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.