Why Delirium Occurs

Delirium occurs as a result of a complex interplay between patient vulnerability to delirium and precipitating factors (See Table). Patients who are highly vulnerable (e.g., 97 year old nursing home patient with severe dementia and is bedridden) require a relatively benign precipitating factor (e.g., simple urinary tract infection) to develop delirium. Patients who have little vulnerability to delirium (e.g., a fully functional 66 year old without dementia who still balances his/her own checkbook) require a more noxious precipitating factor (e.g., severe sepsis) to develop delirium. Because older patients are more likely to have multiple vulnerability factors, they are more susceptible to becoming delirious compared with their younger counterparts. When a patient with little or no vulnerability factors presents with delirium, one should have increased concern for an underlying life threatening illness.

Vulnerability Factors Precipitating Factors
Advanced age
Low education attainment
Functional impairment
Sensory impairment
Substance abuse history
Metabolic disturbances
Electrolyte disturbances
Organ failure
CNS insults
Medication toxicity
Endocrine dysfunction
Recreational drug use
Ethanol or benzodiazepine withdrawal
Trauma / Pain
Hypo- or hyperthermia
Table.Vulnerability and precipitating factors for delirium. CNS, central nervous system.

Read more about why delirium occurs

Altered mental status in older patients in the emergency department.

Han JH, Wilber ST. Altered mental status in older patients in the emergency department. Clin Geriatr Med. 2013;29:101-136.

Read on PubMed.gov

Delirium in elderly people.

Inouye SK, Westendorp RG, Saczynski JS. Delirium in elderly people. Lancet. 2014;383:911-922.

Read on PubMed.gov