Persistent Pulmonary Hypertension of the Newborn
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Clinical syndrome of severe respiratory failure and hypoxia in a neonate characterized by high systemic pulmonary arterial pressures, tricuspid regurgitation, and intracardiac shunting from right to left when pulmonary vascular resistance fails to decrease after birth
- Incidence of ∼2–6 per 1,000 term live newborns, decreasing incidence with the decreased number of deliveries >41 weeks gestation
- Mostly occurs in full-term newborns, owing to the presence of the muscular layer of arterioles, the risk of uteroplacental insufficiency, and the potential for the passage of meconium in utero, but it can complicate the course of an older premature baby with chronic lung disease.
- Meconium aspiration is the number one cause of persistent pulmonary hypertension of the newborn (PPHN).
- PPHN complicates the course of about 10% of newborns with respiratory failure.
- Sporadic in occurrence
- Alveolar capillary dysplasia has been documented to be a rare cause of PPHN. The genetic cause is unknown, but it appears to be familial.
- Surfactant B deficiency has also been implicated, but it is a rare, lethal, autosomal recessive disorder.
- At a neonate’s first breath after delivery, the pulmonary vascular resistance 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 pulmonary vascular resistance increases right ventricular afterload, causing a backflow of blood 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 pressures also cause 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.
- Any hypoxia, acidosis, or stress that occurs after birth further increases pulmonary vascular resistance.
- Abnormal persistence of pulmonary vasculature constriction after birth secondary to underlying disease: infection, pneumonia, or meconium aspiration
- Secondary to an anatomic abnormality that has caused hypoplastic vasculature: congenital diaphragmatic hernia, oligohydramnios and pulmonary hypoplasia, or alveolar capillary dysplasia
- Idiopathic: The pulmonary vasculature is remodeled due to chronic in utero stress or hypoxia or the maternal use of nonsteroidal anti-inflammatory drugs (NSAIDs) near term. Data is unclear on maternal use of selective serotonin reuptake inhibitors (SSRIs) in the 2nd trimester and PPHN.
Commonly Associated Conditions
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