seo Lim from the Scientific Publications Team at Asan Medical Center for his editorial assistance in preparing this manuscript. This work was supported by the Ministry of Trade, Industry & Energy, Korea (Grant Number 10047988).

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Correspondence to Ji-Yeon Bang.

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Lee, JH., Choi, BM., Jung, YR. et al. Evaluation of Surgical Pleth Index and Analgesia Nociception Index as surrogate pain measures in conscious postoperative patients: an observational study. J Clin Monit Comput 34, 1087–1093 (2020). https://doi.org/10.1007/s10877-019-00399-5

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  • Conscious
  • Pain
  • Performance
  • Surgical Pleth Index
  • Analgesia Nociception Index