Acetaminophen reduces acute and persistent incisional pain after hysterectomy

OBJECTIVE: Acetaminophen is effective for acute surgical pain, but whether it reduces persistent incision pain remains unknown. We tested the primary hypothesis that patients given perioperative acetaminophen have less incisional pain three months after surgery. Our secondary hypotheses were that patients randomized to acetaminophen have less postoperative pain and analgesic consumption, and better functional recovery at three months. METHODS: 140 patients having abdominal hysterectomy were randomly assigned to: 1)intravenous acetaminophen (4 g/day for 72 postoperative hours); or, 2) saline placebo. The primary outcome was incisional pain visual analog scale (VAS) at three months after surgery. The secondary outcomes were (1, 2) postoperative VAS scores while laying and sitting and (3) total patient-controlled intravenous tramadol consumption during the initial 24 hours, (4) DN4 questionnaires and (5) SF-12 at three months after surgery. RESULTS: The persistent incisional pain scores at three months were significantly lower in acetaminophen (median [Q1, Q3]: 0 [0, 0]) as compared with saline group (0 [0, 1]) (P = 0.002). Specifically, 89%, 9%, and 2% of acetaminophen patients with VAS pain score at three months of 0, 1, and 2 or more, as compared with 66%, 23%, and 10% in the saline group (odds ratio: 2.19 (95% CI: 1.33, 3.59), P = 0.002). Secondly, postoperative pain scores both laying and sitting were significantly lower in the acetaminophen group. Acetaminophen group had significantly better DN4 score and mental health related but not physical health related quality of life. CONCLUSIONS: Our results suggest that acetaminophen reduces the risk and intensity of persistent incisional pain. However, there are other mechanisms by which acetaminophen might reduce persistent pain. KEY WORDS: Anesthesia, acetaminophen, Persistent surgical pain, Postoperative acute pain.