[Efficacy and safety of 0.1 mg of intrathecal morphine in arthroscopic knee joint surgery].

Background and Objective: Intrathecal morphine provides effective postoperative analgesia but is associated with the risk of respiratory depression. A dose of only 0.1 mg has been shown to be optimal for effective and safe pain relief after abdominal surgery. This study was designed to determine whether the addition of 0.1 mg of morphine to the local anesthetic for spinal anesthesia produces adequate analgesia following arthroscopic knee joint surgery.
Methods: A prospective, randomized, placebo-controlled, double-blind clinical trial was performed. Forty ASA I/II patients undergoing knee arthroscopy under spinal anesthesia were randomized to receive either mepivacaine 4% with 0.1 mg of morphine or mepivacaine 4% with saline (placebo) intrathecally. Postoperative analgesia consisted of intravenous morphine delivered by patient-controlled analgesia (bolus: 2 mg, lockout time: 5 min). During the study period of 24 h, pain intensity at rest and on movement (visual analogue scale, 0: no pain, 100: maximum pain), vigilance, and vital parameters were recorded every hour.
Results: There were no statistically significant differences between the two groups in postoperative pain scores, morphine requirements, vigilance, blood pressure, heart rate, and breathing frequency. The patients of the morphine group required 12.3+/-10.2 mg (mean+/-SD) and those of the placebo group 11.6+/-8.4 mg of intravenous morphine from patient-controlled analgesia. The pain scores at rest and on movement were 10.0+/-8.1 and 16.0+/-12.6 in the morphine group and 8.2+/-7.9 and 11.7+/-11.3 in the placebo group. We did not observe severe side effects in any of the patients.
Conclusion: Intrathecal administration of 0.1 mg of morphine does not contribute to postoperative analgesia after arthroscopic knee joint surgery.