Delirium in the hospitalized elder and recommendations for practice.

Delirium is a mental disorder of acute onset and fluctuating course, characterized by disturbances in consciousness, orientation, memory, thought, perception, and behavior. It occurs in up to 50% of elderly hospital inpatients, many with preexisting dementia, and is associated with significant increases in functional disability, length of hospital stay, rates of death, and health care costs. Despite its clinical importance, delirium often remains undetected or misdiagnosed as dementia or other psychiatric illness.