The effect of blinding on estimates of mortality in randomised clinical trials of intensive care interventions: protocol for a systematic review and meta-analysis

INTRODUCTION: Evidence exists that unblinded randomised clinical trials (RCTs) overestimate intervention effects compared with blinded RCTs. It has been suggested that this is less pronounced for objective (ie, not subject to interpretation) outcome measures, including mortality. This may not apply in the intensive care unit (ICU), as most deaths are preceded by decisions to withhold or withdraw treatments. Lack of blinding of physicians in RCTs of ICU interventions may potentially influence the decision towards a higher threshold for discontinuing treatment in patients who receive the investigational treatment and/or a lower threshold for discontinuing treatment in patients who receive the comparator (control). This may have important implications for patients, caregivers, researchers and society. Accordingly, we aim to assess whether lack of blinding affects mortality effect estimates in RCTs of ICU interventions. METHODS AND ANALYSIS: We will conduct a systematic review with meta-analyses and assess the effect of blinding versus no blinding on mortality effect estimates in RCTs of interventions used in adult ICU patients. We will systematically search the Cochrane Library for systematic reviews reporting mortality effect estimates of any intervention used in adult ICU patients which includes at least one RCT with ‘low risk of bias’ in the bias domains ‘blinding of participants and personnel’ and/or ‘blinding of outcome assessment’ and one RCT with ‘unclear’ or ‘high risk of bias’ in the same bias domain(s). For each intervention, we will compare summary mortality effect estimates in blinded versus unblinded trials. ETHICS AND DISSEMINATION: This research does not require ethical approval as we will use summary data from trials already approved by relevant ethical institutions. We will report the results in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement and submit the final paper to an international peer-reviewed journal. TRIAL REGISTRATION NUMBER: PROSPERO, registration number: CRD42017056212.