|Other names: Acute confusional state|
|Delirium is an acute disturbance of mental abilities|
|Symptoms||Changes in attention, activity, awareness, sleep patterns, ability to think|
|Usual onset||> 70 years old|
|Types||Hyperactive, hypoactive, mixed|
|Causes||Medical conditions, medications, substance intoxication, substance withdrawal|
|Risk factors||Dementia, vision problems, hearing problems, alcoholism|
|Differential diagnosis||Psychosis, dementia, acute stress disorder|
|Treatment||Treating underlying cause, good general care|
|Frequency||1 to 2% of people|
Delirium, also known as acute confusional state, is an altered level of consciousness that develops over a short period and fluctuates over time. There may be changes in attention, activity, awareness, sleep patterns, and ability to think. Onset is typically over hours to days and the person differs from their usual baseline mental functioning. In hospital, the condition typically lasts about a week, though some may have ongoing problems afterwards.
Delirium may be caused by a medical condition, medications, substance intoxication, or substance withdrawal. Often a number of factors are involved. Risk factors include dementia, vision problems, hearing problems, and alcoholism. Medications that may trigger the event include benzodiazepines, antihistamines, opioids, and antipsychotics. Other triggers may include infections, pain, or surgery. The underlying mechanism poorly understood.
Diagnose requires establishing a person's usual mental function. The person's activity may be increased (agitation), decreased (subdued), or be a mix of both. Cases were activity is decreased are more frequently missed or attributed to depression. It should be distinguished from psychotic disorders, acute stress disorder, and dementia.
Treatment is generally directed at the underlying causes. Other measures may include hearing aids, glasses, sufficient fluids to drink, a quiet sleep environment, and a visible clock. While antipsychotics are used, there is no evidence to support a benefit for delirium. Delirium in hospitalized people; however, can be reduced by systematic good general care. About 40% of people with delirium in hospital die within a year.
Delirium affects about 1 to 2% of people overall. Among older adults, rates are around 20% after surgery or when visiting the emergency department, and up to 90% in the intensive care unit. Rates around 20% are also seen among those admitted to hospital. The condition becomes more common with age, affecting about 14% of those over the age of 85. Descriptions of delirium date back to at least Hippocrates around 400 BC.
In common usage, delirium is often used to refer to drowsiness, disorientation, and hallucination. In medical terminology, however, acute disturbance in consciousness/attention and a number of different cognitive symptoms are the core features of delirium. Several medical definitions of delirium exist (including those in the DSM and ICD-10), but the core features remain the same. In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5) with the following criteria for diagnosis:
- A. Disturbance in attention and awareness. This is a required symptom and involves easy distraction, inability to maintain attentional focus, and varying levels of alertness.
- B. Onset is acute (from hours to days), representing a change from baseline mentation with fluctuations throughout the day
- C. At least one additional cognitive disturbance (in memory, orientation, language, visuospatial ability, or perception)
- D. The disturbances (criteria A and C) are not better explained by another neurocognitive disorder
- E. There is evidence that the disturbances above are a "direct physiological consequence" of another medical condition, substance intoxication or withdrawal, toxin, or various combinations of causes
Signs and symptoms
Delirium exists as a stage of consciousness somewhere in the spectrum between normal awakeness/alertness and coma. While requiring an acute disturbance in consciousness/attention and cognition, delirium is a syndrome encompassing an array of neuropsychiatric symptoms.
The range of clinical features include: poor attention/vigilance (100%), memory impairment (64–100%), clouding of consciousness (45–100%), disorientation (43–100%), acute onset (93%), disorganized thinking/thought disorder (59–95%), diffuse cognitive impairment (77%), language disorder (41–93%), sleep disturbance (25–96%), mood lability (43–63%), psychomotor changes (e.g. hyperactive, hypoactive, mixed) (38–55%), delusions (18–68%), and perceptual change/hallucinations (17–55%). These various features of delirium are further described below:
- Inattention: As a required symptom to diagnose delirium, this is characterized by distractibility and an inability to shift and/or sustain attention.
- Memory impairment: Memory impairment is linked to inattention, especially reduced formation of new long-term memory where higher degrees of attention is more necessary than for short-term memory. Since older memories are retained without need of concentration, previously formed long-term memories (i.e. those formed before the onset of delirium) are usually preserved in all but the most severe cases of delirium.
- Disorientation: As another symptom of confusion, and usually a more severe one, this describes the loss of awareness of the surroundings, environment and context in which the person exists. One may be disoriented to time, place, or self.
- Disorganized thinking: Disorganized thinking is usually noticed with speech that makes limited sense with apparent irrelevancies, and can involve poverty of speech, loose associations, perseveration, tangentiality, and other signs of a formal thought disorder.
- Language disturbances: Anomic aphasia, paraphasia, impaired comprehension, agraphia, and word-finding difficulties all involve impairment of linguistic information processing.
- Sleep changes: Sleep disturbances in delirium reflect disturbed circadian rhythm regulation, typically involving fragmented sleep or even sleep-wake cycle reversal (i.e. active at night, sleeping during the day) and often preceding the onset of a delirium episode
- Psychotic symptoms: Symptoms of psychosis include suspiciousness, overvalued ideation and frank delusions. Delusions are typically poorly formed and less stereotyped than in schizophrenia or Alzheimer’s disease. They usually relate to persecutory themes of impending danger or threat in the immediate environment (e.g. being poisoned by nurses).
- Mood lability: Distortions to perceived or communicated emotional states as well as fluctuating emotional states can manifest in a delirious person (e.g. rapid changes between terror, sadness and joking).
- Motor activity changes: Delirium has been commonly classified into psychomotor subtypes of hypoactive, hyperactive, and mixed, though studies are inconsistent as to the prevalence of these subtypes. Hypoactive cases are prone to non-detection or misdiagnosis as depression. A range of studies suggest that motor subtypes differ regarding underlying pathophysiology, treatment needs, and prognosis for function and mortality though inconsistent subtype definitions and poorer detection of hypoactive subtypes impacts interpretation of these findings. Liptzin and Levkoff first described these subtypes in 1992 as following:
- Hyperactive symptoms include hyper-vigilance, restlessness, fast or loud speech, irritability, combativeness, impatience, swearing, singing, laughing, uncooperativeness, euphoria, anger, wandering, easy startling, fast motor responses, distractibility, tangentiality, nightmares, and persistent thoughts (hyperactive sub-typing is defined with at least three of the above).
