Confusion Assessment Method (Delirium)

The Confusion Assessment Method is a bedside instrument for detecting delirium, an acute disturbance of attention and cognition that fluctuates over hours to days. It is based on four features assessed from observation and a short cognitive interview.

The four features are: acute onset and fluctuating course, inattention, disorganised thinking, and altered level of consciousness. Delirium is diagnosed when the first two features are present, together with either the third or the fourth.

Usage. It is used in hospital wards, emergency departments, intensive care and care homes. A version for ventilated patients, the CAM-ICU, uses non-verbal tests of attention.

Indications. Acute confusion or change in behaviour, routine screening of older adults on admission, postoperative patients, and patients in intensive care.

Preparation and technique. The assessor speaks with the patient, observes behaviour, and obtains collateral information about onset and course from staff or family. Inattention is tested with a task such as reciting months of the year backwards or counting digits. The assessment is repeated, because delirium fluctuates.

Contraindications and precautions. Deafness, aphasia and severe dementia limit the assessment. Sensory aids are used, and the assessment is interpreted in context.

Interpretation.

• A positive result requires acute onset and fluctuation plus inattention, plus either disorganised thinking or altered level of consciousness.
• A negative result on one occasion does not exclude delirium, because of fluctuation.
• Hypoactive delirium presents with drowsiness and withdrawal and is easily missed.

Causes of delirium. Infection, medicines (opioids, anticholinergics, benzodiazepines), metabolic disturbance, hypoxia, pain, urinary retention, constipation, alcohol or drug withdrawal, stroke, and postoperative state.

Critical values and findings needing immediate action.

• Delirium is a medical emergency in which the cause must be sought at once.
• Delirium with fever, neck stiffness or focal neurological signs requires urgent assessment for central nervous system infection or stroke.

Limitations and artefacts. Training of the assessor affects accuracy. Pre-existing dementia can mask or mimic delirium, and the assessment uses collateral history to establish change from baseline. The instrument detects delirium but does not identify its cause.

Follow up tests. Full blood count, urea and electrolytes, glucose, calcium, liver function tests, C-reactive protein, urinalysis, blood cultures where infection is suspected, arterial blood gas, ECG, chest X-ray, and CT head where indicated.

Special groups. Older adults and people with dementia are at highest risk. Children are assessed using tools adapted for their age.