ESTABLISHMENT OF 0.05mg MORPHINE AS EFFECTIVE MINIMAL DOSE OF INTRATHECAL MORPHINE FOR ANALGESIA IN LOWER ABDOMINAL AND LOWER LIMB SURGERIES

Abstract

With the discovery of specific opioid receptors in the central nervous system in the 1970s24, a milestone for intrathecally mediated analgesia was set. However, the increased incidence of side effects such as respiratory depression, nausea and pruritus, following intrathecal morphine2, diminished the desire to use intrathecal morphine for post operative analgesia. With the discovery that these side effects were dosedependent2, researchers have therefore, experimented on different doses to obtain a dose that will give effective post- operative analgesia with minimal side effects. This study aimed at establishing a minimal dose of 0.05mg intrathecal morphine as an effective analgesic dose with little side effect, by comparing it to 0.1mg intrathecal morphine and placebo. Each group consisted of 34 ASA I& II patients who underwent a lower abdominal or lower limb surgery, using intrathecal anaesthesia. Their pain scores post- operatively and incidence of side effects were assessed over 24 hours using Visual Analog Scale. Results showed that there was no significant difference in pain score between those that received 0.1mg and those that received 0.05mg intrathecal morphine(p<0.05); while those that received placebo experienced significantly higher post- operative pain score(p<0.05). The 0.1mg intrathecal morphine group experienced significantly higher incidence of pruritus than the 0.05mg group (p< 0.05).
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No patient in each of the three groups experienced significant respiratory depression. The doses of morphine used did not induce significant nausea and vomiting (p< 0.05) In conclusion, the study succeeded in establishing 0.05mg of intrathecal morphine as effective minimal dose of intrathecal morphine for analgesia in lower abdominal and lower limb surgeries with minimal side effects.