What is Persistent Pulmonary Hypertension of the Newborn (PPHN) characterized by?

Persistent Pulmonary Hypertension of the Newborn (PPHN) is characterized by a right-to-left shunt. In PPHN, the pulmonary vasculature remains constricted, leading to increased pulmonary artery pressures. This elevated pressure can prevent normal blood flow through the lungs and, as a result, alters the typical circulatory path.

In a healthy newborn, after birth, the pulmonary circulation should open up to allow for efficient oxygen exchange in the lungs. However, with PPHN, the high pressures in the pulmonary circuit can cause blood to bypass the lungs and flow directly from the right side of the heart to the left side. This happens through existing fetal shunts such as the foramen ovale or ductus arteriosus, which can lead to hypoxemia since the blood is not being oxygenated as it should be.

Understanding the right-to-left shunt in PPHN is crucial, as it highlights the need for interventions aimed at reducing pulmonary artery pressures and improving oxygenation through optimizing lung function and blood flow.