Aetiology

Although delirium can be caused by a single causative agent, usually they are diverse and multifactorial. They are often an initial manifestation of an acute medical illness, drug effect or complication (1).

Development of delirium can be explained by the complex inter-relationship of patient vulnerability (with several predisposing factors) and exposure to noxious insults or precipitating factors (2).

• in vulnerable patients (with predisposing factors such as old age, severe dementia, multiple morbidities etc.), a relatively benign insult/precipitating factor (e.g. - a dose of a sedative–hypnotic drug) can precipitate delirium
• patients who are less vulnerable (e.g. – younger patients or patients with little comorbidty burden etc), exposure to series of noxious stimuli/precipitating factors such as general anaesthesia, major surgery, several psychoactive drugs may result in delirium (2,3)

Some of the common causes of delirium include:

• urinary tract infection or pneumonia - 34 – 43% of cases
• dehydration
• electrolyte abnormalities
• organ failure
• CNS insults (3)

An aide-memoire to help remember the common causes of delirium is HIDEMAP:

• H - hypoxia
• I - infection
• D - drugs
• E - endocrine, e.g. diabetes
• M - metabolic, e.g. hyper/hypocalcaemia
• A - alcohol
• P - psychosis

Reference:

• (1) Fong TG, Tulebaev SR, Inouye SK. Delirium in elderly adults: diagnosis, prevention and treatment. Nature reviews Neurology. 2009;5(4):210-220.
• (2) Inouye SK, Westendorp RG, Saczynski JS. Delirium in  elderly people. Lancet. 2014;383(9920):911-22.
• (3) Han JH, Wilson A, Ely EW. Delirium in the Older Emergency Department Patient – A Quiet Epidemic. Emergency medicine clinics of North America. 2010;28(3):611-631.