Etiology

The etiology of delirium is usually multifactorial.[35][36] In general, delirium occurs owing to a complex interplay of reduced functional reserve (secondary to predisposing factors) and precipitating insults such as infection, metabolic derangements, environmental factors, sleep deprivation, surgery, and/or primary illness.[35][36] This interplay explains why some patients, particularly those with cognitive and functional impairments, become delirious with relatively minor insults such as a UTI while more robust individuals are unaffected.

Predisposing factors

Key predisposing factors or risk factors for delirium include:[35][36]

  • Older age

  • Dementia or cognitive impairment[37]

  • Visual or hearing impairment

  • Functional impairment or immobility

  • History of delirium

  • Decreased oral intake (e.g., dehydration)

  • Polypharmacy

  • Coexisting medical illness

  • Physical frailty

  • Surgery.

Precipitating insults

Important precipitating insults that can result in delirium include:[35][36]

  • Drugs: sedatives, narcotics, anticholinergics, multiple drug use and alcohol, as well as overdose of tricyclic antidepressants, stimulants, opiates, corticosteroids, analgesics, cardiac glycosides, and anti-Parkinson drugs.[38][39][40]

  • Primary neurologic injury: stroke, intracranial bleeding, meningitis

  • Acute illness: infection (e.g., pneumonia, urinary tract infection, sepsis), cardiac illness (e.g., myocardial infarction), hypoxia, shock, dehydration, fever, constipation, iatrogenic complications

  • Metabolic abnormalities

  • Surgery (e.g., orthopedic, cardiac): duration of cardiopulmonary bypass[41]

  • Environmental factors: physical restraint use, use of catheters/invasive monitoring, intensive care unit stay

  • Pain

  • Prolonged sleep deprivation[42]

  • Drug withdrawal: benzodiazepines, alcohol.

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