A term newborn born to a mother with meconium-stained amniotic fluid develops respiratory distress within 2 hours of birth. Chest X-ray shows patchy infiltrates with hyperinflation. What is the most common mechanism of lung injury in meconium aspiration syndrome?
A. Surfactant inactivation and airway obstruction
B. Direct chemical pneumonitis from meconium constituents
C. Pulmonary hypoplasia secondary to oligohydramnios
D. Bacterial superinfection of aspirated meconium
Explanation
Pathophysiology of Meconium Aspiration Syndrome
Key Point
Surfactant inactivation combined with mechanical airway obstruction is the primary mechanism of lung injury in MAS, not direct chemical toxicity.
Mechanism of Injury
Meconium aspiration causes injury through multiple pathways:
1.
Surfactant inactivation — meconium contains bile acids, cholesterol, and other lipids that directly inactivate pulmonary surfactant, reducing its surface tension-lowering ability
2.
Mechanical obstruction — meconium particles occlude small airways, causing ball-valve obstruction with air trapping distal to the blockade
3.
Inflammatory cascade — aspiration triggers release of pro-inflammatory cytokines (TNF-α, IL-6, IL-8) leading to secondary pneumonitis
Clinical Correlation
The combination of surfactant inactivation and airway obstruction explains the characteristic radiographic findings:
Patchy infiltrates (areas of atelectasis from obstruction)
Hyperinflation (air trapping distal to obstructed airways)
"Barrel chest" appearance on physical exam
Clinical Pearl
Exogenous surfactant administration (lung lavage with dilute surfactant) has become standard therapy precisely because surfactant inactivation is the dominant pathophysiologic mechanism.
High-YieldNEET PG
The degree of surfactant inactivation correlates with severity of respiratory distress — infants with thicker, more concentrated meconium have worse outcomes.
Why Hyperinflation Occurs
Ball-valve obstruction allows air entry during inspiration but prevents egress during expiration, leading to progressive air trapping and hyperinflation — this is why MAS often progresses despite initial mild presentation.
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
