Delirium

Delirium, or acute confusional state, is severe confusion that develops quickly, and often fluctuates in intensity. It is a common neuropsychiatric syndrome with a core feature of acute onset, meaning it has been present from hours to days, but not months or years. Delirium represents an organically caused decline from a previously-attained level of cognitive functioning. Delirium typically appears suddenly with a readily-identifiable time of onset, such as a time space of a few hours, or overnight. It is typified by fluctuating course, attentional deficits and generalized severe 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 clinical syndrome (a set of symptoms), which result from an underlying disease or new problem with mentation.

It is a corollary of the criteria that a diagnosis of delirium cannot be made without a previous assessment, or knowledge, of the affected person's baseline level of cognitive function. In other words, a mentally disabled or demented person who is operating at their own baseline level of mental ability would be expected to appear delirious without a baseline mental functional status against which to compare.

Delirium may be caused by a disease process outside the brain that 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 symptomatic manifestation of new organic brain dysfunction (for any reason). Delirium requires both a sudden change in mentation, and an organic cause for this. Thus, 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 treatment of the underlying organic cause(s). In some cases, temporary or palliative or symptomatic treatments are used to comfort patients or to allow better patient management (for example, a patient 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 hospitalized patients and up to 80% of ICU patients. In ICU patients or in other patients requiring critical care, delirium is not simply an acute brain disorder but in fact is a harbinger of much greater likelihood of death within the 12 months which follow the ICU patient's hospital discharge.