Assessment of delirium

Overview 
Theory 
Emergencies 
Diagnosis 
Resources 

Last reviewed: 19 Sep 2025

Last updated: 02 Oct 2025

Introduction

Delirium is an acute, fluctuating change in mental status, with inattention, disorganised thinking, and altered levels of consciousness.[1] It is a potentially life-threatening disorder characterised by high morbidity and mortality. Guidelines address recognition, risk factors, and treatment for delirium.[2][3][4]

Adverse sequelae

Mortality for those diagnosed with delirium in hospital is twice that of patients with similar medical conditions without delirium, and may be as high as 14% within 1 month of diagnosis.[5]

Delirium is common in the intensive care unit, especially among mechanically ventilated patients. In critically unwell patients, it is associated with an increased length of stay and increased mortality.[6][7]

Delirium is associated with elevated risks for functional and cognitive decline, poor rehabilitation potential, institutionalisation, and rehospitalisation.[1][7][8][9][10][11] While delirium has been considered to be a reversible condition, studies suggest that delirium symptoms can last for weeks to months following onset.[12] Persistent delirium has been found to be frequent in older hospitalised patients, and associated with adverse outcomes.[13] There is growing evidence that delirium may be an independent risk factor for longer term cognitive decline.[14]

Classification

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR) notes that in order to be diagnosed with delirium, a patient must show all 4 of the following features.[15]

A disturbance in attention (i.e., reduced clarity of awareness of the environment) is evident, with reduced ability to focus, sustain, or shift attention. This disturbance in consciousness might be subtle, initially presenting solely as lethargy or distractibility, and might be frequently dismissed by clinicians and/or family members as being related to the primary illness.
A change in cognition (such as memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance not better accounted for by a pre-existing or evolving dementia.
The disturbance develops over a short period of time (usually hours to days), represents an acute change from baseline, and tends to fluctuate during the course of the day.
There is evidence from the history, physical examination, or laboratory findings that the disturbance is caused by the direct physiological consequences of a general medical condition, substance intoxication, or substance withdrawal. The changes in attention and cognition must not occur in the context of a severely reduced level of arousal, such as coma.

Three clinical subtypes of delirium have been identified.[16][17][18] These include:

Hyperactive delirium - a condition where a patient might have heightened arousal, with restlessness, agitation, hallucinations, and inappropriate behaviour
Hypoactive delirium - a condition where a patient might display lethargy, reduced motor activity, incoherent speech, and lack of interest
Mixed delirium - a combination of hyperactive and hypoactive signs and symptoms.

The term sub-syndromal delirium has also been used to define partially resolved or incomplete forms of delirium.

Epidemiology

Delirium occurs in ≥20% of hospitalisations annually, and is the most common hospital-related complication in the US.[19][20][21] Prevalence of delirium ranges from 10% to 40% in older hospitalised patients.[19]

Delirium affects up to 35% of people on medical wards.[3][14] Prevalence ranges from: 8% to 18% in the emergency department; 15% to 53% for postoperative patients; and 7% to 50% for intensive care patients.[22][23][24][25] The incidence and prevalence of delirium in medical inpatients appears to have remained broadly stable over the past four decades.[26]

The prevalence of delirium in the community is believed to be 1% to 2%, a figure that increases to 10% for patients aged >85 years.[27]

Delirium is frequently under-recognised. This may be indicative of the fluctuating nature of delirium symptoms, and an overall underappreciation of its clinical significance.

Pathophysiology

The pathophysiology of delirium remains relatively unclear. In general, neuroimaging studies reveal disruptions in higher cortical functioning in multiple disparate areas of the brain, including the prefrontal cortex, subcortical structures, thalamus, basal ganglia, lingual gyri, and frontal, fusiform and temporoparietal cortex.[28][29] Electroencephalographic (EEG) studies show diffuse slowing of cortical activity.

