SERIES: PULMONARY VASCULAR DISEASEPulmonary hypertension in the newborn
Section snippets
INTRODUCTION
Pulmonary hypertension of the newborn (PHN) occurs in 1.9 per 1000 live births, but a wide variation in the incidence (0.43–6.82 per 1000 live births) has been reported between centres.1 Infants with PHN have right-to-left shunting at the level of the ductus arteriosus and the foramen ovale. Persistent pulmonary hypertension of the newborn (PPHN), which persists from fetal life, has been called persistent fetal circulation, but that term is inaccurate as the placenta is missing.
CHANGES IN THE CIRCULATION AT BIRTH
In the fetus, the pulmonary circulation is a high resistance circuit but the systemic circulation includes a low resistance, high flow component, the placenta. Blood is shunted away from the lungs across the ductus arteriosus and only approximately 10% of the right ventricular output enters the pulmonary circulation. After birth, there is no longer a placenta and venous return through the inferior cava to the right side of the heart is reduced and the right atrial pressure falls. The flow
PATHOPHYSIOLOGY
PHN may be primary or secondary to a variety of disorders affecting the cardiac, pulmonary, haematological and metabolic systems; these include severe intrapartum asphyxia, infection, pulmonary hypoplasia, alveolar capillary dysplasia, congenital heart disease, polycythaemia (hyperviscosity resulting in functional obstruction of the pulmonary vascular bed) and drug therapy (for example administration of prostaglandin synthesis inhibitors before delivery). Pulmonary hypertension may occur in
CLINICAL FEATURES
Infants with PPHN present within 12 hours of birth with cyanosis but relatively mild respiratory distress. The second heart sound is loud, because of the high pulmonary artery pressure and there may be a systolic murmur due to tricuspid regurgitation. Infants with secondary PHN will, in addition, have the features of their underlying condition.
DIAGNOSIS
The diagnosis should be considered when the infant's hypoxaemia is out of proportion to the degree of severity of the abnormalities on the chest radiograph. In PPHN, there may be no or only minimal chest radiograph abnormalities, but in secondary PHN there will be the abnormalities associated with the underlying condition. Right-to-left shunting is evidenced by a discrepancy in the pre- and post-ductal saturations; a PaO2 difference of at least 20 mmHg between the pre (right radial) and post
TREATMENT
Infants with PPHN can be extremely ‘brittle’ and can become hypoxaemic following even gentle handling and minimal interventions. As a consequence, chest physiotherapy is contraindicated and suctioning should only be undertaken to ensure patency of the endotracheal tube. Use of sedation and paralysis has been advocated.6 Treatment of babies with PHN is aimed at maximising pulmonary blood flow and minimising pulmonary vascular resistance without compromising cardiac output (Table 1). The size of
MORTALITY AND MORBIDITY
In a recent retrospective review, the mortality rate of infants with PHN in 12 level three neonatal intensive care units was reported to be 11% (range 4–33%).1 The mortality rate, however, varies according to the underlying condition and is as high as 50% in infants with group B streptococcal sepsis; most babies dying from irreversible hypoxia or myocardial failure. Some infants with PHN will have required a high level of respiratory support and develop BPD, others suffer neurological damage as
PRACTICE POINTS
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Pulmonary hypertension may occur in association with a normal number (maladaptation) or a decreased number of arteries (e.g. in association with pulmonary hypoplasia).
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The diagnosis should be suspected if the hypoxaemia is out of proportion to the chest radiograph changes.
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Treatment is directed at reducing the size of the right-to-left shunt by improving the systemic blood pressure and administering pulmonary vasodilators
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Inhaled nitric oxide in infants born at or near term reduces the need for
RESEARCH DIRECTIONS
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The efficacy and optimum use of inhaled nitric oxide (iNO) in prematurely born infants.
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The role of prophylactic iNO in preventing bronchopulmonary dysplasia (BPD).
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The safety and efficacy of vasodilators, such as prostacyclin or tolazoline, given by inhalation.
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The optimum combinations of agents to use in pulmonary hypertension of the newborn (PHN) to minimise pulmonary vascular resistance (PVR) without deterioration in oxygenation or a fall in systemic blood pressure.
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