In neonatal PPHN, what is the role of inhaled nitric oxide and how is it delivered?

• A. Systemic vasodilation to improve perfusion
• B. Cooling of the pulmonary vasculature to decrease inflammation
• C. Bronchodilation to reduce airway resistance
• D. Selective pulmonary vasodilation to improve oxygenation; delivered via the ventilator circuit

Answer: (D)

Inhaled nitric oxide is used in neonatal PPHN for selective pulmonary vasodilation to improve oxygenation. It works by relaxing the smooth muscle of pulmonary vessels, which lowers pulmonary vascular resistance and helps reduce right-to-left shunting. Because the gas is inhaled, its vasodilatory action is concentrated in the lungs, especially in well-ventilated areas, so systemic blood pressure is largely preserved and overall perfusion remains more stable.

Delivery is through the ventilator circuit using a calibrated NO delivery system that meters a precise concentration of NO into the inspiratory flow, with scavenging to prevent exposure to staff and to limit toxic byproducts. The effect is rapid and reversible—dosing is typically started in the low ppm range and adjusted based on response, with careful monitoring for methemoglobinemia and nitrogen dioxide formation. When it's time to wean, gradual reduction is used to avoid rebound hypertension.

So the role is selective pulmonary vasodilation to improve oxygenation, delivered via the ventilator circuit.