Aetiology

The aetiology of delirium is not fully understood. A genetic predisposition is possible. Inflammatory mediators may play a part. There is widespread cortical involvement in delirium, reflected in the wide range of symptoms, disturbances of conscious level and sleep–wake cycle, with illusions and hallucinations.

Although little is known of the pathophysiology of delirium, more is known about its predisposing and precipitating factors. These are shown in Box 3.1. Many of these factors occur commonly. If more predisposing factors are present, a lower severity of precipitating factor may provoke delirium.

Diagnosis

Delirium is particularly common in the post-operative period (43–61% after hip fracture, and higher in intensive care). It is also prevalent in the emergency department, affecting one in seven older patients. It is an acute condition, with symptoms developing over hours or days. People with delirium appear disorientated and are unable to focus their attention. Conversations are difficult to follow. Fluctuation in symptoms occurs, often with a diurnal pattern (i.e. worse at night), and lucid or symptom-free intervals may occur.

Box 3.1 Predisposing and precipitating factors for delirium

Predisposing factors	Precipitating factors
Old age	Immobility
Severe illness	Use of physical restraint
Dementia	Use of urinary catheter
Physical frailty	Iatrogenic events e.g. general
Admission with infection or	anaesthesia
dehydration	Malnutrition
Visual/hearing impairment	Psychoactive medications
Polypharmacy	Intercurrent illness
Surgery e.g. fractured neck of femur	Dehydration
Alcohol excess	Benzodiazepine or alcohol
Renal impairment	withdrawal

From: Royal College of Physicians/British Geriatrics Society. (2006) The prevention, diagnosis and management of delirium in older people. National guidelines. RCP, London.

A diagnosis of delirium can be made when all four of the following features are present.

1 Acute onset.

2 Disturbance of consciousness.

3 Impaired cognition or perceptual disturbance, not due to pre-existing dementia.

4 Clinical evidence of an acute general medical condition, intoxication or substance withdrawal.

The International Classification of Diseases further describes the diagnostic features of delirium; these are outlined in Box 3.2. There are two main patterns of delirium:

hyperactive delirium (agitated and wandering)
hypoactive delirium (quiet and withdrawn).

Some patients may have features of both. The hypoactive pattern is particularly important because it often goes unrecognised. Affective symptoms are sometimes prominent in delirium and may lead to the erroneous diagnosis of a mood disorder. In patients with preexisting dementia, delirium can be hard to spot. Delirium varies in both its severity and duration, and can last from a few days to several weeks.

Box 3.2 Diagnostic criteria for delirium

Symptoms are present in the following areas:

1 Disturbance of consciousness

Reduced clarity of awareness of the environment, on a continuum from ‘clouded consciousness’ to coma, with a reduced ability to direct, focus, sustain and shift attention

2 Global disturbance of cognition

Perceptual distortions
Illusions and hallucinations – usually visual
Impaired abstract thinking and comprehension (with or without transient delusional beliefs)
Impaired immediate and recent memory but with relatively intact long-term memory
Disorientation in time, place or person

3 Psychomotor disturbance

Hyper- or hypoactivity and unpredictable shift from one to the other
Increased or decreased flow of speech

4 Disturbance of the sleep–wake cycle

Insomnia
Daytime drowsiness
Nocturnal worsening of symptoms
Disturbing dreams or nightmares

5 Emotional disturbance

Depression
Anxiety
Fear
Irritability
Euphoria
Apathy
Perplexity

(Acute alcohol and psychoactive substance use are excluded)

From: International Classification of Diseases (ICD) 10.

National guidelines recommend that all older people should have routine cognitive testing on admission to hospital (e.g. using the Abbreviated Mental Test – see Box 3.3). This is to aid the detection of delirium.

The differential diagnosis of delirium includes:

dementia
depression
hysteria
mania
schizophrenia
dysphasia
seizures (temporal lobe seizure or non-convulsive status epilepticus).

The most important aspect of diagnosis in delirium is to get a full history from someone who knows the patient (see Figure 3.1).

Management of delirium

Prevention

Those at high risk for developing delirium (see Box 3.1) can be targeted for proactive care aimed at preventing it. Some risk factors cannot be changed, but many in the list of precipitating factors can be. Other factors, including environmental ones, are also important in the prevention (and management) of delirium, and are listed in Box 3.4.

Box 3.3 The Abbreviated Mental Test

1 How old are you?

2 When is your birthday?

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