A 72-year-old woman admitted to the ICU 2 days ago with pneumonia now presents with acute confusion, disorientation, visual hallucinations, and fluctuating consciousness. Her vital signs are unstable (fever 39.2°C, tachycardia, tachypnea). Laboratory tests show elevated inflammatory markers and hypoxia. She was cognitively intact before admission. What is the drug of choice for managing her acute mental status changes?