Persistent Pulmonary Hypertension of the Newborn
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 includes O2, high-frequency ventilation, nitric oxide, and pressors and/or inotropes; extracorporeal membrane oxygenation is done if other therapies fail.
Persistent pulmonary hypertension of the newborn is a disorder of pulmonary vasculature that affects term or postterm infants.
The most common causes involve
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
Respiratory distress syndrome (see Respiratory Distress Syndrome in Neonates)
Premature ductus arteriosus or foramen ovale closure (see Perinatal Physiology : Neonatal cardiovascular function), which increases fetal pulmonary blood flow and may be triggered by maternal NSAID use
Congenital diaphragmatic hernia (see Diaphragmatic Hernia), in which one lung is severely hypoplastic, forcing most of the pulmonary blood flow through the other lung
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. Both pulmonary and systemic resistances are high, which leads to an increased load on the heart. This load increase may result in right heart dilation, tricuspid insufficiency, and right heart failure.
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, O2saturation in the lower extremities is ≥ 5% lower than in the right upper extremity).
Diagnosis should be suspected in any near-term infant with arterial hypoxemia, cyanosis, or both, especially one with a suggestive history whose O2 saturation does not improve with administration of 100% O2. Diagnosis is confirmed by echocardiogram, which can confirm the presence of elevated pressures in the pulmonary artery and simultaneously can exclude congenital heart disease. On x-ray, lung fields may be normal or may show changes due to the underlying disorder (eg, meconium aspiration syndrome [see Meconium Aspiration Syndrome], neonatal pneumonia, congenital diaphragmatic hernia).
The oxygenation index (mean airway pressure [cm H2O] × fraction of inspired O2[Fio2] × 100/Pao2) is used to assess disease severity and determine timing of interventions (in particular for inhaled nitric oxide [oxygenation index 15 to 25] and extracorporeal membrane oxygenation [ECMO—oxygenation index > 40]). Overall mortality ranges from 10 to 60% and is related to the underlying disorder. However, 25% of survivors exhibit developmental delay, hearing deficits, functional disabilities, or a combination. 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 (see Respiratory Support in Neonates and Infants : 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 persistent pulmonary hypertension of the newborn.
Inhaled nitric oxide relaxes endothelial smooth muscle, dilating pulmonary arterioles, which increases pulmonary blood flow and rapidly improves oxygenation in as many as half of patients. Initial dose is 20 ppm, titrated downward by effect.
ECMO (see Respiratory Support in Neonates and Infants : Extracorporeal membrane oxygenation (ECMO)) may be used in newborns 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. Inotropes and pressors may be required as part of circulatory support.
Prolonged hypoxia or disorders that increase pulmonary blood flow cause smooth muscle hypertrophy in small pulmonary arteries, resulting in persistent pulmonary hypertension.
Persistent pulmonary hypertension causes right-to-left shunting via the ductus arteriosus or a foramen ovale, resulting in intractable systemic hypoxemia; right-sided heart failure may develop.
Confirm diagnosis by echocardiography.
Give O2 to dilate pulmonary vasculature, mechanical ventilation, inhaled nitric oxide, and, for severe cases, ECMO.