Home / Glossary
Delirium glossary
Plain explanations of words you may hear when someone has delirium.
This glossary covers 30 terms used by healthcare staff, families and carers. Some are names for delirium. Others describe symptoms, assessments or different conditions. Each entry explains the distinction.
Sudden confusion needs urgent medical assessment. If someone has become confused or is behaving very differently from usual, read what to do now.
4AT
A short assessment that staff use to help detect delirium. It checks alertness, answers to a few basic questions, attention, and whether there has been a recent change or fluctuation. Information from family or carers can help establish what has changed. Staff interpret the result alongside the person's history and other findings. A clinician makes the final diagnosis; the score alone does not diagnose delirium or dementia.
More information on the 4AT can be found at this website: www.the4AT.com.
Other wording you may hear: 4AT test; 4AT assessment; 4AT delirium test.
Sources and further reading
Acute confusion / acute confusional state
Acute confusion and acute confusional state are terms often used for delirium.
Acute means that the change began over a short time, usually hours or days. These words may appear in a conversation or a medical record before the diagnosis is clear. Ask the team whether they mean delirium, what they think is causing the change, and what assessment and treatment are planned.
Other wording you may hear: acute confusional state.
Sources and further reading
Acute encephalopathy
A medical term for a rapid disturbance in how the brain works. In specialist consensus terminology, acute encephalopathy describes the underlying brain changes that can cause delirium, some features of delirium, or coma. Clinicians use the term in different ways. If it appears in a letter or medical notes, ask what it means for this person and whether they have delirium.
Other wording you may hear: encephalopathy; acute brain dysfunction.
Sources and further reading
Altered mental status / AMS
A broad term used in medical notes when someone's alertness, thinking or behaviour is different from usual. Delirium is by far the most common explanation but unfortunately, it is still common practice to use the looser term "altered mental status" without proceeding to proper evaluation and diagnosis of delirium. There are some causes of altered mental status which would be given other labels, however.
If your relative or friend has been described as having altered mental status, ask the team what changes they have found and if the diagnosis is delirium.
Other wording you may hear: AMS; altered mental state.
Sources and further reading
Baseline / usual self / back to baseline
Baseline means what someone was usually like before the illness or change being discussed. This includes their thinking, communication, movement and everyday activities. Family and friends can help by giving concrete examples of what has changed. Back to baseline means a return to those usual abilities. Because delirium fluctuates, one clear conversation or a good hour may not show that recovery is complete.
Other wording you may hear: usual self; back to baseline; usual abilities.
Sources and further reading
CAM-ICU / ICDSC
Two different tools used by staff to assess delirium in intensive care and some other specialist settings.
CAM-ICU means Confusion Assessment Method for the Intensive Care Unit. It is a structured bedside assessment, including checks of attention and alertness.
ICDSC means Intensive Care Delirium Screening Checklist. Staff use it to record features of delirium from their observations.
The tools have different methods and scoring. Their results help the team assess the person; a clinician makes the final diagnosis.
Other wording you may hear: CAM ICU; Confusion Assessment Method for the Intensive Care Unit; ICDSC; Intensive Care Delirium Screening Checklist.
Delirium information and resources
Sources and further reading
Delirium
Delirium is a sudden change in how a person’s brain is working. It usually develops over hours or days. The person has difficulty paying attention and making sense of what is happening around them. Their thinking, memory or behaviour may change, and symptoms can vary during the day. Some people are restless; others become quiet and withdrawn. Many people with delirium develop hallucinations, which can often be frightening. They may also develop incorrect beliefs, such as that they are being imprisoned or poisoned. Delirium is serious and can be caused by illness, injury or medicines.
Sources and further reading
Delirium superimposed on dementia
This means delirium occurring in a person who already has dementia. You may hear it described as delirium on top of, or alongside, dementia. Look for a change from how the person usually thinks, behaves or manages everyday tasks. They may become much more confused, restless or withdrawn over hours or days. Tell the team what is different and when it began. A new change needs urgent assessment.
Other wording you may hear: delirium on top of dementia; delirium alongside dementia.
Delirium when someone has dementia
Sources and further reading
Delirium tremens / DTs / alcohol withdrawal delirium
A severe form of alcohol withdrawal that can develop after a person who is dependent on alcohol stops drinking or sharply reduces the amount they drink. It causes delirium, often with marked shaking, sweating, agitation or hallucinations. Delirium tremens is a medical emergency and needs immediate hospital treatment. Other alcohol-related conditions can also cause confusion, so the team must assess the cause.
Other wording you may hear: DTs; alcohol withdrawal delirium.
Sources and further reading
Dementia
Dementia is a group of symptoms caused by diseases that damage the brain. It affects thinking and everyday life, and may involve memory, language or judgement. Changes usually develop over months or years, although the pattern varies.
Delirium is not the same as dementia. The main difference is that dementia arises over months or years, and delirium arises over hours or days. There also are differences in the changes in mental functioning, with delirium more often having changes in level of alertness, although that can also happen in dementia.
