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ICD-10 F05
ICD-9 293.0
OMIM [1]
DiseasesDB 29284
MedlinePlus [2]
eMedicine med/3006
MeSH {{{MeshNumber}}}

Delirium is an acute and relatively sudden (developing over hours to days) decline in attention-focus, perception, and cognition. In medical usage it is not synonymous with drowsiness, and may occur without it. Delirium is not the same as dementia (the two entities have different diagnostic criteria), though it commonly occurs in demented patients.

Delirium may be of a hyperactive variety manifested by 'positive' symptoms of agitation or combativeness, or it may be of a hypoactive variety (often referred to as 'quiet' delirium) manifested by 'negative' symptoms such as inability to converse or focus attention or follow commands. While the common non-medical view of a delirious patient is one who is hallucinating, most people who are medically delirious do not have either hallucinations or delusions. Delirium is commonly associated with a disturbance of consciousness (e.g., reduced clarity of awareness of the environment). The change in cognition (memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance, must be one that is not better accounted for by a pre-existing, established, or evolving dementia. Usually the rapidly fluctuating time course of delirium is used to help in the latter distinction.[1]

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. Like its components (inability to focus attention, confusion and various impairments in awareness and temporal and spatial orientation), delirium is simply the common symptomatic manifestation of early brain or mental dysfunction (for any reason).

Without careful assessment, delirium can easily be confused with a number of psychiatric disorders because many of the signs and symptoms are conditions present in dementia, depression, and psychosis.[2] 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.[3]

Treatment of delirium requires treatment of the underlying causes. 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).

Educational information is available for medical and non-medical persons with videos, management protocols, links to references, lectures, recent evidence from studies, implementation packets for hospitals, and even comments to families and loved ones for those witnessing someone going through a delirious episode. [4] See the Resources section.

Common versus medical usage

In common usage, delirium is often used to refer to drowsiness, disorientation, and hallucination. In broader medical terminology, however, a number of other symptoms, including sudden inability of focus attention, and even (occasionally) sleeplessness and severe agitation and irritability, also define "delirium," and hallucination, drowsiness, and disorientation are not required.

There are several medical definitions of delirium (including those in the DSM-IV and ICD-10). However, all include some core features.

The core features are:

  • Disturbance of consciousness (that is, reduced clarity of awareness of the environment, with reduced ability to focus, sustain, or shift attention)
  • Change in cognition (e.g., problem-solving impairment or memory impairment) or a perceptual disturbance
  • Onset of hours to days, and tendency to fluctuate.

Common features also tend to include:

  • Intrusive abnormalities of awareness and affect, such as hallucinations or inappropriate emotional states...


Differential points from other processes and syndromes that cause cognitive dysfunction:

  • Delirium may be distinguished from psychosis, in which consciousness and cognition may not be impaired (however, there may be overlap, as some acute psychosis, especially with mania, is capable of producing delirium-like states).
  • Delirium is distinguished from dementia (chronic organic brain syndrome) which describes an "acquired" (non-congenital) and usually irreversible cognitive and psychosocial decline in function. Dementia usually results from an identifiable degenerative brain disease (for example Alzheimer disease or Huntington's disease). Dementia is usually not associated with a change in level of consciousness, and a diagnosis of dementia requires a chronic impairment.
  • Delirium is distinguished from depression.
  • Delirium is distinguished by time-course from the confusion and lack of attention which result from long term learning disorders and varieties of congenital brain dysfunction. Delirium has also been referred to as 'acute confusional state' or 'acute brain syndrome'. The key word in both of these descriptions is "acute" (meaning: of recent onset), since delirium may share many of the clinical (i.e., symptomatic) features of dementia, developmental disability, or attention-deficit hyperactivity disorder, with the important exception of symptom duration.
  • Delirium is not the same as confusion, although the two syndromes may overlap and be present at the same time. However, a confused patient may not be delirious (an example would be a stable, demented person who is disoriented to time and place), and a delirious person may not be confused (for example. a person in severe pain may not be able to focus attention, but may be completely oriented and not at all confused).

It is a corollary of the above differential 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.

