Purpose: There is an increasing interest in the identification of predictors for individual responses to analgesics and surgical pain. In this study, we aimed to determine psychological factors that might contribute to this response. We hence investigated patients undergoing a standardized surgical intervention (open nephrectomy).
Patients and methods: Between May 2014 and April 2015, we conducted a prospective observational cohort study. The following psychological tests were administered preoperatively: Mini-Mental State Examination, Amsterdam Preoperative Anxiety and Information Scale (APAIS), Hamilton Anxiety Rating Scale, Hamilton Depression Rating Scale, and Pain Catastrophizing Scale. The primary outcome, postoperative pain intensity (11-point numerical rating scale, [NRS]), was assessed in the "immediate early" (first 8 hours), "early" (12 and 24 hours), and "late early" periods (48 and 72 hours).
Results: A total of 196 patients were assessed, and 150 were finally included in the study. NRS scores improved from 4.9 (95% confidence interval [CI]: 4.7-5.1) in the "immediate early" to 3.1 (95% CI: 2.9-3.3) in the "early" and 2.3 (95% CI: 2.1-2.5) in the "late early" postoperative period. Most (87%) patients received intravenous opioids, while 13% received analgesics epidurally. Repeated measures analysis of variance indicated better pain management with epidural analgesia in the first two postoperative periods (F=15.01, p<0.00). Postoperative pain correlated strongly with analgesic strategy and preoperative psychological assessment. Multiple linear regression analysis showed "expected pain" was the only predictor in the "immediate early" phase, and "anxiety" was most important in the "early" postoperative period. In the "late early" phase, catastrophizing was the predominant predictor, alongside "preoperative analgesic usage" and "APAIS anxiety".
Conclusion: After open nephrectomy, epidural analgesia conveys a clear advantage for pain management only within the first 24 hours. Moreover, as the psychological phenotype of patients changes distinctively in the first 72 postoperative hours, psychological variables increasingly determine pain intensity, even surpassing employed analgesic strategy as its main predictor.
Keywords: numeric rating scale; open nephrectomy; postoperative analgesia; postoperative pain; psychological variables.