Assessment of intraoperative high frequency variability index as a predictor of postoperative pain after open liver or pancreatic surgery under combined general and epidural anesthesia: a prospective observational study.

The aim of the present study was to investigate the utility of the intraoperative high frequency variability index (HFVI) / Analgesia Nociception Index (ANI) for predicting postoperative pain in patients undergoing open liver or pancreatic surgery under combined general and epidural anesthesia, with a particular focus on HFVI/ANI measured immediately before extubation. We investigated whether maximum postoperative pain at rest and postoperative morphine consumption were associated with intraoperative HFVI/ANI values, including those measured immediately before extubation, the mean intraoperative values, the difference between values immediately before and 5 min after the first administration of local anesthetics via epidural catheter, and the difference between values immediately before and 5 min after the start of surgery. We analyzed the data obtained from 52 patients and found that HFVI/ANI measured immediately before extubation showed a limited but statistically significant association with postoperative pain at rest. However, receiver operating characteristic curve analysis failed to demonstrate clinically useful predictive performance of HFVI/ANI for postoperative pain defined as Numerical Rating Scale > 3 or > 7. In addition, no association was observed between intraoperative HFVI/ANI measured at any time point and postoperative morphine consumption. The present study demonstrated that intraoperative HFVI/ANI may reflect postoperative pain levels to a limited extent, particularly when measured immediately before extubation, but lacks sufficient accuracy to be used as a standalone predictor of postoperative pain.