Linking intraoperative nociception to postoperative pain: a secondary comparative analysis of opioid-free and...

Nociception monitoring during general anesthesia is evolving to improve intraoperative management and postoperative outcomes. While opioid-based anesthesia (OBA) remains widely used for its strong antinociceptive effects, concerns about opioid-induced adverse effects have fueled interest in opioid-free anesthesia (OFA) approaches. This study aimed to compare perioperative and postoperative hemodynamic parameters, nociceptive dynamics, and depth of consciousness between OFA and OBA.

This secondary analysis used data from the multicenter cohort study Opioid-Sparing Person- Centered Care study, a prospective, multicenter randomized controlled trial (ClinicalTrials.gov number: NCT03756961), including 79 patients undergoing bariatric surgery with OFA or OBA. Hemodynamic parameters, depth of consciousness, and nociception level (NOL) index was collected during anesthesia induction, surgery and in post-anesthesia care unit (PACU), while postoperative pain scores, measured with the Numbers Rating Scale (NRS), were recorded only in the PACU. NOL index values were blinded to clinicians throughout the procedure.

During anesthesia induction, the OFA group exhibited significantly higher hemodynamic and nociceptive responses compared to the OBA group. NOL index values were elevated in the OFA group, indicating increased nociceptive activity. In contrast, the OBA group showed slightly higher NOL index values in the PACU. Bispectral index monitoring demonstrated a lighter depth of anesthesia in the OFA group compared with the OBA group, although both groups remained within an adequate anesthesia range. OFA regime was identified as a strong predictor of lower postoperative NOL index values. However, the OBA group also included a higher proportion of patients that scored postoperative pain with NRS ≥4 compared with the OFA group.

Intraoperative monitoring revealed distinct patterns in nociceptive dynamics and their coupling with anesthetic depth between OFA and OBA techniques. OBA showed a tighter coupling between nociception and anesthetic depth, whereas both approaches appeared suboptimal for postoperative pain control. Despite these intraoperative variations, the overall impact on early postoperative recovery was limited. Larger, prospective studies are warranted to assess how nociception-guided anesthesia strategies and time within specific NOL intervals influence postoperative pain and long-term outcomes.