Basic Facts

What is Delirium?

Delirium is a term that means “sudden confusion.” it refers to an abrupt, rapid change in mental function that goes well beyond the typical forgetfulness of aging.  This syndrome has also been called acute confusional state, toxic psychosis, metabolic encephalopathy, or acute organic brain syndrome.  Delirium is a result of abnormal functioning of the brain.

We all have minor problems with memory and understanding as we get older.  We forget names or take more time to figure out directions.  These problems are a normal part of aging for everyone. But some older adults develop extreme problems with remembering, understanding, or thinking. For example, they can get lost walking to the bathroom, become confused by simple tasks, forget the names of loved ones, and have trouble speaking in a logical way. These problems can be very difficult to cope with, not only for the person affected, but also for their family, friends, and other caregivers.

Many of the characteristics of delirium are the same as those for dementia, but delirium develops far more suddenly and is more often reversible when its causes are identified and treated.  The differences between these two conditions are described more fully later in this chapter. People with dementia are also at high risk of developing delirium, and the two conditions often occur together. Whenever the behavior or thinking of a person with dementia suddenly gets much worse, particularly if the person is sick or in hospital, the cause is likely to be delirium.

A sudden change in mental function in an older person is a serious situation that requires the attention of a healthcare professional.

Types of Delirium

Delirium usually occurs in two forms:

  1. A hyperactive form, in which patients are agitated, have increased arousal, or are very vigilant, or
  2. A hypoactive form in which patients are lethargic, sleepy, move less than usual, and have little awareness of their surroundings. 

Often, doctors and nurses in a hospital are not aware that an older patient is suffering from delirium because the patient becomes less active (hypoactive), rather than more restless (hyperactive). The hypoactive (“quiet”) form is more common, occurring in up to 75% of patients with delirium, and may be mistaken for depression. Some studies suggest that the prognosis for hypoactive delirium may be worse than the prognosis for hyperactive delirium, possibly because hypoactive delirium is less frequently recognized and less likely to be investigated promptly.

Sometimes, the hyperactive and hypoactive forms switch fairly quickly, so that a delirious person cycles between lethargy and agitation within a single day.

How Common is Delirium?

Delirium occurs frequently especially in older people.  Hospital records show that one-third of older adults who arrive at emergency departments are delirious.   For most older adults, the risk of delirium increases with age.

For older adults in the hospital, delirium is one of the most common complications that can happen during a medical illness or following an operation.  Approximately one-third of patients over age 70 who are admitted to the hospital experience delirium, and about two-thirds of older people experience delirium after major surgery.

Residual symptoms of delirium are present in about half of hospital patients transferred to a nursing home, and about two-thirds of patients who are residents of nursing homes. About 80% of people suffer from delirium at the end of life. 


Last Updated September 2017