- Hypoactive symptoms include unawareness, decreased alertness, sparse or slow speech, lethargy, slowed movements, staring, and apathy (hypoactive sub-typing is defined with at least four of the above).
Delirium arises through the interaction of a number of predisposing and precipitating factors.
Individuals with multiple and/or significant predisposing factors are highly at risk for suffering an episode of delirium with a single and/or mild precipitating factor. Conversely, delirium may only result in healthy individuals if they suffer serious or multiple precipitating factors. It is important to note that the factors affecting those of an individual can change over time, thus an individual’s risk of delirium is dynamic.
The most important predisposing factors are:
- Older age (> 65yo)
- Male sex
- Cognitive impairment / dementia
- Physical comorbidity (biventricular failure, cancer, cerebrovascular disease)
- Psychiatric comorbidity (e.g., depression)
- Sensory impairment (vision, hearing)
- Functional dependence (e.g., requiring assistance for self-care or mobility)
- Drugs and drug-dependence
- Alcohol dependence
Any acute factors that affect neurotransmitter, neuroendocrine, or neuroinflammatory pathways can precipitate an episode of delirium in a vulnerable brain. Clinical environments can also precipitate delirium. Some of the most common precipitating factors are listed below:
- Prolonged sleep deprivation
- Environmental, physical/psychological stress
- Inadequately controlled pain
- Admission to an intensive care unit
- Immobilization, use of physical restraints
- Urinary retention, use of bladder catheter,
- Emotional stress
- Severe constipation/fecal impaction
- Primary neurologic diseases
- Concurrent illness
- Infections – especially respiratory (e.g. pneumonia) and urinary tract infections
- Iatrogenic complications
- Hypoxia, hypercapnea, anemia
- Poor nutritional status, dehydration, electrolyte imbalances, hypoglycemia
- Shock, heart attacks, heart failure
- Metabolic derangements (e.g. SIADH, Addison’s disease, hyperthyroidism, )
- Chronic/terminal illness (e.g. cancer)
- Post-traumatic event (e.g. fall, fracture)
- Cardiac, orthopedic, prolonged cardiopulmonary bypass, thoracic surgeries
The pathophysiology of delirium is still not well understood, despite extensive research.
The lack of animal models that are relevant to delirium has left many key questions in delirium pathophysiology unanswered. Earliest rodent models of delirium used atropine (a muscarinic acetylcholine receptor blocker) to induce cognitive and electroencephalography (EEG) changes similar to delirium, and other anticholinergic drugs, such as biperiden and hyoscine, have produced similar effects. Along with clinical studies using various drugs with anticholinergic activity, these models have contributed to a "cholinergic deficiency hypothesis" of delirium.
Profound systemic inflammation occurring during sepsis is also known to cause delirium (often termed sepsis-associated encephalopathy). Animal models used to study the interactions between prior degenerative disease and overlying systemic inflammation have shown that even mild systemic inflammation causes acute and transient deficits in working memory among diseased animals. Prior dementia or age-associated cognitive impairment is the primary predisposing factor for clinical delirium and "prior pathology" as defined by these new animal models may consist of synaptic loss, abnormal network connectivity, and "primed microglia" brain macrophages stimulated by prior neurodegenerative disease and aging to amplify subsequent inflammatory responses in the central nervous system (CNS).
Studies of cerebrospinal fluid (CSF) in delirium are difficult to perform. Apart from the general difficulty of recruiting participants who are often unable to give consent, the inherently invasive nature of CSF sampling makes such research particularly challenging. However, a few studies have exploited the opportunity to sample CSF from persons undergoing spinal anesthesia for elective or emergency surgery.
A 2018 systematic review showed that, broadly, delirium may be associated with neurotransmitter imbalance (namely serotonin and dopamine signaling), reversible fall in somatostatin, and increased cortisol. The leading "neuroinflammatory hypothesis" (where neurodegenerative disease and aging leads the brain to respond to peripheral inflammation with an exaggerated CNS inflammatory response) has been described, but current evidence is still conflicting and fails to concretely support this hypothesis.
Neuroimaging provides an important avenue to explore the mechanisms that are responsible for delirium. Despite progress in the development of magnetic resonance imaging (MRI), the large variety in imaging-based findings has limited our understanding of the changes in the brain that may be linked to delirium. Some challenges associated with imaging people diagnosed with delirium include participant recruitment and inadequate consideration of important confounding factors such as history of dementia and/or depression, which are known to be associated with overlapping changes in the brain also observed on MRI.
Evidence for changes in structural and functional markers include: changes in white-matter integrity (white matter lesions), decreases in brain volume (likely as a result of tissue atrophy), abnormal functional connectivity of brain regions responsible for normal processing of executive function, sensory processing, attention, emotional regulation, memory, and orientation, differences in autoregulation of the vascular vessels in the brain, reduction in cerebral blood flow and possible changes in brain metabolism (including cerebral tissue oxygenation and glucose hypometabolism). Altogether, these changes in MRI-based measurements invite further investigation of the mechanisms that may underlie delirium, as a potential avenue to improve clinical management of people suffering with this condition.
Electroencephalography (EEG) allows for continuous capture of global brain function and brain connectivity, and is useful in understanding real-time physiologic changes during delirium. Since the 1950s, delirium has been known to be associated with slowing of resting-state EEG rhythms, with abnormally decreased background alpha power and increased theta and delta frequency activity.
From such evidence, a 2018 systematic review proposed a conceptual model that delirium results when insults/stressors trigger a breakdown of brain network dynamics in individuals with low brain resilience (i.e. people who already have underlying problems of low neural connectivity and/or low neuroplasticity like those with Alzheimers disease).
Only a handful of studies exist where there has been an attempt to correlate delirium with pathological findings at autopsy. One research study has been reported on 7 patients who died during ICU admission. Each case was admitted with a range of primary pathologies, but all had acute respiratory distress syndrome and/or septic shock contributing to the delirium, 6 showed evidence of low brain perfusion and diffuse vascular injury, and 5 showed hippocampal involvement. A case-control study showed that 9 delirium cases showed higher expression of HLA-DR and CD68 (markers of microglial activation), IL-6 (cytokines pro-inflammatory and anti-inflammatory activities) and GFAP (marker of astrocyte activity) than age-matched controls; this supports a neuroinflammatory cause to delirium, but the conclusions are limited by methodological issues.
