Fig. 7.25 Hyalinemembranedisease(hematoxylin-eosinstain).Alternatingatelectasisanddilationofthealveolicanbeseen.Notetheeosinophilicthickhyalinemembranesliningthedilatedalveoli.
provides a good estimate of the level of surfactant in the alveolar lining. Prophylactic administration at birth of exogenous surfactant to extremely premature infants (born before 28 weeks’ gestational age) has proven very beneficial, such that it is now uncommon for infants to die of acute RDS.
In uncomplicated cases, recovery begins to occur within 3 or 4 days. In affected infants, oxygen is required. Use of high concentrations of ventilator-administered oxygen for prolonged periods, however, is associated with two well-known complications: retrolental fibroplasia (also called retinopathy of prematurity) in the eyes; and bronchopulmonary dysplasia. Fortunately, both complications are now significantly less common as a result of gentler ventilation techniques, antenatal glucocorticoid therapy, and prophylactic surfactant treatments. Hence they are described briefly:
Retinopathy of prematurity has a two-phase pathogenesis. During the hyperoxic phase of RDS therapy (phase I), expression of the proangiogenic vascular endothelial growth factor (VEGF) is markedly decreased, causing endothelial cell apoptosis. VEGF levels rebound after return to relatively hypoxic room air ventilation (phase II), inducing retinal vessel proliferation (neovascularization) characteristic of the lesions in the retina.
The major abnormality in bronchopulmonary dysplasia is a striking decrease in alveolar septation (manifested as large, simplified alveolar structures) and a dysmorphic capillary configuration. Multiple factors—hyperoxemia, hyperventilation, prematurity, inflammatory cytokines, and vascular maldevelopment—contribute to bronchopulmonary dysplasia and probably act additively or synergistically to promote injury.
Infants who recover from RDS also are at increased risk for developing a variety of other complications associated with preterm birth; most important among these are patent ductus arteriosus, intraventricular hemorrhage, and necrotizing enterocolitis. Thus, although technologic advances help save the lives of many infants with RDS, they also bring to the surface the exquisite fragility of the immature neonate.
NeonatalRDS(hyalinemembranedisease)isadiseaseofprematurity;mostcasesoccurinneonatesbornbefore28weeks’gestationalage.
ThefundamentalabnormalityinRDSisinsufficientpulmonarysurfactant,whichresultsinfailureoflungstoinflateafterbirth.
ThecharacteristicmorphologicpatterninRDSisthepresenceofhyalinemembranes(consistingofnecroticepithelialcellsandplasmaproteins)liningtheairways.
RDScanbeamelioratedbyprophylacticadministrationofsteroids,surfactanttherapy,andbyimprovedventilationtechniques.
Long-termsequelaeassociatedwithRDStherapyincluderetinopathyofprematurityandbronchopulmonarydysplasia;theincidenceofbothcomplicationshasdecreasedwithimprovementsinmanagementofRDS.