Statistical analysis
All statistical analyses were performed in R version 4.0.3. For all outcomes bar post-operative introduction of nasogastric tube, mean difference (MD) was used as a treatment estimate and standard error of the mean was deployed as the standard error of treatment estimate. Since outcomes were reported in widely different ways, we reformatted them to MD when needed using the following rules. If the means in each treatment group were available, MD was calculated as the difference between the two means. If median and range were present, we used the formula proposed by Hozo et al. to calculate the means in each group10. If range and IQR were available, we used the formula Mean = (Quartile 1 + Median + Quartile 3) to calculate the means in each group. For post-operative introduction of nasogastric tube, we used the odd ratio (OR) as the unit of treatment effect. When none of the above was available, studies were excluded from analysis in this outcome. Since we aimed to compare pharmacological class treatment size rather than individual treatment or dose, we could not use the multi-arm studies option of network meta-analysis for studies comparing more than one dose of the same treatment to placebo. Therefore, we recalculated a common mean for all treatment arms to calculate the mean difference. The main analysis was a Bayesian network meta-analysis using the packages gemtc, rjags and the software JAGS. We used an identity-link for mean difference and a log-link for the OR. We performed 10e5 iterations with a thinning interval of 10 and a burn-in interval of 5000. Model convergence was assessed using density and trace plots. Results are presented as a network graph, a forest plot comparing each treatment with placebo, ranking probability as well as a surface under the curve cumulative ranking probabilities (SUCRA). As a sensitivity analysis, we performed a frequentist network meta-analysis using the package netmeta. We presented results as comparison to placebo and a matrix presenting both direct and indirect comparisons. Finally, publication bias was assessed for each outcome with a funnel plot and an Egger’s test.