Introduction:

Despite an effective analgesic effect in cesarean sections of intrathecal morphine (ITM), its use has been restricted due to its side effects.

Objective:

To assess whether the reduction in the dose of ITM (100 to 50 μg) retains its desired analgesic effect by avoiding side effects.

Material and methods:

Single blind randomized clinical trial. Sixty-four women scheduled for cesarean section were applied at the time of ITM subarachnoid block at a dose of 100 or 50 μg (30 per group). Post-operative pain was evaluated at 10 and 24 hours with numerical verbal scale, analgesic rescue requirement, as well as: presence of nausea-vomiting, pruritus, respiratory depression and urinary retention.

Results:

There were not found differences in postoperative pain at 10 hours between the groups (both with median score of 3, p = 0.40) or at 24 hours (median of 3 in both groups, p = 0.62). More patients from the ITM 50 μg group required analgesic rescue (16.7% versus 2.9%, p = 0.07). There were no patients with respiratory depression or urinary retention. Nausea, vomiting and pruritus were rare in both groups without differences in their presentation.

Conclusion:

Reducing the dose of ITM to 50 μg retained the postoperative analgesic effect, maintaining a low incidence of side effects.