Effect size and event rate estimation is necessary for sample size calculation in randomised clinical trials. Overestimation of the effect size and event rate can lead to inadequately powered studies and increased probability of false negative results. This is common in trials involving critically ill patients. However, such overestimation has not been systematically evaluated in trials involving neurocritical care. We aimed to conduct a systematic review of published randomised clinical trials involving critically ill neurological patients, to determine the accuracy of effect size and event rate estimation.

We will review randomised clinical trials involving adult critically ill neurological patients that were published from 2015 onwards in selected clinically useful and high-impact journals. We will include randomised clinical trials reporting a binary or time to event outcome, using two study groups, and a superiority design testing the efficacy of diagnostic, monitoring, therapeutic or process interventions. All eligible studies must report an estimated event rate in the control group and estimated effect size. All relevant studies will be identified through database searches. All study selection and data extraction will be conducted by two independent reviewers. We will use a random-effects model for pooling data. This review will be conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses reporting guidelines. Accuracy of effect size and event rate estimation will be evaluated by comparing the estimated and observed values. The association between the accuracy of the individual randomised clinical trial effect size and event rate estimation and rejection of the null hypothesis will be evaluated using logistic regression analysis. Multivariable linear regression analysis will be used to explore the factors associated with accuracy of effect size and event rate estimation. In addition, we will perform subgroup analysis by impact factor of the published journals, sample size of the studies and risk of bias.

As this systematic review will use data from previously published studies, it does not require ethics approval. Findings of this systematic review will be published in a peer-reviewed journal and will be presented at specialty-based conferences. The study will be included in the higher degree research thesis of the primary author.

CRD420251106394.

Postoperative pulmonary complications (PPCs) represent a significant cause of postoperative morbidity and even mortality. However, there is a lack of consensus regarding this composite endpoint, the definition of the individual components, classification and optimal outcome measures. This study aims to refine the PPCs composite framework by evaluating its construct validity, assessing the necessity and risks of a composite measure and exploring the feasibility of differentiating severity categories.

A Delphi consensus process will be conducted, engaging an international multidisciplinary group of 30–40 panellists, including clinicians, researchers, patients, public representatives and health economists. Through iterative rounds, the study will seek agreement on the individual components of the PPCs composite. Additionally, consensus will establish a framework for a composite outcome measure based on a standardised severity classification, appropriate timeframes and weighted grading of PPCs.

Consensus, defined by ≥75% concurrence in multiple choice questions or on Likert–scale statements, will be evaluated from round 2 onwards. Delphi rounds will be continued until all statements have reached stability of responses evaluated by ² tests or the Kruskal-Wallis test.

The study will be conducted in strict compliance with the principles of the Declaration of Helsinki and will adhere to ACCORD guidance for reporting. Ethics approval has been obtained for this study from the University of Wolverhampton, UK (SOABE/202425/staff/3). Informed consent will be obtained from all panellists before the commencement of the Delphi process. The results of the study will be published in a peer–reviewed journal with the authorship assigned in accordance with ICMJE requirements.

NCT06916598 (clinicaltrials.gov).