Abstract
BACKGROUND: Delirium is common in hospitalised older adults and is associated with mortality. Whether this prognostic association varies by baseline cognition is uncertain. We evaluated the association between delirium and 90-day mortality and whether baseline cognitive status modified this relationship. METHODS: We conducted a prospective, multicentre cohort study of adults aged ≥65 years admitted to 43 hospitals in five countries (Brazil, Angola, Chile, Colombia and Portugal; June 2022-December 2023). Delirium was assessed using the Confusion Assessment Method; cognitive status was measured using an informant-based Clinical Dementia Rating (CDR). Mortality within 90 days of admission was ascertained from hospital records, structured telephone follow-up by blinded assessors and registry linkage. We used mixed-effects survival models with random intercepts (state/province and study centre) and sequential adjustment for sociodemographic, clinical and hospital-related factors. Effect modification by CDR was examined with stratified analyses. RESULTS: Among 2556 patients (mean age 79 ± 9 years; 56% women), delirium occurred in 957 (37%). Delirium frequency rose with worsening cognition (CDR 0: 16%; CDR 0.5: 27%; CDR 1: 59%; CDR 2-3: 77%; P < .001). Delirium was associated with higher 90-day mortality (adjusted HR = 3.45; 95% CI = 2.83-4.20). The relative association with mortality was greatest in no dementia and attenuated in moderate-severe dementia. At 90 days, cumulative mortality was 54% with delirium vs. 15% without in CDR 0 (HR = 4.40; 95% CI = 3.15-6.16) and 36% vs. 17% in CDR 2-3 (HR = 2.22; 95% CI = 1.34-3.66). Patients with delirium also experienced more in-hospital complications (nosocomial infection, functional decline and prolonged stay). CONCLUSIONS: Although delirium was more frequent among patients with dementia, its relative association with 90-day mortality was strongest in those with no baseline dementia. The results provide a strong rationale for intervention trials to determine whether delirium prevention and management strategies can reduce mortality, particularly among patients without known dementia.