What Is Delirium?

Delirium is a sudden and severe change in how a person’s brain functions. It causes confusion, difficulty paying attention, and a reduced awareness of what is happening around them. Unlike conditions that develop slowly over time, delirium typically comes on quickly, usually within hours or a few days. The symptoms tend to fluctuate throughout the day, meaning they can come and go, often becoming worse at night when it is dark and surroundings are less familiar.^[1][2]

This condition is not simply “normal confusion.” It represents a serious medical problem where the brain is struggling to cope with stress from illness, medication, or other factors. Delirium is always caused by an underlying medical condition or trigger, and it is not explained by other known brain disorders like dementia (a long-term decline in memory and thinking skills). However, people with dementia are at higher risk of developing delirium.^[3]

There are three main types of delirium based on how a person behaves. Hyperactive delirium involves restlessness, agitation, and feeling overly alert or stressed. People with this type may be fidgety, anxious, or even combative. Hypoactive delirium is the opposite—it involves low energy, excessive sleepiness, and reduced movement. This type is often missed because the person appears calm or withdrawn rather than agitated. Finally, mixed delirium means the person switches back and forth between hyperactive and hypoactive states, sometimes even within the same day.^[2][4]

Epidemiology

Delirium is remarkably common, especially among older adults and people in medical settings. Studies show that it affects between 15 and 50 percent of hospitalized patients at some point during their stay. The rates are even higher in intensive care units, where up to 80 to 89 percent of patients may develop delirium. In nursing homes, up to 15 percent of people entering these facilities already have delirium when they arrive.^[3][10]

Older adults, particularly those aged 70 and above, are at greatest risk. Among hospitalized patients in this age group, approximately one-third will experience delirium. For those undergoing high-risk surgeries, such as hip fracture repair, the rates can climb to 50 percent. Emergency departments see delirium in up to 15 percent of older adults who come in for care.^[4]

Delirium is also very common at the end of life. Up to 85 percent of people experience delirium when they are dying, making it one of the most frequent complications in palliative and hospice care settings. The condition is not limited to older adults, though. Younger people can develop delirium, particularly if they are critically ill, have undergone surgery, or are using or withdrawing from substances.^[4][5]

Despite how common delirium is, healthcare professionals fail to recognize it in up to half of the cases. This is especially true for the hypoactive type, which is less obvious because patients appear quiet and withdrawn rather than agitated. The fact that delirium is so frequently missed means that many patients do not receive the prompt treatment they need.^[4]

Causes

Delirium is always triggered by something that puts too much stress on the brain or body. The brain becomes overwhelmed and cannot function normally, leading to the symptoms of delirium. Many different factors can cause this stress, and often multiple causes are involved at the same time.^[2][3]

One of the most common causes is medication. Certain drugs, especially those with anticholinergic effects (medications that block a chemical messenger in the brain), opioids (strong pain relievers), and sedatives, can trigger delirium. Taking too many medications at once, known as polypharmacy, also increases the risk. Sometimes even starting or stopping a medication that someone has been taking for a long time can lead to delirium.^[5][13]

Infections are another major cause. Pneumonia, bloodstream infections (also called sepsis), urinary tract infections, and any infection that causes a fever or affects the whole body can lead to delirium. Even minor infections, particularly in older adults or those with weakened immune systems, can be enough to trigger confusion.^[2][5]

Imbalances in the body, such as dehydration, low sodium levels, low oxygen levels (called hypoxia), or problems with the kidneys or liver, are also frequent culprits. Surgery and hospitalization themselves are stressful on the body and are associated with high rates of delirium. Pain, especially if it is new or severe and not properly managed, can contribute as well.^[1][5]

Other causes include alcohol or drug use or withdrawal, severe trauma, metabolic problems, and even simple issues like severe constipation or the presence of a urinary catheter. Environmental factors, such as being in an unfamiliar place, lack of natural light, sleep deprivation, and social isolation, can also play a role, particularly in vulnerable individuals.^[3][5]

Risk Factors

Certain groups of people are more vulnerable to developing delirium. The biggest risk factor is older age, particularly being over 65 or 70 years old. As people age, their brains become less resilient to stress, making them more susceptible to delirium when faced with illness or other challenges.^[2][4]

People with pre-existing cognitive impairment or dementia are at much higher risk. Between 25 and 50 percent of patients who develop delirium already have some form of dementia. Having memory problems makes the brain more fragile and less able to handle additional stress.^[3]

Frailty, which refers to being physically weak and vulnerable, is another important risk factor. People with multiple chronic health conditions, such as heart disease, lung disease, or diabetes, are also more likely to develop delirium. A history of having had delirium before increases the chances of it happening again.^[2]

Sensory impairments, such as poor vision or hearing, can make delirium more likely. When people cannot see or hear well, they have a harder time staying oriented to their surroundings, which can contribute to confusion. Similarly, people with mood disorders, substance use disorders, or those who are socially isolated face higher risks.^[5][13]

Hospitalization, particularly in intensive care units, is a major risk factor. Being in an unfamiliar environment, having medical equipment attached to the body (like intravenous lines or catheters), not being able to move around, and experiencing disrupted sleep all increase the likelihood of delirium. Surgery, especially high-risk procedures like hip or heart surgery, dramatically raises the risk as well.^[4][13]

Symptoms

The symptoms of delirium can vary widely from person to person, but they always involve changes in mental function. One of the hallmark symptoms is reduced awareness of surroundings. People with delirium may not know where they are, what time it is, or even recognize family members. They may be easily distracted by unimportant things or become fixated on a single thought or idea, making it hard to follow a conversation or respond to questions.^[1][2]