A person with dementia can also develop delirium. A sudden change needs medical assessment. Tests done during delirium can be difficult to interpret, so further assessment may be needed after the acute illness.
Sources and further reading
Drug-induced / medication-induced delirium
Delirium caused or partly caused by a medicine or another drug. It may follow a new medicine, a change in dose, or withdrawal from some medicines or substances. More than one cause may be present. Give the team a full list of prescribed medicines, over-the-counter products and recent changes. A clinician should review possible effects and decide whether treatment needs to change. Ask for advice before stopping or changing a prescribed medicine.
Other wording you may hear: medication-induced delirium; medicine-induced delirium; delirium caused by medication.
Sources and further reading
Hospital delirium
Hospital delirium means delirium in someone who is in hospital. It may have started before they arrived or developed during their stay. The phrase tells you where the person is being cared for, but it does not explain the cause. Illness, an operation, medicines and other problems may contribute. Ask the team what has changed, what might be causing it, and how they are helping.
Hospital delirium: what the term means and where it has been used.
Sources and further reading
Hospital-acquired delirium
Hospital-acquired delirium usually means delirium that develops after a person has been admitted to hospital. This differs from delirium that was already present at the point of admission. The label does not explain why it happened or show whether it could have been prevented. Information from family about when the change began can help the team understand the episode and look for its causes.
Sources and further reading
Hospital-induced dementia / sudden dementia
These phrases may be used when someone’s memory or thinking has worsened suddenly during a hospital stay. The term is misleading and incorrect. This is because dementia is a condition that evolves over months or years and does not arise suddenly, and is never diagnosed if it has only appeared after a short time in hospital.
Delirium, including delirium in someone who already has dementia, may be responsible. A sudden change should not be dismissed as dementia or ageing. Recovery after delirium varies, and ongoing difficulties need review rather than a promise that everything will return to normal.
Other wording you may hear: sudden dementia.
Sources and further reading
Hyperactive delirium
In hyperactive delirium, a person is unusually restless or agitated. As part of this, they often struggle to pay attention or understand what is happening. They may pace, try to get out of bed, or seem frightened. Some have hallucinations or distressing beliefs. Tell the team what you notice. A calm approach and assessment of discomfort and possible causes are part of their care.
Sources and further reading
Hypoactive / quiet delirium
In hypoactive delirium, a person becomes less active and less engaged with what is happening around them. They may speak little, respond slowly, move less, or struggle to concentrate. Some may not even be able to speak at all. They can seem sleepy or withdrawn, so the change is easy to miss. Quietness does not make delirium less serious. Tell the healthcare team about a new change from the person’s usual behaviour, even if they seem settled. A person who is unresponsive even to pain would be classified as having a coma rather than delirium.
Other wording you may hear: quiet delirium.
Sources and further reading
ICU delirium / intensive care delirium
ICU delirium is delirium in someone being cared for in an intensive care unit. Severe illness and treatments can affect how the brain works. A person may be confused, restless or unusually withdrawn. Medicines used to keep them comfortable or asleep can also affect alertness. Staff take these effects into account when assessing for delirium. Ask the intensive care team what they have found and how you can help.
Other wording you may hear: intensive care delirium.
Intensive care information and support
Sources and further reading
ICU psychosis / hospital psychosis
These are imprecise labels you may hear when someone has become confused or had frightening experiences in hospital, especially in intensive care. The speaker may mean delirium. Ask the team which diagnosis they are describing. Hallucinations, such as seeing things that are not there, can occur in delirium and in other conditions. Those experiences alone do not confirm delirium or explain what caused them.
Other wording you may hear: hospital psychosis.
Sources and further reading
Mental capacity / capacity
A person's ability to make a particular decision at the time it is needed. Delirium can affect this ability, and capacity may change as symptoms fluctuate. A diagnosis of delirium does not automatically mean that someone lacks capacity for every decision. They should have support to take part in decisions as fully as possible. England and Wales use the Mental Capacity Act 2005; Scotland has different law under the Adults with Incapacity (Scotland) Act 2000. Other countries have their own legal frameworks.
Other wording you may hear: capacity; decision-making capacity; lack of capacity.
Sources and further reading
Metabolic / toxic / toxic-metabolic encephalopathy
These terms describe disturbed brain function in relation to its suspected or known cause. Metabolic refers to changes in body chemistry or the effects of organs working poorly. Toxic refers to harmful effects of a substance, which may include a medicine. Toxic-metabolic is a combined label. Hepatic encephalopathy refers specifically to brain effects of liver disease. The label alone does not establish whether the person has delirium, the precise cause, or how fully they will recover.
These terms often are used loosely, and best practice in clinical care is to use the word delirium and then to specify the potential causes, which might be metabolic or to do with infection.
Other wording you may hear: toxic encephalopathy; toxic-metabolic encephalopathy; toxic metabolic encephalopathy; hepatic encephalopathy.
Sources and further reading
Mixed delirium
Mixed delirium means that the person has periods of hyperactive delirium and periods of hypoactive delirium. They may be restless at one time and quiet or drowsy at another. These changes can happen within a day or over several days. The word mixed describes these changing activity patterns. It does not mean that the person necessarily has several causes of delirium or that they also have dementia.
