Almost any medical illness, intoxication, or medication can cause delirium. Often, delirium is multifactorial in etiology, and the physician treating the delirium should investigate each cause contributing to it. Medications are the most common reversible cause of delirium.

• DSM-IV classification of delirium

• Delirium due to general medical condition

   

• Substance intoxication delirium

   

• Substance withdrawal delirium

   

• Delirium due to multiple etiologies

   

• Delirium not otherwise specified

• Some of the other common reversible causes include the following:

• Hypoxia

   

• Hypoglycemia

   

• Hyperthermia

   

• Anticholinergic delirium

   

• Alcohol or sedative withdrawal

• Other causes of delirium include the following:

   

  • Infections

     

  • Metabolic abnormalities

     

  • Structural lesions of the brain

     

  • Postoperative states

     

  • Miscellaneous causes, such as sensory deprivation, sleep deprivation, fecal impaction, urinary retention, and change of environment

   

• In persons who are elderly, medications at therapeutic doses and levels can cause delirium.

   

• Although numerous risk factors have been described, a recent study identified 5 important independent risk factors.

• Use of physical restraints

   

• Malnutrition

   

• Use of a bladder catheter

   

• Any iatrogenic event

   

• Use of 3 or more medications

• Dementia is one of the strongest most consistent risk factors. Underlying dementia is observed in 25-50% of patients. The presence of dementia increases the risk of delirium 2-3 times.

   

• Structural changes

• Closed head injury or cerebral hemorrhage

   

• Cerebrovascular accidents, such as cerebral infarction, subarachnoid hemorrhage, and hypertensive encephalopathy

   

• Primary or metastatic brain tumors

   

• Brain abscess

• Metabolic causes

• Fluid and electrolyte abnormalities, acid-base disturbances, and hypoxia

   

• Hypoglycemia

   

• Hepatic or renal failure

   

• Vitamin deficiency states (especially thiamine and cyanocobalamin)

   

• Endocrinopathies associated with the thyroid and parathyroid

• Hypoperfusion states

• Shock

   

• Congestive heart failure

   

• Cardiac arrhythmias

   

• Anemias

• Infectious causes

• CNS infections such as meningitis

   

• Encephalitis

   

• HIV-related brain infections

   

• Septicemia

   

• Pneumonia

   

• Urinary tract infections

• Toxic causes

• Substance intoxication - Alcohol, heroin, cannabis, PCP, and LSD

   

• Medication-induced delirium

   

  • Anticholinergics (Benadryl, tricyclic antidepressants)

     

  • Narcotics (meperidine)

     

  • Sedative hypnotics (benzodiazepines)

     

  • Histamine-2 (H2) blockers (cimetidine)

     

  • Corticosteroids

     

  • Centrally acting antihypertensives (methyldopa, reserpine)

     

  • Anti-Parkinson drugs (levodopa)

   

• Substance withdrawal from alcohol, opioids, and benzodiazepines

• Other causes

• Postictal state

   

• Unfamiliar environment

• Operation-related delirium

• Preoperative (dementia, polypharmacy, drug withdrawal, fluid and electrolyte imbalance)

   

• Intraoperative (meperidine, long-acting benzodiazepines, anticholinergics such as atropine; however, medications such as glycopyrrolate can be used because, in contrast to atropine, they do not cross the blood brain barrier)

   

• Postoperative (hypoxia, hypotension)

   

• Drugs are a common risk factor for delirium, and drug-induced delirium is commonly seen in medical practice, especially in hospital settings. The risk of anticholinergic toxicity is greater in elderly persons, and the risk of inducing delirium by medications is high in frail, elderly persons and in those with dementia.

By Kent Pinkerton

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