Materials and methods:
Study population.
An observational, retrospective cohort study was designed. Medical records of all of preterm newborns ( gestational ≤36 weeks postmenstrual age ) who were born at Clinica Somer, Rionegro from January 2011 and January 2018 were reviewed (n=451). Rionegro is a city at 2200 meters above sea level in the northeast of Colombia. We included patients who meet the definition of BDP according to the National Heart, Lung, and Blood Institute (NHLBI) (5). Using this definition bronchopulmonary dysplasia is present when supplemental oxygen at any concentration for 28 days in premature newborns with gestational age ≤32 weeks at birth is needed. All research was performed in accordance with relevant guidelines/regulations approved by the Institutional Review Board of Clinica Somer and Uniremington University.
Definition of BPD and respiratory outcomes.
BPD severity was defined according to the National Heart, Lung, and Blood Institute (NHLBI) (5). Severity was also defined based on oxygen requirements at 36 weeks postmenstrual age or at discharge in the following manner: If no supplemental oxygen was required it was classified as mild, if oxygen requirements were less than 0.3 FiO2 it was considered as moderate, and if the requirements were greater than 0.3 FiO2 or if there was a need of some type of ventilator support (invasive, noninvasive), it was considered severe (5, 6). Oxygen requirement is defined as when the patient presents saturation values for hemoglobin pulse oximetry below 90% at sea level.
At baseline, we collected information on the number of courses of antenatal corticosteroids for the acceleration of fetal lung maturation, gender, birth weight, duration of neonatal ventilatory support, maternal age, apgar score, maternal comorbidities, and complications such as pulmonary arterial hypertension (PH) (increased pulmonary vascular resistance and presence of right –left shunt at the foramen ovale and or ductus arteriosus level. Echocardiography was used as screening modality for PH using tricuspid regurgitant jet to estimate systolic pulmonary artery pressure) (7) , persistent ductus arteriosus, neonatal pneumonia, hyaline membrane disease, sepsis, chorioamnionitis (positive amniotic fluid test result (gram stain, glucose level, or culture results consistent with infection) or placental pathology demonstrating histologic evidence of placental infection or inflammation) . Neonatologist utilized oximetry to assess for true oxygen dependence; and there a correction was applied for altitude (10). Oxygen requirement is defined as when the patient presents saturation values for hemoglobin pulse oximetry (SpO2) below 90% at sea level. For the altitude adjustment, we use the same procedure described by Velasquez (8), Briefly we took into account the FiO2 at which an inspiratory oxygen pressure is similar to that found at sea level with a FiO2 of 0.21. In order to classify the severity, the same equation was used, but utilizing a FiO2 of 0.3 that resulted in an equivalent FiO2 of 0.41. With these calculations, the BPD classification adjusted for Rionegro was defined as the use of supplemental oxygen with a FiO2 of at least 0.29 for 28 days. For the severity classification, it was defined as mild if patient had no supplemental oxygen by week 36 PMA or discharge, moderate if patients had oxygen requirement of 0.29–0.41 by 36 weeks PMA or discharge, and it was defined as severe if the oxygen requirements were greater than 0.42 or if they required some kind of assisted ventilation. To determine the FiO2 in patients using conventional cannulas we use the approximation of Benaron (tidal volume [TV] of 6 ml/kg and an inspiratory time (IT) of 0.33 s) (8)
All patients were treated following the recommendation about prevention, diagnosis, resuscitation, early management and treatment of bronchopulmonary dysplasia established in the national guide for the management of the premature newborn (10,11)