BackgroundCognitive dysfunction is an important long-term complication of critical illness associated with reduced quality of life, increase in healthcare costs, and institutionalization. Delirium, an acute form of brain dysfunction that is common during critical illness has been shown to be associated with long-term cognitive dysfunction. The aim of this prospective cohort study was to estimate the prevalence and severity of cognitive dysfunction in an unselected population of medical and surgical ICU patients.MethodsThis prospective observational cohort study included all adult patients admitted to the surgical (13 beds) and medical (32 beds) ICUs of a tertiary hospital over a 12-month period. Patients with impaired cognition were excluded. At least 3 months after hospital discharge, patients were assessed for cognition using a validated battery of tests and were classified as having no cognitive impairment, mild to moderate cognitive impairment, or severe cognitive impairment.ResultsFour hundred thirteen patients were tested an average of 11 (3–18) months after discharge. Fifty-five (13.3%) patients included in the follow-up cohort had delirium. Cognitive impairment was identified in 206 (49.9%) patients, 120 (29.1%) patients had mild or moderate cognitive impairment, and 86 (20%) patients had severe cognitive dysfunction.ConclusionsThis investigation in an unselected and lower severity population of critically ill patients demonstrates that cognitive dysfunction is a frequent and severe long-term complication.