(See also Overview of Perinatal Respiratory Disorders.)
Extensive physiologic changes accompany the birth process, sometimes unmasking conditions that posed no problem during intrauterine life. For that reason, a person with neonatal resuscitation skills must attend each birth. Gestational age and growth parameters help identify the risk of neonatal pathology.
Persistent pulmonary hypertension of the newborn (PPHN) is a disorder of pulmonary vasculature that affects term or postterm infants.
The most common causes of persistent pulmonary hypertension of the newborn involve
A history of meconium staining of amniotic fluid or meconium in the trachea is common. Hypoxia triggers reversion to or persistence of elevated pulmonary vascular resistance, a normal state in the fetus.
Additional causes include
1. Van Marter LJ, Hernandez-Diaz S, Werler MM, et al: Nonsteroidal anti-inflammatory drugs in late pregnancy and persistent pulmonary hypertension of the newborn. Pediatrics 131(1):79–87, 2013. doi: 10.1542/peds.2012-0496
2. Chandrasekharan PK, Rawat M, Madappa R, et al: Congenital diaphragmatic hernia—A review. Matern Health Neonatol Perinatol 3:6, 2017. doi: 10.1186/s40748-017-0045-1
Whatever the cause, elevated resistance 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 of persistent pulmonary hypertension of the newborn include tachypnea, retractions, and severe cyanosis or desaturation unresponsive to supplemental oxygen. 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, oxygen saturation in the lower extremities is ≥ 5% lower than in the right upper extremity).
Diagnosis of persistent pulmonary hypertension of the newborn should be suspected in any near-term infant with arterial hypoxemia, cyanosis, or both, especially one with a suggestive history whose oxygen saturation does not improve with administration of 100% oxygen.
Diagnosis is confirmed by echocardiogram, which can confirm the presence of elevated pressures in the pulmonary artery and simultaneously can exclude congenital heart disease.
Blood cultures should be done because prenatal infection is a possible cause of persistent pulmonary hypertension in the newborn.
The oxygenation index (mean airway pressure [cm H2O] × fraction of inspired oxygen [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 oxygen, which is a potent pulmonary vasodilator, is begun immediately to prevent disease progression. Oxygen 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 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 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 calcium 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 and/or acidosis 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 oxygen to dilate pulmonary vasculature, mechanical ventilation, inhaled nitric oxide, and, for severe cases, extracorporeal membrane oxygenation (ECMO).