Determination of moderate-to-severe postoperative pain on the numeric rating scale: a cut-off point analysis applying four different methods.

BACKGROUND: Cut-off points (CPs) of the numeric rating scale (NRS 0-10) are regularly used in postoperative pain treatment. However, there is insufficient evidence to identify the optimal CP between mild and moderate pain.
METHODS: A total of 435 patients undergoing general, trauma, or oral and maxillofacial surgery were studied. To determine the optimal CP for pain treatment, four approaches were used: first, patients estimated their tolerable postoperative pain intensity before operation; secondly, 24 h after surgery, they indicated if they would have preferred to receive more analgesics; thirdly, satisfaction with pain treatment was analysed, and fourthly, multivariate analysis was used to calculate the optimal CP for pain intensities in relation to pain-related interference with movement, breathing, sleep, and mood.
RESULTS: The estimated tolerable postoperative pain before operation was median (range) NRS 4.0 (0-10). Patients who would have liked more analgesics reported significantly higher average pain since surgery [median NRS 5.0 (0-9)] compared with those without this request [NRS 3.0 (0-8)]. Patients satisfied with pain treatment reported an average pain intensity of median NRS 3.0 (0-8) compared with less satisfied patients with NRS 5.0 (2-9). Analysis of average postoperative pain in relation to pain-related interference with mood and activity indicated pain categories of NRS 0-2, mild; 3-4, moderate; and 5-10, severe pain.
CONCLUSIONS: Three of the four methods identified a treatment threshold of average pain of NRS≥4. This was considered to identify patients with pain of moderate-to-severe intensity. This cut-off was indentified as the tolerable pain threshold.