A 2017 retrospective study correlating autopsy data with MMSE scores from 987 brain donors found that delirium combined with a pathological process of dementia accelerated MMSE score decline more than either individual process.
Using the DSM-5 criteria for delirium as framework, the early recognition of signs/symptoms and a careful history, along with any of multiple clinical instruments, can help in making a diagnosis of delirium. A diagnosis of delirium cannot be made without a previous assessment of the patient's baseline level of cognitive function. In other words, a mentally-disabled or demented person might appear to be delirious, but may actually just be operating at his/her baseline mental ability.
Multiple guidelines recommend that delirium should be diagnosed when it presents to healthcare services. Much evidence reveal, however, that delirium is greatly under-diagnosed. Higher rates of detection of delirium in general settings can be assisted by the use of validated delirium screening tools. Many such tools have been published. They differ in duration, complexity, need for training, etc.
Examples of tools in use in clinical practice are:
- Richmond Agitation and Sedation Scale (RASS) – highly sensitive and specific for diagnosing delirium in older patients
- Observational Scale of Level of Arousal (OSLA) – highly sensitive and specific for diagnosing delirium in older patients
- Confusion Assessment Method (CAM)
- Delirium Observation Screening Scale (DOS)
- Nursing Delirium Screening Scale (Nu-DESC)
- Recognizing Acute Delirium As part of your Routine (RADAR)
- 4AT (4 A's Test)
Intensive care unit
In the ICU, international guidelines recommend that every patient gets checked for delirium every day (usually twice or more a day) using a validated clinical tool. The definition of delirium that healthcare professionals use at the bedside is whether or not a patient can pay attention and follow simple commands. The two most widely used are the Confusion Assessment Method for the ICU (CAM-ICU) and the Intensive Care Delirium Screening Checklist (ICDSC). Translations of these tools exist in over 20 languages and are used ICUs globally with instructional videos and implementation tips available.
More emphasis is placed on regular screening over the choice of tool used. This, coupled with proper documentation and informed awareness by the healthcare team, can affect clinical outcomes. Without using one of these tools, 75% of ICU delirium can be missed by the healthcare team, leaving the patient without any likely interventions to help reduce the duration of delirium.
There are conditions that might have similar clinical presentations to those seen in delirium. These include dementia, depression, psychosis, and other conditions that affect cognitive function.
- Dementia: This group of disorders is acquired (non-congenital) with usually irreversible cognitive and psychosocial functional decline. Dementia usually results from an identifiable degenerative brain disease (e.g. Alzheimer disease or Huntington's disease), requires chronic impairment (versus acute onset in delirium), and is typically not associated with changes in level of consciousness.
- Depression: Similar symptoms exist between depression and delirium (especially the hypoactive subtype). Gathering a history from other caregivers can clarify baseline mentation.
- Other mental illnesses: Some mental illnesses, such as a manic episode of bipolar disorder, depersonalization disorder, or some types of acute psychosis may cause a rapidly fluctuating impairment of cognitive function and ability to focus. These, however, are not technically causes of delirium per DSM-5 criteria D (i.e. fluctuating cognitive symptoms occurring as part of a primary mental disorder are results of the said mental disorder itself), while physical disorders (e.g. infections, hypoxia, etc.) can precipitate delirium as a mental side-effect/symptom.
- Psychosis: 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).
Using a tailored multi-faceted approach as outlined above can can decrease rates of delirium by 27% among the elderly. At least 30–40% of all cases of delirium could be prevented, and high rates of delirium reflect negatively on the quality of care. Episodes of delirium can be prevented by identifying hospitalized people at risk of the condition: those over age 65, those with a known cognitive impairment, those with hip fracture, those with severe illness. Close observation for the early signs is recommended in such populations.
Delirium may be prevented and treated by using non-pharmacologic approaches focused on risk factors, such as constipation, dehydration, low oxygen levels, immobility, visual or hearing impairment, sleep deprivation, functional decline and removing or minimizing problematic medications. Ensuring a therapeutic environment (e.g. individualized care; clear communication; adequate reorientation and lighting during daytime; promoting uninterrupted sleep hygiene with minimal noise and light at night; minimizing bed relocation; having familiar objects like family pictures; providing earplugs; and providing adequate nutrition, pain control, and assistance toward early mobilization) can also yield benefit toward preventing delirium. Research into pharmacologic prevention and treatment is weak and insufficient to make proper recommendations.
Melatonin and other pharmacological agents have been studied for prevention of postoperative delirium, but evidence is not clear. Avoidance or cautious use of benzodiazepines has been recommended for reducing the risk of delirium in critically ill individuals. It is unclear if the medication donepezil, a cholinesterase inhibitor, reduces delirium following surgery. There is also no clear evidence to suggest that citicoline, methylprednisolone, or antipsychotic medications prevent delirium.
A review of intravenous versus inhalational maintenance of anaesthesia for postoperative cognitive outcomes in elderly people undergoing non-cardiac surgery showed little or no difference in postoperative delirium according to the type of anaesthetic maintenance agents in five studies (321 participants). The authors of this review were uncertain whether maintenance of anaesthesia with propofol-based total intravenous anaesthesia (TIVA) or with inhalational agents can affect incidences of postoperative delirium.
Treatment of delirium involves two main strategies: 1. identify and treat the underlying medical disorder or cause(s), and 2. manage behavioral disturbances. This involves optimizing oxygenation, hydration, nutrition, electrolytes/metabolites, comfort, mobilization, pain control, mental stress, therapeutic medication levels, and addressing any other possible predisposing and precipitating factors that might be disrupting brain function.
These interventions are the first steps in managing acute delirium and there are many overlaps with delirium preventative strategies. In addition to treating immediate life-threatening causes of delirium (e.g. low O2, low blood pressure, low glucose, dehydration), interventions include optimizing the hospital environment by reducing ambient noise, providing proper lighting, offering pain relief, promoting healthy sleep-wake cycles, and minimizing room changes. Although multicomponent care and comprehensive geriatric care are more specialized for a person experiencing delirium, several studies have been unable to find evidence showing they reduce the duration of delirium.
