Underdeveloped Lungs

What is Lung Hypoplasia?

In general terms lung hypoplasia means under developed lungs. Hypo means small, plasia means formed. The lungs are a vital organ and without them we can not live. The lung is made up of small gas exchange units called alveoli. Alveoli are thin walled structures that are surrounded by small veins and arteries called capillaries. Gas in the alveoli is exchanged with gas in the blood allowing oxygen to be delivered to tissue as a key element for body function and carbon dioxide to be eliminated from the body.

When the lung is hypoplastic the number of alveoli that are available for gas exchange are decreased. If the lungs are very hypoplastic the number of gas exchange units reaches a critically low level and adequate gas exchange can not be maintained.

What Causes Lung Hypoplasia?
The lung begins forming very early in fetal development. Any thing that restricts growth of the chest can cause the lung to be under developed. It is important to distinguish lung hypoplasia from lung immaturity. They are not the same things though, functionally, they have the same effect. Both lead to inadequate gas exchange and lung failure. Babies born prematurely have immature lungs with a developmental normal number of alveoli. The goal in caring for these babies is to support them in a manner that prevents injury to the lung. If injury is avoided these babies can have normal lung development.

In contrast events that impact fetal lung growth may effect future lung growth and may prevent babies with lung hypoplasia from ever developing a normal complement of alveoli.

One of the most common causes of poor fetal lung growth are: inadequate amniotic fluid,  the fetal lung does not grow to its normal size. Inadequate amniotic fluid is most commonly due to early leaking of amniotic fluid due to premature rupture of the membranes that surround the fetus. This is known as oligohydramnios (too little amniotic fluid). If amniotic fluid leaks out from around the baby, the chest wall movement that occurs with fetal breathing may be restricted. Fetal breathing and adequate fluid pressure are both believed vitally important for normal lung development.




Who Gets It?

1. Babies born to mothers with prolong rupture of amniotic membranes and oligohydramnios.
2. Newborns with severe renal anomalies, born to mother with resultant oligohydramnios.
3. Newborns with certain congenital anomalies
   - Congenital diaphragmatic hernia
   - Thanatophoric dwarfism
   - Cystic hydroma
   - Cystic adenomatosis malformation
4. Newborns with hydrops fetalis
5. Newborns with neuromuscular diseases
 

How does it cause disease?  Small lungs fail to accomplish normal gas exchange (oxygen in, carbon dioxide out.)    

Common Findings  The presentation is variable and dependent on the severity of the hypoplasia. Some babies may present with mild tachypnea (fast breathing).   

Diagnosis  The most important factors leading to a diagnosis are: history of fetal anomalies associated with lung hypoplasia, history of mom having too little amniotic fluid, and a chest radiograph showing small lungs.   

Treatment Currently, treatment is primarily supportive. This means that there is currently no available medicine that makes babies grow lungs. So, until lung growth occurs to an extent that the lung can support normal gas exchange, the babies must be supported by artificial means. The main problem is that all modes of artificial respiratory support are associated with lung injury. The trick is to support normal gas exchange without causing injury and to support good nutrition so that the lung can grow. Babies have an incredible capacity to grow and develop.    

Prevention There are no methods for preventing babies with certain anomalies from developing lung hypoplasia.