What are the common causes of acute delirium in elderly patients admitted to hospital?

Common Causes of Acute Delirium in Elderly Hospitalized Patients

Infection—particularly urinary tract infections and pneumonia—is the most common precipitating factor for acute delirium in hospitalized elderly patients, though medications (especially anticholinergics, benzodiazepines, and opioids) account for up to 39-64% of cases and represent the leading reversible cause. 1, 2, 3, 4

Infectious Causes

• Urinary tract infections and pneumonia are the two most frequently encountered infectious precipitants of delirium in older adults 1, 2, 5
• Over 80% of elderly patients with bacteremia demonstrate neurological symptoms ranging from lethargy to coma 2
• Prompt evaluation and treatment of underlying infection is critical, as delayed treatment prolongs delirium and increases morbidity and mortality 2, 5

Medication-Induced Delirium (Leading Reversible Cause)

Medications are responsible for 39-64% of delirium cases in hospitalized elderly patients and should be the first target for intervention 3, 4

High-Risk Medications:

• Anticholinergic medications (including antihistamines like cyclizine) are among the highest-risk drugs and should be discontinued immediately 1, 2, 5, 3
• Benzodiazepines are potent precipitants of delirium and should be discontinued unless treating alcohol or benzodiazepine withdrawal 1, 2, 5, 3
• Opioids are the most frequent medication culprit, especially in patients with renal insufficiency or on high doses, as metabolites accumulate 2, 3, 4
• Corticosteroids are frequently implicated, particularly at higher doses 3
• Any medication can potentially cause delirium in elderly patients and all drugs should be considered suspect 6, 4

Metabolic and Electrolyte Disturbances

Metabolic abnormalities are present in approximately 46% of hospitalized delirious patients 3

• Dehydration is a common precipitating factor, demonstrated by elevated blood urea nitrogen/creatinine ratio ≥18 1, 2, 3
• Hypercalcemia should be suspected even with indolent symptoms (confusion, asthenia, somnolence), as delirium from hypercalcemia is reversible in 40% of cases 2, 3
• Hyponatremia (including SIADH), hypernatremia, and glucose abnormalities are common contributors 1, 3
• Hypoalbuminemia is an independent risk factor for delirium 1, 3

Organ System Dysfunction

• End-stage cardiac disease, including heart failure and arrhythmias 1, 3
• Renal failure with accumulation of toxic metabolites 1, 3
• Hepatic failure 1, 3
• End-stage lung disease and respiratory failure with hypoxia 1, 3
• Endocrinopathy 1

Neurological Causes

• Cerebrovascular disease, including stroke and transient ischemic attacks 1, 2, 5
• Traumatic brain injury 1, 2
• Less frequent but important causes include: status epilepticus, nonconvulsive seizure, intracranial mass effect, chronic subdural or subarachnoid hemorrhage, meningitis, encephalitis, and hydrocephalus 1, 2
• CNS diseases or trauma, history of stroke 1

Frequently Overlooked Reversible Causes

A thorough physical examination must identify these often-missed factors 2

• Untreated pain is both a precipitant and perpetuating factor 2, 3
• Constipation 1, 2, 3
• Urinary retention or catheterization 1, 2, 3
• Visual and hearing impairments—patients must use their glasses and hearing aids 1, 2, 5, 3
• Sleep deprivation from frequent vital sign checks, medication rounds, and noise 1, 3

Predisposing Baseline Vulnerability Factors

These factors increase susceptibility to delirium with any precipitating insult 1

• Advanced age (≥65-70 years) 1, 3, 7
• Pre-existing cognitive impairment or dementia (OR 5.2; strongest risk factor) 1, 3, 7
• Severity of underlying illness 1, 3
• Poor functional status and frailty 3
• Depression 3, 7
• Alcohol abuse or withdrawal (OR 3.3) 1, 3, 7
• Male gender 7

Environmental and Iatrogenic Factors

The hospital environment itself becomes increasingly delirogenic with longer stays 3

• Immobility and physical restraints worsen delirium and should be avoided 1, 5, 3
• Sensory deprivation, including removal of hearing aids and eyeglasses 3
• Frequent relocations between units disrupt orientation 1
• Excessive noise disrupts sleep-wake cycles 1

Critical Clinical Context: Multiple Simultaneous Causes

In 69% of hospitalized delirious patients, multiple factors contribute simultaneously, with a median of three probable causes 3

• Frail elderly patients may develop delirium from relatively minor insults, while younger patients require more severe precipitants 1, 3
• Each additional day of hospitalization increases cumulative exposure to delirogenic factors 3

Important Pitfall to Avoid

Do NOT treat asymptomatic bacteriuria in elderly patients with delirium—it is associated with worse functional recovery and increased risk of Clostridioides difficile infection, and does not improve delirium resolution 3