The primary purpose of this proposal will be to identify potentially modifiable risk factors of long-term cognitive impairment (i.e. development of delirium and exposure to sedative and analgesic medications) in ICU patients. The investigators will quantify the independent contribution of these risk factors to the incidence of long-term cognitive impairment, controlling for other established risk factors including age, pre-existing cognitive impairment, and apolipoprotein E (apoE) genotype. Quantifying the contributions of these modifiable risk factors will pave the way for the development of preventive and/or treatment strategies to reduce the incidence, severity and/or duration of long-term cognitive impairment and improve functional recovery for patients with critical illness.