Delirium is a state of mental confusion which develops quickly and usually fluctuates in intensity. Rather than being a specific disease, delirium is a syndrome, or group of symptoms, caused by a disturbance in the normal functioning of the brain. The delirious patient has a reduced awareness of and responsiveness to the environment, which may be manifested as disorientation, incoherence, and memory disturbance. Delirium is often marked by hallucinations, delusions, and a dream-like state.

Delirium affects at least one in ten hospitalized patients, and is a common part of many terminal illnesses. Delirium is more common in the elderly than in the general population. While it is not a specific disease itself, patients with delirium usually fare worse than those with the same illness who do not have delirium.

There are a large number of possible causes of delirium. Metabolic disorders are the single most common cause, accounting...