Asphyxia and PPHN: Fetal hypoxia (secondary to in-utero asphyxia and meconium aspiration) causes pulmonary vascular remodeling, which down regulates iNO signaling pathways and causes PPHN. In infants with perinatal hypoxia, the combination of hypoxia and acidosis increases the risk of PPHN. Preexisting PPHN may be exacerbated by therapeutic hypothermia. Errors in PaCO2 measurement secondary to body temperature changes may result in fluctuations in PCO2 leading to changes in cerebral and pulmonary vascular resistance (see text for details). (copyright Satyan Lakshminrusimha).