Delirium (also known as acute brain failure) is an acute syndrome characterized by impaired intellect, awareness and concentration. Typically, the cognitive impairment fluctuates throughout the day. In contrast to dementia, delirium tends to be reversible.


The number of synonyms for delirium is bewildering , and includes more modern terms, e.g. acute brain failure, acute brain syndrome, acute brain dysfunction, archaic terms, such as a dysergastic reaction, terms with a more psychiatric flavor, for example, exogenous psychosis, and those from a geriatric perspective, like pseudosenility or subacute befuddlement.

Other synonyms include acute cerebral insufficiency, acute mental status change, acute organic psychosis, acute organic reaction, acute confusional state, acute organic syndrome, agitated confusional state, altered mental status, cerebral insufficiency syndrome, metabolic encephalopathy, reversible cognitive dysfunction, reversible dementia, reversible toxic psychosis, toxic confusional state, toxic delirious reaction, toxic encephalopathy, toxic-metabolic encephalopathy and toxic psychosis.

Delirium is surprisingly often misspelt as delerium .


Delirium is a common condition in hospitals, especially in the greater than 65 years old age bracket. Up to 17% older adults presenting as medical emergencies have delirium .

Clinical presentation

Delirium is formally defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM V), by five criteria :

  • impaired attention and awareness
  • acute onset (hours to days), diurnal fluctuation, clear change from normal functioning
  • impaired cognitive function, e.g. disordered memory, communicative skills, spatial awareness
  • unexplained by known neuropsychiatric illness or a suppressed alertness level
  • disturbance can be linked to a physical illness, medication side-effect or substance toxicity/withdrawal (e.g. alcohol)
  • Delirium is often subdivided into three main motoric subtypes,

    • hypoactive
    • hyperactive
    • mixed
    • aggressive
    • restless
    • delusional
    • hallucinatory
    • show pronounced psychomotor movements, which tend to lack purpose and are often repetitive, such as fidgeting, tapping fingers, pacing, etc.
    • lacking interest in surroundings
    • lassitude
    • depressed psychomotor activity
    • alternate between periods of hyperactivity and hypoactivity



    The pathogenesis of delirium is complex and not well understood.

    The current science identifies two main phenomena, firstly the importance of a neurotransmitter disturbance, in particular acetylcholine and dopamine. Secondly is that inflammation is key, with cytokines being a central actor.

    It is usually a multifactorial syndrome and is especially common on the critical care unit and in postoperative patients .

    Host factors
    • greater than 65 years old
    • male gender
    • pre-existing dementia
    • previous episodes of delirium
    • alcohol excess
    • depression
    • visual and/or hearing impairment
    • hypertension
    • smoking
    Acute disease
    • infection and sepsis
    • fever
    • acid-base disturbances
    • anemia
    • metabolic derangements including of sodium, potassium, glucose, etc.
    • cardiorespiratory impairment
    • hypoxia
    • hypothermia
    • pain
    Iatrogenic/environmental factors
    • medication, e.g. benzodiazepines, anticholinergics
    • postoperative
    • immobility
    • sleep upset

    Radiographic features

    Imaging features tend to be those of the contributory conditions.

    Treatment and prognosis

    The treatment of delirium is difficult, requiring a multipronged multidisciplinary approach.

    Delirium has a significant impact on morbidity and mortality, it causes elevated inpatient, 30-day and 6-month mortality. It is associated with a more rapid cognitive deterioration, posttraumatic stress disorder and loss of independence.

    History and etymology

    Delirium derives from the Latin “de lira,” or “off the tracks.”