Delirium Causes

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Delirium is a state of mental confusion that can occur as a result of illness, surgery or with the use of some medications or drugs of abuse. The syndrome is difficult to define exactly, but involves disorder of perception, thought and awareness.

deliriumImage Credit: Vectorium/

The symptoms of delirium are often acute and intermittent and the syndrome is also referred to as “acute confusional state.” Delirium is usually temporary and reverses when the problem causing it is resolved, but it can still be very frightening for people who experience it, as well as for those around them.

Delirium occurs in around 15 to 20% of all hospital admissions and is the most common reason for hospitalization of the elderly. The incidence of delirium increases with age, with the syndrome diagnosed in 0.4% of those aged between 18 and 55 years; 1.1% of those aged between 55 and 85 years and 13.6% of those older than 85 years.

Some of the problems people experience when they develop delirium include the following:

  • Reduced awareness of surroundings
  • Inability to follow the conversation and speak clearly
  • Auditory hallucination
  • Visual hallucination
  • Sleeping during the day but wakefulness at night
  • Vivid, frightening dreams that sometimes continue once awake
  • A paranoia that people are trying to harm them
  • Agitation and restlessness
  • Mood swings that vary between anxiety, depression, irritability and fear

Causes of delirium

Delirium is common in patients who have undergone surgery and in patients in nursing homes or intensive care units. When the syndrome affects younger people, it is usually caused by the use of drugs or a life-threatening systemic illness.

Often, conditions that cause delirium are those that prevent oxygen or other important substances from reaching the brain. The most common causes of delirium are dehydration, infection and the use of drugs, especially psychoactive drugs, anticholinergics and opioids. Other precipitating factors include shock, anemia, hypoxia, undernutrition, sleep deprivation and emotional stress. Liver or kidney disease that has been overlooked can also lead to drug toxicity and delirium through impaired metabolism and reduced clearance of a drug that had previously been well tolerated.

Recent exposure to anesthesia also increases the risk of delirium developing, particularly in cases of prolonged exposure or when anticholinergics are administered during an operation. Pain and the use of opiate analgesics post-surgery can also increase the delirium risk. The risk of delirium is especially high among elderly ICU patients.

The patient groups most commonly affected by dementia include the following:

  • Critically ill patients
  • Elderly patients
  • Those with memory problems or dementia
  • Those who have had recent major surgery
  • Those with poor hearing or vision
  • Stroke patients or those with brain injury or infection
  • Those with a terminal illness
  • Alcoholics

Many medical conditions can cause delirium and examples of these are listed below. In around 10 to 20% of patients, however, no cause can be identified.

Neurological causes of delirium

  • Cerebrovascular disorders: ischemic stroke, hemorrhagic stroke, transient ischemic attack
  • Trauma: traumatic brain injury and subdural hematoma
  • Migraine: confusional migraine, where the consciousness is altered
  • Seizure: including postictal state and nonconvulsive status epilepticus
  • Tumor: primary or metastatic brain tumor, meningeal carcinomatosis
  • Inflammation or infection: CNS vasculitis, meningitis, encephalitis, meningoencephalitis
What is delirium? | Mental health | NCLEX-RN | Khan Academy

Non-neurological causes of delirium

  • Endocrine disorders: Cushing syndrome, adrenal insufficiency, pituitary insufficiency, thyroid disorders
  • Hematologic disorders: thrombocytopenia, polycythemia, leukemic blast cell crisis, hyperviscosity syndrome
  • Drugs: Anticholinergics, antihistamines, antiemetics, antihypertensives, benzodiazepines, corticosteroids, dopamine agonists, muscle relaxants, recreational drugs, antispasmodics, digoxin, hypnotics, opioids, sedatives, tricyclic antidepressants
  • Infection: Sepsis, systemic infection, urinary tract infection, pneumonia, fever
  • Injury: Burns, fat embolism, hypothermia, heatstroke, electrical injury
  • Metabolic disorders: fluid and electrolyte disorders such as hypernatremia, hyponatremia, hypocalcemia, hypercalcemia, dehydration, hyperthermia, hypoglycemia, hyperosmolality, hypoxia.
  • Vascular and circulatory abnormality: Cardiac arrhythmia, heart failure, shock, hypoperfusion states, anemia
  • Vitamin deficiency: Vitamin B12 deficiency, thiamine deficiency
  • Substance withdrawal: Withdrawal from alcohol, benzodiazepines, opioids, or barbiturates

Other causes of delirium

Liver failure, long ICU stays, sensory deprivation, sleep deprivation, CNS toxins, fecal impaction, change of environment, hypertensive encephalopathy, post-operative states, urinary retention and mental disorders.


Further Reading

Last Updated: Jun 5, 2023

Sally Robertson

Written by

Sally Robertson

Sally first developed an interest in medical communications when she took on the role of Journal Development Editor for BioMed Central (BMC), after having graduated with a degree in biomedical science from Greenwich University.


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