Minimizing ICU Neurological Dysfunction With Dexmedetomidine-induced Sleep (MINDDS II)

Inclusion Criteria:

* Aged 60 years or older
* Scheduled to undergo a cardiac surgical procedure with cardiopulmonary bypass
* Planned postoperative admission to the intensive care unit (ICU)

Exclusion Criteria:

* Allergy or hypersensitivity to dexmedetomidine or the placebo study medication
* Preexisting diagnosis of Alzheimer's Disease or Related Dementia, severe cognitive impairment or delirium at baseline
* Severe liver failure (Child-Pugh score \> 5)
* Severe deficit(s) due to structural or anoxic brain damage
* Undergoing a surgical procedure requiring total circulatory arrest
* SARS-CoV-2 positive or symptomatic (e.g., fever, cough, loss of taste/smell)
* Blind, deaf, or unable to communicate in English
* Patients experiencing circumstances for which long-term follow-up might be difficult (e.g., homelessness, active psychotic disorder, or substance abuse)
* Co-enrollment in other interventional studies that, in the opinion of the site investigator and/or PI, might interfere with study participation, collection, or interpretation of the study data