Objectives: to inform development of a core outcome set, we evaluated outcomes, definitions, measures and measurement time points in clinical trials of interventions to prevent and/or treat delirium in older adults resident in long-term care (LTC).

Data sources: we searched electronic databases, systematic review repositories and trial registries (1980 to 10 December 2021). STUDY SELECTION AND

Data extraction: we included randomised, quasi-randomised and non-randomised intervention studies. We extracted data on study characteristics, outcomes and measurement features. We assessed outcome reporting quality using the MOMENT study scoring system. We categorised outcomes using the Core Outcome Measures in Effectiveness Trials taxonomy.

Data synthesis: we identified 18 studies recruiting 5,639 participants. All evaluated non-pharmacological interventions; most (16 studies, 89%) addressed delirium prevention. We identified 12 delirium-specific outcomes (mean [SD] 2.4 [1.5] per study), of which delirium incidence (14 studies, 78%) and severity (6 studies, 33%) were most common. We found heterogeneity in description of outcomes and measurement time points. The Confusion Assessment Method (three versions) was the most common measure used to ascertain delirium incidence (7 of 14 studies, 50%). We identified 25 non-delirium specific outcomes (mean [SD] 4.0 [2.3] per study), with hospital admission the most commonly reported (9 studies, 50%).

Conclusions: we identified few studies of interventions for the prevention or treatment of delirium in older adults resident in LTC. These studies were heterogeneous in the outcomes reported and measures used. These data inform the consensus-building stage of a core outcome set.