Which statement best describes the role of inhaled nitric oxide in neonates with respiratory distress syndrome complicated by pulmonary hypertension?

• A. It is effective in all preterm infants
• B. It is contraindicated in patent ductus arteriosus
• C. It improves oxygenation in infants with RDS and pulmonary hypertension
• D. It has no effect on pulmonary vasculature

Answer: (C)

Inhaled nitric oxide works as a selective pulmonary vasodilator, lowering pulmonary vascular resistance and improving ventilation–perfusion matching. In neonates with respiratory distress syndrome and pulmonary hypertension, the lungs are both under-ventilated and vasoconstricted, creating right-to-left shunting and severe hypoxemia. By dilating the pulmonary arteries in ventilated regions, nitric oxide enhances blood flow to well-ventilated alveoli, reduces shunting, and markedly improves oxygenation. This effect is most evident in infants with persistent pulmonary hypertension of the newborn accompanying RDS; it does not universally help all preterm infants with RDS, and its benefits are primarily on the pulmonary vasculature rather than causing systemic changes. It is not contraindicated in the presence of a patent ductus arteriosus.