Prediction of postoperative pain and analgesic requirements using surgical pleth index: a observational study

The aim of this study was to evaluate the performance of surgical pleth index (SPI) measured before arousal from general anaesthesia for prediction of immediate postoperative pain and postoperative opioid requirement during postoperative 48 h. After obtaining ethical approval and written informed consent, we enrolled 51 patients undergoing liver resection under isoflurane based general anaesthesia using laryngeal mask airway in this prospective observational study. Data relating to SPI values were recorded every 30 s for the last 3 min of surgery (bispectral index < 60 at all times). Postoperative pain intensity was assessed using a 0-10 numerical rating scale (NRS) every 10 min in the recovery room. The relationships between SPI with postoperative pain score and opioid requirement were analysed. A receiver-operating characteristic curve (ROC) was used to evaluate the performance of SPI to predict NRS ≥ 5. SPI value was significantly associated with the highest pain score in the recovery room (r = 0.63, p < 0.001). An SPI value of 60, which showed the highest sensitivity and specificity, was defined post hoc as the cut-off for moderate-severe pain (NRS ≥ 5). When compared the patients who showed SPI value over 60 or not, there was significant difference in the amount of fentanyl consumption during postoperative 48 h (1093 ± 406 µg vs. 766 ± 369 µg, p = 0.014; SPI ≥ 60 vs. SPI < 60). SPI measured before arousal after inhalation anaesthesia was associated with immediate postoperative pain and postoperative opioid consumption.