Pulmonary hypertension (PH) is a condition characterized by high blood pressure within the arteries of the lungs. It is a serious medical challenge for premature infants, significantly impacting their delicate developing systems. This condition forces the right side of the heart to work harder to pump blood into the lungs, where it collects oxygen. The elevated pressure in the pulmonary vessels can lead to poor right heart function and, in severe cases, right heart failure.
In premature babies, pulmonary hypertension presents unique challenges due to their underdeveloped lungs and cardiovascular systems. The normal transition of circulation that should occur after birth often fails, leading to persistent elevated pressures in the lung arteries. This can limit oxygen delivery to the brain and other organs, making it a potentially life-threatening emergency. This condition in preemies requires specialized medical attention.
Understanding Pulmonary Hypertension in Preemies
During fetal development, the lungs are not used for oxygen exchange, and most blood bypasses them through specific circulatory shunts. After birth, these shunts should close, and blood flow to the lungs should increase as the pulmonary blood vessels widen.
In premature infants, this crucial transition often does not happen effectively, a condition sometimes referred to as persistent fetal circulation (PFC) or persistent pulmonary hypertension of the newborn (PPHN). The pulmonary blood vessels may remain constricted or fail to fully open, maintaining high pressure in the lungs. This can result from underdeveloped or abnormally developed blood vessels in the lungs, or their inability to adapt to breathing outside the womb.
Lung developmental disorders, such as bronchopulmonary dysplasia (BPD), are significant contributors to PH in preterm infants. Early injury to the lung circulation can lead to the rapid development of PH. Conditions like respiratory distress syndrome (RDS) or a lack of oxygen during or around birth (birth asphyxia) can also contribute to the persistence of elevated pulmonary vascular resistance.
Recognizing Signs and Symptoms
Signs and symptoms of pulmonary hypertension in premature infants can appear at birth or within the first few hours of life. Parents or caregivers might observe rapid breathing (tachypnea) or difficulty breathing, which may include flaring nostrils or grunting sounds.
Cyanosis, where the baby’s skin (especially around the lips, hands, and feet) has a bluish tint, indicates low oxygen levels even when receiving supplemental oxygen. Infants with pulmonary hypertension may also exhibit a rapid heart rate or a heart murmur. Poor feeding and lethargy can also be clues.
Diagnosing and Treating Pulmonary Hypertension
Diagnosing pulmonary hypertension in premature infants involves several methods to assess lung and heart function. An echocardiogram, an ultrasound of the heart, is the most reliable non-invasive test. This imaging technique evaluates blood flow within the heart and lungs, estimates pulmonary artery pressures, and identifies structural heart abnormalities. It can reveal right ventricular hypertrophy or dilatation, and flattening of the interventricular septum, indicating elevated pulmonary pressures.
Oxygen saturation monitoring, often through a pulse oximeter, checks oxygen levels in the blood. A significant difference (10% or more) between preductal (right wrist) and postductal (legs) oxygen saturation measurements can suggest right-to-left shunting, a hallmark of PPHN. Chest X-rays provide information about lung disease or an enlarged heart, although findings may appear normal even with significant hypoxemia. Blood tests, including arterial blood gas, assess oxygen and carbon dioxide levels and can indicate oxygen utilization or infection.
Treatment approaches for pulmonary hypertension in preemies aim to reduce pulmonary pressures and improve oxygen delivery. Oxygen therapy is the first line of treatment, as increasing oxygen levels can help widen the pulmonary blood vessels. Inhaled nitric oxide (iNO) is a common therapy that acts as a selective pulmonary vasodilator, relaxing blood vessels in the lungs without significantly affecting systemic blood pressure.
For infants not responding sufficiently to inhaled nitric oxide or for longer-term management, specific medications are used. Sildenafil, a phosphodiesterase-5 inhibitor, works by increasing nitric oxide activity in the lungs, promoting vasodilation and improving blood flow. It can be administered intravenously or orally. In severe cases where conventional treatments are insufficient, mechanical ventilation may be required to support breathing. Extracorporeal membrane oxygenation (ECMO) is a specialized life support system that takes over the function of the lungs and sometimes the heart, allowing these organs to rest and recover.
Long-Term Care and Outcomes
The long-term outlook for premature infants with pulmonary hypertension is variable and requires ongoing medical attention to monitor their respiratory and cardiovascular health. A common long-term complication is chronic lung disease, such as bronchopulmonary dysplasia (BPD).
Pulmonary hypertension impacts long-term growth and neurodevelopmental outcomes in extremely preterm infants with BPD. Infants with BPD and PH have poorer respiratory outcomes, including prolonged mechanical ventilation, longer hospital stays, and a higher incidence of requiring supplemental oxygen at home. Developmental assessments are recommended to identify delays, as these infants are at increased risk for neurodevelopmental impairments and hearing difficulties.
Multidisciplinary care, involving neonatologists, pulmonologists, cardiologists, and developmental specialists, is necessary for managing these complex needs. While PH in preterm infants with BPD can be severe, it improves over time with growth, and in many surviving infants, the pulmonary hypertension resolves. However, subclinical ventricular dysfunction may still be detectable with sensitive echocardiographic techniques in children with a history of BPD-associated PH, necessitating meticulous cardiovascular assessment over time.