Definition
The definition of BPD has evolved over the years as viability
thresholds for preterm infants have decreased; thus,
it is often described as “old BPD” versus “new BPD.” This
is a reflection on the distinct embryologic differences in
pulmonary development at different gestational ages. It
is also influenced by changes in treatment strategies and
by technological and pharmacological options that exist
today.
Old BPD
This form of chronic lung disease was first described in
the 1960s by Northway and colleagues, who observed radiographic
changes in late preterm infants who had been
exposed to aggressive mechanical ventilation and high
concentrations of oxygen (Northway, 1990). This damage
occurred in the late saccular stage of lung development
with X-ray findings consistent with extensive inflammation
and fibrotic and cystic changes in the lung parenchyma
and airways. The diagnosis of BPD was assigned to
the infant if he or she was oxygen dependent at 28 days
of age.
As the practice of neonatology evolved and new technological
and treatment modalities were developed, the
gestational age at which infants were surviving became
lower and lower. Exogenous surfactants improved lung
compliance and reduced oxygen requirements. Ventilators
designed for use in this patient population became
increasingly more sophisticated. These innovations and
others allowed for gentler methods of ventilation and,
in some cases, reduced damage to airways and resultant
fibrosis. However, as survival improved in extremely
preterm infants, there was an inverse relationship seen
in the severity of BPD with gestational age. Today, approximately
two-thirds of infants who develop BPD are
extremely low birth weight (< 1,000 g) and less than 28
weeks at the time of their birth.