ABSTRACT
Oxygenation of the fetus is dependent on the umbilical circulation and placental function, but at birth, the lung must rapidly assume its role as the organ of gas exchange. In addition to clearance of fetal lung liquid, establishment of a gasliquid interface, and onset of ventilation, pulmonary blood flow must increase nearly 8-to 10-fold to allow sufficient gas exchange for postnatal survival. Some infants fail to achieve or sustain the normal decrease in pulmonary vascular resistance (PVR) at birth, leading to severe hypoxemia and profound neonatal morbidity and mortality, which is known as persistent pulmonary hypertension of the newborn (PPHN). The syndrome PPHN is characterized by sustained elevation of PVR that causes extrapulmonary shunting of blood flow from right to left across the patent ductus arteriosus (PDA) and/or foramen ovale (PFO), which results in hypoxia with severe cardiorespiratory distress. The syndrome PPHN is associated with diverse cardiopulmonary disorders, or can be idiopathic, affecting nearly 10% of full-term and preterm infants cared for in the neonatal intensive care unit (NICU) (1,2). Newborns with PPHN are at risk for severe asphyxia and its complications, including death, chronic lung disease, neurodevelopmental sequelae, and other problems. This chapter will briefly review normal fetal pulmonary vascular physiology, the pathophysiology of PPHN, and clinical strategies that apply a physiologic approach to the treatment
of newborns with severe PPHN. Discussion of other settings associated with chronic pulmonary hypertension (PH) in neonates, such as late PH associated with bronchopulmonary dysplasia, congenital diaphragmatic hernia, congenital heart disease, and others, are not included in this chapter.
