A 2-hour-old term newborn with meconium-stained amniotic fluid develops severe hypoxemia (SpO₂ 75% on 100% oxygen) and clinical signs of pulmonary hypertension despite surfactant administration and conventional mechanical ventilation. Echocardiography confirms right-to-left shunting across the foramen ovale. Which drug is indicated to reduce pulmonary vascular resistance in this scenario?
A. Inhaled nitric oxide
B. Milrinone
C. Sildenafil
D. Dobutamine
Explanation
Meconium Aspiration Syndrome with Pulmonary Hypertension: Selective Pulmonary Vasodilation
Meconium aspiration triggers severe pulmonary inflammation and hypoxia, leading to reactive pulmonary vasoconstriction and right-to-left shunting through fetal channels (foramen ovale, ductus arteriosus).
iNO is the ONLY inhaled selective pulmonary vasodilator approved for neonatal use in the US and is guideline-recommended for MAS with refractory hypoxemia and pulmonary hypertension.
Why Other Options Are Suboptimal
Clinical Pearl
Systemic vasodilators (sildenafil, milrinone, dobutamine) cause systemic hypotension, which is catastrophic in a hypoxemic newborn with right-to-left shunting. They may worsen oxygenation by dropping systemic pressure below pulmonary artery pressure, increasing shunt fraction.
Adjunctive Therapies
High-frequency oscillatory ventilation (HFOV): Reduces barotrauma; synergistic with iNO
Milrinone or dobutamine: Reserved for systemic hypotension after iNO is established; used to maintain systemic perfusion
Sildenafil: Emerging role in chronic pulmonary hypertension; not first-line in acute MAS
ECMO: Rescue therapy if iNO + optimal ventilation fail
