Introduction
Bronchopulmonary dysplasia (BPD) is the most common cause of chronic lung disease of infancy, occurring primarily in extremely low birth weight (ELBW) newborns. (1, 2) Extreme preterm birth disrupts alveolar growth, frequently resulting in poor gas exchange due to alveolar hypoplasia. (3) As such, many ELBW infants require supplemental oxygen and/or positive pressure support during their initial hospitalization. Nevertheless, many ELBW survivors with BPD will undergo alveolar catch-up growth and be weaned off respiratory support, prior to initial hospital discharge or during their preschool years. (4, 5)
It has been recognized that children with BPD are commonly diagnosed with small airflow obstruction, and that abnormalities in airway flow can persist into adolescent and adult life. (4, 6) The development of small airflow obstruction in early life, can adversely influence lung function trajectories in later life (7) and can be a risk factor for the development of chronic obstructive lung disease (COPD) in adults. (8) The traditional marker of small airway disease is evidence of airflow obstruction on spirometry. However, since spirometry is difficult to perform reliably prior to 6 years of age, a non-invasive method for identifying young children with BPD who are at risk for a small airway phenotype is needed. Earlier identification of those at risk for a small airway phenotype may allow for more timely interventions that may improve lung function trajectories.
Although BPD severity is formally diagnosed based on respiratory support needs at 36 weeks post menstrual age (PMA), recent studies indicate that BPD severity scores assigned in the neonatal intensive care unit (NICU) may not predict respiratory outcomes in the outpatient setting. (9, 10) This lack of predictive value of outpatient respiratory outcomes based on inpatient BPD severity scores suggests the importance of establishing new criteria for assessing outpatient phenotypes in children with BPD. Currently, there are no established phenotypes or framework for classification of respiratory diseases associated with prematurity after NICU discharge.
Inhaled corticosteroids (ICSs) are commonly used to treat and control symptoms of small airflow obstruction in children with asthma. Children with BPD are also frequently prescribed ICSs, however their use and effectiveness in the outpatient setting is less well described.(11, 12). In this study we hypothesized that young children with BPD prescribed an ICS in the outpatient setting, will have different clinical characteristics and a greater likelihood of adverse respiratory outcomes when compared to children who are not prescribed an ICS. Furthermore, we sought to determine if ICS use correlated with the timing and likelihood of an asthma diagnosis.
Understanding the use and timing of ICS initiation in the outpatient setting may be a proxy for identifying young children with BPD who have clinical features of small airway obstruction. Identifying these children earlier in life may allow for interventions that could improve respiratory outcomes. This study was preformed using electronic patient medical records from children with BPD seen in outpatient pulmonary clinics over a six-year period.