Delirium refers to an acute confusional state that causes disturbed consciousness, attention, cognition & perception.

Delirium is essentially a state of acute confusion that affects normal brain functioning. The terminology can be confusing as delirium is often used synonymously with ‘acute confusion’, ‘acute confusional state’ and ‘encephalopathy’.

It should be considered a clinical syndrome typified by abnormal consciousness, attention, perception and cognition.

Delirium is characterised by:

  • Acute onset (hour to days)
  • Fluctuating symptoms (alters throughout the day)
  • Disturbance in awareness and attention (reduced awareness, distractible)
  • Disturbance in cognition (e.g. memory, language, disorientation)
  • Evidence of an organic cause (e.g. medical condition, medication, intoxication)

These features outline the diagnostic criteria provided by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria.

In clinical practice, delirium may be observed as an acutely confused patient (or acute change from baseline function) who has fluctuating altered level of consciousness (e.g. hyperactive or hypoactive), poor attention (e.g. cannot count backwards from 20) and disorganised thinking (e.g. disorientated to time or place, memory difficulty, incoherent speech).


Delirium is very common, particularly in the elderly population.

An estimated 50% of older adults (> 65 years) admitted to hospital will develop delirium during the course of their stay. In addition, delirium may complicate up to 87% of intensive care admissions.


Delirium may be classified into hyperactive, hypoactive or mixed.

The clinical features of delirium allow it to be divided into three subtypes:

  • Hyperactive delirium: characterised by inappropriate behaviour, agitation or hallucinations. Wandering and restlessness are common
  • Hypoactive delirium: characterised by reduced activity. Patients may appear quiet, lethargic, withdrawn and have reduced concentration
  • Mixed delirium: characterised by the presence of both hypoactive and hyperactive features


The cause of delirium is usually multifactorial.

Many conditions can precipitate the development of delirium and assessment involves a wide look into all the possible precipitating factors. It is important not to forget simple problems such as a change in environment, hearing impairment, emotional stress and constipation.

We can think about precipitating factors based on systems:

  • Neurological: brain injury, subdural haematoma, stroke, cerebrovascular disease
  • Cardiovascular: heart failure, myocardial infarction, atrial fibrillation
  • Respiratory: aspiration, pneumonia, exacerbation of chronic obstructive pulmonary disease
  • Gastrointestinal: constipation, malnutrition, bleeding
  • Urological: urinary retention, urinary tract infections
  • Skin & joints: cellulitis, pressure sores
  • Metabolic / endocrine: thyroid disease, hypo-/hyperglycaemia, hypo-/hypernatraemia
  • Medications: anti-histamines, tricyclic antidepressants, anti-cholinergics
  • Other: alcohol, uncontrolled pain, sleep deprivation, change in environment, hearing impairment.

Risk factors

Older age is one of the major risk factors for developing delirium.

Several factors predispose to the development of delirium:

  • Age (> 65 years)
  • Multiple co-morbidities
  • Frailty
  • Malnutrition
  • Sensory impairment (vision, hearing)
  • Functional impairment
  • Alcohol excess
  • Major injury (e.g. hip fracture)
  • Cognitive impairment (e.g. dementia)


There is global cortical dysfunction in delirium but the underlying cause is poorly understood.

Delirium results from a wide range of structural and physiological insults to the brain. Due to the numerous causes, there is unlikely to be a single dominant mechanism for development of the condition.

In general, it can be considered as a problem with global cortical dysfunction of which one of the dominant mechanisms is abnormal neurotransmitters in the brain such as reduced levels or acetylcholine or increased levels of dopamine. This is reflected by the precipitation of delirium in elderly patients taking anti-cholinergic medications (e.g. oxybutynin) and treatment of delirium in severe cases with anti-psychotic medications (e.g. haloperidol) that have anti-dopaminergic activity.

Clinical features

Hallmark features of delirium include disturbances in consciousness and cognitive function.

Delirium should be suspected in a patient with a sudden change in behaviour. Delirium is typically acute onset and fluctuates throughout the course of the day. There is often an identifiable precipitating cause (e.g. urinary tract infection, constipation).

A variety of behavioural disturbances can occur in delirium.

