Understanding Pulmonary Interstitial Emphysema (PIE)

Pulmonary interstitial emphysema (PIE) is when air gets trapped in the tissue outside the tubes and air sacs of the lungs. It affects newborn babies. PIE is fairly common in neonatal intensive care units. PIE usually affects low-weight infants who need a ventilator. This is a device that helps with breathing. These infants often have a lung problem that is caused by preterm birth. PIE usually affects infants in the first few days of life. It may affect one or both lungs.

How the lungs work

When you breathe, air travels in through your mouth through a series of tubes to your lungs. At the ends of these tubes are tiny air sacs called alveoli. In these sacs is where gases get exchanged. Here, the lungs deliver oxygen to the blood. And they release carbon dioxide, a waste product. The oxygen then travels through the blood to all the organs of your body. 

Normally, air is only found in these respiratory tubes or tiny sacs of the lungs. But in some cases, air can escape into the nearby tissue around the tiny sacs. This tissue is called the interstitium. This can happen if the wall of an air sac breaks open. If enough air leaks out, this can cause problems with breathing and blood flow. PIE is 1 type of pulmonary air leak syndrome.

PIE is classified by how long it lasts. Acute PIE lasts for less than a week. If it lasts longer, it is called persistent PIE. PIE may also be called diffuse or localized. Diffuse means it occurs in more than 1 place in the lungs. Localized means it occurs in 1 place.

What causes PIE?

Air can leak from an air sac when the sac is overstretched. This may happen when air becomes trapped inside the sac. Or it may happen when the air is not evenly distributed in the lungs.

Being on a ventilator may cause PIE. During artificial ventilation, a ventilator puts air pressure on the air sacs of your child’s lungs. This helps your child breathe by opening closed-off lung sacs. But in some cases this extra pressure can create a leak in an air sac. Lung disease makes it more likely that these air leaks will happen. Lung disease may be caused by immature lungs or other health conditions.

Most cases of PIE happen in newborns who have other lung problems. It is common in infants who need to be on a ventilator. Careful adjustment of ventilator settings may help reduce your child’s risk for PIE. Conditions that can increase the risk for PIE include:

• Preterm birth, which often leads to respiratory disease
• Failure of the lungs to develop properly (pulmonary hypoplasia)
• Breathing in the first intestinal discharge (meconium) at birth
• Pneumonia, a lung infection
• Very fast breathing right after birth (transient tachypnea of the newborn)

Signs of PIE

Signs of PIE usually appear within 4 days of birth. Mild PIE may have no signs. More severe PIE may cause signs of breathing difficulty, such as:

• Grunting or other signs of trouble breathing
• Fast breathing (tachypnea) because of abnormally elevated (raised) levels of carbon dioxide in the blood. This is also known as carbon dioxide retention.
• Pale appearance
• Parts of the body tinted blue (cyanosis) because of low oxygen in the blood

Diagnosing PIE

You may be asked about your and your child’s health history. This may include information before, during, and after birth. Your child will have a physical exam. His or her heart and lungs may be checked. Blood tests may be done to look for signs of low levels of oxygen and high levels of carbon dioxide.

Your child may also have an imaging test, such as a chest X-ray or a chest CT scan. Leaked air will often appear on both of these imaging tests.