Family, friends, and other caregivers can offer frequent reassurance, tactile and verbal orientation, cognitive stimulation (e.g. regular visits, familiar objects, clocks, calendars, etc.), and means to stay engaged (e.g. making hearing aids and eyeglasses readily available). Sometimes verbal and non-verbal deescalation techniques may be required to offer reassurances and calm the person experiencing delirium. Restraints should rarely be used as an intervention for delirium. The use of restraints has been recognized as a risk factor for injury and aggravating symptoms, especially in older hospitalized people with delirium. The only cases where restraints should sparingly be used during delirium is in the protection of life-sustaining interventions, such as endotracheal tubes.
Another approached called the "T-A-DA (tolerate, anticipate, don't agitate) method" can be an effective management technique for older people with delirium, where abnormal patient behaviors (including hallucinations and delusions) are tolerated and unchallenged, as long as caregiver and patient safety is not threatened. Implementation of this model may require a designated area in the hospital. All unnecessary attachments are removed to anticipate for greater mobility, and agitation is prevented by avoiding excessive reorientation/questioning.
Low-dose haloperidol when used short term (one week or less) is the most studied and standard drug for delirium. Evidence for efficacy of atypical antipsychotics (i.e. risperidone, olanzapine, ziprasidone, and quetiapine) is emerging, with the benefit for fewer side effects Use antipsychotic drugs with caution or not at all for people with conditions such as Parkinson's disease or dementia with Lewy bodies.
Benzodiazepines themselves can trigger or worsen delirium, and there is no reliable evidence for use in non-alcohol-related delirium. If the delirium involves alcohol withdrawal, benzodiazepine withdrawal, or contraindications to antipsychotics (e.g. in Parkinson's disease or neuroleptic malignant syndrome), then benzodiazepines are recommended. Similarly, people with dementia with Lewy bodies may have significant side effects to antipsychotics, and should either be treated with a none or small doses of benzodiazepines.
There is substantial evidence that delirium results in long-term poor outcomes in older persons admitted to hospital. This systematic review only included studies that looked for an independent effect of delirium (i.e., after accounting for other associations with poor outcomes, for example co-morbidity or illness severity).
In older persons admitted to hospital, individuals experiencing delirium are twice as likely to die than those who do not (meta-analysis of 12 studies). In the only prospective study conducted in the general population, older persons reporting delirium also showed higher mortality (60% increase).
Institutionalization was also twice as likely after an admission with delirium (meta-analysis of 7 studies). In a community-based population examining individuals after an episode of severe infection (though not specifically delirium), these persons acquired more functional limitations (i.e. required more assistance with their care needs) than those not experiencing infection. After an episode of delirium in the general population, functional dependence increased threefold.
The association between delirium and dementia is complex. The systematic review estimated a 13-fold increase in dementia after delirium (meta-analysis of 2 studies). However, it is difficult to be certain that this is accurate because the population admitted to hospital includes persons with undiagnosed dementia (i.e. the dementia was present before the delirium, rather than caused by it). In prospective studies, people hospitalised from any cause appear to be at greater risk of dementia and faster trajectories of cognitive decline, but these studies did not specifically look at delirium. In the only population-based prospective study of delirium, older persons had an eight-fold increase in dementia and faster cognitive decline. The same association is also evident in persons already diagnosed with Alzheimer’s dementia.
Recent long-term studies showed that many patients still meet criteria for delirium for a prolonged period after hospital discharge, with up to 21% of patients showing persistent delirium at 6 months post-discharge.
Dementia in ICU survivors
Dementia is supposed to be an entity that continues to decline, such as Alzheimer’s disease. Another way of looking at dementia, however, is not strictly based on the decline component, but on the degree of memory and executive function problems. It is now known, for example, that between 50% and 70% of ICU patients have tremendous problems with ongoing brain dysfunction similar to those experienced by Alzheimer’s or TBI (traumatic brain injury) patients, leaving many ICU survivors permanently disabled. This is a distressing personal and public health problem and is getting an increasing amount of scrutiny in ongoing investigations.
The implications of such an "acquired dementia-like illness" can profoundly debilitate a person's livelihood level, often dismantling his/her life in practical ways like impairing one's ability to find a car in a parking lot, complete shopping lists, or perform job-related tasks done previously for years. The societal implications can be enormous when considering work-force issues related to the inability of wage-earners to work due to their own ICU stay or that of someone else they must care for.
The highest rates of delirium (often 50% to 75% of people) is seen among those who are critically ill in the intensive care unit (ICU) As a result, this was referred to as "ICU psychosis" or "ICU syndrome", terms largely abandoned for the more widely accepted term ICU 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) and the Intensive Care Delirium Screening Checkllist (IC-DSC)., of the hundreds of thousands of ICU patients who develop delirium in ICUs every year, it has been recognized that most of them belong to the hypoactive variety, which 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, where the prevalence of delirium among older adults is about 10%. A systematic review of delirium in general medical inpatients showed that estimates of delirium prevalence on admission ranged from 10 to 31%. About 5% to 10% of older adults who are admitted to hospital develop a new episode of delirium while in hospital. Rates of delirium vary widely across general hospital wards. Estimates of the prevalence of delirium in nursing homes are between 10%  to 45%.
Society and culture
Delirium is one of the oldest forms of mental disorder known in medical history. The Roman author Aulus Cornelius Celsus used the term to describe mental disturbance from head trauma or fever in his work De Medicina.
The American Delirium Society is a community of professionals dedicated to improving delirium care." The Critical Illness, Brain Dysfunction, and Survivorship (CIBS) Center is an academic center dedicated to studying and treating delirium in critically ill patient populations.
In the US, the cost of a patient admission with delirium is estimated at between $16k and $64k, suggesting the national burden of delirium may range from $38 bn to $150 bn per year (2008 estimate). In the UK, the cost is estimated as £13k per admission.
- Diagnostic and statistical manual of mental disorders : DSM-5 (Fifth ed.). Arlington, VA: American Psychiatric Association. 2013. p. 596-601. ISBN 9780890425596. OCLC 847226928.
- Ramírez Echeverría, MdL; Paul, M (January 2020). "Delirium". PMID 29261982. Cite journal requires
- Gleason OC (March 2003). "Delirium". American Family Physician. 67 (5): 1027–34. PMID 12643363. Archived from the original on 2011-06-06.
