Delirium prevention in Danish Nursing Homes (Delis-H): a complex intervention protocol with realist evaluation

Background: Delirium is common among older patients and is associated with functional decline, acceleration of dementia and mortality. While multicomponent prevention programs are developed and tested in hospital settings, evidence for nursing homes remains limited. Methods: Delis-H is a three-year mixed-methods project guided by the Medical Research Council (MRC) framework, comprising three interrelated studies: (1) co-creation and feasibility testing of a delirium prevention intervention, (2) a pragmatic non-randomised controlled evaluation across eight nursing homes, and (3) a realist evaluation of implementation and sustainability. Outcomes include hospital admissions, psychotropic medication use, mortality and delirium incidence, reported in accordance with SPIRIT guidance. Discussion: By detailing the study design, this protocol strengthens transparency and reproducibility and contributes to cumulative knowledge development on delirium prevention in nursing homes, with direct relevance for nursing practice. Trial registration: Open Science Framework (OSF) on 6 February 2026 (osf.io/f8b4k).