Which statement best explains how surfactant deficiency leads to hypoxemia in neonates?

• A. Increased alveolar surface tension leading to atelectasis and V/Q mismatch.
• B. Decreased airway resistance improving ventilation.
• C. Increased surfactant production.
• D. Excessive oxygen diffusion causing hyperoxia

Answer: (C)

Surfactant lowers alveolar surface tension, keeping the tiny air sacs open at the end of expiration and maintaining lung compliance. When surfactant is deficient, surface tension rises and many alveoli collapse (atelectasis). This reduces the amount of open, gas-exchanging surface and lowers functional residual capacity. Blood perfusing these non-ventilated areas cannot be adequately oxygenated, creating a ventilation-perfusion mismatch and often an intrapulmonary shunt. The resulting drop in oxygen transfer leads to hypoxemia in the neonate. So the best explanation is that surfactant deficiency increases alveolar surface tension, causing atelectasis and V/Q mismatch. The other statements don’t fit the biology: increased surfactant production wouldn’t cause hypoxemia; decreased airway resistance wouldn’t explain low oxygenation; and hyperoxia from excessive diffusion isn’t driven by surfactant status.