A 55-year-old post-cardiac surgery patient in the ICU develops acute onset confusion, agitation at night, and lucid periods during the day. EEG shows diffuse slowing. What is the MOST likely psychiatric diagnosis and the preferred pharmacological treatment?

• A Delirium; low-dose haloperidol ✓
• B Dementia; donepezil
• C Psychotic depression; fluoxetine
• D Bipolar mania; lithium

Explanation

Post-operative delirium is characterised by acute onset, fluctuating course, inattention, and disorganised thinking — hallmarks that distinguish it from dementia (chronic, stable). Diffuse EEG slowing is the characteristic finding in delirium. Low-dose haloperidol (0.5–1 mg) remains the most widely used and evidence-supported agent for managing delirium-associated agitation and perceptual disturbances in the ICU; it has minimal respiratory depression. Addressing the underlying cause (hypoxia, infection, medication) is paramount. Benzodiazepines are used only in alcohol/benzodiazepine withdrawal delirium.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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