Hyperalgesia induced by low-dose opioid treatment before orthopaedic surgery An observational case-control study

BACKGROUND Chronic pain and opioid consumption may trigger diffuse hyperalgesia, but their relative contributions to pain vulnerability remain unclear. OBJECTIVES To assess preoperative opioid-induced hyperalgesia and its postoperative clinical consequences in patients with chronic pain scheduled for orthopaedic surgery. DESIGN A prospective observational study. SETTINGS Raymond Poincare teaching hospital. PATIENTS Adults with or without long-term opioid treatment, scheduled for orthopaedic surgery. PRIMARY OUTCOME MEASURE Preoperative hyperalgesia was assessed with eight quantitative sensory tests, in a pain-free zone. SECONDARY OUTCOME MEASURES Postoperative morphine consumption and pain intensity were evaluated using a numerical rating scale (NRS) in the recovery room and during the first 72 h. RESULTS We analysed results from 68 patients (28 opioid-treated patients and 40 controls). Mean daily opioid consumption was 42 +/- 25mg of morphine equivalent. The opioid-treated group displayed significantly higher levels of preoperative hyperalgesia in three tests: heat tolerance threshold (47.1 degrees C vs. 48.4 degrees C; P = 0.045), duration of tolerance to a 47 degrees C stimulus (40.2 vs. 51.1 s; P = 0.03) and mechanical temporal summation [1.79 vs. 1.02 (Delta NRS10-1); P = 0.036]. Patients in the opioid-treated group consumed more morphine (19.1 vs. 9.38 mg; P = 0.001), had a higher pain intensity (7.6 vs. 5.5; P = 0.001) in the recovery room and a higher cumulative morphine dose at 72 h (39.8 vs. 25.6 mg; P = 0.02). CONCLUSION Chronic pain patients treated with low doses of opioid had hyperalgesia before surgery. These results highlight the need to personalise the management of patients treated with opioids before surgery.