1. Recognise the pattern

Three core features are acute onset or change, inattention, and fluctuation. The change develops over hours or days rather than months or years. The person may lose the thread of a conversation, struggle to follow an instruction, or vary between drowsiness and alertness. A period of apparent improvement does not exclude delirium.

Delirium can occur with or without dementia. If a person with dementia becomes suddenly less attentive, less alert, or otherwise different from their usual self, consider delirium superimposed on dementia. If the distinction is difficult, NICE advises managing the delirium first.

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2. Do not miss the quiet presentation

Hypoactive delirium can be clinically subtle. The person may be quiet, withdrawn, drowsy, slow to respond, less mobile, and less interested in food. This presentation may be mistaken for fatigue, depression, or progression of dementia and is particularly liable to be missed.

Hyperactive delirium may present with restlessness or agitation, while mixed delirium alternates between hypoactive and hyperactive features. Motor and behavioural features are non-specific and do not identify the underlying cause.

Delirium can also cause new changes in perception, including visual or auditory hallucinations, and sometimes frightening or suspicious ideas. These features are not specific to delirium, but when they are new or fluctuating they should prompt the same acute-change assessment.

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3. Use the 4AT appropriately

The 4AT is a brief bedside assessment that looks at alertness, orientation, attention, and acute change or fluctuation. Its AMT4 component is the four-item Abbreviated Mental Test: age, date of birth, place, and current year. Months Backwards directly tests attention. Information about acute change may come from someone who knows the person or from the clinical record (Lin et al. 2023).

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4. Help prevent delirium

Delirium prevention is not a single intervention. For an adult at risk in hospital or long-term care, assess the factors that apply to that person and provide several relevant measures together. These can include orientation and familiar contact; hydration and nutrition; assessment and management of infection, hypoxia, pain, and constipation; medication review; hearing and visual aids; supported mobility or movement appropriate to current ability; and protecting sleep. Prevention is a shared multidisciplinary responsibility and should be adapted to the person and care setting (Zhao et al. 2023; Sánchez et al. 2026).

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5. Act on suspected delirium

Delirium often has several contributors (Ormseth et al. 2023). Look promptly for urgent physical or medical problems, then identify and manage the likely causes and contributing factors. The exact assessment depends on the person and the setting.

1. Notice the change. Look for a new or fluctuating change in attention, alertness, thinking, communication, behaviour, appetite, sleep, mobility, or ability to take part in care. Quiet withdrawal matters as much as agitation.
2. Check promptly. Establish the usual baseline and time course. Check observations and urgent physical problems. Complete the 4AT where appropriate while urgent assessment and treatment proceed.
3. Escalate concerns. Communicate concerns promptly. State clearly that this is an acute change from baseline, describe the exact observations, and identify the current clinical priorities.
4. Support the person and address causes. As a team, identify and manage likely causes and address relevant factors such as pain, hydration, nutrition, constipation, mobility, sensory impairment, sleep, orientation, and the care environment.
5. Review and communicate. Delirium fluctuates. Reassess the course, response, and remaining concerns. Document the baseline, change, assessment, findings, actions, and next review, and communicate these across shifts and transfers.

For a frightened or distressed person, look for pain, urinary retention, constipation, hunger, thirst, fear, noise, and unfamiliar surroundings. Reorientation, reassurance, a suitable environment, and verbal and non-verbal de-escalation come first. Antipsychotic medication used for delirium-related distress or risk has a restricted role: consider it only when the person is distressed or a risk to themselves or others and de-escalation is ineffective or inappropriate, using individual clinical judgement and local guidance.

Role boundary: Only an authorised prescriber should make medication decisions. Other staff should report the observed distress or risk, measures tried and the response, and follow the local escalation pathway.

Where medication is considered, use current national guidance and check contraindications. Haloperidol is contraindicated in Parkinson’s disease and dementia with Lewy bodies; see the MHRA safety advice for use in older people.

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Brain care: find and treat triggers; optimise physiology, including oxygen saturation and blood pressure; attend to hydration and nutrition; check for urinary retention; avoid constipation; and review medication.

Mind care: use a smiling, gentle manner; introduce yourself; provide context and reorientate; ask about distress; detect hallucinations and delusions; reassure and explain; tell the person they have delirium when appropriate; and give hope.

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