Several valid and reliable rating scales now exist which can be used to accurately diagnose delirium.[5][6]

Occurrence in hospitals

The highest prevalence of delirium (often 50% to 75% of patients) is generally seen in critically ill patients in the intensive care unit or ICU (which used to be referred to by the misnomer ICU Psychosis, a term largely abandoned now for the more widely accepted and scientifically supported term delirium). Since the advent of validated and easy to implement delirium instruments for ICU patients such as the Confusion Assessment Method for the ICU (CAM-ICU)[7] and the Intensive Care Delirium Screening Checkllist (IC-DSC)[8]. Of the hundreds of thousands of ICU patients develop delirium in ICUs every year, it has been recognized that most of them being of the hypoactive variety that is easily missed and invisible to the managing teams unless actively monitored using such instruments. The causes of delirium in such patients depend on the underlying illnesses, new problems like sepsis and low oxygen levels, and the sedative and pain medicines that are nearly universally given to all ICU patients. Outside the ICU, on hospital wards and in nursing homes, the problem of delirium is also a very important medical problem, especially for older patients. The most recent area of the hospital in which delirium is just beginning to be monitored routinely in many centers is the Emergency Department. Also, one on four geriatric patients suffer from an episode of delirium at least once during their stay in the hospital.....

Commonly co-occurring mental symptoms, with a note on severity

Since delirium may occur in very many grades of severity, all symptoms may occur with varying degrees of intensity. A mild disability to focus attention may result in only a disability in solving the most complex problems. As an extreme example, a mathematician with the flu may be unable to perform creative work, but otherwise may have no difficulty with basic activities of daily living. However, as delirium becomes more severe, it disrupts other mental functions, and may be so severe that it borders on unconsciousness or a vegetative state. In the latter state, a person may be awake and immediately aware and responsive to many stimuli, and capable of coordinated movements, but unable to perform any meaningful mental processing task at all.

Inability to focus attention, confusion and disorientation

The delirium-sufferer loses the capacity for clear and coherent thought. This may be apparent in disorganised or incoherent speech, the inability to concentrate (focus attention), or in a lack of any goal-directed thinking.

Disorientation (another symptom of confusion, and usually a more severe one) describes the loss of awareness of the surroundings, environment and context in which the person exists. It may also appear with delirium, but it is not required, as noted. Disorientation may occur in time (not knowing what time of day, day of week, month, season or year it is), place (not knowing where one is) or person (not knowing who one is).

Cognitive function may be impaired enough to make medical criteria for delirium, even if orientation is preserved. Thus, a patient who is fully aware of where they are and who they are, but cannot think because they cannot concentrate, may be medically delirious. The state of delirium most familiar to the average person is that which occurs from extremes in pain, lack of sleep, or emotional shock.

Because most high level mental skills are required for problem solving, including ability to focus attention, this ability also suffers in delirium. However, this is a secondary phenomenon, since problem-solving involves many sub-skills and basic mental abilities, any of which may be impaired in a delirious patient.

Memory formation disturbance

Impairments to cognition may include temporary reduction in the ability to form short-term or long-term memory. Difficult short-term memory tasks like ability to repeat a phone number may be continuously disrupted during a delirium, but easier short-term memory tasks like repeating single words, or remembering simple questions long enough to give an answer, may not be impaired. Reduction in formation of new long-term memory (which by definition survive withdrawal of attention), is common in delirium, because initial formation of (new) long-term memories generally requires an even higher degree of attention, than do short-term memory tasks. Since older memories are retained without need of concentration, previously formed long-term memories (i.e., those formed before the period of delirium) are usually preserved in all but the most severe cases of delirium (and when destroyed, are destroyed by the underlying brain pathology, not the delirious state per se).

Abnormalities of awareness and affect

Hallucinations (perceived sensory experience with the lack of an external source) or distortions of reality may occur in delirium, but they are not essential for the diagnosis. Commonly these are visual distortions, and can take the form of masses of small crawling creatures (particularly common in delirium tremens, caused by severe alcohol withdrawal) or distortions in size or intensity of the surrounding environment.

Strange beliefs may also be held during a delirious state, but these are not considered fixed delusions in the clinical sense as they are considered too short-lived (i.e., they are temporary delusions - such as thinking that a nurse is a person from his/her past trying to cause injury). Interestingly, in some cases sufferers may be left with false or delusional memories after delirium, basing their memories on the confused thinking or sensory distortion which occurred during the episode of delirium. Other instances would be inability to distinguish reality from dreams.

Abnormalities of affect which may attend the state of delirium may include many distortions to perceived or communicated emotional states. Emotional states may also fluctuate, so that a delirious person may rapidly change between, for example, terror, sadness and jocularity.


The duration of delirium is typically affected by the underlying cause. If caused by a fever, the delirious state often subsides as the severity of the fever subsides. However, it has long been suspected that in some cases delirium persists for months and that it may even be associated with permanent decrements in cognitive function. Barrough said in 1583 that if delirium resolves, it may be followed by a "loss of memory and reasoning power." Recent studies bear this out, with cognitively normal patients who suffer an episode of delirium carrying an increased risk of dementia in the years that follow. In many such cases, however, delirium undoubtedly does not have a causal nature, but merely functions as a temporary unmasking with stress, of a previously unsuspected (but well-compensated) state of minimal brain dysfunction (early dementia).


