Risk Factors and Pathogenesis of Bronchopulmonary Dysplasia

Primary Causative Factors

Extreme prematurity (birth < 30 weeks gestation and very low birth weight) is the single most important risk factor, with roughly one‑third of such infants developing BPD. 1
The immature antioxidant system of preterm infants makes them especially vulnerable to oxygen‑derived free‑radical injury. 1
Prolonged exposure to high concentrations of supplemental oxygen produces complex biochemical, microscopic, and gross anatomic lung damage, including peak lipid peroxidation around day 5 of life. 1
Oxygen toxicity is recognized as one of the two major contributors to BPD pathogenesis. 2
Barotrauma or volutrauma from mechanical ventilation is a critical causative factor; lower carbon‑dioxide levels (hypocarbia) are inversely related to subsequent BPD development. 1
The most severe long‑term lung function abnormalities are observed in children who required neonatal ventilation. 1
Pulmonary interstitial emphysema, a direct consequence of barotrauma, is strongly associated with a high incidence of BPD. 1
The immature lung is typically exposed simultaneously to oxygen toxicity and barotrauma, with oxygen toxicity producing more pronounced physiological, inflammatory, and histologic changes. 1, 2

Post‑natal infections (e.g., cytomegalovirus, Ureaplasma spp.) markedly increase BPD risk, especially in infants weighing < 1250 g (relative risk ≈ 1.9). 3
Antenatal chorioamnionitis induces fetal inflammation that predisposes to BPD. 3
Nosocomial infection amplifies the adverse effect of a patent ductus arteriosus (PDA) on BPD development. 2
PDA is consistently associated with BPD, particularly in extremely low‑birth‑weight infants. 2
Late‑onset PDA episodes occurring together with nosocomial infection contribute to BPD even in infants who initially present with mild respiratory distress. 2
Infection occurring temporally with PDA further potentiates the risk of chronic lung disease. 2
Relative adrenocortical insufficiency in preterm infants may enhance inflammatory responses to pulmonary insults. 1, 2
Delayed diuresis is more common among infants who develop BPD. 2
Higher early fluid and sodium administration, reflecting increased parenteral fluid loads, is observed in infants who later develop BPD, but proactive diuresis using diuretics or albumin does not improve respiratory outcomes. 2

Improved survival of very low‑birth‑weight infants has shifted the disease pattern toward a “new BPD” phenotype. 1, 3
“New BPD” is characterized by alveolar simplification due to interrupted lung development in extremely premature infants, contrasting with the fibrosis and architectural disruption of “old BPD.” 3
The underlying pathogenesis depends on post‑conceptional age at birth; oxygen toxicity and barotrauma act on increasingly immature and susceptible lungs. 4

The cumulative effect of multiple risk factors (extreme prematurity, mechanical ventilation, supplemental oxygen, and post‑natal infection) leads to an exponentially higher risk of BPD than any single factor alone. 1, 2

All facts are derived from peer‑reviewed sources cited above.

Infants delivered before 26 weeks gestation (corresponding to the canalicular stage) have the highest risk of developing respiratory distress syndrome because surfactant production is insufficient and the air‑blood barrier is not yet fully formed. 5

Very preterm infants born before 30 weeks gestation and weighing less than 1 kg frequently develop bronchopulmonary dysplasia, which is characterized by simplification of alveolar structures due to interruption of normal lung development. 5

The gestational age at which premature birth occurs influences both immediate survival prospects and long‑term pulmonary health, with earlier births associated with greater respiratory morbidity. [6][5]