Persistent Pulmonary Hypertension of the Newborn
Clinical syndrome characterized by hypoxia and respiratory failure in a neonate due to a failure of the pulmonary vascular resistance (PVR) to decrease after birth, resulting in high pulmonary arterial pressures which causes intracardiac right to left shunting
- Incidence of 1.8 per 1,000 live newborns, with a higher incidence in late preterm infants (5.4 per 1,000 births) than term infants (1.6 per 1,000 births)
- Typically occurs in newborns >34 weeks’ gestation, owing to the presence of the muscular layer of pulmonary arterioles, the risk of uteroplacental insufficiency, and the potential for the passage of meconium in utero
- Meconium aspiration is the leading cause of persistent pulmonary hypertension of the newborn (PPHN).
- Males are affected more often than females.
- Mortality from PPHN is currently estimated at 7–15%.
- Alveolar capillary dysplasia is a rare, inheritable cause of PPHN in which there is abnormality in the air–blood interface, with increased distance between the alveolar epithelium and capillaries.
- Surfactant B deficiency has also been implicated, but it is a rare, lethal, autosomal recessive disorder.
- Infants with trisomy 21 are at increased risk of PPHN.
- At a neonate’s first breath after delivery, PVR normally decreases to redirect ~50% of the cardiac output to the pulmonary circulation. This phenomenon fails to occur in PPHN, hence, the previous name of this condition, “persistent fetal circulation.”
- Increased PVR increases right ventricular afterload, causing retrograde blood flow to the right heart. This leads to increased right heart pressures (and subsequent tricuspid regurgitation), which can lead to right ventricular failure.
- Increased pulmonary arterial pressure also causes intracardiac shunting across any patent foramen ovale, ductus arteriosus, or atrioseptal or ventriculoseptal defect that may be present. This shunting causes more deoxygenated blood to go to the left heart and to be pumped to the body. The oxygen saturations postductally are lower than preductally.
- Deoxygenated blood in the left heart can lead to ischemic damage to the heart and right or left ventricular failure.
- If there is no shunting of blood, or the blood cannot get from the right to left heart because of a lack of persistent fetal pathways, a neonate may develop poor systemic perfusion, severe acidosis, shock, right ventricular failure, and even death.
- Hypoxia, acidosis, or stress occurring after birth further increases PVR.
- Abnormal persistence of pulmonary vasculature constriction after birth secondary to underlying disease:
- Meconium aspiration
- Abnormality that has caused hypoplastic vasculature secondary to an anatomic condition:
- Congenital diaphragmatic hernia
- Pulmonary hypoplasia
- Alveolar capillary dysplasia
- Other disease states such as hypoxic-ischemic encephalopathy, polycythemia, neonatal leukemia, and hydropis fetalis can all cause PPHN.
- Maternal factors can contribute such as a cigarette smoking, obesity, gestational or pregestational diabetes, and in utero drug exposure (NSAIDs, salicylates, and selective serotonin reuptake inhibitors [SSRIs]).
Related to the underlying disease or as a complication of treatment
- Pneumothorax or air leak syndrome
- Chronic lung damage
- Long-term developmental delays
- Cerebral palsy
- Sensorineural hearing loss
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