Cut-off points between pain intensities of the postoperative pain using receiver operating characteristic (ROC) curves

Background: Pain assessment and management are important in postoperative circumstances as overdosing of opioids can induce respiratory depression and critical consequences. We aimed this study to check the reliability of commonly used pain scales in a postoperative setting among Korean adults. We also intended to determine cut-off points of pain scores between mild and moderate pain and between moderate and severe pain by which can help to decide to use pain medication. Methods: A total of 180 adult patients undergoing elective non-cardiac surgery were included. Postoperative pain intensity was rated with a visual analog scale (VAS), numeric rating scale (NRS), faces pain scale revised (FPS-R), and verbal rating scale (VRS). The VRS rated pain according to four grades: none, mild, moderate, and severe. Pain assessments were performed twice: when the patients were alert enough to communicate after arrival at the postoperative care unit (PACU) and 30min after arrival at the PACU. The levels of agreement among the scores were evaluated using intraclass correlation coefficients (ICCs). The cut-off points were determined by receiver operating characteristic curves. Results: The ICCs among the VAS, NRS, and FPS-R were consistently high (0.839-0.945). The pain categories were as follow: mild 5.3 / moderate 5.4 similar to 7.1 /severe 7.2 in VAS, mild 5 / moderate 6 similar to 7 / severe 8 in NRS, mild 4 / moderate 6 / severe 8 and 10 in FPS-R. The cut-off points for analgesics request were VAS 5.5, NRS 6, FPS-R 6, and VRS 2 (moderate or severe pain). Conclusions: During the immediate postoperative period, VAS, NRS, and FPS-R were well correlated. The boundary between mild and moderate pain was around five on 10-point scales, and it corresponded to the cut-off point of analgesic request. Healthcare providers should consider VRS and other patient-specific signs to avoid undertreatment of pain or overdosing of pain medication.