Postoperative pain after laparoscopic cholecystectomy is not reduced by intraoperative analgesia guided by analgesia nociception index (AN®) monitoring: a randomized clinical trial

Background. Laparoscopic cholecystectomy frequently results in significant immediate postoperative pain. A new pain monitor, analgesic nociception index (ANI), based on heart rate variability, has recently been approved for intraoperative nociception monitoring. We designed a single-blind, parallel-group, randomized control trial to test the hypothesis that protocol-driven intraoperative analgesia guided by ANT during laparoscopic cholecystectomy would improve titration of intraoperative analgesics leading to decreased postoperative pain. Methods. One hundred and twenty consecutive adult participants presenting for elective laparoscopic cholecystectomy were recruited. Participants were randomly allocated by sealed envelope to receive intraoperative morphine either guided by ANT via a protocol (intervention group) or guided by the anaesthetist with ANT concealed (control group). All participants received paracetamol, parecoxib, fentanyl at induction, and local anaesthetic to port sites. The primary endpoint was the presence of moderate/severe pain (visual analogue scale >50 mm) at any of the four time points in the first postoperative hour. Secondary endpoints included postoperative rescue morphine. Results. Sixty participants were randomized to each group, and all but one drop-out from the intervention group were analysed. The usage ofANI guidance did not result in a decrease in the rate of moderate/severe pain (50.8% vs 45.0%: difference of 5.8%, 95% confidence interval, 23.7% to 12.1%, P=0.58), or the use of postoperative rescue analgesia. Conclusions. This randomized control trial of intraoperative ANT-guided morphine administration in elective laparoscopic cholecystectomy failed to show any advantage over the current standard of care, and demonstrated a high level of postoperative pain, despite the use of multinnodal analgesia.