A 28-week gestation male infant born to a 24-year-old primigravida mother is delivered via emergency cesarean section for fetal distress. The mother had no antenatal corticosteroid prophylaxis. At 2 hours of life, the infant develops progressive respiratory distress with tachypnea (68 breaths/min), grunting, intercostal retractions, and cyanosis on room air. Chest X-ray shows a diffuse ground-glass appearance with air bronchograms. Blood gas analysis reveals pH 7.22, PaCO₂ 58 mmHg, PaO₂ 48 mmHg on FiO₂ 0.6. What is the most appropriate immediate management?