Nociception level index: do intra-operative values allow the prediction of acute postoperative pain?

Nociception Level Index (NOL) guided analgesia has previously been found to correlate with noxious stimuli during surgery. It was aim of this study to investigate the relationship between intra-operative NOL and acute postoperative pain. After IRB approval, 80 patients scheduled for non-emergency surgery were enrolled. NOL data were recorded from induction of anaesthesia until the end of surgery. After admission to the postoperative acute care unit (PACU), pain scores (numeric rating scale [NRS, 0–10] were obtained 5-minutely for 15 min. NOL data of 74 patients were analyzed. Receiver-operating curve (ROC) analysis identified the NOL reaction to the knife to skin incision (median NOL within 60 s post knife to skin) vs. the median NOL during surgery vs. NOL at the end of surgery to have the highest correlation coefficient (ρ = 0.3; P = 0.01) as well as the highest area under the ROC curve (AUC 0.68; P = 0.01) for the prediction of moderate-severe pain in PACU. A NOL > 20 after skin incision predicted moderate-severe postoperative pain with the highest combined sensitivity (73%) and specificity (58%). A NOL < 10 after skin incision excluded moderate-severe pain in PACU with a negative predictive value of 83%. The NOL reaction to skin incision, but not NOL during surgery appears to allow the exclusion and, to a lesser degree the prediction of moderate-severe pain in PACU. The results may also strengthen the manufacturers recommendation of an intraoperative NOL range of 10–25. Australian New Zealand Clinical Trials Registry: ACTRN12619001596190.