Delirium's Arousal Subtypes and Their Relationship with 6-Month Functional Status and Cognition.

OBJECTIVE: We sought to determine how delirium subtyped by arousal affected 6-month function and cognition in acutely ill older patients.

METHODS: This was secondary analysis of a prospective cohort study which enrolled hospitalized patients ≥65 years old. Delirium and arousal were ascertained daily in the emergency department and the first 7 days of hospitalization using the modified Brief Confusion Assessment Method and Richmond Agitation Sedation Scale, respectively. For each day, patients were categorized as having no delirium, delirium with normal arousal, delirium with decreased arousal, or delirium with increased arousal. Preillness and 6-month functional status were determined using the Older American Resources and Services activities of daily living scale which ranges from 0 (completely dependent) to 28 (completely independent). Preillness and 6-month cognition were determined using the Informant Questionnaire on Cognitive Decline in the Elderly which ranges from 1 (markedly improved cognition) to 5 (severe cognitive impairment). Multiple linear regression was performed adjusted for preillness Older American Resources and Services activities of daily living and Informant Questionnaire on Cognitive Decline in the Elderly and other relevant confounders.

RESULTS: In 228 older patients, delirium with normal arousal was the only subtype independently associated with poorer 6-month function and cognition. For every day spent in this subtype, the 6-month Older American Resources and Services activities of daily living decreased by 0.84 points (95% confidence interval: -1.59 to -0.09) and the patient's 6-month Informant Questionnaire on Cognitive Decline in the Elderly significantly increased by 0.14 points (95% confidence interval: 0.06-0.23).

CONCLUSIONS: Delirium with normal arousal, as opposed to delirium with decreased or increased arousal, was the only arousal subtype significantly associated with worsening 6-month function and cognition. Subtyping delirium by arousal may have important prognostic value.