Intraoperative Analgesia Guided by the Nociception Level (NOL) in Laparoscopic Colorectal Surgery: A Preliminary Outcome Study

Introduction: Most of postoperative patients report moderate to severe pain, possibly related to opioid underdosing or overdosing during surgery. Nociception Level (NOL) Index has been proposed for the evaluation of the nociceptionantinociception balance in the perioperative period and by that, may lead to a more appropriate analgesic regimen. NOL-index is scaled from 0 to 100; with previous studies suggesting that values >25 can indicate inadequate analgesia. We designed a NOL-guided and Observational study, 2-cohort (retrospective and prospective) trial to test the hypothesis that protocol-driven intraoperative analgesia guided by NOL during laparoscopic colorectal surgery would improve and reduce titration of intraoperative analgesics. Method: This monocentric, observational, and guided study aimed to compare perioperative data during laparoscopic colorectal surgery with or without the use of NOL monitor (NOL-guided vs. Control group). Intraoperative analgesia was provided by injection of fentanyl, which was performed according to the clinician’s assessment in the Control group or to the NOL monitor in the NOL-guided group. The primary outcome was a reduction in fentanyl consumption during surgery in the NOL-guided group. Results: Between 2017 and 2019, 70 patients (i.e., 36 in the Control group and 34 patients in the NOL-guided group) were included. The mean consumption fentanyl was significantly lower in the NOL-guided group (450mg) versus 600mg in the Control group (P = 0.005). Median postoperative pain score in T0, when the patient woke up in the operation room, was2 (inter-quartile range 0-5) and 0 (0-4) in Control and NOL-guided group, respectively (p=0.132). Conclusion: The NOL index in laparoscopic colorectal surgery decreased with incremental fentanyl doses during sevoflurane anaesthesia. This reduction in the intraoperative analgesia suggests its interesting potential as a nociception monitor during general anaesthesia (GA). Future studies should employ more robust design, be appropriately powered and seek to follow longer term outcomes.