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Persistent
pulmonary hypertension of the newborn is the persistence of or reversion
to pulmonary arteriolar constriction, causing a severe reduction
in pulmonary blood flow and right-to-left shunting. Symptoms and
signs include tachypnea, retractions, and severe cyanosis or desaturation
unresponsive to O2. Diagnosis is by history,
examination, chest x-ray, and response to O2. Treatment
is with O2, alkalinization, inhaled nitric
oxide, or, if medical therapy fails, extracorporeal membrane oxygenation.
Etiology
and Pathophysiology
Persistent pulmonary hypertension of the newborn (PPHN) is a disorder of pulmonary vasculature that affects term or postterm infants. The most common causes involve perinatal asphyxia or hypoxia (a history of meconium staining of amniotic fluid or meconium in the trachea is common); hypoxia triggers reversion to or persistence of intense pulmonary arteriolar constriction, a normal state in the fetus. Additional causes include premature ductus arteriosus or foramen ovale closure, which increases fetal pulmonary blood flow and may be triggered by maternal NSAID use; polycythemia, which obstructs blood flow; congenital diaphragmatic hernia, in which the left lung is severely hypoplastic, forcing most of the pulmonary blood flow through the right lung; and neonatal sepsis, presumably from production of vasoconstrictive prostaglandins by activation of the cyclo-oxygenase pathway by bacterial phospholipids. Whatever the cause, elevated pressure in the pulmonary arteries causes abnormal smooth muscle development and hypertrophy in the walls of the small pulmonary arteries and arterioles and right-to-left shunting via the ductus arteriosus or a foramen ovale, resulting in intractable systemic hypoxemia.
Symptoms and Signs
Symptoms and signs include tachypnea, retractions, and severe cyanosis or desaturation unresponsive to supplemental O2. In infants with a right-to-left shunt via a patent ductus arteriosus, oxygenation is higher in the right brachial artery than in the descending aorta; thus cyanosis may be differential, ie, O2 saturation in the lower extremities is 5% lower than in the right upper extremity.
Diagnosis
Diagnosis should be suspected in any near-term infant with arterial hypoxemia and/or cyanosis, especially one with a suggestive history whose O2 saturation does not improve with 100% O2. Diagnosis is confirmed by echocardiogram, which can confirm the presence of elevated pressures in the pulmonary artery using Doppler interrogation and simultaneously excludes congenital heart disease. Lung fields on x-ray may be normal or may demonstrate changes due to the underlying cause (eg, meconium aspiration syndrome, neonatal pneumonia, congenital diaphragmatic hernia).
Prognosis
and Treatment
An oxygenation index (mean airway pressure [cm H2O] × fraction of inspired O2 [Fio2] × 100/Pao2) > 40 predicts mortality of > 50%. Overall mortality ranges from 10 to 80% and is directly related to the oxygenation index but also varies with underlying disorder. However, many survivors (perhaps 1⁄3) exhibit developmental delay, hearing deficits, and/or functional disabilities. This rate of disability may be no different from that of other infants with severe illness.
Treatment with O2, which is a potent pulmonary vasodilator, is begun immediately to prevent disease progression. O2 is delivered via bag and mask or mechanical ventilation; mechanical distention of alveoli aids vasodilation. Fio2 should initially be 1 but can be titrated downward to maintain Pao2 between 50 and 90 mm Hg to minimize lung injury. Once Pao2 is stabilized, weaning can be attempted by reducing Fio2 in decrements of 2 to 3%, then reducing ventilator pressures; changes should be gradual, because a large drop in Pao2 can cause recurrent pulmonary artery vasoconstriction. High-frequency oscillatory ventilation expands and ventilates the lungs while minimizing barotrauma and should be considered for infants with underlying lung disease in whom atelectasis and ventilation/perfusion (V/Q) mismatch may exacerbate the hypoxemia of PPHN.
Inhaled nitric oxide relaxes endothelial smooth muscle, dilating pulmonary arterioles, which increases pulmonary blood flow and rapidly improves oxygenation in as many as 1⁄2 of patients. Initial dose is 20 ppm, titrated downward by effect.
Extracorporeal membrane oxygenation (see Respiratory Disorders in Neonates, Infants, and Young Children: Extracorporeal membrane oxygenation (ECMO)) may be used in patients with severe hypoxic respiratory failure defined by an oxygenation index > 35 to 40 despite maximum respiratory support.
Normal fluid, electrolyte, glucose, and Ca levels must be maintained. Infants should be kept in a neutral thermal environment and treated with antibiotics for possible sepsis until culture results are known.
Last full review/revision November 2005
Content last modified November 2005
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