Intrathecal morphine 100 µg versus 150 µg for post-cesarean delivery analgesia: a retrospective cohort study...

In the context of multimodal analgesia, the optimal dose of intrathecal morphine (ITM) for post-cesarean analgesia remains unclear. In January 2022, the dose of ITM was reduced from 150 µg to 100 µg without other changes in our analgesic regimen with the assumption that ITM 100 µg provides comparable analgesia to ITM 150 µg with fewer opioid-related side effects.

In this retrospective cohort study including cases from January 2020 through October 2022, we identified all cesarean delivery cases with a neuraxial technique with ITM. The primary outcome was oral opioid use in the first 24 hours. Opioid use in oral morphine equivalents (OME) was compared using zero-inflated negative binomial models, and antiemetic and antipruritic use was compared using logistic regression models.

There were 3293 cases included in the analysis (1689 with ITM 150 µg and 1604 with ITM 100 µg). There was no significant difference between the groups in the primary outcome of opioid consumption in the first 24 hours in both the unadjusted and adjusted analysis [mean ratio (95% CI) = 1.03 (0.96 to 1.11); P = 0.373]. With ITM 100 µg, antiemetic use was less likely [OR = 0.65 (0.55 to 0.76)] and so was treatment for pruritus [OR = 0.16 (0.12 to 0.21)] compared with ITM 150 µg.

When used with multimodal analgesia, a lower ITM dose of 100 µg provided comparable analgesia with lower incidence of opioid-related side effects compared with an ITM dose of 150 µg.