Delirium, like mental confusion, is a very general and nonspecific symptom of organ dysfunction, where the organ in question is the brain. In addition to many organic causes relating to a structural defect or a metabolic problem in the brain (analogous to hardware problems in a computer), there are also some psychiatric causes, which may also include a component of mental or emotional stress, mental disease, or other "programming" problems (analogous to software problems in a computer).

Delirium may be caused by severe physical illness, or any process which interferes with the normal metabolism or function of the brain.[9] For example, fever, pain, poisons (including toxic drug reactions), brain injury, surgery, traumatic shock, severe lack of food or water or sleep, and even withdrawal symptoms of certain drug and alcohol dependent states, are all known to cause delirium.

In addition, there is an interaction between acute and chronic symptoms of brain dysfunction; delirious states are more easily produced in people already suffering with underlying chronic brain dysfunction.[10]

A very common cause of delirium in elderly people is a urinary tract infection, which is easily treatable with antibiotics, reversing the delirium.

Too many to list by specific pathology, major categories of the cause of delirium include:

Critical illness

The most common behavioral manifestation of acute brain dysfunction is delirium, which occurs in up to 60% to 80% of mechanically ventilated medical and surgical ICU patients and 50% to 70% of non-ventilated medical ICU patients.[11] During the ICU stay, acute delirium is associated with complications of mechanical ventilation including nosocomial pneumonia, self-extubation, and reintubation.[3] ICU delirium predicts a 3- to 11-fold increased risk of death at 6 months even after controlling for relevant covariates such as severity of illness.[3] Of late, delirium has been recognized by some as a sixth vital sign, and it is recommended that delirium assessment be a part of routine ICU management.[12] The elderly may be at particular risk for this spectrum of delirium and dementia.[12] A firm understanding of the pathophysiologic mechanisms of delirium remains elusive despite improved diagnosis and potential treatments.

Gross structural brain disorders

  • Head trauma (i.e., concussion, traumatic bleeding, penetrating injury, etc.)
  • Gross structural damage from brain disease (stroke, spontaneous bleeding, tumor, etc.)

Neurological disorders


Lack of essential metabolic fuels, nutrients, etc.


  • Intoxication various drugs, alcohol, anesthetics
  • Sudden withdrawal of chronic drug use ("de-tox") in a person with certain types of drug addiction (e.g. alcohol, see delirium tremens, and many other sedating drugs)
  • Poisons (including carbon monoxide and metabolic blockade)
  • Medications including psychotropic medications

Mental illness per se is not a cause, as a matter of definition

Some mental illnesses, such as mania, or some types of acute psychosis, may cause a rapidly fluctuating impairment of cognitive function and ability to focus. However, they are not technically causes of delirium, since any fluctuating cognitive symptoms that occur as a result of these mental disorders are considered by definition to be due to the mental disorder itself, and to be a part of it. Thus, physical disorders can be said to produce delirium as a mental side-effect or symptom; however primary mental disorders which produce the symptom cannot be put into this category, once identified. However, such symptoms may be impossible to distinguish clinically from delirium resulting from physical disorders, if a diagnosis of an underlying mental disorder has yet to be made.


Delirium is not a disease, but a syndrome (i.e. collection of symptoms) indicating dysfunction of the brain, in the same way shortness of breath describes dysfunction of the respiratory system, but does not identify the disorder. Treatment of delirium is achieved by treating the underlying dysfunction cause, or in many cases, the causes (plural), as delirium is often multi-factorial.

Palliative or symptomatic treatment of delirium is sometimes necessary to make a patient comfortable. Distressing symptoms of delirium are sometimes treated with antipsychotics, preferably those with minimal anticholinergic activity, such as haloperidol or risperidone, or else with benzodiazepines, which decrease the anxiety felt by a person who may also be disoriented, and has difficulty completing tasks. Conversely, recent research however suggests that delirium may in fact be exacerbated by benzodiazepines.[13] Bearing this in mind, any drug does not address the underlying cause of delirium, and may mask changes in delirium which themselves may be helpful in assessing the patient's underlying changes in health, their use is difficult. Other evidence also suggests that non-pharmacological measures may also be effective in decreasing the incidence of delirium.[14] Because delirium is a mere symptom of another problem which may be very subtle, the wisdom of treatment of the delirious patient with drugs must overcome natural skepticism, and requires a high degree of skill.

Benzodiazepines are usually used in the treatment of delirium associated with alcohol withdrawal.