- Siddiqi N, Harrison JK, Clegg A, Teale EA, Young J, Taylor J, Simpkins SA (March 2016). "Interventions for preventing delirium in hospitalised non-ICU patients" (PDF). The Cochrane Database of Systematic Reviews. 3: CD005563. doi:10.1002/14651858.CD005563.pub3. PMID 26967259. Open access repository
- Neufeld KJ, Yue J, Robinson TN, Inouye SK, Needham DM (April 2016). "Antipsychotic Medication for Prevention and Treatment of Delirium in Hospitalized Adults: A Systematic Review and Meta-Analysis". Journal of the American Geriatrics Society. 64 (4): 705–14. doi:10.1111/jgs.14076. PMC 4840067. PMID 27004732.
- Burry L, Mehta S, Perreault MM, Luxenberg JS, Siddiqi N, Hutton B, et al. (June 2018). "Antipsychotics for treatment of delirium in hospitalised non-ICU patients". The Cochrane Database of Systematic Reviews. 6: CD005594. doi:10.1002/14651858.CD005594.pub3. PMC 6513380. PMID 29920656.
- Lindesay, James; Rockwood, Kenneth; Macdonald, Alastair (2002). Delirium in Old Age. Oxford University Press. p. 1. ISBN 978-0-19-263275-3.
- Hales, Robert E.; Yudofsky, Stuart C.; Gabbard, Glen O., eds. (2008). The American Psychiatric Publishing textbook of psychiatry (5th ed.). Washington DC: American Psychiatric Publishing. ISBN 9781585622573. OCLC 145554590.
- Leentjens AF, Rundell J, Rummans T, Shim JJ, Oldham R, Peterson L, et al. (August 2012). "Delirium: An evidence-based medicine (EBM) monograph for psychosomatic medicine practice, comissioned by the Academy of Psychosomatic Medicine (APM) and the European Association of Consultation Liaison Psychiatry and Psychosomatics (EACLPP)". Journal of Psychosomatic Research. 73 (2): 149–52. doi:10.1016/j.jpsychores.2012.05.009. PMID 22789420.
- Lipowski ZJ (March 1989). "Delirium in the elderly patient". The New England Journal of Medicine. 320 (9): 578–82. doi:10.1056/NEJM198903023200907. PMID 2644535.
- de Rooij SE, Schuurmans MJ, van der Mast RC, Levi M (July 2005). "Clinical subtypes of delirium and their relevance for daily clinical practice: a systematic review". International Journal of Geriatric Psychiatry. 20 (7): 609–15. doi:10.1002/gps.1343. PMID 16021665.
- Meagher D (February 2009). "Motor subtypes of delirium: past, present and future". International Review of Psychiatry. 21 (1): 59–73. doi:10.1080/09540260802675460. PMID 19219713.
- Liptzin B, Levkoff SE (December 1992). "An empirical study of delirium subtypes". The British Journal of Psychiatry. 161 (6): 843–5. doi:10.1192/bjp.161.6.843. PMID 1483173.
- Magny E, Le Petitcorps H, Pociumban M, Bouksani-Kacher Z, Pautas É, Belmin J, et al. (2018-02-23). "Predisposing and precipitating factors for delirium in community-dwelling older adults admitted to hospital with this condition: A prospective case series". PLOS ONE. 13 (2): e0193034. Bibcode:2018PLoSO..1393034M. doi:10.1371/journal.pone.0193034. PMC 5825033. PMID 29474380.
- Fong TG, Tulebaev SR, Inouye SK (April 2009). "Delirium in elderly adults: diagnosis, prevention and treatment". Nature Reviews. Neurology. 5 (4): 210–20. doi:10.1038/nrneurol.2009.24. PMC 3065676. PMID 19347026.
- Hughes CG, Patel MB, Pandharipande PP (October 2012). "Pathophysiology of acute brain dysfunction: what's the cause of all this confusion?". Current Opinion in Critical Care. 18 (5): 518–26. doi:10.1097/MCC.0b013e328357effa. PMID 22941208.
- McCusker J, Cole M, Abrahamowicz M, Han L, Podoba JE, Ramman-Haddad L (October 2001). "Environmental risk factors for delirium in hospitalized older people". Journal of the American Geriatrics Society. 49 (10): 1327–34. doi:10.1046/j.1532-5415.2001.49260.x. PMID 11890491.
- Inouye SK (March 2006). "Delirium in older persons". The New England Journal of Medicine. 354 (11): 1157–65. doi:10.1056/NEJMra052321. PMID 16540616.
- Clegg A, Young JB (January 2011). "Which medications to avoid in people at risk of delirium: a systematic review". Age and Ageing. 40 (1): 23–9. doi:10.1093/ageing/afq140. PMID 21068014.
- Hshieh TT, Fong TG, Marcantonio ER, Inouye SK (July 2008). "Cholinergic deficiency hypothesis in delirium: a synthesis of current evidence". The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences. 63 (7): 764–72. doi:10.1093/gerona/63.7.764. PMC 2917793. PMID 18693233.
- Zampieri FG, Park M, Machado FS, Azevedo LC (2011). "Sepsis-associated encephalopathy: not just delirium". Clinics. 66 (10): 1825–31. doi:10.1590/S1807-59322011001000024. PMC 3180153. PMID 22012058.
- Cunningham C, Maclullich AM (February 2013). "At the extreme end of the psychoneuroimmunological spectrum: delirium as a maladaptive sickness behaviour response". Brain, Behavior, and Immunity. 28: 1–13. doi:10.1016/j.bbi.2012.07.012. PMC 4157329. PMID 22884900.
- Hall RJ, Watne LO, Cunningham E, Zetterberg H, Shenkin SD, Wyller TB, MacLullich AM (November 2018). "CSF biomarkers in delirium: a systematic review". International Journal of Geriatric Psychiatry. 33 (11): 1479–1500. doi:10.1002/gps.4720. PMID 28585290.
- Cerejeira J, Firmino H, Vaz-Serra A, Mukaetova-Ladinska EB (June 2010). "The neuroinflammatory hypothesis of delirium". Acta Neuropathologica. 119 (6): 737–54. doi:10.1007/s00401-010-0674-1. hdl:10400.4/806. PMID 20309566.
