Causes of Delirium
Delirium is most commonly caused by infection (particularly urinary tract infections and pneumonia), with multiple coexisting precipitating factors frequently present in the same patient. 1
Primary Etiologic Categories
Delirium results from direct physiologic consequences affecting the brain, which can be organized into several key categories:
Medical Conditions
- Infections (34% of cases): Most common precipitating factor 1, 2
- Urinary tract infections
- Pneumonia
- Sepsis 3
- Metabolic disturbances 3, 4
- Hypoglycemia
- Dysnatremia (hypo- or hypernatremia)
- Uremia
- Ammonemia
- Electrolyte imbalances 5
- Organ dysfunction 1
Neurological Processes
- Traumatic brain injury 1
- Cerebrovascular disease 1
- Status epilepticus/nonconvulsive seizures 1
- Intracranial mass effect or elevated intracranial pressure 1
- Subdural or subarachnoid hemorrhage 1
- Meningitis or encephalitis 1
- Transient ischemic attack 1
- Hydrocephalus 1
Medications and Substances
- Psychoactive medications (particularly benzodiazepines) 3, 4
- Drug-induced coma 3
- Intoxication 1, 3, 1
- Toxin exposure 1
- Withdrawal syndromes 1, 3, 6, 1
- Alcohol withdrawal
- Benzodiazepine withdrawal
- Opioid withdrawal
Other Contributing Factors
- Hypoxia 7, 4
- Pain (poorly controlled) 7, 4
- Sleep alterations/deprivation 3, 4
- Immobility or limited mobility 8, 4
- Poor nutrition/malnutrition 8, 9
- Sensory impairment 8, 4, 2
- Dehydration or constipation 8
- Anemia 7
Critical Clinical Context
Multiple causes coexist in most patients - 25% of delirium cases have multiple equally contributory causes 2, and 64.2% are multifactorial 5. This means you must search for and address all contributing factors simultaneously, not just the most obvious one.
Predisposing vs. Precipitating Factors
The threshold concept explains delirium development 9:
Predisposing (vulnerability) factors:
- Advanced age (strongest independent risk factor; 3.3-fold higher odds in patients ≥80 years) 5
- Pre-existing cognitive impairment or dementia 3, 11, 9
- Multimorbidity 9
- Substance use history 9
Precipitating (hospital-related) factors:
- Acute illness 3
- Surgery 1, 12
- Invasive procedures (e.g., bladder catheterization, OR 1.4) 10
- ICU admission 1, 12
Patients with high vulnerability may develop delirium from minimal precipitating factors, while those with low vulnerability require more severe insults. 3
Common Pitfalls
- Missing hypoactive delirium: This is the most common subtype but frequently goes unrecognized because patients appear calm or withdrawn rather than agitated 6
- Attributing confusion solely to "old age" or dementia: Delirium represents acute brain dysfunction requiring immediate investigation 1, 13
- Overlooking medication-related causes: Beyond traditional anticholinergics, consider medications causing severe electrolyte disturbances or direct neurological effects 5
- Failing to identify multiple simultaneous causes: Always search for coexisting precipitating factors rather than stopping after finding one 1, 2