Delirium in the intensive care unit: occurrence and clinical course in older patients

OBJECTIVES: To describe the occurrence of delirium in a cohort of older medical intensive care unit (ICU) patients and its short-term duration in the hospital and to determine the association between preexisting dementia and the occurrence of delirium. DESIGN: Prospective cohort study. SETTING: Fourteen-bed medical ICU of an 800-bed university teaching hospital. PARTICIPANTS: One hundred eighteen consecutive patients aged 65 and older admitted to the ICU. MEASUREMENTS: Baseline characteristics were obtained through surrogate interviews and medical chart review. Dementia was determined using two validated surrogate-rated instruments. Delirium was assessed daily in the ICU using the Confusion Assessment Method (CAM) for the ICU (CAM-ICU). After discharge from the ICU, patients were followed for up to 7 days using the CAM. RESULTS: Delirium was present in 37 of 118 (31%) patients on admission. Only 45 patients had a normal mental status on admission, of whom 14 (31%) became delirious during their hospital stay. In the post-ICU period, delirium occurred in 40% of patients. Almost half of patients with delirium in the ICU had persistent delirium in the post-ICU period. Overall, 83 of 118 (70%) had delirium during hospitalization. Stupor or coma occurred in 44% of the patients overall, and 89% of survivors of stupor/coma progressed to delirium. Patients with dementia were 40% more likely to be delirious (relative risk = 1.4, 95% confidence interval = 1.1-1.7), even after controlling for comorbidity, baseline functional status, severity of illness, and invasive procedures. CONCLUSION: Delirium is a frequent complication in older ICU patients and often persists beyond their ICU stay. Delirium in older ICU persons is a dynamic and complex process. Dementia is an important predisposing risk factor for the development of delirium in this population during and after the ICU stay.