A 68-year-old man with a 3-year history of progressive memory loss and cognitive decline presents to the emergency department with acute onset confusion, visual hallucinations, and disorientation to time and place over the past 6 hours. His daughter reports he was well yesterday. On examination, he is febrile (38.5°C), tachycardic, and has a productive cough. Chest X-ray shows right lower lobe consolidation. Mini-Cog score is 1/3. What is the most appropriate immediate next step in management?