Fourteen RCTs were included (796 patients): 11 trials of adults, two trials of children and one trial of adults and children.
Compared with IV-PCA with demand dose only, addition of a background infusion to the demand dose for IV-PCA with opioids was significantly associated with an increased rate of respiratory depression (OR 4.68, 95% CI 1.20 to 18.21; 14 RCTs). Moderate heterogeneity was found for this outcome (Ι²=49.5%). There were no significant differences between treatment groups in terms of the rates of pruritis (seven RCTs) and sedation (four RCTs) with no significant heterogeneity observed in the two outcomes.
Subgroup analyses showed similar results on the rate of respiratory depression in adults (OR 10.18, 95% CI 2.97 to 34.89; 11 RCTs, 674 participants) but there was no significant difference between treatment groups for studies in children (OR 0.68, 95% CI 0.16 to 2.96; three RCTs, 122 participants). No significant heterogeneity was observed in these outcomes.
Data on other outcomes (pain, postoperative nausea and vomiting and opioid consumption) were too heterogeneous to permit pooling. However, eight out of 10 trials studies reported a significant increase in the use of morphine in the groups that received a background infusion.