NORD gratefully acknowledges Steven H. Abman, MD, Professor, Department of Pediatrics, University of Colorado School of Medicine and Director, Pediatric Heart Lung Center, The Children's Hospital, for assistance in the preparation of this report.
Some infants who develop BPD have a condition called respiratory distress syndrome (RSD), which is a breathing disorder that affects some premature infants immediately after birth. It is characterized by rapid, shallow breathing and leads to the need for oxygen and respiratory support in the first days of life. Affected infants may also exhibit shortness of breath, a chronic cough, flaring of the nostrils when breathing, and bluish discoloration of the skin due to low levels of oxygen in the blood (cyanosis). Some infants may grunt when breathing out (exhaling). Additional symptoms may include abnormally fast breathing (tachypnea), wheezing, or a “crackling” or “rattling” sound that is heard in the lungs when inhaling.
In most cases, infants with BPD recover fully and damage to the lungs progressively improves with growth. In a few rare cases, BPD can cause life-threatening complications during infancy such as high blood pressure of the main artery of the lungs (pulmonary hypertension) and failure of the right side of the heart (cor pulmonale).
As affected infants and children grow, they may be at a greater risk than the general population of developing asthma, respiratory infections, or viral pneumonia.
BPD is caused by damage to the delicate tissue of the lungs. This damage is most often occurs in infants who have required extended treatment with supplemental oxygen or breathing assistance with a machine (mechanical ventilation) such as infants who are born prematurely and have acute respiratory distress syndrome.
When infants receive mechanical ventilation, a tube is inserted through the windpipe and the machine pushes air into the lungs, which are often underdeveloped in premature infants. In some cases, the levels of oxygen required for an affected infant to survive are higher than normally would be found in the air we breathe. Over time, the constant pressure from the ventilator and the excess oxygen levels can damage the delicate tissues of an infant’s lungs causing inflammation and scarring.
Although many cases of BPD are associated with mechanical ventilation or excess oxygen levels, BPD can arise from other conditions that affect the development of the lungs such as infection that occurs before birth (antenatal infection) or other maternal complications, such as smoking, drug use, placental abnormalities (preeclampsia) and inflammation of the fetal membranes (chorioamnionitis). In rare cases, some older infants who are born closer to term gestation can have abnormal lung development and develop BPD.
Infants who have patent ductus arteriosus are at a greater risk than other infants of developing BPD. Patent ductus arteriosis is a congenital heart defect in which the passage (ductus) between the blood vessel that leads to the lungs (pulmonary artery) and the major artery of the body (aorta) fails to close after birth. Infants with this condition may require supplemental oxygen or mechanical ventilation.
Many infants now diagnosed with BPD are born at earlier gestational age than in the past. These cases are sometimes referred to as “new BPD.” These cases generally have less inflammation and scarring than in classic BPD. These cases are believed to be less associated with mechanical ventilation and damage to the lungs and more likely due to disrupted or abnormal lung development. Researchers theorize that the formation of new blood vessels (angiogenesis) is abnormal or disrupted in infants with “new” BPD. Lung angiogenesis plays a key role in the development of the lung’s alveoli, which are thin, capillary-rich sacs in the lungs where the exchange of oxygen and carbon dioxide takes place. Capillaries are very small blood vessels. Researchers believe that disrupted lung angiogenesis impairs the proper development of the alveoli, which contributes to the development of BPD in some cases.
The exact, underlying mechanisms that cause classic or new BPD are complex and not fully understood. The causes of BPD in one infant may be different from the causes in another. Most likely, multiple different environmental and genetic factors all play a role in the development of the disorder. Some individuals may have a genetic predisposition to developing BPD. A person who is genetically predisposed to a disorder carries a gene (or genes) for the disease, but it may not be expressed unless it is triggered or “activated” under certain circumstances, such as due to particular environmental factors (multifactorial inheritance). More research is necessary to determine the exact causes and underlying mechanisms involved in the development of the BPD.
Bronchopulmonary dysplasia can affect both males and females. The exact incidence of BPD is unknown. The National Institutes of Health estimates that 10,000-15,000 babies born in the United States develop BPD each year. The risk of developing BPD increases the earlier a baby is born and the lower the birth weight. Infants born weighing less than 2.2 pounds are at the greatest risk for developing BPD. The number of cases of BPD has been increasing most likely because of modern advances in medicine, which have enabled doctors to keep more low birth weight, premature babies alive than in the past. BPD was first described in the medical literature in 1967.
