Background Delirium is a serious problem that can occur in many older people admitted to hospital. Delirium has the potential to dramatically complicate the hospitalisation of a patient, and often results in functional decline, an increased likelihood of complications associated with longer hospital stays, increasing the risk of admission to a care facility post discharge, a greater incidence of falls and is associated with high mortality and morbidity rates. Understanding the factors that contribute to delirium can provide insights into the mechanisms that underlie the syndrome. Objectives The primary focus of this systematic review was to synthesise the best available evidence to determine which risk factors are most strongly related to the development of incident delirium in medical patients. Types of participants Adults who were admitted to a medical setting (eg general medical units, stroke units, short stay units and neuro-medical units) who were not delirious on admission but who developed incident delirium during hospitalisation. Types of intervention(s)/phenomena of interest This review considered studies that evaluated any risk factors that might have contributed to the development of delirium during in-patient hospitalisation. Types of studies This review considered any high quality quantitative papers that addressed factors causing incident delirium in medical patients. Types of outcomes This review considered studies that included the incidence of delirium as related to individual risk factors. Search strategy A three-step search strategy was utilised using identified keywords and MeSH (Medline Subject Headings). References lists of all identified studies were examined. All searches were limited to studies published between 1996 and 2012 in English. Methodological quality The Joanna Briggs Institute Critical Appraisal Checklist for Cohort/Case Control Studies was used to assess methodological quality. Data collection Data were extracted using the standardised data extraction tool from the Joanna Briggs Institute. Data synthesis Meta analysis was conducted for the following risk factors: dementia, male sex, age greater than 80, pneumonia and visual impairment. The remainder of results were presented in a narrative summary. Results Nine papers were included in this review. Factors which were common across the papers were included in the results. Dementia and cognitive impairment had the greatest association with delirium and were also the most commonly investigated. Other factors such as functional impairment, severe illness and visual impairment also had a moderate association with delirium. Conclusions The most significant risk factors in the medical population were dementia and cognitive impairment. The age of all the patients was not significantly related to delirium development, suggesting that factors that generally occur in the medical population such as visual impairment, functional impairment and cognitive impairment play a more significant role in incident delirium in the medical population. Implications for practice All elderly people must be screened on admission for cognitive impairment and the diagnosis of dementia needs to be recognised as a significant risk factor for delirium, hence appropriate interventions must be put in place for these individuals. Family members of patients identified as high risk need to be made aware of the patient's increased risk of delirium. Furthermore, risk factor assessment should be carried out on all patients admitted to an acute medical setting. Implications for research Future research should investigate delirium risk factors, in particular, settings, as well as separating incident from prevalent delirium (delirium present on admission) in order to find factors that only relate to incident delirium. © the authors 2013.
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