What Is Delirium, and What Causes It?

A fellow caregiver asked...

What is delirium, and what causes it?

Expert Answer

Dr. Leslie Kernisan is the author of a popular blog and podcast at BetterHealthWhileAging.net. She is also a clinical instructor in the University of California, San Francisco, Division of Geriatrics.

Delirium is a state of acute mental confusion, meaning a person's state of mind suddenly becomes worse than usual. Delirium can cause a person with a perfectly healthy mind to behave like a person who has dementia. For persons with dementia, delirium makes their mental state worse. The key is that it's a sudden change from what's normal for that individual.

The main signs of delirium usually include:

  • Confused thinking.

  • Difficulty focusing.

  • Difficulty paying attention.

The person with delirium may also:

  • Appear agitated (or "revved up"), or the opposite: drowsier or quieter than usual.

  • Hallucinate or have delusions (false beliefs not in sync with the person's usual cultural beliefs).

It's common for the mental confusion to fluctuate throughout the day, with the delirious person sometimes seeming like his or her usual self and then, say an hour later, appearing much altered.

Delirium is usually a sign of a stress, such as an illness, affecting the body overall. Common serious causes include infections (such as urinary tract infections or pneumonia), abnormalities of blood chemistry (such as high levels of blood sugar or sodium), dehydration, or even excessive pain after surgery. Delirium can also be caused by or worsened by intoxication or by certain medications (such as antihistamines, which have side effects that influence brain chemistry).

Although younger people with healthy minds can develop delirium, elderly people and people with dementia are especially prone to becoming delirious when sick. A frail elder may also develop delirium when stressed by seemingly minor issues such as constipation, lack of sleep, or not having eyeglasses and hearing aids while in the hospital.

Research has shown that delirium is common in hospitalized patients; up to 50 percent of postsurgical patients may be affected. Unfortunately, delirium is often missed by hospital personnel.

Especially in a frail older person, delirium can be the only outward sign of a serious medical illness. For this reason, any new or suddenly worsened mental confusion needs to be promptly brought to the attention of a medical provider. Since a delirious person may not be able to answer questions properly, it's especially important for a caregiver to help describe the problem. Be sure the doctors realize that the mental confusion is new, or worse than usual.