- Nitchingham, Anita; Kumar, Varun; Shenkin, Susan; Ferguson, Karen J.; Caplan, Gideon A. (2018). "A systematic review of neuroimaging in delirium: predictors, correlates and consequences: Neuroimaging in delirium". International Journal of Geriatric Psychiatry. 33 (11): 1458–1478. doi:10.1002/gps.4724. PMID 28574155.
- Soiza, Roy L.; Sharma, Vijay; Ferguson, Karen; Shenkin, Susan D.; Seymour, David Gwyn; MacLullich, Alasdair M.J. (September 2008). "Neuroimaging studies of delirium: A systematic review". Journal of Psychosomatic Research. 65 (3): 239–248. doi:10.1016/j.jpsychores.2008.05.021. PMID 18707946.
- Shafi MM, Santarnecchi E, Fong TG, Jones RN, Marcantonio ER, Pascual-Leone A, Inouye SK (June 2017). "Advancing the Neurophysiological Understanding of Delirium". Journal of the American Geriatrics Society. 65 (6): 1114–1118. doi:10.1111/jgs.14748. PMC 5576199. PMID 28165616.
- Engel GL, Romano J (Fall 2004). "Delirium, a syndrome of cerebral insufficiency. 1959". The Journal of Neuropsychiatry and Clinical Neurosciences. 16 (4): 526–38. doi:10.1176/appi.neuropsych.16.4.526. PMID 15616182.
- Janz DR, Abel TW, Jackson JC, Gunther ML, Heckers S, Ely EW (September 2010). "Brain autopsy findings in intensive care unit patients previously suffering from delirium: a pilot study". Journal of Critical Care. 25 (3): 538.e7–12. doi:10.1016/j.jcrc.2010.05.004. PMC 3755870. PMID 20580199.
- Munster BC, Aronica E, Zwinderman AH, Eikelenboom P, Cunningham C, Rooij SE (December 2011). "Neuroinflammation in delirium: a postmortem case-control study". Rejuvenation Research. 14 (6): 615–22. doi:10.1089/rej.2011.1185. PMC 4309948. PMID 21978081.
- Davis DH, Muniz-Terrera G, Keage HA, Stephan BC, Fleming J, Ince PG, et al. (March 2017). "Association of Delirium With Cognitive Decline in Late Life: A Neuropathologic Study of 3 Population-Based Cohort Studies". JAMA Psychiatry. 74 (3): 244–251. doi:10.1001/jamapsychiatry.2016.3423. PMC 6037291. PMID 28114436.
- Bellelli G, Nobili A, Annoni G, Morandi A, Djade CD, Meagher DJ, et al. (November 2015). "Under-detection of delirium and impact of neurocognitive deficits on in-hospital mortality among acute geriatric and medical wards". European Journal of Internal Medicine. 26 (9): 696–704. doi:10.1016/j.ejim.2015.08.006. PMID 26333532.
- McCoy TH, Snapper L, Stern TA, Perlis RH (2016). "Underreporting of Delirium in Statewide Claims Data: Implications for Clinical Care and Predictive Modeling". Psychosomatics. 57 (5): 480–8. doi:10.1016/j.psym.2016.06.001. PMID 27480944.
- Quispel-Aggenbach DW, Holtman GA, Zwartjes HA, Zuidema SU, Luijendijk HJ (September 2018). "Attention, arousal and other rapid bedside screening instruments for delirium in older patients: a systematic review of test accuracy studies". Age and Ageing. 47 (5): 644–653. doi:10.1093/ageing/afy058. PMID 29697753.
- Ely EW, Truman B, Shintani A, Thomason JW, Wheeler AP, Gordon S, et al. (June 2003). "Monitoring sedation status over time in ICU patients: reliability and validity of the Richmond Agitation-Sedation Scale (RASS)". JAMA. 289 (22): 2983–91. doi:10.1001/jama.289.22.2983. PMID 12799407.
- Tieges Z, McGrath A, Hall RJ, Maclullich AM (December 2013). "Abnormal level of arousal as a predictor of delirium and inattention: an exploratory study". The American Journal of Geriatric Psychiatry. 21 (12): 1244–53. doi:10.1016/j.jagp.2013.05.003. PMID 24080383.
- Inouye SK, van Dyck CH, Alessi CA, Balkin S, Siegal AP, Horwitz RI (December 1990). "Clarifying confusion: the confusion assessment method. A new method for detection of delirium". Annals of Internal Medicine. 113 (12): 941–8. doi:10.7326/0003-4819-113-12-941. PMID 2240918. S2CID 7740657.
- Schuurmans MJ, Shortridge-Baggett LM, Duursma SA (2003-01-01). "The Delirium Observation Screening Scale: a screening instrument for delirium". Research and Theory for Nursing Practice. 17 (1): 31–50. doi:10.1891/rtnp.188.8.131.52169. PMID 12751884.
- Gaudreau JD, Gagnon P, Harel F, Tremblay A, Roy MA (April 2005). "Fast, systematic, and continuous delirium assessment in hospitalized patients: the nursing delirium screening scale". Journal of Pain and Symptom Management. 29 (4): 368–75. doi:10.1016/j.jpainsymman.2004.07.009. PMID 15857740.
- Voyer P, Champoux N, Desrosiers J, Landreville P, McCusker J, Monette J, et al. (2015-01-01). "Recognizing acute delirium as part of your routine [RADAR]: a validation study". BMC Nursing. 14: 19. doi:10.1186/s12912-015-0070-1. PMC 4384313. PMID 25844067.
- "4AT - RAPID CLINICAL TEST FOR DELIRIUM". Retrieved 14 May 2020. CS1 maint: discouraged parameter (link)
- Tieges, Zoë; MacLullich, Alasdair M. J.; Anand, Atul; Brookes, Claire; Cassarino, Marica; O'Connor, Margaret; Ryan, Damien; Saller, Thomas; Arora, Rakesh C.; Chang, Yue; Agarwal, Kathryn (2020-06-12). "Diagnostic Accuracy of the 4AT for delirium detection: systematic review and meta-analysis". medRxiv: 2020.06.11.20128280. doi:10.1101/2020.06.11.20128280.
- Jacobi J, Fraser GL, Coursin DB, Riker RR, Fontaine D, Wittbrodt ET, et al. (January 2002). "Clinical practice guidelines for the sustained use of sedatives and analgesics in the critically ill adult". Critical Care Medicine. 30 (1): 119–41. doi:10.1097/00003246-200201000-00020. PMID 11902253. S2CID 16654002.