A diagnosis of BPD is made based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and a variety of specialized tests including blood tests, chest x-rays, and echocardiograms. Blood tests may show low levels of oxygen in the blood. Chest x-rays may show distinctive changes in the lungs including abnormal development of the lungs. An echocardiogram is used to rule out other conditions that can cause breathing difficulties in infants such as congenital heart defects. During an echocardiogram, sound waves are directed toward the heart, enabling physicians to study cardiac function and motion.
The lungs of infants with respiratory distress syndrome and underdeveloped and cannot produce enough surfactant, which is a substance secreted by the tiny air sacs (alveoli) of the lungs that serves to reduce the tension of pulmonary fluids. These infants may be treated with surfactant-replacement therapy, which may be able to prevent the development of BPD in some cases. Most importantly, maternal steroid treatments prior to birth reduce the risk for BPD in preterm infants.
Infants with respiratory distress syndrome are also treated with mechanical ventilation and oxygen supplementation. Continued medical advances have lessened the risk of damage to infants’ lungs during these therapies and lowered the risk of these infants developing BPD.
The treatment for infants with BPD is geared toward minimizing damage to the lungs and providing enough support to allow an affected infant’s lungs heal and grow. The specific therapies used may change as an affected infant grows and the clinical picture changes.
Newborns with BPS usually receive care in the hospital. Treatment may include mechanical ventilation. Ventilators are only used when absolutely necessary and affected infants are taken off as early as possible. Some infants may require supplemental oxygen after being taking off mechanical ventilation. Proper nutritional management is also necessary to ensure the proper growth and development of the lungs. Some affected infants may require the insertion of a gastrointestinal (GI) tube directly into the stomach to ensure the sufficient intake of calories and nutrients. Because infants with BPD are at risk for the accumulation of excess fluid in the lungs, daily fluid intake may be monitored and adjusted.
Infants with BPD may receive different medications including bronchodilators, diuretics and antibiotics. Bronchodilators are medications that widen the airway tubes and improve the flow of air through the lungs. Diuretics are medications that reduce the amount of water in the body and may be administered to help remove excess fluid in the lungs. Antibiotics are used to help control infections and prevent pneumonia. In addition, intermittent use of steroids may reduce lung inflammation and congestion, reducing the need for high levels of respiratory support and oxygen. However, early and high doses of steroids may have adverse effects on neurocognitive and developmental outcomes. As a result, steroids are used selectively later in the clinical course, and for shorter periods of time.
Infants with BPD may spend several weeks or even months in the hospital. In most cases, lung function and development gradually improves, although it is often a slow process. After leaving the hospital, infants require proper nutrition, should avoid cigarette smoke and should receive regular follow up checkups from their pediatrician. Some infants may require supplemental oxygen or nutritional supplementation even after returning home.
Infants with BPD remain at a greater risk of developing respiratory infections and pneumonia than the general population. They should avoid individuals who have upper respiratory infections. In some cases, affected infants may receive preventive therapy with palivizumab, an antibody that protects against respiratory syncytial virus (RSV) infection. RSV is a common and contagious winter infection that can potentially cause pneumonia.
In infants with severe forms of BPD, treatment with a short course of steroids may be necessary. Steroids may also be used in infants at risk of developing BPD. Steroids are powerfully anti-inflammatory drugs. Studies have shown that low-dose, short-term therapy with steroids has improved lung function and neurodevelopmental outcomes. However, steroid therapy can be associated with a variety of side-effects. More research is necessary to determine the safest and most effective dose, timing and length of steroid therapy for infants with BPD. More research is necessary to determine the long-term consequences of steroid therapy as well. The use of caffeine has been shown to reduce BPD in preterm infants, but the mechanism underylying this affect is uncertain.
Inhaled nitric oxide therapy is being studied to determine what role, if any, it may play in preventing the development of BPD in at-risk infants. Nitric oxide is a vasodilator, a drug that relaxes the smooth muscles of blood vessels causing the vessels to widen. Inhaled nitric oxide may be able to improve ventilation and decrease inflammation in children at risk for BPD. At this time, the effects of inhaled NO in preventing BPD has been inconsistent. More research is necessary to determine the long-term safety and effectiveness of inhaled nitric oxide as a potential preventive therapy for infants at risk of developing BPD.
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