Evidence-based recommendations for blinding in surgical trials

Rationale Blinding reduces performance and detection bias in randomized controlled trials (RCT). There is evidence that lack of blinding leads to overestimation of treatment effects in pharmacological trials. Since surgical trials use interventions with a physical component, blinding is often complicated. The aim of this study was to analyze, in general and abdominal surgery RCT, the status of blinding, the potential for blinding, and the influence of blinding on outcomes. Methods A systematic search of the literature in CENTRAL, MEDLINE, and Web of Science was conducted to identify RCT with a surgical intervention, starting in 1996, the year when the first CONSORT statement was published. Information on general study characteristics and blinding methods was extracted. The presence or absence of blinding of the study contributors—patients, surgeons, data collectors, outcome assessors, and data analysts—was analyzed. The association of blinding with the trial outcome was investigated for every study contributor. Results Out of 29,119 articles, 378 RCT were included in the analysis. These investigated a total of 62,522 patients, of whom 15,025 were blinded (24.0%). Contributors could have been blinded in far more trials, as the potential for blinding measures ranged from 69% for outcome assessors to 98% for data analysts. If blinding of surgeons would have been possible but had not been performed, this was associated with more significant trial outcomes (OR 13.670; 95% CI 1.308 to 142.840; p = 0.0289). Discussion The potential of blinding, an important quality measure in surgical RCT, has not been exhausted. This study summarizes the existing evidence on blinding in surgical trials and gives evidence-based recommendations for the use of blinding in future surgical trials. Systematic review registration PROSPERO 2015:CRD42015026837.