Theories on the pathogenesis of delirium point to the role of neurotransmitters, inflammation, and chronic stress on the brain. For example, the role of cholinergic deficiency in inducing delirium is strengthened by the clear association of anticholinergic drug use with increased incidence.[30] Studies in surgical patients have demonstrated a dysfunctional interaction between the cholinergic and immune systems in patients who developed postoperative delirium.[31]

Dopaminergic excess is also believed to contribute. Evidence does not appear to support the use of antipsychotic drugs (dopamine antagonists) for the prevention or treatment of delirium, but is not entirely consistent.[32][33][34][35][36][37][38][39] Other neurotransmitters implicated in the pathophysiology of delirium include noradrenaline, serotonin, gamma-aminobutyric acid, glutamate, and melatonin.

Cytokines, including interleukins 1 and 2, TNF-alpha, and interferon, may contribute to delirium onset.[40] Chronic hypercortisolism, as induced by chronic stress secondary to illness or trauma, may contribute to delirium initiation.[41][42]

Differentials

Common

Dementia
Pain
Stroke and transient ischaemic attack
Myocardial infarction
Acute systemic infection
Hypoglycaemia
Hyperglycaemia
Hypoxia
Hypercapnia
Acute urinary obstruction
Drug- or illicit drug-related
Alcoholic ketoacidosis
Hepatic encephalopathy
Renal failure
Hypernatraemia
Hyponatraemia
Hypercalcaemia
Meningitis/encephalitis
Brain tumour
Post-ictal state
Dehydration (volume depletion)
Constipation

Full details

Uncommon

Traumatic head injury
Adrenal crisis
Thyrotoxicosis
Myxoedema coma
Brain abscess
Neurosyphilis
Wernicke's encephalopathy

Full details

Contributors

Authors

Natalia Jaworska, MD, MSc, FRCPC

Intensivist and Clinical Assistant Professor

Department of Critical Care Medicine

University of Calgary

Calgary

Canada

Disclosures

NJ has held and holds several grants from the University of Calgary and Alberta Health Services related to the topic of sedation and delirium prevention in critically ill adult patients. The University of Calgary and Alberta Health Services did not play any role in the development or administration of the research projects.

Acknowledgements

Dr Natalia Jaworska would like to gratefully acknowledge Dr Margret Pisani and David M. Dosa, previous contributors to this topic.

Disclosures

MP and DMD declare that they have no competing interests.

Peer reviewers

Marquis Foreman, PhD, RN, FAAN

Professor and Associate Dean for Nursing Science Studies

College of Nursing

University of Illinois at Chicago

Disclosures

MF declares that he has no competing interests.

Andrew Parfitt, MBBS, FFAEM

Clinical Director

Acute Medicine

Associate Medical Director

Consultant Emergency Medicine

Guy's and St Thomas' NHS Foundation Trust

Clinical Lead and Consultant

Accident Emergency Medicine

St Thomas' Hospital

London

Disclosures

AP declares that he has no competing interests.

Peer reviewer acknowledgements

BMJ Best Practice topics are updated on a rolling basis in line with developments in evidence and guidance. The peer reviewers listed here have reviewed the content at least once during the history of the topic.

Disclosures

Peer reviewer affiliations and disclosures pertain to the time of the review.

References

Our in-house evidence and editorial teams collaborate with international expert contributors and peer reviewers to ensure that we provide access to the most clinically relevant information possible.

Key articles

Devlin JW, Skrobik Y, Gélinas C, et al; American College of Critical Care Medicine. Clinical Practice Guidelines for the Prevention and Management of Pain, Agitation/Sedation, Delirium, Immobility, and Sleep Disruption in Adult Patients in the ICU. Crit Care Med. 2018 Sep;46(9):e825-73.Full text Abstract

National Institute for Health and Care Excellence. Delirium: prevention, diagnosis and management in hospital and long-term care. Jan 2023 [internet publication].Full text Abstract

American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 5th ed., text revision (DSM-5-TR). Washington, DC: American Psychiatric Publishing; 2022

Reference articles

A full list of sources referenced in this topic is available here.

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Assessment of delirium

Summary

Introduction

Adverse sequelae

Classification

Epidemiology

Pathophysiology

Differentials

Common

Uncommon

Contributors

Authors

Natalia Jaworska, MD, MSc, FRCPC

Disclosures

Acknowledgements

Disclosures

Peer reviewers

Marquis Foreman, PhD, RN, FAAN

Disclosures

Andrew Parfitt, MBBS, FFAEM

Disclosures

Peer reviewer acknowledgements

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available here.

Guidelines

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