A neonate born at 36 weeks gestation develops progressive respiratory distress within 2 hours of birth with grunting, nasal flaring, and reticular-granular pattern on CXR. Which surfactant phospholipid component, most critical for alveolar stability, is deficient?

• A Sphingomyelin — the L:S ratio is used to assess maturity
• B Dipalmitoylphosphatidylcholine (DPPC) — the primary surface tension-reducing component of surfactant ✓
• C Phosphatidylglycerol — a marker of functional maturity but not the surface-active component
• D Phosphatidylinositol — the dominant surfactant phospholipid in early gestation

Explanation

Surfactant is composed primarily of phospholipids (80%), of which dipalmitoylphosphatidylcholine (DPPC) constitutes ~40–50% and is the key surface tension-reducing component that prevents alveolar collapse at end-expiration. In premature neonates, type II pneumocytes have not yet produced adequate surfactant, causing IRDS. The lecithin:sphingomyelin (L:S) ratio in amniotic fluid measures surfactant maturity (mature ≥2.0); lecithin here refers to phosphatidylcholine (mainly DPPC). Sphingomyelin serves as a reference standard (stays constant after 32 weeks). Phosphatidylglycerol is a maturity marker and appears at ~35–36 weeks; its presence confirms full lung maturity.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.