Mini-dose (0.05 mg) intrathecal morphine provides effective analgesia after transurethral resection of the prostate.

Purpose: To determine the optimal dose of intrathecal morphine that produces satisfactory analgesia with minimum side effects in elderly patients undergoing transurethral resection of the prostate (TURP).

Methods: In this double-blind prospective study, 42 patients undergoing TURP with spinal anesthesia were allocated to one of three groups. Group A (n = 14) received tetracaine, 10 mg, alone. Group B (n = 13) and Group C (n = 15) received morphine 0.05 mg and 0.10 mg, respectively, in combination with tetracaine. Postoperative pain, nausea and pruritus were evaluated using visual analogue scales (VAS). SpO(2) and respiratory rate were also assessed.

Results: At three, five, seven and 24 hr after spinal anesthesia, the VAS scores for pain in Groups B and C were significantly less than in Group A. Group C experienced significantly greater VAS scores for pruritus as compared to Groups A and B. There was no significant difference in the intensity of nausea among the three groups. No patient experienced hypoxemia (SpO(2) < 90%) and respiratory depression (respiratory rate < 10 beats*min(-1)) in any group.

Conclusion: A dose of 0.05 mg in intrathecal morphine with spinal anesthesia would be optimal for elderly patients undergoing TURP.