Aetiology

The aetiology of delirium is usually multifactorial.[41][43] In general, delirium occurs due 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.[41][43]

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 for delirium include:​[42][43]​​[44]​​

  • Older age

  • Dementia or cognitive impairment

  • Visual or hearing impairment

  • Functional impairment or immobility

  • History of delirium

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

  • Polypharmacy

  • Co-existing medical illness

  • Physical frailty

  • Surgery.

Precipitating insults

Important precipitating insults that can result in delirium include the following:[42]​​[43]​​[45][46][47][48][49][50]​​​[51]​​​

  • Drugs: sedatives, anticholinergics, multiple drug use, alcohol, tricyclic antidepressants, stimulants, opiods, corticosteroids, analgesics, cardiac glycosides, anti-Parkinson's drugs​​. The general use of these drugs can contribute to delirium, particularly in the elderly and critically unwell; in the setting of overdose, they may cause delirium at any age.

  • Primary neurological 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., orthopaedic, cardiac): duration of cardiopulmonary bypass

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

  • Pain

  • Prolonged sleep deprivation

  • Drug withdrawal: benzodiazepines, alcohol.

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