Master the board step 3

Master the Boards: USMLE Step 3
Basic Science Correlate
Mechanism of Surfactant
••
Surfactant prevents collapse of the aveoli by decreasing surface tension.
••
Surfactant is produced by Type II pneumocytes, which start to develop
around 24 weeks gestation. However, not enough surfactant is secreted until
35 weeks gestation.
Do the following for primary prevention:
··
Antenatal betamethasone: This is most effective if > 24 hours before delivery
and < 34 weeks gestation.
··
Avoid prematurity: Give tocolytics.
··
Give corticosteroids immediately to any fetus in danger of preterm delivery
< 34 weeks.
··
Postnatal corticosteroids do not help and are not indicated.
Possible complications:
··
Retinopathy of prematurity (ROP) (hypoxemia)
··
Bronchopulmonary dysplasia (prolonged high-concentration oxygen):
Prevent with CPAP.
··
Intraventricular hemorrhage
Transient Tachypnea of the Newborn (TTN)
This presents as tachypnea after a term birth of infant delivered by cesarean
section or rapid second stage of labor, likely related to retained lung fluid. The
condition usually resolves in 24–48 hours.
Basic Science Correlate
TTN is caused by retained lung fluid. That is, fluid present in the lungs
in utero does not get squeezed out in passage through the birth canal.
Increased fluid in the lungs causes increased airway resistance and decreased
lung compliance.
Diagnostic Testing
Perform a chest x-ray to look for the following:
··
Air trapping
··
Fluid in fissures
··
Perihilar streaking
360