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Bronchopulmonary dysplasia (BPD)—sometimes called chronic
lung disease of infancy—is a disorder of lung
injury and repair in infants who developed respiratory failure after
birth and is characterized by persistent respiratory signs and symptoms.
The pathogenesis of BPD is related to prematurity and the treatment
of the accompanying early respiratory failure; the treatment interacts
with the immature developing lung, causing further injury and delayed
repair. The injurious effects of treatment include barotrauma from
positive-pressure ventilation and oxygen toxicity. However, other
therapies developed in the past 40 years have led to a different
clinical, histological, and radiographic presentation and have redefined
the condition. For a more detailed discussion of the pathogenesis,
risk factors and prevention of BPD see Chapter 59.
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In 1960, Wilson and Mikity described five premature infants1,2 who
developed respiratory disease between 1 and 5 weeks of age; the
radiographic and histological findings in these infants were similar
to the first description of BPD. In 1967, Northway and colleagues3 described
a chronic lung disease occurring in premature infants with respiratory
distress syndrome treated with positive-pressure mechanical ventilation
and supplemental oxygen. The original definition of BPD was based
on clinical criteria, consisting of a set of historical facts: needing
mechanical ventilation for a minimum of 3 days in the first 2 weeks
of life; having an abnormal chest radiograph by 28 days of life;
being oxygen dependent for greater than 28 days; and showing persistent
signs of respiratory distress beyond 28 days.
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The definition and presentation of BPD has changed since the
advent of surfactant replacement therapy. The classic histological
findings of BPD—a patchy distribution of alveolar septal
fibrosis and hyperinflated lung parenchyma—are now less
common. Disruption of distal airway, blood vessel, and parenchymal
development with impaired alveolar and vascular growth, in a more
homogeneous distribution, are now more commonly found. New histological
findings reflect an evolution in treatment and hence a change in
the patient population that develops the disease; now BPD is found
in very premature infants of a younger postconceptual age who are
treated with surfactant. The differences between the original definitions
of BPD and what has been termed the “new BPD” will
be discussed in the following sections.
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Epidemiology,
Specific Populations at Risk, and Associated Disorders
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Calculating the incidence of bronchopulmonary dysplasia (BPD)
and defining populations at risk is made difficult by evolution
and variation in definitions used in the literature and in the care
of premature infants. Although the use of surfactant replacement
therapy led to a decrease in the incidence of BPD, the overall incidence
of this disorder has not changed much over the past decade.4 Neonatal
centers vary widely in reported incidence of BPD, which is about
20% of all ventilated premature newborns.5 The
reported incidence for all newborns is lower (2 to 3/1000
live births) than the incidence among premature infants surviving
the neonatal period or those at ...