Delirium, also known as acute confusional state, is an organically-caused decline from a previously baseline level of mental function that develops over a short period of time (hours to days). Delirium is not a disease itself, but a syndrome encompassing disturbances in attention, consciousness, and cognition. It may also involve other neurological deficits, like psychomotor disturbances (e.g. hyperactive, hypoactive, or mixed), impaired sleep-wake cycle, emotional disturbances, and perceptual disturbances (e.g. hallucinations and delusions), although these features are not required for diagnosis.
|Synonyms||Acute confusional state|
Delirium is caused by an acute organic process (i.e. a physically identifiable structural, functional, or chemical problem in the brain), which may arise from a disease process outside the brain that, nonetheless, affects the brain. It may result from an underlying disease process (e.g. infection, hypoxia), side effect of a medication, withdrawal from drugs, over-consumption of alcohol, or from any number of factors affecting one's overall health (e.g. malnutrition, pain, etc). In contrast, fluctuations in mentation due to changes in primarily psychiatric processes or diseases (e.g. schizophrenia, bipolar disorder) are, by definition, not termed 'delirium.' Delirium may be difficult to diagnose without the proper establishment of a person's usual mental function. Without careful assessment and history, delirium can easily be confused with a number of psychiatric disorders or chronic organic brain syndromes because of many overlapping signs and symptoms in common with dementia, depression, psychosis, etc. Delirium may manifest from a baseline of existing mental illness, baseline intellectual disability, or dementia, without being due to any of these problems.
Treatment of delirium requires treating the underlying cause and multi-faceted interventions are thought to be most effective. In some cases, temporary and/or symptomatic treatments are used to comfort the person or to facilitate other care (e.g. preventing a delirious patient from pulling out a breathing tube required for survival). Antipsychotics are not supported for the treatment or prevention of delirium among those who are in hospital. When delirium is caused by alcohol or sedative hypnotic withdrawal, benzodiazepines are typically used.
Delirium affects 14-24% of all hospitalized individuals. The overall prevalence for the general population is 1-2% but this increases with age, reaching 14% of adults over age 85. Among older adults, delirium occurs in 15-53% of those post-surgery, 70-87% of those in the ICU, up to 60% of those in nursing homes or post-acute care settings. Among those requiring critical care, delirium is a risk for death within the next year.
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-V) 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 symptomsEdit
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%). Thinking is also slow and muddled but the content is often complex.
The 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: This 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: Usually noticed with speech that makes limited sense with apparent irrelevancies, this can involve symptoms of 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: Disruption of sleep-wake cycle often precedes the appearance of a delirium episode. In delirium, sleep disturbances typically involves fragmented sleep or even sleep-wake cycle reversal (i.e. active at night, sleeping during the day), both reflecting disturbed circadian rhythm regulation.
- Psychotic symptoms: Such thought content abnormalities 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).
It was thought for many years that all delirium was a transient state of brain dysfunction that fluctuated on an hourly basis. English medical writer Philip Barrow noted in 1583 that if delirium resolves, it may be followed by a "loss of memory and reasoning power." Recent long-term studies showed that many patients still meet criteria for delirium for an alarmingly long time after hospital discharge, with up to 21% of patients showing persistent delirium at 6 months post-discharge.
Dementia in ICU survivorsEdit
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 disabled and unable to go back to work and unable to serve effectively as the matriarchs and patriarchs of their families. 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” (note: the term here is being used in a circumstance in which not all patients continue to decline as some have persistent yet stable brain dysfunction and others with newly acquired brain problems can recover fully) are profound at the private level, dismantling the person’s life in very practical ways, such as impairing ability to find a car in a parking lot, complete shopping lists, or perform job-related tasks done previously for years. The societal relevance is also huge when one considers work-force issues related to the inability of a young wage-earner to work due to their own ICU stay or that of someone they must care for.
Delirium arises through the interaction of a number of predisposing and precipitating factors. A "predisposing factor" may be any biological, psychological, or social factor that increases an individual’s susceptibility to delirium, while a "precipitating factor" is one that can trigger delirium. Although there may be a significant degree of overlap between the two categories, the distinction between predisposing and precipitating causes is helpful in assessing one's risk for developing delirium and in guiding management of the syndrome.
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 a 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 listed below:
- 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 and/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
In general, the pathophysiology of delirium is still not well understood, despite diverse research techniques used to elucidate this question.
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 (i.e. biperiden and scopolamine) 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).
Cerebrospinal fluid biomarkersEdit
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.
Although neuroimaging offers a non-invasive way to understand delirium, it has been challenge to establish correlates with delirium. Many attempts to image people with concurrent delirium are unsuccessful. In addition, there is a more general bias selecting younger and fitter participants amenable to scanning, especially if using intensive techniques such as MRI.
Despite similar heterogeneity in study design as described in an older 2008 analysis, a 2017 systematic review summarizes evidence of associated white matter disease (including cerebral atrophy, ventricular enlargement, and white matter lesions), abnormal changes in diffusion MRI characteristics and brain metabolites (reflecting microscopic tissue damage and non-neuronal nervous cell activity), and abnormal connectivity between different functional regions of the brain (consistent with interruptions in executive function, sensory processing, attention, emotional regulation, memory, and orientation as seen in delirium).
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. A case series 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-V 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 unitEdit
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.
Other processes and syndromes that cause cognitive dysfunction resembling delirium include the following:
- 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)
- 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
- Longterm learning disorders or Congenital brain dysfunction: Despite potentially sharing many symptomatic features with, for example, developmental disabilities like attention deficit hyperactivity disorder, these would not have an acute presentation or duration as in delirium
- 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-V 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.
Using a tailored multi-faceted approach as outlined above can can decreases 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 by systematically addressing the common contributing factors, such as constipation, dehydration, low oxygen levels, immobility, and the simultaneous use of multiple and/or 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.
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.
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.
Such interventions are the first measures in managing active delirium and has many overlaps with delirium preventative strategies, including optimizing the hospital environment by reducing ambient noise, providing proper lighting for the time of day, minimizing room changes and restraint use.
Family, friends, and other caregivers can offer frequent reassurance, tactile and/or verbal orientation, cognitive stimulation (e.g. regular visits, familiar objects, clocks and/or calendars), 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. Of note, severe agitation that endangers self or others may require physical restraints and professional supervision, but only as a last resort.
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 trespassed. 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.
The treatment for delirium with medications depends on its cause.
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 Antipsychotics however are not supported for the treatment or prevention of delirium among those who are in hospital.
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).
Institutionalisation 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.
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 cultureEdit
Delirium is one of the oldest forms of mental disorder known in medical history.
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.
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