Factors associated with prolonged delirium: a systematic review.

BACKGROUND: Delirium frequently accompanies acute illness. With treatment of the illness, some individuals recover from delirium while for others the symptoms persist. It is not understood why some individuals improve but others do not. The purpose of this paper is to review systematically what is known about the factors associated with the persistence of delirium.
METHODS: A medical literature search was conducted using several bibliographic databases, supplemented by manual searches of the references. English or French studies were included if they compared two groups of delirious individuals in delirium duration or persistence up to six months after the onset of delirium, diagnosed prospectively with the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria (or a scale derived and validated against the DSM). Information was collected on the association between possible non-therapeutic prognostic variables and delirium persistence.
RESULTS: Twenty-one observational studies were included, in various settings (e.g. mixed medical-surgical, medical or geriatric, surgical, psychiatric, cancer or palliative care units). Variables assessed included patient characteristics (e.g. age, dementia, medical comorbidity, functional status), delirium characteristics (e.g. presence of hypoactive symptoms, delirium severity) and illness characteristics (e.g. severity of illness, and underlying acute illness). Overall, studies suggested that delirium is often persistent at discharge or beyond. Persistence was associated with dementia, increasing numbers of medical conditions, increasing severity of delirium, hypoactive symptoms and hypoxic illnesses.
CONCLUSIONS: Preliminary findings suggest that some factors may identify those at risk for persistent delirium; however, more research is needed.