There are many causes that may bring on a state of delirium.

For example, if a person already has dementia, then a relatively minor injury or upset may bring on delirium. This can include things like a single dose of a new medication or a change in residence. In fact, dementia is the most common risk factor for delirium, and two-thirds of cases of delirium occur in people who already have dementia. In other people who aren’t as vulnerable, delirium may develop when several factors occur together, such as general anesthesia, major surgery, and change in psychiatric medications.

Addressing just one contributing factor is unlikely to resolve delirium in an older person.  They should all be addressed when possible. Any single action or intervention in a care plan may have a small impact, but several actions together, even if individually small, can add up to significant improvement. A key goal for the healthcare provider is to identify as many causes as possible and correct those that are reversible.

Reversible causes of delirium are outlined by the following acronym (DELIRIUM):

  • Drugs, including any new medications, increased dosages, drug interactions, over-the-counter drugs, alcohol, etc.
  • Electrolyte disturbances, especially dehydration and thyroid problems.
  • Lack of drugs, such as when long-term sedatives (including alcohol and sleeping pills) are stopped, or when pain drugs are not being given adequately.
  • Infection, commonly urinary or respiratory tract infection.
  • Reduced sensory input, which happens when vision or hearing are poor.
  • Intracranial (referring to processes within the skull) such as a brain infection, hemorrhage, stroke, or tumor (rare).
  • Urinary problems or intestinal problems, such as constipation or inability to urinate.
  • Myocardial (heart) and lungs, such as heart attack, problems with heart rhythm (arrhythmia), worsening of heart failure, or chronic obstructive lung disease. 

Delirium can result from an imbalance in brain chemicals (neurotransmitters), which are crucial molecules that relay signals between nerves. A particularly important neurotransmitter is acetylcholine. One reason that people with dementia (such as Alzheimer’s disease) are at high risk of delirium is that the brain damage found in dementia kills the brain cells that produce acetylcholine. If oxygen or glucose levels in the brain decrease, even a little, the amount of acetylcholine drops even more dramatically. In such cases, the brain functions abnormally, producing delirium. 

Other brain chemicals, such as dopamine, also contribute to delirium, because they regulate the amount of acetylcholine in the brain.

  • Medications. Side effects of familiar medications or sudden withdrawal from drugs are the most common and most treatable causes of delirium. Since many older people take multiple medications which may interact in harmful ways, it is important that healthcare professionals are told about every prescription and non-prescription medication being taken.
  • Alcohol. Alcohol abuse is frequently overlooked as a cause of delirium in older adults. Either excessive use (intoxication) or a sudden withdrawal from alcohol can cause delirium. Delirium caused by withdrawal of alcohol appears to be as common in older adults with alcoholism as in their younger counterparts, although the death rate after withdrawal is higher in older alcoholics.
  • Medical conditions. Virtually any physical illness or condition can bring on delirium, especially when more than one illness is present. Sometimes, delirium is also the first sign of a serious, life-threatening illness such as a heart attack. In a hospital, the most common causes are sudden blood loss, dehydration, low blood pressure, fluid retention, infections, low levels of oxygen (hypoxia), kidney or liver failure, high blood sugar (hyperglycemia) or low blood sugar (hypoglycemia), intestinal blockage (impaction), sleep deprivation, or inability to urinate. Delirium caused by a sudden change in the nervous system, such as a stroke, brain tumor, or brain infection, is less common. Immobility, sleep deprivation or fragmented sleep, and pain can all contribute to bringing on delirium.
  • Environmental conditions. Delirium can also result from too little stimulation of the senses, especially in people who already have some degree of mental impairment, or who are confined to a featureless room in a hospital or nursing home. In one study, delirium after an operation occurred twice as often in patients in intensive care units without windows as in patients in similar units with windows. In addition, a form of delirium that occurs in the evening (known as “sundowning”) may be partly due to sensory deprivation. Vision and hearing loss may also make it more difficult for the person to perceive reality and increases the likelihood of delusions or hallucinations.
  • Delirium after surgery. Delirium may be the most common complication after surgery in older adults, and leads to longer hospital stays, a higher death rate, and a greater need for nursing home care afterwards. It may also signal that there will be complications after surgery.

The chance that a patient will become delirious after an operation increases if a patient is an older adult, already has dementia or a physical disability, drinks excessive alcohol, or has very abnormal blood tests. Also, certain types of operations are more frequently associated with delirium. For example, delirium is much more common after hip surgery and heart surgery.


Last Updated July 2020

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