Discussion.
In this study population, the incidence of BPD was 25.7%. Our incidence of BPD is higher than rates reported in developed countries but similar to cities with higher altitudes in Colombia such as Bogota(12,13). A previous case-control study found variations in the prevalence of BPD according to altitude in Colombia. In cities located a higher altitude (more than 2600  meters above sea level), the prevalence of BPD were higher than other cities with lower altitude as Bucaramanga and Cali (10). Highest altitude city (Bogotá) was associated with a higher risk of dysplasia (OR 1.82 95% CI 1.31-2.53) (12). Infants who are born in cities with higher altitudes (> 2000 meters above sea level) have twice the risk of developing BPD than infants born in cities with lower altitudes, independently of differences in maternal, infant, and therapeutic risk factors(12,14). Altitude play an important role in the pathogenesis of BPD. The decreased partial pressure of oxygen in the environment, in cities with higher altitudes, has also been associated with higher pulmonary artery pressures, delayed in the functional closure of the ductus arteriosus in the newborn, tortuous transition from oxygenation via placenta to oxygenation across the lungs resulting in postnatal persistence of fetal circulation(15). As a result of these events, it is possible that premature infants born at high altitudes have an early dependency on high concentrations of oxygen and ventilatory support compared to patients born at lower altitudes. In our study, sepsis was a risk factor associated with BPD severity. Multiple studies indicate that postnatal sepsis independently increases the incidence of BPD
Preterm infants are more susceptible to infections since their immune defenses are not fully developed, have vulnerable skin barrier, and require multiple invasive procedures. Late-onset sepsis induces a pro-inflammatory and pro-fibrotic response in the preterm lung predisposing it to BPD . Neonatal mice injected with intraperitoneal LPS demonstrated reduced lung inflammation and apoptosis after 24 h as compared to adults, and this was associated with activation of the transcription factor, nuclear factor kappa B. Inhibition of NF-κB resulted in increased cell death and alveolar simplification and disruption of angiogenesis via vascular growth factor (VEGF)-R2 (9-11)
We found that pulmonary arterial hypertension (PH) was an independent predictor of BPD severity. PH is a common complication of neonatal respiratory diseases including BPD. Up to 18% of all extremely low birth weight infants will develop some degree of PH, and the incidence rises to 25–40% of infants with established BPD (12). PH worsens the clinical course, morbidity, and mortality of BPD(12). PH also is a common disease in individuals living at high altitudes, yet this is a understudied disorder especially in patients with BPD (13). A better understanding of the pathogenesis is necessary to optimize current drugs and newer therapeutic targets.
A number of important limitations need to be considered. As occurs in longitudinal studies, information bias cannot be excluded. However we include all patients registered in the hospital and the reported incidence cannot be attributed to the bias of selection; nor can it be attributed to overdiagnosis of oxygen dependence, since the neonatologist in all patient verified with physiological tests (dynamic oximetry standardized) that children truly require supplemental oxygen. Second, hospitalizations due to other medical conditions sometimes can prolong the hospital stay and the withdrawal of oxygen (inefficiencies within the healthcare system, placement difficulties, operational delays, and payer-related issues). However, the plausibility of the identified clinical factors suggests that the above-mentioned non-medical factors account for a minimal part of the causality in the studied population. Third , in our study used the echocardiography for PH diagnosis. However in infants with BPD can be especially challenging due to the presence of lung hyperinflation and heart rotation, both of which impact the sensitivity of imaging and identification of the tricuspid regurgitant jet. The echocardiography correctly diagnosed the presence or absence of PH 79% of the time, but correctly determined the severity PH only 47% of the time. These results imply that in the absence of a quantifiable TR jet, the currently available indirect measurements are insufficient for the assessment of the degree of PH in infants with BPD(13).
In conclusion, the incidence of BPD was higher than the average rates reported in populations with similar gestational ages in developed countries but similar to cities with higher altitudes. In our population, the variables associated with BPD severity levels were: duration of oxygen therapy and pulmonary hypertension. It is necessary to increase the awareness of risk factors, the effect of clinical practices, and early recognition of bronchopulmonary dysplasia to reduce morbidity in patients with this pathology.
Acknowledgements: None