Delirium, also known as acute confusional state, is an organically caused decline from a previous baseline mental functioning that develops over a short period of time, typically hours to days. Delirium is a syndrome encompassing disturbances in attention, consciousness, and cognition. Delirium may also involve other neurological deficits, such as 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.

Figure 1. Delirium is an acute disturbance of mental abilities.

Delirium is caused by an acute organic process, which is a physically identifiable structural, functional, or chemical problem in the brain that may arise from a disease process outside the brain that nonetheless affects the brain. Delirium may result from an underlying disease process (e.g., infection or hypoxia), a side effect of a medication, withdrawal from drugs, over-consumption of alcohol, usage of hallucinogenic deliriants, or from any number of factors affecting one’s overall health (e.g., malnutrition, pain, etc.). In contrast, fluctuations in mental status/function due to changes in primarily psychiatric processes or diseases (e.g., schizophrenia or bipolar disorder) do not, by definition, meet the criteria for 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 development disorder (intellectual disability), or dementia, without being due to any of these problems. Delirium is distinguished from dementia (chronic organic brain syndrome), which describes an acquired (non-congenital) and usually irreversible cognitive and psychosocial decline in function.

Delirium exists as a stage of consciousness somewhere in the spectrum between normal awake/alert state and coma. While requiring an acute disturbance in consciousness/attention and cognition, delirium is a syndrome encompassing an array of neuropsychiatric symptoms. Delirium arises through the interaction of a number of predisposing and precipitating factors.

The most important predisposing factors are

• older age (> 65 years old)
• male sex
• cognitive impairment / dementia
• physical comorbidity (biventricular failure, cancer,  and cerebrovascular disease)
• psychiatric comorbidity (e.g., depression)
• sensory impairment (vision, hearing)
• functional dependence (e.g., requiring assistance for self-care or mobility)
• dehydration/malnutrition
• drugs and drug-dependence
• alcohol dependence

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. The factors affecting an individual may change over time, thus an individual’s risk of delirium is dynamic.

Some of the most common precipitating factors of delirium are listed below:

• prolonged sleep deprivation
• environmental or physical/psychological stress
  • inadequately controlled pain
  • admission to an intensive care unit
  • immobilization or use of physical restraints
  • urinary retention or use of a bladder catheter
  • emotional stress
  • severe constipation and/or fecal impaction
• medications
  • sedatives (benzodiazepines, opioids), anticholinergics, dopaminergics, corticosteroids, polypharmacy
  • general anesthetic
  • substance intoxication or withdrawal
• primary neurologic diseases
  • severe drop in blood pressure, relative to the patient’s normal blood pressure (orthostatic hypotension) resulting in inadequate blood flow to the brain (cerebral hypoperfusion)
  • stroke/Transient ischemic attack (TIA)
  • intracranial bleeding
  • brain inflammation from meningitis or encephalitis
• Concurrent illness
  • Infections – especially respiratory (e.g. pneumonia) and urinary tract infections
  • Latrogenic complications
  • Hypoxia, hypercapnea, anemia
  • Poor nutritional status, dehydration, electrolyte imbalances, hypoglycemia
  • Cardiac shock, heart attacks, heart failure
  • Metabolic derangements (e.g. SIADH, Addison’s disease, hyperthyroidism)
  • Chronic or terminal illness (e.g. cancer)
  • Post-traumatic event (e.g. fall, fracture)
• Surgery
  • Cardiac, orthopedic, prolonged cardiopulmonary bypass, thoracic surgeries

The range of clinical features includes 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 clinical features of delirium are further described below and can be assessed by several specialized tests, such as The Delirium Rating Scale-Revised-98 (DRS-R-98):

Figure 2. Sleep disturbances and deprivation are risk factors for delirium.

• Inattention: As a required symptom to diagnose delirium, inattention 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 the need for 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, disorientation describes the loss of awareness of the surroundings, environment, and context in which the person exists. An individual 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 and 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. The delusions 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 impact the interpretation of these findings.

Treatment of delirium requires identifying and managing the underlying causes, managing delirium symptoms, and reducing the risk of complications. In some cases, temporary or symptomatic treatments are used to comfort the person or to facilitate other care (e.g., preventing people from pulling out a breathing tube). 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. Evidence has found that the risk of delirium in hospitalized people can be reduced by systematic good general care. Delirium affects 14–24% of all hospitalized individuals. The overall prevalence for the general population is 1%-2% but this prevalence 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 individuals requiring critical care, delirium is a risk for death within the next year.

Prevention

There is substantial evidence that delirium results in long-term poor outcomes in older persons admitted to hospital. Recent long-term studies showed that many patients still meet the criteria for delirium for a prolonged period after hospital discharge, with up to 21% of patients showing persistent delirium at six months post-discharge.

Using a tailored multifaceted approach clinicians 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.

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.