Acute confusional state

Definition. Acute confusional state is the older clinical name for delirium (also called acute brain failure or altered mental status). It is an acutely developing, fluctuating disturbance of attention, awareness and cognition caused by an underlying medical illness, drug or withdrawal state. It is a syndrome, not a diagnosis — the cause must always be sought.

Clinical picture. There is impaired consciousness with global cognitive impairment of acute onset, disorientation, and a disturbed sleep–wake cycle. Psychomotor activity may be increased (hyperactive) or reduced (hypoactive) or both (mixed). Illusions (misinterpreting bedsheet patterns as insects), visual hallucinations and paranoid delusions occur. Symptoms are worse at night with lucid intervals by day.

Causes. Almost always multifactorial — a vulnerable brain plus a precipitant. Use the Pathy mnemonic "DELIRIUM IS VERY PAINFUL": Drugs and withdrawal, Eyes/Ears, Low oxygen or perfusion, Infection, Retention of urine (cystocerebral syndrome), Indwelling catheter, Underhydration (BUN:creatinine > 17:1), Metabolic, Immobility, Sleep problems, Vascular change on imaging, Endocrinopathy, Restraints, psYchiatric disorder, Pain, Attachments, Impaction, Neurological injury, Frailty, Undernutrition, Lights and loud noise. In a highly predisposed patient a single dose of diphenhydramine may be enough to precipitate it.

Differential diagnosis. Dementia (gradual, no clouding of consciousness, attention preserved), delirium superimposed on dementia, depression (pseudodementia), late-onset psychosis or mania, non-convulsive status epilepticus and Wernicke's encephalopathy. The most reliable discriminator is to focus on the core features — attention, awareness and level of consciousness — not on behaviour. Kane's three questions: was the onset acute? are there physical factors? are there psychological factors?

Approach. Screen with CAM or 4AT, confirm against DSM-5/ICD-10, then perform a targeted search for every reversible contributor — drug chart, infection screen, glucose, electrolytes, hydration, bladder and bowel, oxygenation, pain. Neuroimaging, lumbar puncture and EEG are not routine; they are ordered only for focal signs, head injury, unexplained coma, suspected encephalitis or suspected seizures. Treatment is to correct the cause plus multicomponent non-pharmacologic care; drugs are reserved for danger to self or others.

The APA Practice Guideline for the Prevention and Treatment of Delirium (September 2025) — the first full revision since 1999 — shifts the emphasis of the whole field from treatment to prevention and early identification. It requires a thorough medication, predisposing- and precipitating-factor history in every patient, restricts physical restraints to circumstances of "imminent harm", and adds a structured transitions-of-care requirement covering medication reconciliation, delirium follow-up and caregiver education. NICE CG103 (updated January 2023) complements this by recommending the 4AT as the routine bedside assessment tool.