An optimal dose study of intrathecal morphine in gynecological patients

Post-operative pain after gynecological surgery can be controlled by intrathecal administration of opioids and local anesthetics. Effective intrathecal analgesia can be achieved from low dose narcotics with less adverse effects, prolonged duration and reduced narcotics requirement. Therefore, we undertook a prospective randomized study to find out optimal dose of intrathecal morphine for long lasting post-operative analgesia with less adverse effect in this group of patients.

Spinal anesthesia was induced in 343 patients, the American Society of Anesthesiologists (ASA) I-III, age between 15-65 years, who were enrolled into double-blind randomized study to three different groups. Each patients will receive a mixture of 0.5 per cent bupivacaine and morphine to the total volume of 4 ml. Intrathecally, Group I, II and III will receive preservative-free morphine 0.2, 0.25 and 0.3 mg, respectively. At 1, 2, 3, 6, 24, 48 and 60 h after surgery, assessment of pain (Verbal Numeric Pain Score: 0-10), pruritus, sedation, nausea, vomiting and the time to the first dose of analgesics requirement were recorded. Patients' satisfactions were also recorded at the last visit.

Time to first dose of narcotics or nubain were not different between groups (p = 0.13). Although 64.91 per cent, 66.67 per cent and 76.52 per cent of patients from group I, II and III, respectively did not require narcotics treatment but the difference was not statistically significant (p = 0.121). However, the percentage of patients with moderate to severe pruritus (treatment desirable) were 30.7 per cent, 30.7 per cent and 39.1 per cent in group I, II and III respectively (p = 0.296).

Intrathecal morphine 0.2 mg produced adequate analgesia and less side effect. Increasing dose of intrathecal morphine showed no more efficacy and also increased the number of pruritic patient who required treatment.