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Classic bronchopulmonary dysplasia (BPD) is a neonatal form of chronic pulmonary disorder. BPD was solely defined as persistent oxygen dependency up to 28 days of life. The severity of BPD-related pulmonary dysfunction and neurodevelopmental impairment in early childhood is more accurately predicted by an oxygen dependence at 36 weeks’ postmenstrual age (PMA) in infants <32 weeks’ gestational age (GA) and at 56 days of age in infants with older GA. BPD is thus classified at this later postnatal age according to the type of respiratory support required to maintain a normal arterial oxygen saturation (>89%) among infants who had been requiring supplemental oxygen during the first 28 days of life.
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Mild bronchopulmonary dysplasia. Infants who have been weaned from supplemental oxygen.
Moderate bronchopulmonary dysplasia. Infants who continue to need up to 30% oxygen.
Severe bronchopulmonary dysplasia. Infants whose requirements exceed 30% and/or include continuous positive airway pressure (CPAP) or mechanical ventilation. However, recently, it has been suggested to further classify severe BPD (sBPD) into type 1 sBPD, which consists of oxygen dependency of >30% or need for nasal CPAP/high-flow nasal cannula, and type 2 sBPD if mechanical ventilation was needed, regardless of the degree of oxygen dependency, at or beyond 36 weeks’ PMA.
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The old or “classic” form of BPD was described by Northway in 1967 during the presurfactant era and prior to the use of “gentler” mechanical ventilation strategies. It consisted of tissue damage in both airways and alveoli. In contrast, the recent and new form of BPD consists of no injuries but rather arrested lung growth and lack of both alveolar septation and vascular simplification (remodeling).
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The incidence of BPD is influenced by many risk factors, the most important of which is degree of immaturity. The incidence of BPD increases with decreasing birthweight and affects approximately 30% of infants with birthweights <1000 g. The large variability in rates among centers is partly related to differences in clinical practices, such as criteria used for the management of mechanical ventilation.
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A primary lung injury is not always evident at birth. The secondary development of a persistent lung injury is the result of abnormal repair process of recurrent injuries occurring during a critical window of lung development.
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The major factors contributing to bronchopulmonary dysplasia are as follows:
Inflammation. Central to the development of BPD. An exaggerated inflammatory response (alveolar influx of numerous proinflammatory cytokines as well as macrophages and leukocytes) occurs in the first few days of life in infants in whom BPD subsequently develops.
Mechanical ventilation. Volutrauma/barotrauma is 1 of the key risk factors for the development of BPD. Minimizing the use of mechanical ventilation by the use of early nasal CPAP, noninvasive ventilatory support (nasal intermittent positive-pressure ventilation), and early use of ...