Delirium etiology subtypes and their effect on six-month function and cognition in older emergency department patients

Background: Delirium is heterogeneous and can vary by etiology. Objectives: We sought to determine how delirium subtyped by etiology affected six-month function and cognition. Design: Prospective cohort study. Setting: Tertiary care, academic medical center. Participants: A total of 228 hospitalized patients > 65 years old were admitted from the emergency department (ED). Measurements: The modified Brief Confusion Assessment Method was used to determine delirium in the ED. Delirium etiology was determined by three trained physician reviewers using a Delirium Etiology checklist. Pre-illness and six-month function and cognition were determined using the Older American Resources and Services Activities of Daily Living (OARS ADL) questionnaire and the short-form Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE). Multiple linear regression was performed to determine if delirium etiology subtypes were associated with six-month function and cognition adjusted for baseline OARS ADL and IQCODE. Two-factor interactions were incorporated to determine pre-illness function or cognition-modified relationships between delirium subtypes and six-month function and cognition. Results: In patients with poorer pre-illness function only, delirium secondary to metabolic disturbance (beta coefficient = -2.9 points, 95%CI: -0.3 to -5.6) and organ dysfunction (beta coefficient = -4.3 points, 95%CI: -7.2 to -1.4) was significantly associated with poorer six-month function. In patients with intact cognition only, delirium secondary to central nervous system insults was significantly associated with poorer cognition (beta coefficient = 0.69, 95%CI: 0.19 to 1.20). Conclusions: Delirium is heterogeneous and different etiologies may have different prognostic implications. Furthermore, the effect of these delirium etiologies on outcome may be dependent on the patient's pre-illness functional status and cognition.