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Neonatal respiratory distress syndrome
(hyaline membrane disease)
The neonatal respiratory distress syndrome (NRDS) is due to
deficiency of surfactant in the lungs. It is primarily a
disease affecting premature infants, but is also seen in
infants born to diabetic mothers, as excess production of
insulin by the fetus suppresses surfactant production.
A very common condition, the incidence of NRDS increases with
increasing prematurity (20% incidence at 32-36 weeks' gestation;
60% incidence at <28 weeks' gestation).
With development of disease, the chest radiograph shows a 'ground
glass' opacity in the lung fields.
The mortality from NRDS is 50%
in infants weighing under 1000 g.
The lungs from infants who die from the condition appear airless,
dark red and dense.
Depending on the stage of disease, atelectasis,
epithelial necrosis, hyaline membranes, and organization may
be seen histologically.
There are four main risk factors for development of NRDS.
immature or damaged lung is unable to make enough surfactant,
the lecithin-rich surface-active lipid secreted by Type II pneumocytes.
Normally this reduces surface tension in alveoli and keeps
alveoli open. In NRDS, lack of surfactant means that alveoli
collapse with microatelectasis.
Hypoxia leads to damage of alveolar lining cells, hypoxia and
pulmonary arterial constriction.
Endothelial damage causes
plasma to leak into alveoli, being deposited as fibrin.
appears as bright, pink-stained membranes lining alveoli, hence
the name hyaline membrane disease. The presence of fibrin further
impairs gas exchange and makes hypoxia worse.
The process is
similar to that in diffuse alveolar damage.
Later, regenerative changes in the lung lead to organization
of hyaline membranes and fibrosis.
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We give here simplified and accurate information about the disease
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