A preterm neonate at 28 weeks gestation is mechanically ventilated for RDS. Chest X-ray shows diffuse granular haziness with air bronchograms and low lung volumes. Arterial blood gas shows PaO2 45 mmHg, PaCO2 58 mmHg, pH 7.19 on FiO2 0.6. What is the most specific pathophysiological defect?
- A Meconium aspiration causing mechanical airway obstruction
- B Pulmonary hypertension causing right-to-left shunting
- C Deficiency of surfactant (SP-B and SP-C) causing increased surface tension and alveolar collapse ✓
- D Infectious pneumonia causing exudative consolidation
Explanation
Respiratory distress syndrome (RDS/HMD) in preterm neonates results from surfactant deficiency, primarily of SP-B and SP-C, which are responsible for maintaining alveolar stability by reducing surface tension. Deficiency leads to alveolar collapse, diffuse atelectasis, ventilation-perfusion mismatch, progressive hypoxia and hypercapnia. Chest X-ray shows bilateral granular haziness with air bronchograms and low lung volumes. Treatment includes exogenous surfactant instillation and ventilatory support. Meconium aspiration causes overdistension and patchy infiltrates. Persistent pulmonary hypertension (PPHN) causes hypoxia without characteristic X-ray changes.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.