Persistent Pulmonary Hypertension
Persistent pulmonary hypertension is a serious disorder in which the newborn's arteries to the lungs remain constricted after delivery, thus limiting the amount of blood flow to the lungs and therefore the amount of oxygen in the bloodstream.
Normally, the blood vessels to the lungs are tightly constricted during fetal life. The lungs do not need much blood flow before birth because the placenta eliminates carbon dioxide and transports oxygen to the fetus. Immediately after birth, the umbilical cord is cut and the newborn's lungs must take over the role of oxygenating the blood and removing carbon dioxide. To achieve this, it is necessary not only that the fluid filling the air sacs be replaced by air, but that the arteries bringing blood to the lungs widen (dilate) so that an adequate amount of blood flows through the lungs.
In response to severe respiratory distress, or as a consequence of certain drugs taken by the mother before delivery (such as large doses of aspirin), the blood vessels to the lungs may not dilate as they normally should. As a result, there is insufficient blood flow to the lungs and not enough oxygen reaches the blood.
Persistent pulmonary hypertension is more common in newborns who are term or postterm and in newborns whose mothers were regular users of aspirin or indomethacin during pregnancy. In many newborns, the respiratory distress that initiates persistent pulmonary hypertension results from other lung diseases, such as meconium aspiration syndrome or pneumonia, but persistent pulmonary hypertension can also develop in newborns with no other lung disorder.
Symptoms and Diagnosis
Sometimes persistent pulmonary hypertension is present from birth; other times, it develops over the first day or two. Breathing is usually rapid, and there may be severe respiratory distress if the newborn has an underlying lung disease (see Section 23, Chapter 264). The most prominent feature is a bluish discoloration of the skin (cyanosis) due to low blood oxygen levels. Sometimes low blood pressure (hypotension) leads to symptoms such as weak pulses and a pale, grayish hue to the skin.
A doctor may suspect persistent pulmonary hypertension if the mother used aspirin or indomethacin during pregnancy or had a stressful delivery, or if the newborn has severe respiratory distress and measurement of oxygen levels is unexpectedly low. A chest x-ray is performed, but definitive diagnosis requires an echocardiogram.
Treatment
Treatment involves placing the newborn in an environment with 100% oxygen to breathe. Alternatively, a ventilator providing 100% oxygen may be needed. A high percentage of oxygen in the blood helps open the arteries going to the lungs. To make the blood slightly alkaline, which may also open these arteries, the newborn is often given intravenous sodium bicarbonate.
In more severe cases, a very small concentration of the gas nitric oxide may be added to the oxygen that the newborn is breathing. Inhaled nitric oxide opens the arteries in the newborn's lungs and reduces pulmonary hypertension. This treatment may be needed over several days. If all other treatments fail, extracorporeal membrane oxygenation (ECMO) can be used. In this procedure, blood from the newborn is circulated through a machine that adds oxygen and removes carbon dioxide and then returns the blood to the newborn. ECMO has been lifesaving, allowing many newborns to survive until the pulmonary hypertension resolves.
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