Inclusion Criteria:  Baseline normal neurological function pre-operatively. Planned use of mechanical ventilator with endotracheal tube post-operatively after planned cardiothoracic surgical procedure.  Exclusion Criteria:  Chronic dementia, Alzheimer's disease, or other chronic neurological disease (i.e., Bi-Polar). Chronic use of neurological altering medications such as benzodiazepines, psychotropic, anti-depressants, anxiolytics. Patient undergoing emergent surgery. Use of post-operative cardiopulmonary support devices such as ECMO (extracorporeal membrane oxygenation), intra-aortic balloon pump, total artificial heart, or other similar device.