Persistent Pulmonary Hypertension of the Newborn (PPHN)

Persistent pulmonary hypertension of the newborn (PPHN) is a term which describes elevated pulmonary vascular resistance (PVR) resulting in right-to-left shunting of blood and hypoxemia (low blood oxygen). This means that the infant is unable to transition properly from fetal circulation to normal circulation after birth and so hypertension occurs in the arteries that lead to the lungs. This forces the oxygenated blood out of the lungs, causing a decrease in the body’s supply of oxygen. PPHN is a life-threatening illness and is seen in roughly 2/1000 live born infants.

PPHN can either occur on its own or, as it commonly does, as a component of either:

Some parenchymal lung disease, such as meconium aspiration syndrome (MAS), respiratory distress syndrome (RDS), or neonatal pneumonia (with or without sepsis)
Lung hypoplasia with congenital diaphragmatic hernia or oligohydramnios.

In newborns with hypoxic-ischemic encephalopathy, hypoxemic respiratory failure and PPHN can be caused by low oxygen in the blood, ischemia, right and left ventricular dysfunction, coagulation defects, meconium aspiration, hyperoxic resuscitation, and effects of mechanical ventilation.

PPHN can be characterized as one of the following types:

• Maladaptation: Secondary to a lung parenchymal disease.
• Maldevelopment: Idiopathic PPHN, when the lungs have remodeled pulmonary vasculature and normal parenchyma.
• Underdevelopment: Hypoplastic vasculature and other causes of pulmonary hypoplasia.
• Intrinsic Obstruction: PPHN which is caused by some intrinsic obstruction.

Perinatal risk factors for PPHN include:

• Perinatal acidosis and asphyxia and HIE
• Meconium stained amniotic fluid
• Perinatal exposure to nicotine
• Birth depression
• Low body temperature
• Infection
• A congenital disorder that results in underdeveloped lungs or congenital heart disease

Maternal risk factors for PPHN include:

• Fever
• Obesity
• Prolonged premature rupture of membranes (PROM)
• Positive Group B Streptococcal carrier status

Any process that obstructs or interferes with the transition from fetal circulation to neonatal circulation can cause PPHN.

There are a series of circulatory events that occur around birth to ensure a smooth labor and delivery:

1. Oxygen-rich blood leaves the placenta via the umbilical vein, goes through the ductus venosus, and enters the inferior vena cava.
2. The blood then empties into the right atrium and is mostly shunted across the foramen ovale to the left atrium, effectively bypassing the lungs.
3. The blood then enters the left ventricle, leaves through the aorta, and perfuses the carotid and coronary arteries so the heart and brain receive oxygenated blood.
4. Blood drains from the brain into the superior vena cava, reenters the right atrium, then the right ventricle, and is then able to exit the main pulmonary artery.
5. The ductus arteriosus, which connects the pulmonary artery and the aorta, carries the blood leaving the right side of the heart and shunts most of the cardiac output away from the lungs and towards the systemic system. This is called right-to-left shunting.

After birth, the following should happen:

1. The foramen ovale and the ductus arteriosus should close in response to certain biochemical processes, dilation of the pulmonary vessels, and pressure changes within the heart.
2. Then essentially all of the cardiac output will be able to enter the lungs, become oxygenated, and provide the oxygen-rich blood to the tissues for normal metabolism.

Meconium aspiration syndrome (MAS) is the most common interference that leads to PPHN, and it occurs when meconium causes mechanical obstruction in the airways. It can lead to acute respiratory failure and has a mortality rate of 10%.

Infants with PPHN typically show the following signs (usually appearing within the first 72 hours of life):

• Respiratory distress
• Grunting or moaning
• Retractions
• Tachypnea (rapid breathing)
• Pale or blotchy color
• Cyanosis (bluish or purplish discoloration) around lips or mouth
• Tachycardia: Rapid heart rate
• Low blood pressure
• Low blood oxygen levels, even after giving oxygen
• Labile hypoxemia (hypoxemia may change quickly)
• Severe respiratory compromise with concomitant acidosis
• Low Apgar scores
• Swelling
• Decreased urine output

Medical professionals can make a definitive diagnosis of PPHN using echocardiography. This test will confirm PPHN and show the structure of the heart in order to rule out structural heart disease. Evidence of an underlying parenchymal lung disease can be seen on a chest x-ray.

Infants with PPHN may receive treatment in the form of:

• Oxygen hood
• CPAP (Continuous Positive Air Pressure): Oxygen is provided through tubes in the nose.
• Endotracheal intubation
• Bag and mask ventilation
• Inhaled nitric oxide (iNO) to reduce the ratio of pulmonary to systemic vascular resistance
• Extracorporeal membrane oxygenation (ECMO) to provide adequate tissue oxygenation until PVR falls
• High-frequency ventilation: A method which delivers small volumes of gas at high frequencies.

They may also require medicine in the form of:

• Blood pressure medicine
• Specific medications required for any associated lung disease(s)
• Surfactant: medicine which improves oxygen uptake
• Antibiotics
• Sedation: to allow rest and decrease need for oxygen

The information presented above is intended only to be a general educational resource. It is not intended to be (and should not be interpreted as) medical advice.