Edema formation in the lungs and its relationship to neonatal respiratory distress.

Pulmonary edema is an important feature of many newborn lung diseases, including respiratory distress from severe perinatal asphyxia, heart failure, hyaline membrane disease, pneumonitis from group B beta-hemolytic streptococcus, and chronic lung disease (bronchopulmonary dysplasia). Neonatal pulmonary edema often results from increased filtration pressure in the microcirculation of the lungs. This occurs during sustained hypoxia, in left ventricular failure associated with congenital heart disease or myocardial dysfunction, following excessive intravascular infusions of blood, colloid, fat, or electrolyte solution, and in conditions that increase pulmonary blood flow. Low intravascular protein osmotic pressure from hypoproteinemia may predispose infants to pulmonary edema. Hypoproteinemia is common in infants who are born prematurely. Large intravascular infusions of protein-free fluid further decrease the concentration of protein in plasma and thereby facilitate edema formation. Lymphatic obstruction by air (pulmonary interstitial emphysema) or fibrosis (long-standing lung disease) also may contribute to the development of edema. Bacteremia, endotoxemia, and prolonged oxygen breathing injure the pulmonary microvascular endothelium and cause protein-rich fluid to accumulate in the lungs. The risk of neonatal pulmonary edema can be reduced by several therapeutic measures designed to lessen filtration pressure, increase plasma protein osmotic pressure, and prevent or reduce the severity of lung injury.