Understanding the types of delirium
Sources and further reading
Perioperative neurocognitive disorders
A group term for problems with thinking identified around surgery. It includes pre-existing cognitive impairment, postoperative delirium and the conditions below.
Delayed neurocognitive recovery: cognitive decline identified within 30 days after surgery.
Postoperative neurocognitive disorder: cognitive decline diagnosed from 30 days to 12 months after surgery, using specific clinical criteria.
These time windows help clinicians classify the problem. They are not waiting periods for assessment. The word postoperative describes timing; it does not prove that the operation or anaesthetic caused the change.
Other wording you may hear: peri-operative neurocognitive disorders; perioperative NCD; delayed neurocognitive recovery; postoperative neurocognitive disorder.
Sources and further reading
Persistent / prolonged delirium
Persistent or prolonged delirium means that delirium continues rather than settling over a small number of days. There isn't a strict cutoff used for when persistent delirium is diagnosed, but many clinicians see that 5 days or more would qualify as persistent delirium.
Persistent delirium can last for weeks or months in some people. Continued symptoms need review, even when the original illness or illnesses thought to have triggered the delirium have been treated. The team may need to look again for ongoing or new causes and review medicines and care needs. Recovery varies. Some people recover fully; others have lasting changes and need further assessment and support.
Other wording you may hear: prolonged delirium.
Sources and further reading
Postoperative cognitive dysfunction / POCD
An older research term for a decline in memory or other thinking abilities measured after an operation. Studies have used different tests and time points, so POCD has not had one consistent definition. The term alone does not tell you whether someone has delirium or another problem. If it appears in a letter, ask which difficulties were found, when they started and what follow-up is planned.
Other wording you may hear: POCD; post-operative cognitive dysfunction.
Sources and further reading
Postoperative delirium / delirium after surgery
Delirium that occurs after an operation. Several factors may contribute, including the illness that triggered the need for surgery (especially if this was an emergency), pain, medicines and complications such as infection. Staff need to distinguish delirium from the expected effects of anaesthetic medicines and other problems with thinking or memory. Tell the team promptly about a new change.
Other wording you may hear: postoperative delirium; post-operative delirium; post-op confusion; confusion after surgery; brain fog after surgery.
Sources and further reading
Sudden confusion
Sudden confusion describes a change in thinking or awareness that develops over hours or days. Sudden confusion is a descriptive term but not a formal diagnosis. A person with sudden confusion usually has delirium.
The person may struggle to follow a conversation, seem disorientated, or behave very differently from usual. They need urgent medical assessment to find out whether they have delirium or potentially another medical problem. Outside a care setting, phone local emergency services now. In hospital or a care home, tell staff immediately.
Sources and further reading
Sundowning / sundowner’s syndrome
Sundowning describes a pattern in which someone with dementia becomes more confused, anxious or restless later in the day, often in the late afternoon or evening. Delirium can also become worse at these times. The time of day alone does not tell you which is happening. If the person has a sudden new change or is much worse than usual, seek urgent medical assessment rather than assuming it is sundowning.
Other wording you may hear: sundowner’s syndrome.
Why symptoms may be worse in the evening
Sources and further reading
Terminal agitation / terminal restlessness
Words used for agitation or restlessness in someone who is dying. The person may seem distressed, move about repeatedly or struggle to settle. Delirium can cause these symptoms, but other explanations include pain, anxiety or discomfort from a full bladder. Staff should assess possible causes and help relieve distress, taking account of the person's wishes and overall care.
Other wording you may hear: terminal restlessness; end-of-life agitation; end-of-life restlessness.
Sources and further reading
Terminal delirium / delirium near the end of life
Delirium in someone who is thought to be approaching the end of life, usually thought of as the days or a small number of weeks leading up to death. The word terminal describes that situation; delirium by itself does not mean that death is imminent. Some causes of delirium may still be treatable. The team should consider the person's wishes, comfort and overall condition when deciding what to investigate or treat. Families can ask what may be causing the changes and how distress will be relieved.
Other wording you may hear: end-of-life delirium; delirium in the dying phase.
Sources and further reading
UTI delirium / UTI confusion
Phrases used when a urinary tract infection (UTI) is thought to have caused delirium.
Urinary tract infections or UTIs are common causes of delirium.
Sometimes people assume that a UTI (urinary tract infection) is the cause when there are other causes. In such situations, prescribing antibiotics may not have any effect on the delirium itself and simply cause side effects. One important issue is that older people often have bacteria in urine which are not causing an active infection. If a person has delirium and these bacteria are detected, there is an assumption made that there is a urinary tract infection.
When a person develops delirium (otherwise known as sudden confusion or acute confusion) although a urinary tract infection (UTI) may be the cause, it's always important to consider other causes at the same time and make a decision based on all the evidence.
Other wording you may hear: UTI confusion; urine infection confusion; urinary tract infection and delirium; confusion from a urine infection.
Can a urine infection cause confusion?