Delirium is an abrupt change in the brain that causes confusion. It is common when a patient is in the ICU, and it is one of the main predictors of having problems with thinking months or years after the illness has resolved. Unfortunately, the underlying cause of these problems is unknown. Changes in the function and structure of the brain, in particular inflammation, may be the cause. We are testing this question in patients enrolled in our studies by measuring the activity of 2 proteins (butyrylcholinesterase and acetylcholinesterase) in the blood to see if they will predict which patients have delirium or develop thinking problems after the hospital.