Analgesia Nociception Index (ANI) has been proposed for the evaluation of the nociception–antinociception balance in the perioperative period. In obese patients, where the management of analgesia may be rendered difficult by pharmacological changes, we hypothesised that the monitoring of analgesia with ANI would reduce intraoperative opioid consumption during bariatric surgery.

This monocentric, observational, unmatched case-control study aimed to compare perioperative data from obese subjects (body mass index ≥35kgm⁻²) during bariatric surgery with or without the use of ANI monitoring (ANI+ group versus ANI− group). Intraoperative analgesia was provided by injection of sufentanil, which was performed according to the clinician's assessment in the ANI− group or to the ANI value in the ANI+ group. The primary outcome was the mean hourly intraoperative sufentanil requirement. Secondary outcomes included the need for postoperative morphine titration, incidence of nausea and vomiting, respiratory distress and pain scores in the first 24hours.

Between December 2013 and September 2016, 60 obese patients (i.e. 30 per group) were included. The mean hourly consumption of sufentanil was significantly lower in the ANI+ group (0.15±0.05μgkg⁻¹h⁻¹ versus 0.17±0.05μgkg⁻¹h⁻¹, P=0.038). We found no difference between groups regarding the incidence of nausea and vomiting, acute respiratory distress, the need for postoperative morphine titration, or pain scores in the first 24 postoperative hours.

The use of ANI monitoring might reduce intraoperative consumption of sufentanil during bariatric surgery but does not appear to be accompanied by a reduction in its side effects.