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  • Clinical diagnosis based on detailed history, cognitive assessment, and physical and neurologic examination.

  • The pathognomonic feature is an acute change in baseline mental status developing over hours to days.

  • Other key features include fluctuating course with an increase or decrease in symptoms over a 24-hour period; inattention, with difficulty focusing attention; and either disorganized thinking, such as rambling or incoherent speech, or altered level of consciousness (vigilant or lethargic).

  • Perceptual disturbances, such as hallucinations, or paranoid delusions present in approximately 15% to 40% of cases.

  • Search for organic or physiologic causes (eg, illness, drug related, or metabolic derangement).

  • Delirium is often misdiagnosed as dementia, depression, or psychosis.

  • Accepted delirium criteria provided by Confusion Assessment Method.


Delirium is an acute disorder of attention and cognitive function that may arise at any point in the course of an illness. It is often the only sign of a serious underlying medical condition, especially in older persons who are frail or who have underlying dementia. Delirium can result in serious clinical outcomes, such as functional decline, cognitive impairment, dementia, and decreased quality of life; delirium also results in significant caregiver burden and health care expenditures.

The prevalence of delirium on admission can range from 10% to 40%. During hospitalization, it may affect an additional 25% to 50%. Delirium is the most common postoperative complication among older adults, with rates estimated at 15% to 52%. Even higher rates (70%–87%) are seen in intensive care units (ICUs). In addition, 80% of terminally ill patients become delirious before death.

Three forms of delirium have been recognized: the hyperactive, hyperalert form; the hypoactive, hypoalert, lethargic form; and the mixed form, which combines elements of both. The hypoactive form is often unrecognized but more common among older hospitalized patients; it is associated with a poorer overall prognosis. Delirium can range from mild to severe, with increased severity associated with worse outcomes.

Delirium as a geriatric syndrome is inherently multifactorial and develops as a result of interactions between predisposing risk factors and noxious insults or precipitants. Thus, it is imperative that clinicians identify and address all potential factors and observe patients closely for resolution.


The major predisposing risk factor for delirium is preexisting cognitive impairment, specifically dementia, which increases the risk of delirium two- to five-fold. Virtually all chronic medical illnesses can predispose older persons to delirium, as can specific neurologic and metabolic disorders. A full list of risk factors is included in Table 36–1.

Table 36–1.Risk factors and precipitating factors for delirium.

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