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Bronchopulmonary dysplasia (BPD) was described by Northway and
colleagues1 in 1967 as a syndrome of severe lung
injury in preterm infants who had received mechanical ventilation
and high levels of supplemental oxygen. This initial description
of BPD occurred in the era when mechanical ventilation was just
beginning to be used for preterm infants and the mean birth weight
of the infants who survived mechanical ventilation to develop BPD
was 2.3 kg. The pathology was characterized by prominent airway
injury, epithelial metaplasia, smooth muscle hypertrophy, and parenchymal fibrosis
alternating with emphysema. The experimental work during that era demonstrated that
the causes of BPD were primarily mechanical ventilation of and oxygen
exposure to the developing lung.2
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Neonatal care practices have changed over the last 30 years with
the use of antenatal corticosteroids, continuous positive airway
pressure, surfactant, improved ventilation strategies, improvements
in nutrition, and other care practices. Many extremely
low-birth-weight infants (< 1 kg) with gestational ages under
28 weeks now survive, and these more immature infants are at higher
risk for BPD.3 The epidemiology of BPD has changed
because factors other than mechanical ventilation and oxygen exposure
contribute to the occurrence of BPD in extremely low-birth-weight
infants. Major associations are postnatal sepsis, patent ductus
arteriosus, and antenatal chorioamnionitis.4 Some
extremely low-birth-weight infants now develop BPD without initially
having severe respiratory distress syndrome or initially requiring
much supplemental oxygen or mechanical ventilation.5
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The diagnosis of BPD is confounded by a series of definitions
that have changed over the years as the patients at risk have become
increasingly premature.6 Many recent reports define
BPD as the need for supplemental oxygen at 36 weeks postconceptional
age. However, because clinicians use supplemental oxygen inconsistently, oxygen
use and target saturations vary widely in clinical practice. A National
Institutes of Health workshop in 2000 recommended a graded diagnosis
for BPD to better describe the clinical status of infants with BPD6 (see eTable 59.1). More recently, Walsh and colleagues7 developed
an oxygen-need test to make the diagnosis of BPD more uniform. Neonates
on positive pressure support or receiving >30% supplemental
oxygen with saturations between 90% and 96% were
diagnosed with BPD and not tested further. Those receiving <30% oxygen
or effective oxygen >30% with saturations >96% underwent
a room-air challenge with continuous observation and oxygen-saturation
monitoring. Those that could not maintain saturations >90% during
weaning and in room air for 30 minutes were also diagnosed with
BPD. With the use of the oxygen-need test, the diagnosis of BPD
decreased from 35% to 25% of the infants with
birth weights below 1250 grams. The diagnostic definition of BPD
as oxygen need at 36 weeks does not require antecedent exposures
(eg, respiratory distress syndrome, mechanical ventilation), abnormalities
on a chest radiograph, or any laboratory test.
This is not a precise diagnosis relative to most diagnoses in medicine,
which generally include specific clinical associations and laboratory
findings. While the diagnosis of BPD is ...