[Intrathecal morphine for postoperative pain]

Abstract

At the beginning, the way intrathecal morphine was used for postoperative pain relief was quite unfortunate, because the doses derived from experience with morphine-tolerant cancer patients were considerably too high and respiratory depression occurred frequently. Subsequent dose-finding studies showed that the doses of morphine used initially could be reduced by a factor of ten without loss of the analgesic effect and with a marked reduction in side-effects. No respiratory depression has been reported when doses below 0.1 mg morphine are used. METHOD. In this prospective study the effect of 0.06 to 0.08 mg intrathecal morphine, mixed with the local anaesthetic for spinal anesthesia, was investigated in surgical patients aged 21 to 81 years, ASA grade I or II, scheduled for orthopaedic operations or herniorraphies. Thirty unpremedicated patients were enrolled in the study and were, after informed consent, randomly allocated to a control group without morphine or to a morphine group. The analgesic effect was assessed by the time interval between the administration of the spinal anaesthesia and the first demand for an analgesic medication. The mood state was evaluated with the adjective checklist of Janke and Debus 6 h after the spinal anaesthesia. RESULTS AND DISCUSSION. In the control group half of the patients asked for an analgesic medication within 275 min (median) after the spinal anaesthesia, and all patients within 420 min, whereas in the morphine group half of the patients asked for an analgesic within 1170 min (median). Seven patients had not required an analgesic at the termination of the observation period 20 h after the spinal anaesthesia. The mood status showed no difference between the two groups, in particular, no dizziness or drowsiness after morphine. There was no difference in the incidence of side-effects such as nausea or urinary retention between the two groups. Pruritus was not reported spontaneously but was found upon questioning in five patients. It was in no case disturbing. CONCLUSIONS. Morphine (0.06 to 0.08 mg) mixed with the local anaesthetic for spinal anaesthesia provided for an analgesia of more than 20 h duration in half of the patients. This technique is safe, simple, reliable and virtually free of side-effects. No particular supervision due to the administration of intrathecal morphine is necessary in this dose range if systemic opiates are avoided. If the analgesia is unsatisfactory, a non-opioid analgesic is recommended.