Intrathecal morphine 100 and 200 μg for post-cesarean delivery analgesia: a trade-off between analgesic efficacy and side effects

Abstract Introduction Intrathecal morphine is highly effective for post-cesarean analgesia; however, the optimal dose is yet to be established. The aim of this study was to compare analgesia and side effects after a change in institutional practice to give 200 μg rather than 100 μg. Methods We conducted a retrospective chart review of 241 patients who had an elective cesarean delivery and received either 100 or 200 μg of intrathecal morphine. The primary outcome variables were mean and peak verbal pain scores (0–10) and analgesic use (milligram-morphine equivalents). Postoperative administration of antiemetics, antipruritics and episodes of nausea or vomiting were recorded. Data are reported as mean ± SD or percentages with P < 0.05 considered statistically significant. Results Women receiving intrathecal morphine 200 μg had lower pain scores and opioid use compared with morphine 100 μg. Mean verbal pain scores were 1.6 ± 1.1 versus 2.0 ± 1.1 ( P = 0.01) and peak verbal pain scores were 4.9 ± 2.0 versus 5.6 ± 1.8, respectively ( P = 0.008). The group receiving 200 μg used less opioids in the first 24 h after surgery (44 ± 35 versus 54 ± 35 milligram-morphine equivalents, respectively, P = 0.04) and received less intravenous opioids (18% versus 30%, P = 0.02). However, women receiving intrathecal morphine 200 μg had more nausea (mean number of episodes of nausea 1.9 ± 1.3 versus 1.6 ± 1.3, P = 0.037) and used more antiemetics (52% versus 24%, P < 0.0001). Conclusions Intrathecal morphine 200 μg provided better analgesia but with more nausea compared with morphine 100 μg. Our results can be used to help guide intrathecal morphine dosing in cesarean delivery based on patient preference for analgesia versus side effects.