Bronchopulmonary dysplasia (BPD) is a chronic lung condition developing in premature infants as a consequence of injury to their underdeveloped lungs. These infants require oxygen therapy or mechanical ventilation to breathe, but this life-saving support can interfere with lung formation. This intervention can cause inflammation and scarring, disrupting the normal growth of the air sacs (alveoli) where gas exchange occurs.
The risk of BPD increases the earlier an infant is born. For instance, nearly 80% of infants born between 22 and 24 weeks of gestation are diagnosed with BPD, while the rate is about 20% for those born at 28 weeks. The result is a less efficient lung structure with fewer and larger alveoli, leading to long-term breathing difficulties. BPD develops after birth as a direct result of necessary medical treatments.
The Process of Diagnosis
The diagnosis of bronchopulmonary dysplasia is a clinical determination based on an infant’s history of needing breathing support. A primary requirement is that a premature infant has needed supplemental oxygen for at least 28 consecutive days after birth. This extended need indicates the lungs are not developing as expected.
The assessment is timed to specific developmental milestones. For infants born before 32 weeks of gestation, the formal evaluation for BPD is performed when they reach 36 weeks postmenstrual age (PMA). For infants born at or after 32 weeks, this assessment is conducted around 56 days of life.
The diagnostic process involves more than noting the duration of oxygen use. Clinicians assess the infant’s overall respiratory status, observing their work of breathing and checking for signs of distress like rapid breathing or retractions. Blood gas levels are also analyzed to measure oxygen and carbon dioxide, providing a comprehensive picture of lung function to confirm the diagnosis.
Classifying BPD Severity
Once BPD is established, the condition is classified by severity based on the level of respiratory support required at 36 weeks PMA. This modern framework, established by the National Institute of Child Health and Human Development (NICHD) in 2001, categorizes BPD into three levels: mild, moderate, and severe. This system helps medical teams predict an infant’s future needs and communicate the degree of lung injury.
An infant is classified with mild BPD if they required supplemental oxygen for at least 28 days but are breathing room air without support by the 36-week PMA assessment. This indicates their lungs have recovered enough to breathe independently.
Moderate BPD is diagnosed when an infant still requires a small amount of supplemental oxygen (less than 30%) at 36 weeks PMA. This support is needed to maintain stable oxygen saturation levels and is delivered through a nasal cannula.
Severe BPD is the most serious classification, diagnosed when infants need a higher level of respiratory support at 36 weeks PMA. An infant falls into this category if they require supplemental oxygen at a concentration of 30% or more. A diagnosis of severe BPD is also given if the infant needs positive pressure support, like CPAP or mechanical ventilation, regardless of oxygen concentration.
Evolution of Staging Systems
The classification of BPD has evolved, reflecting a deeper understanding of the condition. The original staging system from 1967 was based on radiological findings. This system defined four stages (I-IV) based on progressive changes on chest X-rays, including inflammation, scarring, and cyst formation.
While this X-ray-based system was important, its limitations became apparent as neonatal care advanced. The survival of smaller, more premature infants changed how BPD presented, often with less severe X-ray findings but significant functional impairment. The original stages did not always correlate well with an infant’s clinical condition or future respiratory health.
This disconnect led the medical community to a more functional definition of BPD. The current system, focusing on the need for respiratory support, provides a more practical and predictive measure of disease severity. This approach better reflects the infant’s actual lung function and is more accurate in forecasting long-term outcomes, like future hospitalizations or the need for ongoing therapies.
Long-Term Outlook Based on Severity
The severity of an infant’s BPD diagnosis is closely linked to their long-term health and respiratory function. The classification of mild, moderate, or severe BPD provides a general guide for what families might expect as the child grows.
Infants diagnosed with mild BPD have the most positive long-term outlook. Many experience significant improvement in lung function during their first few years. While they may have a higher risk of respiratory infections, most have normal or near-normal lung capacity by school age.
Children with moderate BPD may face more persistent respiratory challenges and have a higher risk for developing asthma-like symptoms, such as wheezing and shortness of breath. They are more likely to be hospitalized for viruses like RSV and may require ongoing treatments, like daily inhalers, to manage inflammation.
Severe BPD carries the highest risk for long-term complications. These children often require extended respiratory support, like supplemental oxygen or ventilation, for months or even years. They face a greater likelihood of frequent hospitalizations from severe respiratory infections. Severe BPD can also be associated with other challenges, including feeding difficulties, poor growth, and neurodevelopmental delays requiring therapeutic support.