Intraarticular fentanyl compared with morphine for pain relief following arthroscopic knee surgery

Purpose: To compare the analgesia produced by comparable doses of intra- articular (IA) morphine and fentanyl. Methods: Sixty-nine healthy patients undergoing arthroscopic surgery received a standardized general anesthetic of 4 mg·kg^-1 thiopental and 2 μg·kg^-1 fentanyl followed by 2 mg·kg^-1 succinylcholine prior to tracheal intubation and controlled ventilation. Maintenance of anesthesia was achieved with N₂O/O₂ and isoflurane.. At the conclusion of surgery intra-articular injection was: Group I (n = 23) 50 μg fentanyl in 20 ml saline; Group II (n = 24) 3 mg morphine in 20 ml saline; Group III (n = 22) 20 ml saline. Pain scores at rest using a visual analogue scale were recorded by a separate blinded observer at one, two, four, and eight hours postoperatively. Results: Pain scores at one, two, four, and eight hours were 36, 26.3, 20.9, and 12.8 vs 35.8 33.8, 28.8, and 21.9 vs 70.5, 57.7, 58.4, and 53.6 for the IA-fentanyl, IA-morphine, and control groups respectively. Pain scores were greater at all times for Group III. Pain scores for Groups I and II were similar at one hour, but thereafter were less (P < 0.001) for the IA-fentanyl group. Conclusion: Better postoperative analgesia was achieved with 50 μg intraarticular fentanyl than with 3 mg intraarticular morphine.