Procedures involved in the Research When patients are diagnosed with a critical illness such as shock or respiratory failure, they are treated with intravenous fluids, medications to raise their blood pressure, and can be placed on a ventilator to assist with their breathing. They are observed in an intensive care unit (ICU). This research protocol does NOT interfere with the normal treatment of patients with critical illness. The procedure involved in this research protocol requires the placement of two stickers to either side of the patient's forehead, and information about oxygen delivery to the brain will be recorded. When the patient has recovered from the critical illness, they will be asked to perform several neurological tests. Some of these tests will be done with a pencil and paper, while others will use a robotic device to test arm movements, reaction time, and concentration.