As survival rates from critical illness improve, strategies to return patients to their baseline cognitive and functional status are important research priorities. Up to 100% of ICU survivors will suffer some degree of cognitive impairment at hospital discharge and approximately 50% will have decrements that persist for years. While the mechanisms for this newly acquired brain injury are poorly understood, several risk factors have been identified. Unfortunately, it is unclear how to accurately predict long-term cognitive impairment.

Immediate opportunities to improve cognitive outcomes through risk reduction exist. The investigators propose to comprehensively study the prevalence of sleep abnormalities and their association with cognitive impairment, as it may yield potential targets for effective therapy. Moreover, the investigators will examine for gene x environment associations [APOE ε4] that may allow for genetic risk stratification of individuals at greatest risk of cognitive impairment. The investigators hypothesize that EEG [a sensitive longitudinal marker of brain dysfunction] is a novel and independent predictor of long-term cognitive impairment, and possibly a candidate intermediate end point for future clinical trials.

This study has the potential to identify novel biomarkers and risk factors for post-critical illness cognitive impairment, and may lay the foundation for rational interventions to mitigate risk in high-risk individuals.

Inclusion Criteria:

• ≥16 years of age
• Admission to study ICU for invasive mechanical ventilation [minimum of 72 hours]

Exclusion Criteria:

• Advanced cognitive impairment or unable to follow simple commands before their acute illness [e.g. end-stage Alzheimer's disease]
• Primary neurological injury [e.g. anoxic brain injury, stroke or traumatic brain injury]
• Anticipated death within 3 months of discharge [e.g. palliative]
• Uncontrolled psychiatric illness at hospital admission
• Not fluent in English
• Unlikely to adhere with follow-up [e.g. no fixed address]
• Residence greater than 300 kms from referral centre

Critically ill individuals who require mechanical ventilation for one week or greater