- "Critical Illness, Brain Dysfunction, and Survivorshpi (CIBS) Center". www.icudelirium.org. Retrieved 2019-03-22.
- Ely EW, Inouye SK, Bernard GR, Gordon S, Francis J, May L, et al. (December 2001). "Delirium in mechanically ventilated patients: validity and reliability of the confusion assessment method for the intensive care unit (CAM-ICU)". JAMA. 286 (21): 2703–10. doi:10.1001/jama.286.21.2703. PMID 11730446.
- Bergeron N, Dubois MJ, Dumont M, Dial S, Skrobik Y (May 2001). "Intensive Care Delirium Screening Checklist: evaluation of a new screening tool". Intensive Care Medicine. 27 (5): 859–64. doi:10.1007/s001340100909. PMID 11430542.
- Jones SF, Pisani MA (April 2012). "ICU delirium: an update". Current Opinion in Critical Care. 18 (2): 146–51. doi:10.1097/MCC.0b013e32835132b9. PMID 22322260.
- "Treating Delirium & Agitation in the Emergency Room, 2015 | EB Medicine". www.ebmedicine.net. Retrieved 2019-11-25.
- Soiza; Myint (2019-08-15). "The Scottish Intercollegiate Guidelines Network (SIGN) 157: Guidelines on Risk Reduction and Management of Delirium". Medicina. 55 (8): 491. doi:10.3390/medicina55080491. ISSN 1010-660X. PMC 6722546. PMID 31443314.
- Oh, Esther S.; Fong, Tamara G.; Hshieh, Tammy T.; Inouye, Sharon K. (September 26, 2017). "Delirium in Older Persons: Advances in Diagnosis and Treatment". JAMA. 318 (12): 1161–1174. doi:10.1001/jama.2017.12067. ISSN 1538-3598. PMC 5717753. PMID 28973626.
- "Making Sense of Delirium in the Emergency Department". www.reliasmedia.com. Retrieved 2019-11-25.
- Grover, Sandeep; Avasthi, Ajit (February 2018). "Clinical Practice Guidelines for Management of Delirium in Elderly". Indian Journal of Psychiatry. 60 (Suppl 3): S329–S340. doi:10.4103/0019-5545.224473 (inactive 2020-05-20). ISSN 0019-5545. PMC 5840908. PMID 29535468.CS1 maint: DOI inactive as of May 2020 (link)
- ProQuest 2175238208
- O'Sullivan R, Inouye SK, Meagher D (September 2014). "Delirium and depression: inter-relationship and clinical overlap in elderly people". The Lancet. Psychiatry. 1 (4): 303–11. doi:10.1016/S2215-0366(14)70281-0. PMC 5338740. PMID 26360863.
- Martinez F, Tobar C, Hill N (March 2015). "Preventing delirium: should non-pharmacological, multicomponent interventions be used? A systematic review and meta-analysis of the literature". Age and Ageing. 44 (2): 196–204. doi:10.1093/ageing/afu173. PMID 25424450.
- National Institute for Health and Clinical Excellence. Clinical guideline 103: Delirium. London, 2010.
- Poongkunran C, John SG, Kannan AS, Shetty S, Bime C, Parthasarathy S (October 2015). "A meta-analysis of sleep-promoting interventions during critical illness". The American Journal of Medicine. 128 (10): 1126–1137.e1. doi:10.1016/j.amjmed.2015.05.026. PMC 4577445. PMID 26071825.
- Flannery AH, Oyler DR, Weinhouse GL (December 2016). "The Impact of Interventions to Improve Sleep on Delirium in the ICU: A Systematic Review and Research Framework". Critical Care Medicine. 44 (12): 2231–2240. doi:10.1097/CCM.0000000000001952. PMID 27509391.
- Gosch M, Nicholas JA (February 2014). "Pharmacologic prevention of postoperative delirium". Zeitschrift für Gerontologie und Geriatrie. 47 (2): 105–9. doi:10.1007/s00391-013-0598-1. PMID 24619041.
- Slooter AJ, Van De Leur RR, Zaal IJ (2017). Delirium in critically ill patients. Handb Clin Neurol. Handbook of Clinical Neurology. 141. pp. 449–466. doi:10.1016/B978-0-444-63599-0.00025-9. ISBN 9780444635990. PMID 28190430.
- Miller D, Lewis SR, Pritchard MW, Schofield-Robinson OJ, Shelton CL, Alderson P, Smith AF (August 2018). "Intravenous versus inhalational maintenance of anaesthesia for postoperative cognitive outcomes in elderly people undergoing non-cardiac surgery". The Cochrane Database of Systematic Reviews. 8 (8): CD012317. doi:10.1002/14651858.CD012317.pub2. PMC 6513211. PMID 30129968.
- Risk reduction and management of delirium : a national clinical guideline. Scottish Intercollegiate Guidelines Network., Scotland. Healthcare Improvement Scotland. Edinburgh. 2019. ISBN 9781909103689. OCLC 1099827664.CS1 maint: others (link)
- Rudolph JL, Marcantonio ER (May 2011). "Review articles: postoperative delirium: acute change with long-term implications". Anesthesia and Analgesia. 112 (5): 1202–11. doi:10.1213/ANE.0b013e3182147f6d. PMC 3090222. PMID 21474660.
- DeWitt, Marie A.; Tune, Larry E. (2018-07-06), "Delirium", The American Psychiatric Association Publishing Textbook of Neuropsychiatry and Clinical Neurosciences, American Psychiatric Association Publishing, doi:10.1176/appi.books.9781615372423.sy08, ISBN 978-1-61537-187-7
- Oh ES, Fong TG, Hshieh TT, Inouye SK (September 2017). "Delirium in Older Persons: Advances in Diagnosis and Treatment". JAMA. 318 (12): 1161–1174. doi:10.1001/jama.2017.12067. PMC 5717753. PMID 28973626.
- Tyrer, Peter J; Silk, Kenneth R (2008). Cambridge Textbook of Effective Treatments in Psychiatry. Leiden: Cambridge University Press. ISBN 9780511393020. OCLC 437204638. Unknown parameter
- "Overview | Delirium in adults | Quality standards | NICE". www.nice.org.uk. Retrieved 2019-11-25.
