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What is Bronchopulmonary dysplasia and explain in detail?
Bronchopulmonary dysplasia (BPD; part of the spectrum of chronic lung disease of infancy) is a chronic lung disease in which premature infants, usually those who were treated with supplemental oxygen, require long-term oxygen. The alveoli that are present tend to not be mature enough to function normally. It is more common in infants with low birth weight (LBW) 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 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 infants maturity, growth and overall severity of illness. The new system offers a better description of underlying pulmonary disease and its severity.

Presentation
Complications
Feeding problems are common in infants with bronchopulmonary dysplasia, often due to prolonged intubation. Such infants often display oral-tactile hypersensitivity (also known as oral aversion).
Physical findings:
hypoxemia;
hypercapnia;
crackles, wheezing, & decreased breath sounds;
increased bronchial secretions;
hyperinflation;
frequent lower respiratory infections;
delayed growth & development;
cor pulmonale;
CXR shows with hyperinflation, low diaphragm, atelectasis, cystic changes.

Cause
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.

Diagnosis
Earlier criteria
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.

Newer criteria
The 2006 National Institute of Health (US) criteria for BPD (for neonates treated with more than 21% oxygen for at least 28 days) is as follows:,
MildBreathing 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.ModerateNeed 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) for babies born after 32 weeks gestation.SevereNeed 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.

Management
Infants with bronchopulmonary dysplasia are often treated with diuretics that decrease fluid in the alveoli where gas exchange occurs and bronchodilators that relax the airway muscles to facilitate breathing. Viral immunization is important for these children who have a higher risk of infections in the respiratory tract.

Corticosteroid treatment
There is evidence that steroids (systemic corticosteroid treatment) given to babies less than 7 days old can prevent bronchopulmonary dysplasia. This treatment increases the risk of neurodevelopmental sequelae (cerebral palsy) and gastrointestinal perforation.For babies 7 days old and older, "late systemic postnatal corticosteroid treatment" may reduce the risk of death and of bronchopulmonary dysplasia. There is some evidence that this treatment does not increase the risk of cerebral palsy, however, long-term studies considering the neurodevelopmental outcomes is needed to further understand the risk of this treatment option. Late systemic postnatal corticosteroid treatment is therefore only recommended for babies 7 days old or older who cannot be taken off of a ventilator