Abnormal consciousness

  • Reduced level of awareness and focus
  • Drowsy or semicomatose
  • Hyperactive

Abnormal cognition

  • Memory loss
  • Disorientation (e.g. to place, person or time)
  • Poor language (e.g. loss ability to speak a second language)
  • Poor speech

Abnormal thinking

  • Distractible and inattention (e.g. unable to follow commands)
  • Disorganised thinking (e.g. poor flow of ideas, disorganised speech, unable to express their needs)

Abnormal perception

  • Visual or auditory hallucinations
  • Paranoid delusions
  • Misperception

Other features

  • Labile changes in mood (e.g. irritable, paranoid, fear, depression)
  • Agitation
  • Sleep-cycle disturbances
  • Hypersensitive (light/sound)

It is pertinent to determine a patients ‘functional baseline’ that refers to what they are normally like and able to do day-to-day. This may involve discussion with a relative or carer as part of a ‘collateral history’. Otherwise, it can be very difficult to determine whether current behaviour is normal or abnormal, particularly those who have dementia or are very frail.


A variety of criteria are available to help make a formal diagnosis of delirium.

In clinical practice, a short cognitive assessment can be completed at the bedside to help make a diagnosis of delirium. These cognitive tools align with the DSM-5 diagnostic criteria.

DSM-5 criteria

This is divided into five domains that we have simplified:

  1. Disturbance in awareness (e.g. disorientated to time, place, person) and attention (e.g. unable to subtract serial 7’s)
  2. Acute onset (hours to days), acute change from baseline, and fluctuant
  3. Disturbance in cognition (e.g. memory loss, misperception)
  4. Not better explained by a pre-existing, established, or evolving neurocognitive disorder and absence of severely reduced GCS
  5. Evidence of an organic cause (i.e. medical condition, medication, intoxication)

Cognitive assessment

A number of cognitive assessment tools can be used at the bedside to enable a diagnosis of delirium. Three commonly used criteria include:

  • Confusion Assessment Method (CAM)
  • The 4A’s test (4AT)
  • Abbreviated mental test (AMT)

These are discussed further below.

Differentiating delirium from dementia

It may be difficult to differentiate delirium from dementia and vice versa. It is usually important to gather a good collateral history from a relative or carer to determine any change in the patients behaviour over time.

  • Features supportive of dementia: changes are slowly progressive with limited fluctuation. Attention is usually in tact and very early memories may be preserved (i.e. short term memory more affected).
  • Features supportive of delirium: changes are acute, transient and usually reversible. There is often an associated acute illness.

Patients may present with ‘acute-on-chronic’ confusion that represents development of delirium on a background of cognitive impairment that may be undiagnosed.

Cognitive testing

An assessment of mental status can be completed using recognised cognitive assessment tools.

A number of quick, cognitive tests may be utilised at the bedside to make a diagnosis of delirium.

Confusion Assessment Method (CAM)

  • Overview: brief assessment tool based on four features
    • (1) Acute & fluctuating course
    • (2) Inattention
    • (3) Disorganised thinking
    • (4) Altered level of consciousness
  • Time: < 5 minutes
  • Setting: hospital or community
  • Diagnosis for delirium: presence of 1 AND 2 plus either 3 OR 4

The 4A’s test (4AT)

  • Overview: a screening tool for delirium that involves four screening questions
    • (1) Alertness
    • (2) Four AMT questions: age, date of birth, place, current year
    • (3) Attention: list months in reverse order starting with December
    • (4) Acute change or fluctuating course
  • Time: < 5 minutes
  • Setting: hospital
  • Score: 1-3 (possible dementia), 4-12 (possible dementia/delirium)

Abbreviated mental test (AMT)

  • Overview: a ten item scoring tool predominantly used in hospital settings (e.g. hospital ward).
  • Time: < 5 minutes
  • Setting: hospital and General practice
  • Cut-off for delirium: 6-7/10


Patients with delirium are often elderly and acutely unwell requiring hospital admission.

Due to the wide number of causes a number of investigations are usually required as part of a ‘work-up’ for patients with delirium. These are usually requested as part of a ‘confusion’ screen.


  • Observations
  • ECG
  • Cultures: sputum, urine, stool
  • Capillary blood glucose


  • Full blood count
  • Urea & electrolytes
  • Liver function tests
  • Bone profile
  • Calcium
  • HbA1c
  • Haematinics: vitamin B12, folate
  • Thyroid function tests
  • C-reactive protein
  • Drug levels
  • Syphilis serology: classically part of the confusion screen


  • Chest x-ray
  • CT head: if intracerebral pathology suspected (e.g. subdural)
  • Echocardiogram: if heart failure suspected

More specialist investigations may be requested depending on the suspected underlying cause.


Treating patients with delirium can be very challenging due to their marked disturbance in behaviour.

Managing patients with delirium can be very difficult. It is important to involve relatives and carers whenever possible who can make a huge difference with management of behavioural abnormalities.

Management involves addressing the underlying precipitating cause(s) and ensuring the patient is safe. Part of this process involves completely a mental capacity assessment in line with the Mental Capacity Act and imposing the least restrictive measures necessary to ensure safety.

