The design is a prospective cohort study of all people aged 65 years and over with an acute medical emergency admission to the Medical Admissions Unit (MAU) in one district general hospital in the Fife region of Scotland over an 2 year period.
Starting in 2009 and funded by the Scottish Government Joint Improvement Team, the NHS Fife Dementia Co-ordinating Group designed and implemented the Older Persons Routine Acute Assessment (OPRAA). OPRAA is based on the principles of “comprehensive geriatric assessment , with trained specialist nurses carrying out a structured assessment during the first 24 hours of admission, including an assessment of their functional ability at the time of admission and 3 months prior to admission, a cognitive assessment using the Abbreviated Mental test (AMT) ; the Confusion Assessment Method (CAM) for the presence of delirium ; an assessment of the presence of delirium based on clinical history, examination, and informant report; and documentation of the presence of a pre-admission diagnosis of dementia from self/informant report and/or hospital and primary care records.
All people aged 65 years and older admitted to the MAU were identified from Scottish Morbidity Records 01 (SMR01) data, which is a validated NHS Scotland routine dataset including age, sex, date of admission and discharge, type of admission, and whether the patient was admitted from a residential care or nursing home. The SMR01 dataset was then linked to the Community Health Index (CHI – the NHS Scotland patient register), the OPRAA dataset, SMR04 data on psychiatric admissions, CHI national mortality data and community dispensed prescribing data. Data linkage used the CHI number (the NHS Scotland unique patient identifier), and was carried out by the University of Dundee Health Informatics Centre (HIC). HIC Standard Operating Procedures have been reviewed and approved by the NHS East of Scotland Research Ethics Service and consent for research using this data was obtained from the NHS Fife Caldicott Guardian, based on researcher access only to anonymised data held in a secure safe haven that did not permit data export.
The OPRAA cohort is currently being used in a number of studies. Within the cohort the presence of a cognitive spectrum disorder is defined as one or more of known dementia diagnosed before admission, delirium and unspecified cognitive impairment. Dementia was defined as a reported dementia diagnosis in the OPRAA assessment, a prior community prescription of drug for dementia (anticholinesterase inhibitors or memantine), or a prior dementia diagnosis recorded in SMR01 or SMR04. Delirium was defined as both full syndromic delirium (a positive score on the CAM) or a clinical diagnosis of delirium made by the specialist nurses.
Mortality appears to be higher in patients with cognitive impairment following an emergency hospital admission, but the long-term implications on survival of the different patterns of cognitive impairment are less well known. This study evaluates the risk of mortality in the OPRAA cohort.
We defined ‘cognitive spectrum disorder’ as one or more of known dementia diagnosed before admission, delirium and unspecified cognitive impairment for those with Abbreviated Mental Test (AMT) score<8. A two-year follow-up of mortality for these patients was provided using linked national data.
A non-proportional hazards survival model with time varying coefficients was developed to appropriately estimate changes in mortality hazard ratios over time in people with different forms of cognitive spectrum disorders. Comparison of unadjusted hazard ratios estimates and estimates adjusted for model co-variates such as patient’s demographic characteristics and co-morbidities as well as ADL functions was performed.
In general, survival at 2 year follow up time was significantly lower in patients with any form of CSD as compared to patients with no CSD. The non-proportional hazard survival model adjusted for the demographic characteristics and co-morbidities, showed that patients admitted with delirium are at a significant increased risk of death during the 90 days after admission (HR=1.47, 95%CI 1.27-1.70) and 1 year after admission until the end of 2 year follow up time (HR=1.45, 95%CI 1.18-1.78), whereas they are at a lower and non-significant risk in the period 90 days to 1 year following admission (HR=1.20, 95%CI 0.99-1.45). In turn, patients with known dementia (either alone or superimposed on delirium) do not pose a significant risk of death in the first 90 days following admission (HR=1.04, 95%CI 0.84-1.29 and HR=1.20, 95%CI 0.97-1.44), but they become significantly at risk after the 90 days (HR=1.83, 95%CI 1.55-2.17 and HR=1.78, 95%CI 1.50-2.12 respectively). For patients with unspecified cognitive disorder, the risk of death becomes significantly higher only after 1 year from admission (HR=1.65, 95%CI 1.19-2.29). Finally, the survival model adjusted for ADL functions, managed to explain only partially the increased risk of death in patients with CSD.
Risk of death is high in those with CSD. Immediate high risk is worst in those with delirium while those with known dementia or unspecified cognitive impairment tend to have more medium to long term risk.
Hospital costs for patients with cognitive impairments in the OPRAA cohort
As part of the OPRRA project, this study examines the relationship between hospital service. As part of the OPRAA project, this study examines the relationship between hospital service costs and cognitive spectrum disorder (CSD) conditions. We use the Scottish Morbidity Record (SMR) data, which is linked with data from the Patient-level Information and Costing Systems (PLICS), to obtain an estimate of the associated hospital cost. Preliminary results obtained from ordinary least squares (OLS) regression models show that hospital services costs vary greatly among patients with different CSD conditions. Patients with delirium or dementia are more likely to generate higher total hospital costs within the same period compared with patients without cognitive impairment. However, their average day costs are significantly lower. This being said, we acknowledge that the OLS estimates are likely to underestimate the differences because patients with delirium or dementia are subject to higher mortality rates thus less time to accumulate costs over time. To deal with this problem, we will use a joint modelling approach for further analysis.