Impact of delirium and dementia on 30-day readmission to hospital by place of residence in older adults: ORCHARD-EPR cohort

Background: Cognitive frailty, defined as dementia, delirium or low cognitive test score, is prevalent in older in-patients. Current guidance (eg National Audit Dementia 2022) suggests hospital readmission as a performance metric in dementia care but reliable data are lacking. We therefore determined readmission risk by cognitive frailty status in care home residents vs those living at home.

Methods: ORCHARD-EPR (2017-2019) includes de-identified EPR data for patients ≥70 years with length of stay (LoS)≥1 day (2017–2019) admitted to four Oxfordshire, UK hospitals. Cognitive frailty was assessed using a standard cognitive screen mandated on admission comprising the 10-point Abbreviated Mental Test (AMT),  dementia, and delirium diagnosis informed by the  Confusion Assessment Method (CAM). Care home residence was determined by cross-referencing postal codes against Care Quality Commission repositories. Hazard ratios for 30-day readmission were adjusted for age, sex, comorbidity and illness severity.

Results: Among 28,590 patients (mean/SD age=81.8/7.4 years, 52% female), 3,569/26,596 (13%) were readmitted within 30 days of discharge: adjHR=1.18 (95% CI 1.07-1.30; 505/3,192 [16%], p<0.001) for delirium only, 1.17 (1.03-1.32; 301/1,993 [15%], p=0.013) for delirium on dementia, 1.10 (0.97-1.25; 279/1,930 [14%], p=0.13) for dementia only and 1.13 (0.93-1.38; 109/706 [15%], p=0.2) for low cognitive test score compared to no cognitive frailty (2,329/17,994 [13%]). After stratification by place of residence, in those living at home delirium but not dementia, predicted 30-day readmission: delirium alone adjHR=1.18 (95% CI 1.06-1.32; 411/2,1640 [16%], p=0.002), delirium on dementia 1.25 (1.08-1.45; 194/1,211 [15%], p=0.004), dementia alone (p>0.1). In contrast, cognitively frail vs robust patients previously resident in care homes had no increased risk of readmission (p>0.1).

Discussion: Only delirium in patients living at home prior to admission predicted 30-day readmission. Dementia alone was not associated with readmission irrespective of residence. Readmission may not therefore be a useful performance metric in assessing dementia care quality.