5th June 2023

Delirium

The Diagnostic and Statistical Manual for Mental Disorders 5th Edition (DSM-5) defines delirium as “a disturbance in awareness, attention and with a change in baseline cognition”. The core clinical feature is inattention occurring in the context of acute deterioration in the patient’s usual cognition, which fluctuates. The onset is acute, generally over hours or days, and there is usually a trigger, such as a change in medication or acute illness.

The pathogenesis is thought to be a mixture of neuroinflammation, neurotransmitter imbalance and changes in brain metabolism.

Types of delirium

There are three types of delirium: hypoactive, hyperactive and mixed type. In hypoactive delirium, the clinical features include apathy and hypersomnia with reduced appetite and oral intake. This type is the most easily missed amongst hospital inpatients and, therefore, underdiagnosed. It also has the worst prognosis. In the hyperactive type of delirium, the patient is agitated, restless and can have paranoid or persecutory delusions and hallucinations. Behaviour can become aggressive, necessitating the use of antipsychotic agents to reduce the risk of harm to the patient or others around them. The mixed type of delirium contains features of both hypoactive and hyperactive delirium.

Risk factors for delirium

Delirium is more common in older patients with pre-existing dementia, and NICE defines high-risk patient groups as:

• Age 65 years or older
• Cognitive impairment (and/or dementia)
• Current hip fracture
• Severe illness (an illness which is deteriorating or at risk of deteriorating)

Some factors make an individual more susceptible to developing delirium, such as pre-existing dementia, depression, visual or hearing impairment, a history of alcohol excess or previous episodes of delirium.

Causes of delirium

There are multiple other factors which can act as a trigger for delirium in a susceptible individual. The most common triggers in the older population are:

• Constipation
• Urinary retention
• Drugs – an abrupt withdrawal of long-term drugs (e.g. benzodiazepines) or the addition of a new drug which precipitates delirium, such as steroids or opiates.

Other causes include metabolic abnormalities, systemic infections, and vascular events such as a myocardial infarction or stroke.

Epidemiology

Delirium is common, occurring in some studies in >50% of medical inpatients aged over 50 years. It is more common after surgery, a stroke or intensive care admission. It is also common in the palliative care setting, where it occurs in up to 88% of patients in the final weeks before death.

Delirium is underdiagnosed, and it is thought that up to 50% of cases are missed in hospital inpatients. It is a marker of frailty and poor prognosis, both in the short and long term. In the short term, it leads to a higher risk of pressure sores, pneumonia, falls and an increased length of stay in hospital. Longer term, it leads to an accelerated rate of cognitive decline, higher rates of institutionalisation and death.

Management of delirium

Management of delirium involves identifying and treating any underlying triggers and an individualised multicomponent intervention addressing hydration and nutrition, pain, sensory impairment, involving family and carers, maintaining mobility and day-night sleep cycles. Pharmacological treatments, such as antipsychotics, do not reduce the incidence or duration of delirium but can be used to treat severe agitation or distressing symptoms, particularly where the patient or others are deemed to be at risk.

Prognosis

Prognosis is variable and depends on the patient’s premorbid functional and cognitive status and whether a cause is identified and treated early. Most patients recover within days, but in some (~20%), the recovery can take months.