A 58-year-old man from Delhi presents to the emergency department with a 5-day history of fever, cough, and dyspnea. His oxygen saturation is 88% on room air. Chest X-ray shows bilateral ground-glass opacities. RT-PCR for SARS-CoV-2 is positive. ABG shows pH 7.32, PaCO₂ 48 mmHg, PaO₂ 62 mmHg, HCO₃⁻ 24 mEq/L. What is the most appropriate immediate next step in management?