Edema formation in the newborn lung.

Pulmonary edema is an important cause of respiratory distress in newborn infants. It occurs with severe perinatal asphyxia, heart failure, hyaline membrane disease, persistent patency of the ductus arteriosus, pneumonitis from group B beta-hemolytic streptococcus, and chronic lung disease (bronchopulmonary dysplasia). Neonatal pulmonary edema often develops from increased pressure in the microcirculation of the lungs. This may occur in conjunction with sustained hypoxia; 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 of fibrosis (chronic 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. Epithelial protein leaks may develop when the transpulmonary pressure needed to inflate the lungs increases because of high surface tension at the air-liquid interface. Fibrin clots from in some of the air spaces, which in combination with atelectasis and edema constitute the pathologic features of hyaline membrane disease. The risk of neonatal pulmonary edema can be reduced by several therapeutic measures designed to lessen fluid filtration pressure, increase plasma protein osmotic pressure, and prevent or reduce the severity of lung injury.