- Inouye SK (March 2006). "Delirium in older persons". The New England Journal of Medicine. 354 (11): 1157–65. doi:10.1056/NEJMra052321. PMID 16540616.[verification needed]
- Witlox J, Eurelings LS, de Jonghe JF, Kalisvaart KJ, Eikelenboom P, van Gool WA (July 2010). "Delirium in elderly patients and the risk of postdischarge mortality, institutionalization, and dementia: a meta-analysis". JAMA. 304 (4): 443–51. doi:10.1001/jama.2010.1013. PMID 20664045. S2CID 13402729.
- Davis DH, Muniz Terrera G, Keage H, Rahkonen T, Oinas M, Matthews FE, et al. (September 2012). "Delirium is a strong risk factor for dementia in the oldest-old: a population-based cohort study". Brain. 135 (Pt 9): 2809–16. doi:10.1093/brain/aws190. PMC 3437024. PMID 22879644.
- Iwashyna TJ, Ely EW, Smith DM, Langa KM (October 2010). "Long-term cognitive impairment and functional disability among survivors of severe sepsis". JAMA. 304 (16): 1787–94. doi:10.1001/jama.2010.1553. PMC 3345288. PMID 20978258.
- Ehlenbach WJ, Hough CL, Crane PK, Haneuse SJ, Carson SS, Curtis JR, Larson EB (February 2010). "Association between acute care and critical illness hospitalization and cognitive function in older adults". JAMA. 303 (8): 763–70. doi:10.1001/jama.2010.167. PMC 2943865. PMID 20179286.
- Wilson RS, Hebert LE, Scherr PA, Dong X, Leurgens SE, Evans DA (March 2012). "Cognitive decline after hospitalization in a community population of older persons". Neurology. 78 (13): 950–6. doi:10.1212/WNL.0b013e31824d5894. PMC 3310309. PMID 22442434.
- Fong TG, Jones RN, Shi P, Marcantonio ER, Yap L, Rudolph JL, et al. (May 2009). "Delirium accelerates cognitive decline in Alzheimer disease". Neurology. 72 (18): 1570–5. doi:10.1212/WNL.0b013e3181a4129a. PMC 2677515. PMID 19414723.
- Cole MG, Ciampi A, Belzile E, Zhong L (January 2009). "Persistent delirium in older hospital patients: a systematic review of frequency and prognosis". Age and Ageing. 38 (1): 19–26. doi:10.1093/ageing/afn253. PMID 19017678.
- Hopkins RO, Jackson JC (September 2006). "Long-term neurocognitive function after critical illness". Chest. 130 (3): 869–78. doi:10.1378/chest.130.3.869. PMID 16963688. S2CID 8118025.
- Harris, Richard (October 10, 2018). "When ICU Delirium Leads To Symptoms Of Dementia After Discharge". National Public Radio. Retrieved 29 April 2019.
- Ely EW, et al. "ICU Delirium and Cognitive Impairment Study Group". Vanderbilt University Medical Center. Archived from the original on 10 October 2013. Retrieved 6 December 2012.
- Ryan DJ, O'Regan NA, Caoimh RÓ, Clare J, O'Connor M, Leonard M, et al. (January 2013). "Delirium in an adult acute hospital population: predictors, prevalence and detection". BMJ Open. 3 (1): e001772. doi:10.1136/bmjopen-2012-001772. PMC 3549230. PMID 23299110.
- Canadian Coalition for Seniors' Mental Health (2006). National Guidelines for Seniors' Mental Health: The Assessment and Treatment of Delirium. Canadian Coalition for Seniors' Mental Health. Archived from the original on 2014-09-08.
- Siddiqi N, House AO, Holmes JD (July 2006). "Occurrence and outcome of delirium in medical in-patients: a systematic literature review". Age and Ageing. 35 (4): 350–64. doi:10.1093/ageing/afl005. PMID 16648149.
- McCoy TH, Hart KL, Perlis RH (May 2017). "Characterizing and predicting rates of delirium across general hospital settings". General Hospital Psychiatry. 46: 1–6. doi:10.1016/j.genhosppsych.2017.01.006. PMID 28622808.
- Voyer P, Richard S, Doucet L, Carmichael PH (March 2009). "Detecting delirium and subsyndromal delirium using different diagnostic criteria among demented long-term care residents". Journal of the American Medical Directors Association. 10 (3): 181–8. doi:10.1016/j.jamda.2008.09.006. PMID 19233058.
- Berrios GE (November 1981). "Delirium and confusion in the 19th century: a conceptual history". The British Journal of Psychiatry. 139 (5): 439–49. doi:10.1192/bjp.139.5.439. PMID 7037094.
- Adamis D, Treloar A, Martin FC, Macdonald AJ (December 2007). "A brief review of the history of delirium as a mental disorder". History of Psychiatry. 18 (72 Pt 4): 459–69. doi:10.1177/0957154X07076467. PMID 18590023.
- Barrough, Philip (1583). The methode of phisicke conteyning the causes, signes, and cures of invvard diseases in mans body from the head to the foote. VVhereunto is added, the forme and rule of making remedies and medicines, which our phisitians commonly vse at this day, with the proportion, quantitie, & names of ech [sic] medicine. London: By Thomas Vautroullier dwelling in the Blacke-friars by Lud-gate. p. 18.
- Sims A (2002). Symptoms in the mind: an introduction to descriptive psychopathology. Philadelphia: W. B. Saunders. ISBN 978-0-7020-2627-0.
- Dickens C (1837) The Pickwick Papers. Available for free on Project Gutenberg.
- "Home | American Delirium Society". americandeliriumsociety.org. Retrieved 2019-03-27.
- Leslie DL, Marcantonio ER, Zhang Y, Leo-Summers L, Inouye SK (January 2008). "One-year health care costs associated with delirium in the elderly population". Archives of Internal Medicine. 168 (1): 27–32. doi:10.1001/archinternmed.2007.4. PMC 4559525. PMID 18195192.
- Akunne A, Murthy L, Young J (May 2012). "Cost-effectiveness of multi-component interventions to prevent delirium in older people admitted to medical wards". Age and Ageing. 41 (3): 285–91. doi:10.1093/ageing/afr147. PMID 22282171.
|Wikisource has the text of the 1911 Encyclopædia Britannica article Delirium .|