Thinking skills are also impaired. This can show up as poor memory, especially forgetting recent events or conversations. People may have trouble understanding what others are saying, struggle to find the right words, or speak in a way that does not make sense. They may ramble or have difficulty reading or writing. Disorganized thinking and trouble concentrating are common.^[1][2]

Behavioral and emotional changes are also part of delirium. Some people become anxious, fearful, irritable, or angry. Others may experience mood swings, shifting rapidly from calm to agitated or from happy to sad. Restlessness, fidgeting, and pulling at medical equipment or bedding are common in hyperactive delirium. In contrast, hypoactive delirium causes people to become unusually quiet, withdrawn, and drowsy, moving much less than usual.^[1][2]

Sleep disturbances are very typical. People with delirium often have their sleep-wake cycle reversed, staying awake at night and sleeping during the day. They may also have trouble falling or staying asleep. In some cases, people experience hallucinations (seeing or hearing things that are not there) or delusions (believing things that are not true). For example, they might think that hospital staff are trying to harm them or that they are in a different place than they actually are.^[2][7]

Symptoms of delirium tend to fluctuate throughout the day. There may be periods when the person seems relatively normal, followed by times when they are very confused. Symptoms are often worse in the late afternoon, evening, and nighttime, a pattern sometimes referred to as “sundowning.”^[1][7]

Prevention

Preventing delirium is one of the most important steps in caring for vulnerable individuals, especially older adults in hospitals or those undergoing surgery. Research has shown that many cases of delirium can be prevented through proactive, non-drug-based interventions that address multiple risk factors at once.^[13][22]

One key strategy is to keep people oriented to their surroundings. This can be done by frequently reminding them of the date, time, and where they are. Having a clock with a large, easy-to-read face and a calendar visible in the room helps. Family members and caregivers play an important role by visiting regularly, bringing familiar objects from home, and providing calm reassurance.^[12][22]

Maintaining a normal sleep-wake cycle is critical. During the day, rooms should be kept well-lit with natural light whenever possible, and people should be encouraged to stay awake and active. At night, the environment should be quiet and dark, with unnecessary noise and lights minimized. Avoiding nighttime disruptions, such as checking vital signs or drawing blood in the middle of the night, can help people get better rest.^[12][17]

Early and frequent mobilization is another effective preventive measure. Encouraging people to get out of bed, sit in a chair, and walk around as much as their condition allows helps keep the brain active and reduces the risk of delirium. Physical therapy can be helpful for those who need assistance with movement.^[12][13]

Ensuring adequate nutrition and hydration is important. Dehydration and poor nutrition can contribute to delirium, so offering fluids and nourishing meals throughout the day is essential. Helping people at mealtimes, especially if they need assistance eating or drinking, can make a big difference.^[9][22]

Addressing sensory impairments is another preventive step. Making sure that people have access to their glasses, hearing aids, and dentures helps them stay connected to their environment and reduces confusion. Removing unnecessary medical equipment, such as catheters or intravenous lines, as soon as it is safe to do so also helps. These devices can be uncomfortable, restrict movement, and contribute to disorientation.^[12][22]

Pain management is crucial. Untreated pain is a significant risk factor for delirium, so healthcare providers should regularly assess and manage pain appropriately. However, the medications used to treat pain, particularly opioids, must be chosen carefully, as they can also contribute to delirium.^[13]

Reducing unnecessary medications, especially those that are known to increase the risk of delirium, is an important preventive measure. Healthcare providers should review medication lists regularly and discontinue any drugs that are not essential.^[13]

Pathophysiology

The exact mechanisms by which delirium develops are not fully understood, but researchers believe it involves disruptions in how the brain functions at multiple levels. When the body or brain is under significant stress, normal communication between brain cells becomes impaired, leading to the symptoms of delirium.^[3]

One leading theory is that delirium involves imbalances in chemicals called neurotransmitters, which are messengers that brain cells use to communicate with each other. In particular, a reduction in a neurotransmitter called acetylcholine is thought to play a key role. Acetylcholine is important for attention, memory, and consciousness, and when its levels drop, confusion and disorientation can result. This is why medications with anticholinergic effects, which block acetylcholine, are common triggers for delirium.^[8]

Other neurotransmitters, such as dopamine, serotonin, and gamma-aminobutyric acid (GABA), may also be involved. An excess of dopamine, for example, can lead to agitation and hallucinations, while changes in serotonin and GABA can affect mood and arousal levels.^[8]

Inflammation throughout the body or in the brain itself may also contribute to delirium. When the body fights an infection or deals with injury, it releases substances that promote inflammation. These substances can cross into the brain and interfere with normal brain function. This is one reason why infections and surgeries are such common triggers for delirium.^[8]

Changes in blood flow to the brain, disruptions in the brain’s energy supply, and stress responses also play a role. When the brain does not get enough oxygen or glucose (its main fuel source), brain cells cannot function properly, leading to confusion and other symptoms. Conditions like low blood pressure, low oxygen levels, or severe metabolic disturbances can all disrupt the brain’s energy supply.^[8]

Advanced imaging studies have shown that delirium can be associated with changes in brain structure and activity, although these findings are still being researched. Some studies suggest that delirium may cause actual damage to brain cells, which could explain why people who have had delirium are at higher risk for long-term cognitive decline and dementia.^[8]