Evolution of Lung Disease in the Premature Infant

In 2007 premature births, defined as births <36 weeks of gestation, accounted for 12.7% of live births in the United States. ¹ Prematurity is the greatest risk factor for the development of bronchopulmonary dysplasia (BPD), as an estimated 44%–77% of infants born with a birth weight of <1,000 g and at ≤32 weeks develop BPD. ² Even late preterm infants (32–36 weeks of gestation) have a higher risk for respiratory morbidities than do full-term infants. ³ Much of the morbidity and mortality seen in preterm infants is attributable to respiratory causes and related infections ⁴ ; approximately 50% of preterm infants are re-hospitalized within the first year of life.^5–7 Although recent cost estimates for caring for these infants and children are not available, in 1998 the estimated cost of caring for infants with BPD in the United States was reported to be $2.4 billion. ⁸

Assessing, managing, and studying the evolution of lung disease in the preterm infant can be a difficult proposition outside of the neonatal intensive care unit (NICU). Although data exist for NICU management strategies, little is known about optimal outpatient management, including diuretic use, inhaled corticosteroid use, and weaning of supplemental oxygen. Even defining the disease is problematic outside the NICU as the consensus definition of BPD is only applicable at 28 days of age or 36 weeks postmenstrual age. ⁹ Part of this issue relates to the lack of a readily available outpatient tests to measure lung function before school age; current infant pulmonary testing is limited to a few tertiary care centers and may require sedation. Furthermore, the lung disease of preterm infants is not static and may evolve or resolve rapidly. Lastly and perhaps most importantly, the lung disease of preterm infants is not uniform and may have varying components of vascular, interstitial, and/or airway disease.

This review series follows the evolution of lung disease in preterm infants from fetal life through adulthood. In this issue, Drs. Pamela Zeitlin and Lawrence Nogee's review examines the role of prenatal and genetic factors that impact the development of BPD, recognizing that many disease processes may have their origins during fetal development. ¹⁰ Dr. McGrath-Morrow's review follows the evolution of BPD into various phenotypes of vascular, interstitial, and airway disease during infancy and childhood. ¹¹ Recognizing that early environmental factors may impact respiratory outcomes, Dr. Collaco's review examines post-NICU environmental modifiers of disease in infancy. ¹² Drs. Brian McGinley and John Carroll's review focuses on an understudied phenotype of BPD, sleep-disordered breathing, which may have important respiratory and developmental consequences. ¹³

This series will continue in future issues of this journal, with discussion of advances in care in the NICU, which have led to an evolving presentation of BPD, such as surfactant therapy, and the long-term effects of BPD, which may persist into adulthood and bear some similarities to other adult lung diseases, such as chronic obstructive pulmonary disease.

We thank Dr. Harold Farber, the editor of Pediatric Allergy, Immunology, and Pulmonology, for inviting us to serve as Guest Editors for this special series on the evolution of lung disease in premature infants. We hope that this series proves to be illuminating and useful for all who care for these infants and children.