A 2-hour-old male neonate born to a 28-year-old primigravida at 38 weeks gestation presents with respiratory distress. The mother had meconium-stained amniotic fluid (MSAF) noted at rupture of membranes 6 hours before delivery. The infant was vigorous at birth with Apgar scores 8/9, but now shows tachypnea (RR 68/min), intercostal retractions, and grunting. Chest X-ray reveals bilateral patchy infiltrates with hyperinflation and areas of atelectasis. Arterial blood gas shows pH 7.28, PaCO₂ 52 mmHg, PaO₂ 68 mmHg on FiO₂ 0.40. What is the most appropriate immediate management?