BPD begins with an immature lung that is forced to function before it is developmentally ready. In the extremely premature infant, the lung is still forming alveoli and pulmonary vessels. When the infant develops respiratory distress syndrome, infection, inflammation, or apnea of prematurity, respiratory support may be necessary to maintain oxygenation and ventilation. That support is lifesaving, but it can also contribute to lung injury. Mechanical ventilation can injure delicate lung tissue through pressure injury, volume injury, and repetitive opening and closing of unstable alveoli. Oxygen therapy can contribute to oxidative stress when high oxygen concentrations are required. Inflammation from prenatal infection, postnatal sepsis, aspiration, or prolonged respiratory support further disrupts lung growth. Reviews of BPD The end result is a lung with fewer and larger alveoli, reduced surface area for gas exchange, abnormal pulmonary vascular development, and variable airway reactivity. Because there are fewer effective gas-exchange units, the infant may remain tachypneic, oxygen dependent, and unable to tolerate feeding or handling without desaturation. In more severe cases, increased pulmonary vascular resistance can lead to BPD-associated pulmonary hypertension, which significantly...