Mental capacity assessment

Patients with delirium usually lack capacity to make decisions about their care. Therefore, we have to treat them in their best interests using the Mental Capacity Act (MCA). See chapter on MCA.

Treat underlying cause

Any precipitating factors should be treated (e.g. antibiotics for an infection, laxatives for constipation) and co-morbidities should be optimised. The choice of treatment depends on the underlying cause.

Deescalation methods

A variety of methods may be needed to help manage abnormal behaviour. This should always involve simple, non-invasive strategies first as part of the least restrictive option.

Simple deescalation methods can include:

  • Address underlying cause of behaviour (e.g. thirst, need for toilet, pain)
  • Maintain adequate distance
  • Consider moving to a safe, low-stimulant environment
  • Use non-threatening verbal and non-verbal techniques (e.g. active listening, pictures, symbols)
  • Involve relatives or carers who are close to the patient
  • Consider advise from specialist elderly care psychiatrists or geriatricians
  • Consider involvement of the local delirium and dementia team

Rapid tranquillisation

Despite simple deescalation methods, patients with delirium may still pose significant psychological or physical harm to themselves and there may be risk of harm to others within the environment (e.g. patients, staff).

In these situations, the use of short-term pharmacological measures may be needed that is often referred to as rapid tranquillisation. Most hospitals set out local guidelines for the appropriate use of medications to manage severe behavioural abnormalities or agitation.

Two commonly used medications include:

  • Benzodiazepines (e.g. lorazepam)
  • Anti-psychotics (e.g. haloperidol, olanzepine)

The lowest possible dose should always be used with particular care taken to reduce the dose in elderly patients. The oral route should always be used in preference, but if not possible, then the intramuscular route is used. It is important to give time between doses and patients should be appropriately monitored.

NOTE: use anti-psychotics with caution in patients with cardiac disease and assess the QT interval (risk of prolonged QT and cardiac arrhythmias)

Mental Capacity Act

Patients who lack capacity should be treated in their best interests according to the Mental Capacity Act.

The Mental Capacity Act (MCA) is legal documentation that is designed to help protect and empower people that may lack the capacity to make decisions about their care. It applies to people 16+ years old. The legal framework essentially states that we should assume a person has capacity to make a decision unless proved otherwise. We cannot assume someone lacks capacity just because it is an unwise decision.

Assessment of mental capacity

Mental capacity should be assessed in two stages:

  1. Does the person have an impairment of their mind or brain, whether as a result of an illness, or external factors such as alcohol or drug use?
  2. Does the impairment mean the person is unable to make a specific decision when they need to?

A person lacks capacity if they cannot do one or more of the following:

  • Understand the information relevant to the decision
  • Retain the information long enough to be able to make the decision
  • Use or weigh up information available to make the decision
  • Communicate their decision

When a patient lacks capacity

If someone does lack capacity, we treat them in their best interests with the least restrictive option of their basic human rights. As part of this process, we should involve people closest to the patient (e.g. next of kin) who can advocate for them when lacking capacity. If patients do not have someone, an independent mental capacity advocate (IMCA) can be requested.

Before deciding a patient lacks capacity, it is important we take all necessary steps to enable them to make a decision. This may include providing alternative options, using different methods of communication, involving an advocate or delaying a decision.

Deprivation of Liberty Safeguarding

In some cases, if the least restrictive options placed on a patient deprive them of their liberty (e.g. using mittens, hospital bed rails or not allowing them to leave hospital) then we must apply for a deprivation of liberty safeguarding (DoLS).

A DoLS is a formal application to the local authority who arrange a formal assessment to decide on whether the deprivation of liberty is in the best interests of the patient and thus grant the legal authorisation.


Recovery from an episode of delirium may take weeks to months.

Older patients who develop delirium are at an increased risk of having prolonged delirium with adverse outcomes. Patients with pre-exiting cognitive impairment has an acceleration in cognitive decline after an episode of delirium.

Importantly, delirium is associated with an increased mortality, length of hospital stay, incidence of dementia and admission to long-term care. There is an estimated 70% risk of death within the first 6 months after admission to accident and emergency with delirium.

Last updated: May 2022

British Geriatrics Society. Patients presenting with confusion and delirium. 2019. Available online.
Raju, K. et al. An overview of delirium for the community and hospital clinician. Progress in Neurology and Psychiatry. 2015.
NICE. Delirium: Evidence Update April 2012 to NICE clinical guideline 103 ‘Delirium: diagnosis, prevention and management’. 2010.
Han, J. et al. Delirium in the emergency department: an independent predictor of death within six months. Annals of Emergency Medicine. 2010
Author The Pulsenotes Team A dedicated team of UK doctors who want to make learning medicine beautifully simple.

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