Aspects of intrathecal morphine for postoperative pain relief in major orthopedic surgery

The optimal site to administer opioids e.g. morphine is as close as possible to the opiate receptor site (spinal cord) by the intrathecal route, as it is the place of effectiveness. To improve the clinical effectiveness of intrathecal morphine two strategies are proposed: 1. to lower the intrathecal dose of morphine and thereby reduce the supraspinal adverse effects while maintaining the analgesic effects; 2. further research to synthesize highly selective endorphin mimetic drugs with a minimum of side effects. We hypothesized that low doses of intrathecal morphine might probably result in similar pain relief scores but might minimize the incidence of adverse effects. The first study was designed to determine the optimal intrathecal dose of morphine in total hip surgery. The optimal intrathecal dose was defined as the dose, which provides effective analgesia with minimal side effects during 24 h after total hip surgery. Patients (n=143) scheduled for total hip surgery were randomized to four double-blinded groups with a standardized bupivacaine dose but different doses of intrathecal morphine: group I, 0.025 mg; group II, 0.05 mg; group III, 0.1 mg; and, group IV, 0.2 mg. Pain scores, intravenous morphine intake {patient controlled analgesia (PCA)} and morphine related side effects (respiratory depression, postoperative nausea and vomiting, itching, urinary retention) were recorded for 24 h after surgery. Excellent postoperative pain relief was present in all groups. The highest pain scores were found in group I. The mean use of systemic morphine administered by PCA infusion pump was: 23.7 mg, 17.8 mg, 10.9 mg and 9.9 mg, in group I, II, III, and IV, respectively (p