Delirium, also known as acute confusional state, is an organically caused decline from a previously baseline level of mental function. It often varies in severity over a short period of time, and includes attentional deficits, and disorganization of behavior. It typically involves other cognitive deficits, changes in arousal (hyperactive, hypoactive, or mixed), perceptual deficits, altered sleep-wake cycle, and psychotic features such as hallucinations and delusions. Delirium itself is not a disease, but rather a set of symptoms. It may result from an underlying disease, over-consumption of alcohol, from drugs administered during treatment of a disease, withdrawal from drugs or from any number of health factors. Delirium may be caused by a disease process outside the brain that nonetheless affects the brain, such as infection (urinary tract infection, pneumonia) or drug effects, particularly anticholinergics or other CNS depressants (benzodiazepines and opioids). Although hallucinations and delusions are sometimes present in delirium, these are not required for the diagnosis, and the symptoms of delirium are clinically distinct from those induced by psychosis or hallucinogens (with the exception of deliriants.) Delirium must by definition be caused by an organic process, i.e., a physically identifiable structural, functional, or chemical problem in the brain (see organic brain syndrome), and thus, fluctuations of mentation due to changes in purely psychiatric processes or diseases, such as sudden psychosis from schizophrenia or bipolar disorder, are (by definition) not termed delirium. Like its components (inability to focus attention, mental confusion and various impairments in awareness and temporal and spatial orientation), delirium is the common manifestation of new organic brain dysfunction (for any reason). Delirium requires both a sudden change in mentation, and an organic cause for this. Delirium may be difficult to diagnose without the proper establishment of a person's usual mental function. Without careful assessment and history, delirium can easily be confused with a number of psychiatric disorders or long term organic brain syndromes, because many of the signs and symptoms of delirium are conditions also present in dementia, depression, and psychosis. Delirium may newly appear on a background of mental illness, baseline intellectual disability, or dementia, without being due to any of these problems. Treatment of delirium requires treating the underlying cause, and multi-component interventions are thought to be most effective. In some cases, temporary or palliative or symptomatic treatments are used to comfort the person or to allow other care (for example, a person who, without understanding, is trying to pull out a ventilation tube that is required for survival). Delirium is probably the single most common acute disorder affecting adults in general hospitals. It affects 10-20% of all hospitalized adults, and 30-40% of elderly who are hospitalized and up to 80% of those in ICU. Among those requiring critical care, delirium is a risk for death within the next year. Antipsychotics are not supported for the treatment or prevention of delirium among those who are in hospital. When delirium is caused by alcohol or sedative hypnotic withdrawal, benzodiazepines are typically used.