Respiratory Distress Syndrome

C onsidering the complex series of cardiorespira-tory changes that occurs at birth, it is not surprising that the transition to extrauterine life does not always proceed smoothly. Neonatal respiratory disorders account for the majority of admissions to intensive care units and result in significant morbidity and mortality. Once the infant shows signs of respiratory distress, prompt diagnosis is essential. Respiratory distress may be related to structural problems such as poor lung development or defects of the chest wall or diaphragm. Biochemical and physical immaturity may exist. Abnormalities in the central nervous system may cause alterations in the respiratory regulatory apparatus. Perfusion abnormalities may impair gas exchange. Aspiration and infection can also occur. Not all infants with respiratory distress have a respiratory disease (Figure 2-1). In some cases, congenital heart disease may be difficult to distinguish from primary lung disease. Labored breathing may also result from a metabolic problem. The coexistence of other factors , such as cold stress and polycythemia, may compound respiratory distress. Most neonatal respiratory problems are treated medically, but a number of conditions that present with respiratory distress may require surgical intervention. Institution of appropriate therapy requires an accurate diagnosis. Knowledge of the patho-physiology of neonatal pulmonary diseases is essential to ensure comprehensive management. This chapter discusses the pathophysiology of the most common pulmonary disorders that present as acute respiratory distress in the newborn period. Respiratory distress syndrome (RDS), also known as hyaline membrane disease and surfactant deficiency syndrome, is the major pulmonary problem occurring in the neonate. This syndrome affects approximately 40,000 infants annually in the U.S. Nearly 65 percent of these infants are born at gestational ages of 30 weeks or less. 1 Infants of 37–40 weeks gestational age rarely develop RDS. The prematurity rate is the main reason RDS remains a major neonatal problem. The frequency of RDS, which primarily affects preterm infants less than 35 weeks gestational age, increases inversely with gesta-tional age. However, susceptibility to RDS depends more on the neonate's stage of lung maturity than on precise gestational age. Table 2-1 lists risk factors known to pre-dispose the neonate to developing RDS. Despite significant advances in understanding the pathophysiology of the disease, RDS ranks eighth among the top ten causes of neonatal deaths. Extreme prematu-rity; congenital anomalies; chromosomal abnormalities; bacterial sepsis; maternal complications of pregnancy; and complications of the placenta, cord, and fetal membranes currently outrank RDS as causes of neonatal …