Inclusion and exclusion criteria
The studies included were randomised controlled trials comparing at least two different therapies for the treatment and prevention of POI. The treatments studied were medicinal treatments. We excluded all non-medicinal interventions. Studies focusing on peri-operative protocol management were excluded (e.g. early rehabilitation measures on post-operative course, enhanced recovery pathways, surgical techniques). Also excluded were paediatric surgical studies (patients under 18 years of age), observational studies, reviews, congress abstracts, letters to the Editor and articles not written in English. The Cochrane Collaboration tool for assessing risk of bias in randomised controlled trials was utilised to assess quality of studies7. Studies with a high risk of bias in one domain (randomisation, deviations from intended intervention, missing outcome data, measurement of outcome, selection of the reported results) and in the overall bias were excluded.