Persistent pulmonary hypertension of the newborn (PPHN) is a serious condition in which a baby’s circulatory system fails to make the normal transition from fetal to newborn life, keeping blood pressure dangerously high in the lungs. It affects roughly 1 to 2 out of every 1,000 live births in industrialized countries, with a mortality rate approaching 10%. PPHN causes severe oxygen deprivation and requires immediate treatment in a neonatal intensive care unit.
How a Newborn’s Circulation Normally Changes
Before birth, a baby doesn’t use its lungs to breathe. Oxygen comes from the placenta, and blood largely bypasses the lungs through two natural shortcuts: a small opening between the upper chambers of the heart (the foramen ovale) and a vessel connecting the lung artery to the body’s main artery (the ductus arteriosus). Resistance in the lung blood vessels is high during fetal life because the lungs are filled with fluid, not air.
At birth, a baby takes its first breaths, the lungs expand, and resistance in the lung blood vessels drops rapidly. Blood begins flowing through the lungs to pick up oxygen, and the two fetal shortcuts gradually close. In PPHN, this drop in lung vessel resistance never happens. The blood vessels in the lungs stay constricted, forcing blood to keep flowing through those fetal shortcuts and bypassing the lungs entirely or partially. The result is a baby whose blood carries dangerously little oxygen despite being born and breathing.
What Causes PPHN
PPHN is not a single disease but a circulatory failure that can be triggered by several different problems. The most common are lung conditions that prevent the blood vessels from relaxing after birth. Meconium aspiration, where the baby inhales its first stool into the lungs during or before delivery, is one of the best-recognized triggers. Meconium blocks airways, traps gas, causes inflammation, and inactivates a substance called surfactant that helps keep the lungs open. All of this drives up resistance in the lung blood vessels.
Pneumonia and sepsis (a blood infection) in newborns can also trigger PPHN by causing inflammation and oxygen deprivation in lung tissue. Some babies develop PPHN because their lung blood vessels never formed normally during pregnancy, a condition sometimes linked to congenital diaphragmatic hernia, where abdominal organs push up into the chest and prevent the lungs from developing fully. In rarer cases, no underlying lung disease is found at all; the blood vessels simply fail to relax.
Maternal use of certain antidepressants during pregnancy has also been linked to a modest increase in risk. A large study published in JAMA Network Open found that exposure to SSRIs (a common class of antidepressants) at any point during pregnancy was associated with roughly 1.7 times the odds of PPHN, rising to about 1.9 times when exposure occurred after 20 weeks of pregnancy. The absolute risk remains low, but it’s a factor clinicians consider.
Signs and Symptoms
The hallmark of PPHN is low blood oxygen that fluctuates unpredictably, a pattern called labile hypoxemia. A baby with PPHN may look blue (cyanotic), breathe rapidly, and have oxygen levels that swing from acceptable to critically low within minutes. One characteristic clue is differential cyanosis: the baby’s right hand (which receives blood pumped before the ductus arteriosus shortcut) may have higher oxygen levels than the feet (which receive blood after it). This gap indicates that oxygen-poor blood is being shunted past the lungs and into the lower body.
Low oxygen itself worsens the problem. Oxygen deprivation and the resulting acid buildup in the blood are powerful triggers for further constriction of lung blood vessels, creating a vicious cycle: low oxygen tightens the vessels, which sends even less blood to the lungs, which lowers oxygen further.
How PPHN Is Diagnosed
Doctors suspect PPHN when a full-term or near-term baby has severe, fluctuating low oxygen levels that don’t improve with standard oxygen support. The gold standard for confirming the diagnosis is echocardiography, an ultrasound of the heart. This allows the medical team to see the direction of blood flow through the fetal shortcuts, check whether the wall between the heart’s ventricles is being pushed out of position by high right-sided pressure, and estimate lung artery pressure by measuring the speed of blood leaking backward through the valve on the right side of the heart.
Echocardiography also rules out structural heart defects that could mimic PPHN. The imaging is repeated during treatment to track whether the baby is responding.
Treatment in the NICU
Treatment focuses on opening up the lung blood vessels while supporting the baby’s oxygen levels and overall circulation. The first steps involve supplemental oxygen and, in most cases, mechanical ventilation to keep the lungs properly inflated.
If those measures aren’t enough, inhaled nitric oxide (iNO) is the primary targeted therapy. Nitric oxide is a molecule naturally produced by blood vessel walls that relaxes the smooth muscle around vessels, widening them. When delivered as a gas directly into the lungs, it selectively dilates the lung blood vessels without dropping blood pressure throughout the rest of the body. That selectivity is key: the gas is immediately neutralized once it enters the bloodstream, so its effects stay local to the lungs. The standard dose of 20 parts per million produces the maximum vasodilating effect in most infants with PPHN.
Babies are also kept warm, given IV fluids, and sometimes receive medications to support heart function and blood pressure. Sedation is often used to reduce agitation, since crying and struggling can spike lung vessel resistance and worsen the cycle.
When Standard Treatment Fails
For the most critically ill babies who don’t respond to ventilation and inhaled nitric oxide, extracorporeal membrane oxygenation (ECMO) may be used. ECMO is essentially a heart-lung bypass machine: it draws the baby’s blood out of the body, adds oxygen and removes carbon dioxide, then returns the blood. This buys time for the lung blood vessels to relax on their own while preventing organ damage from prolonged oxygen deprivation. ECMO is reserved for the most severe cases and is only available at specialized centers.
Long-Term Outlook for Survivors
Most babies with PPHN survive, but the condition carries a real risk of lasting effects. A follow-up study of 133 survivors with moderately severe PPHN found that at one year of age, 46% had some form of developmental or hearing impairment. Specifically, 30% showed cognitive delays, 19% had hearing loss, and 13% had major neurological abnormalities. About 22% were rehospitalized during the first year of life.
These numbers reflect babies who had significant disease at the time of diagnosis. Milder cases likely fare better, though long-term data on that group is more limited. Because of these risks, babies who recover from PPHN are typically followed closely with developmental assessments and hearing tests during infancy and early childhood. Early intervention services, when needed, can make a meaningful difference in a child’s trajectory.