Persistent pulmonary hypertension of the newborn (PPHN) happens when the pressure in the blood vessels supplying the lungs of a newborn baby remains high after birth. This results in a lack of oxygen in the body and can be fatal if not treated.
Pulmonary hypertension occurs when there is abnormally high pressure in the blood vessels supplying the lungs from the heart, known as the pulmonary arteries.
Before a baby is born, the lungs are filled with amniotic fluid and not needed for oxygen transfer, as the mother delivers oxygen directly to her baby through the umbilical cord.
The pulmonary arteries are narrowed, reducing blood flow through the lungs and causing the pressure to be naturally high. The blood mostly bypasses the lungs through blood vessels called the ductus arteriosus and foramen ovale. These are “shortcuts” that allow blood to flow between the blood vessels connecting the right and left sides of the heart, rather than the blood having to travel via the lungs.
Immediately after birth, the baby takes its first breaths, quickly replacing the fluid in the lungs with air. At this stage the pulmonary arteries should relax and widen, allowing blood to flow through the lungs and quickly carry oxygen around the body. The ductus arteriosus constricts and closes, ensuring that blood flows from the heart to the lungs. This is known as the cardiopulmonary transition.
In PPHN, the blood vessels do not open completely, and the ductus arteriosus can remain open. This keeps the pressure high, making it difficult for blood to flow through the lungs to pick up oxygen and can cause the blood to be directed away from the lungs. This means oxygen cannot be transported quickly and this can limit oxygen reaching the brain and other organs.
Causes of PPHN
PPHN is very rare but is more common in full and post-term babies, or babies born after 34 weeks. The exact cause of the condition might not always be known, but there are several factors that can contribute. These include:
- Meconium aspiration, when fetal feces (or meconium) is passed into the amniotic fluid before birth and is breathed into the lungs;
- Congenital heart disease, or developmental defects in the heart;
- Respiratory distress syndrome, or underdeveloped lungs;
- Lack of oxygen before or during birth.
Symptoms of PPHN
The following symptoms could indicate the presence of PPHN in the newborn:
- Breathing abnormalities, such as rapid breathing, grunting on exhaling, or retracting (when rapid breathing causes the skin around and under the ribs to pull in);
- Cyanosis, or a blue tint to the skin;
- Cool-feeling hands and feet;
- Low blood pressure in the rest of the body;
- Low blood oxygen levels;
- Reduced urination;
Normally symptoms will show within 72 hours of birth.
Multiple tests may be carried out to confirm a diagnosis of PPHN.
Blood tests may also be used to confirm whether the baby has an infection.
The initial treatment of PPHN involves keeping the baby warm, supplied with additional oxygen, and antibiotics if an infection is confirmed.
Oxygen can be supplied through a mask, hood, incubator or tubes inserted into the mouth or nostrils. In some cases, assisted ventilation can be used, where the oxygen is supplied by a machine that will breathe for the baby through a tube inserted into the windpipe. A high-frequency oscillator may be used to pump air in and out of the lungs at a faster rate if required.
Nitric oxide gas therapy may be delivered along with oxygen to the lungs, to open the blood vessels in the lungs.
Medications to increase blood pressure in the rest of the body can be administered, such as inotropic agents.
In extreme cases, extra-corporeal membrane oxygenation (ECMO) may be considered. This directly delivers oxygen to the brain and other parts of the body.
There have been clinical trials investigating whether therapies used to treat adult hypertension could be safe and effective in opening the blood vessels in babies with PPHN, but currently, none of these therapies are approved by the U.S. Food and Drug Administration.
However, the results, published in The Journal of Pediatrics, suggested that while the therapy appeared to be well-tolerated, it did not significantly improve the condition compared to the placebo. Other therapies, such as Revatio (sildenafil) may be effective, but there is a lack of substantial evidence to confirm how safe and effective the treatment is.
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