CORE-ALI: protocol for a pan-European mixed-methods study to develop a core outcome set for acute lower limb ischaemia.

BACKGROUND: Acute lower limb ischaemia (ALI) is a life- and limb-threatening vascular emergency requiring urgent intervention. Despite advancements in therapeutic strategies, outcome reporting for ALI remains inconsistent, limiting evidence synthesis and guideline development. The CORE-ALI study aims to develop a Core Outcome Set (COS) to standardise outcome reporting and ensure the inclusion of both clinical and patient-centred metrics. METHODS: CORE-ALI will use a structured, multi-phase methodology guided by the Core Outcome Measures in Effectiveness Trials (COMET) initiative and the Core Outcome Set-STAndards for Reporting (COS-STAR) guidelines. Phase 1 involves stakeholder engagement through semi-structured interviews with patients, clinicians and policymakers from diverse European healthcare systems. Qualitative data will be analysed using thematic analysis to generate a preliminary list of outcomes. In Phase 2, a multi-round Delphi survey (anticipated two to three rounds) will prioritise and refine outcomes through consensus building, with quantitative data analysed using descriptive and non-parametric statistical methods. Phase 3 will culminate in a consensus meeting to finalise the COS. Multilingual accommodations will ensure inclusivity, and General Data Protection Regulation (GDPR)-compliant platforms will secure data handling. ETHICS AND DISSEMINATION: The study has received ethics approval from the Ethics Committee of the Medical University of Innsbruck (EK Nr: 1082/2025) on 20/05/2025. Additional local ethics approvals are required and will be obtained at all participating sites prior to the initiation of recruitment. The final Core outcome set will be disseminated through peer-reviewed publications, presentations at international conferences and engagement with professional societies and patient organisations. TRIAL REGISTRATION NUMBER: COMET initiative (Registration No. 3346).