Ten RCTs were included in the meta-analysis (n=442 women). Four trials compared epidural morphine with placebo, and six compared epidural morphine with parenteral morphine. The median quality score was 4 points (range 2 to 5).
The pooled analysis of six trials revealed a mean time to request for a rescue analgesic after caesarean section in the epidural morphine group was 19 hours (range 5.4 to 29.2) compared with 3.4 hours (range 2.0 to 4.4) in the parenteral opioid group (Emax 29.7 hours, 95% CI 25.2 to 33.9). Increasing the dose of epidural morphine corresponded with an increase in time to request, but with a ceiling effect at 30 hours.
There was a statistically significant linear relationship between epidural morphine dose and rescue parenteral morphine request during the first 24 hour postoperative period (five trials). VAS scores were lower for epidural morphine in all five trials reporting data (four trials at six hours; two trials at 12 hours; and one trial at 24 hours).
Statistically significant adverse effects relating to epidural morphine at doses between 2mg and 8mg were reported for postoperative nausea (RR 1.95, 95% CI 1.17 to 3.26; six trials) and pruritus (RR 2.71, 95% CI 2.05 to 3.58; nine trials).