Final answer:
The initial management of the elderly patient should prioritize supplemental oxygen and airway management to address life-threatening hypoxemia before proceeding with treatment for the underlying infection.
Step-by-step explanation:
The first step in the initial management of a 70-year-old man presenting with these symptoms should be supplemental oxygen and airway management (D). His low oxygen saturation of 80% without oxygen supplementation is life-threatening and warrants immediate action to stabilize his breathing and oxygen levels. The right lower lobe infiltrate seen on the chest radiograph, along with fever and pleuritic chest pain, suggests pneumonia, potentially leading to sepsis, given the patient's hypotension and altered mental status. While antibiotic therapy (A) is crucial for treating the underlying infection, immediate oxygen support takes precedence. Once oxygenation is addressed, intravenous (IV) fluid resuscitation (C) may also be necessary to address the hypotension and prevent septic shock.