Identification of the intraoperative antinociceptive effect of intravenous fentanyl using the Nociception Level (NOL) index versus clinical parameters in patients undergoing gynecological laparoscopic surgery: A secondary analysis of the NOLGYN study

•In previous studies, it has been shown that the Nociception Level (NOL) index was superior to clinical parameters to discriminate nociceptive stimuli under general anesthesia.•In this study, the NOL index, heart rate (HR), and mean arterial pressure (MAP) all statistically discriminated the analgesic effect of fentanyl but only the NOL index proved clinically relevant to identify the analgesic effect of one fentanyl injection.•We first demonstrated here that the NOL index is adequate to continuously evaluate the analgesic balance during general anesthesia. While we typically assess nociception balance during general anaesthesia through clinical parameters such as heart rate (HR) and mean arterial pressure (MAP) variation, these parameters are not specific to nociception. We hypothesized that using the Nociception Level (NOL) index to assess the analgesic effect of a fentanyl bolus would be superior to standard clinical parameters. Ancillary study of the NOLGYN study, a randomized controlled trial comparing intraoperative NOL-guided administration of fentanyl (NOL group) versus standardized care (SC group). University hospital in Montréal, Canada between November 2018, and December 2019. Women undergoing gynecological laparoscopic surgery. In our evaluation of intraoperative nociception, we analyzed the analgesic effect of fentanyl using three parameters: MAP, HR, and the Nociception Level (NOL) index. All fentanyl injection events were extracted from the database. The primary endpoint was the difference between values before and after each injection. The median of the NOL index before fentanyl injection was 30.5 (IQR 19.4 to 40.7) versus 18.9 (IQR 11.5 to 27.4) after (P