There have been reports that cholinesterase inhibitors might be effective in treating delirium, but there is little evidence for this.[15]

Accounts of delirium

Sims (1995, p.31) points out a "superb detailed and lengthy description" of delirium in The Stroller's Tale from Charles Dickens' The Pickwick Papers.[16][17]


Further information and resources, including guidelines from other countries are also available on the European Delirium Association website

There is a powerful presentation including delirium on the older peoples mental health website which includes further statistics relating to delirium in older adults in hospitals in England. Also further resources on delirium are available on this site.

See also


  1. Delirium - Cleveland Clinic. URL accessed on 2007-06-11.
  2. American Family Physician, March 1, 2003 Delirium
  3. 3.0 3.1 3.2 Ely EW, Shintani A, Truman B, et al. (2004). Delirium as a predictor of mortality in mechanically ventilated patients in the intensive care unit. JAMA 291 (14): 1753–62..
  4. ICU URL accessed on 2008-03-24.(see
  5. E. W. Ely, S. K. Inouye, G. R. Bernard, S. Gordon, J. Francis, L. May, B. Truman, T. Speroff, S. Gautam, R. Margolin, R. P. Hart, and R. Dittus. Delirium in mechanically ventilated patients: validity and reliability of the confusion assessment method for the intensive care unit (CAM-ICU). JAMA 286 (21):2703-2710, 2001.
  6. N. Bergeron, M. J. Dubois, M. Dumont, S. Dial, and Y. Skrobik. Intensive Care Delirium Screening Checklist: evaluation of a new screening tool. Intensive Care Med 27 (5):859-864, 2001.
  7. E. W. Ely, S. K. Inouye, G. R. Bernard, S. Gordon, J. Francis, L. May, B. Truman, T. Speroff, S. Gautam, R. Margolin, R. P. Hart, and R. Dittus. Delirium in mechanically ventilated patients: validity and reliability of the confusion assessment method for the intensive care unit (CAM-ICU). JAMA 286 (21):2703-2710, 2001.
  8. N. Bergeron, M. J. Dubois, M. Dumont, S. Dial, and Y. Skrobik. Intensive Care Delirium Screening Checklist: evaluation of a new screening tool. Intensive Care Med 27 (5):859-864, 2001.
  9. Loss of IQ in the ICU brain injury without the insult. Med Hypotheses. 2007;69(6):1179-82. Epub 2007 Jun 6. PMID: 17555884
  10. Gunther ML, Jackson JC, Ely EW. The cognitive consequences of critical illness: practical recommendations for screening and assessment. Crit Care Clin. 2007 Jul;23(3):491-506. Review. PMID: 17900482
  11. Gunther ML, Morandi, A, Ely EW, et al. (2008). Pathophysiology of delirium in the intensive care unit.. Critical Care Clinics 24 (1): 45–65..
  12. 12.0 12.1 Flaherty JH, Rudolph J, Shay K, et al. (2007). Delirium is a serious and under-recognized problem: why assessment of mental status should be the sixth vital sign. J Am Med Dir Assoc 8 (5): 273–5.. Cite error: Invalid <ref> tag; name "pmid17570303" defined multiple times with different content
  13. Pandharipande PP, Pun BT, Herr DL, Maze M, Girard TD, Miller RR, Shintani AK, Thompson JL, Jackson JC, Deppen SA, Stiles RA, Dittus RS, Bernard GR, Ely EW. Effect of sedation with dexmedetomidine vs lorazepam on acute brain dysfunction in mechanically ventilated patients: the MENDS randomized controlled trial. JAMA. 2007 Dec 12;298(22):2644-53. PMID: 18073360
  14. Inouye SK, Bogardus ST Jr, Charpentier PA, Leo-Summers L, Acampora D, Holford TR, Cooney LM Jr. A multicomponent intervention to prevent delirium in hospitalized older patients. N Engl J Med. 1999 Mar 4;340(9):669-76. PMID: 10053175
  15. PMID 18254077
  16. Sims, Andrew (2002). Symptoms in the mind: an introduction to descriptive psychopathology, Philadelphia: W. B. Saunders.
  17. Dickens, C. (1837) The Pickwick Papers. Available for free on Project Gutenberg.

Further reading

  • Burns A, Gallagley A, Byrne J (2004). Delirium. J. Neurol. Neurosurg. Psychiatr. 75 (3): 362–7.
  • Macdonald, Alastair; Lindesay, James; Rockwood, Kenneth (2002). Delirium in old age, Oxford [Oxfordshire]: Oxford University Press.
  • Sims, A. (1995) Symptoms in the mind: An introduction to descriptive psychopathology. Edinburgh: Elsevier Science Ltd. ISBN 0-7020-2627-1
  • Dickens, C. (1837) The Pickwick Papers. Available for free on Project Gutenberg.
  • Burns A, Gallagley A, Byrne J. (2004) "Delirium." Journal of Neurology, Neurosurgery and Psychiatry 75 (3), 362-367.
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