Chronic lung disease of infancy
Bronchopulmonary dysplasia (BPD; formerly chronic lung disease of infancy) is a chronic lung disorder of infants and children first described in 1967. It is more common in infants with low birth weight and those who receive prolonged mechanical ventilation to treat respiratory distress syndrome (RDS). It results in significant morbidity and mortality. The definition of BPD has continued to evolve since then primarily due to changes in the population, such as more survivors at earlier gestational ages, and improved neonatal management including surfactant, antenatal glucocorticoid therapy, and less aggressive mechanical ventilation.
Currently the description of BPD includes the grading of its severity into mild, moderate and severe. This correlates with the infant's maturity, growth and overall severity of illness. The new system offers a better description of underlying pulmonary disease and its severity.
Prolonged high oxygen delivery in premature infants causes necrotizing bronchiolitis and alveolar septal injury, with inflammation and scarring. This results in hypoxemia. Today, with the advent of surfactant therapy and high frequency ventilation and oxygen supplementation, infants with BPD experience much milder injury without necrotizing bronchiolitis or alveolar septal fibrosis. Instead, there are usually uniformly dilated acini with thin alveolar septa and little or no interstitial fibrosis. It develops most commonly in the first 4 weeks after birth.
Most BPD cases occur in premature infants, usually those who are born at 34 weeks' gestation or before and weigh less than 4.5 pounds (2,000 grams). These babies are more likely to be affected by the condition infant respiratory distress syndrome (RDS), or hyaline membrane disease, which occurs as a result of tissue damage to the lungs from being on a mechanical ventilator for a significant amount of time. Mechanical ventilators do the breathing for babies whose lungs are too immature to allow them to breathe on their own. The ventilators also supply necessary oxygen to the lungs of these premature infants. Oxygen is delivered through a tube that has been inserted into the baby's trachea (windpipe) and is given under pressure from the machine to properly move air into stiff, underdeveloped lungs. Sometimes, for these babies to survive, the amount of oxygen given must be higher than the oxygen concentration in the air we commonly breathe.
The classic diagnosis of BPD may be assigned at 28 days of life if the following criteria are met:
- Positive pressure ventilation during the first 2 weeks of life for a minimum of 3 days.
- Clinical signs of abnormal respiratory function.
- Requirements for supplemental oxygen for longer than 28 days of age to maintain PaO2 above 50 mm Hg.
- Chest radiograph with diffuse abnormal findings characteristic of BPD.
The newer National Institute of Health (US) criteria for BPD (for neonates treated with more than 21% oxygen for at least 28 days) is as follows:
- Breathing room air at 36 weeks post-menstrual age or discharge (whichever comes first) for babies born before 32 weeks, or
- breathing room air by 56 days postnatal age, or discharge (whichever comes first) for babies born after 32 weeks gestation.
- Need for <30% oxygen at 36 weeks postmenstrual age, or discharge (whichever comes first) for babies born before 32 weeks, or
- need for <30% oxygen to 56 days postnatal age, or discharge (whichever comes first).
- Need for >30% oxygen, with or without positive pressure ventilation or continuous positive pressure at 36 weeks postmenstrual age, or discharge (whichever comes first) for babies born before 32 weeks, or
- need for >30% oxygen with or without positive pressure ventilation or continuous positive pressure at 56 days postnatal age, or discharge (whichever comes first) for babies born after 32 weeks' gestation.
There is evidence to show that steroids given to babies less than 8 days old can prevent bronchopulmonary dysplasia. However, the risks of treatment may outweigh the benefits. It is unclear if starting steroids more than 7 days after birth is harmful or beneficial. It is thus recommended that they only be used in those who cannot be taken off of a ventilator.