Eight RCTs (768 patients) were included in the review. All trials were blinded and were free of selective reporting. Seven trials addressed incomplete data, one trial had adequate allocation concealment and seven had inadequate allocation concealment. Six trials had adequate sequence generation and two were unclear.
Postoperative vomiting and nausea: Dexamethasone statistically significantly reduced the incidence of postoperative nausea compared to placebo (RR 0.57, 95% CI 0.45 to 0.72; eight RCTs; NNT=six) and postoperative vomiting compared to placebo (RR 0.56, 95% CI 0.43 to 0.72; seven RCTs; NNT=seven). Dexamethasone doses of 5mg, 8mg and 10 mg showed statistically significant reductions for both outcomes but the 2.5mg dose did not. There was no evidence of statistical heterogeneity for either outcome.
Meta-regression showed no evidence of a dose-response relationship for either outcome. Subgroup analyses did not significantly alter the findings except for studies in which intrathecal morphine was administered which showed no statistical difference between treatment groups for either outcome.
Postoperative rescue treatment: Dexamethasone statistically significantly reduced use of postoperative rescue antiemetic therapy compared to placebo (RR 0.47, 95% CI 0.36 to 0.61; eight RCTs; figures as reported in the text) and postoperative rescue analgesics compared to placebo (RR 0.76, 95% CI 0.62 to 0.93; eight RCTs). There was no evidence of statistical heterogeneity.
Other secondary outcome and subgroup analyses results were reported in the review. There was evidence of publication bias for both postoperative vomiting and nausea according to funnel plots and Egger’s test.