Respiratory Problems.

The respiratory distress syndrome (RDS), frequently referred to as hyaline membrane disease, is the most common complication of prematurity. In the United States, RDS develops in approximately 10% to 15% of newborns weighing less than 2500 g and 60% of infants born at 29 weeks' gestation. The incidence of RDS is lower in African-American than in white infants and in female than in male infants.

The primary cause of RDS is the lack of surfactant in the lungs (see respiratory distress syndrome, Chapter 30). Surfactant is produced by type II alveolar cells in the lungs. It is a combination of several phospholipids that lowers the alveolar surface tension and facilitates lung expansion (see Chapters 29). At 24 weeks' gestation, there are small amounts of surfactant and few terminal air sacs (i.e., prim­itive alveoli) with underdeveloped pulmonary vascularity. If an infant is born at this time, there is little chance of sur­vival. By 26 to 28 weeks' gestation, there usually is suffi­cient surfactant and lung development to permit survival.

The availability of exogenous surfactant replacement therapy has improved the outcome of RDS and has been recognized as the main factor responsible for the 6.2% de­crease in the infant mortality rate in the United States from 1989 to 1990. However, because the survival rate of the sick­est infants has improved and because their management is more complex, the incidence of other complications has increased. These include air leak syndromes, broncho­pulmonary dysplasia, and intracranial hemorrhage.¹²,²¹

Apnea and periodic breathing are other common respi­ratory problems in premature infants. Because the respira­tory center in the medulla oblongata is underdeveloped in the premature infant, the ability for sustained ventilatory drive often is impaired. Apnea is defined as cessation of breathing; it is characterized by failure to breathe for 20 sec­onds or more and often is accompanied by bradycardia or cyanosis. Among infants weighing less than 1.5 kg, 50% re­quire intervention for significant apneic spells.¹²,²¹ Although apnea may be caused by an underlying disease process such as infection, this is not apnea of prematurity and should not be treated as such.

Periodic breathing commonly occurs in those infants weighing less than 1.8 kg. It is an intermittent failure to breathe for periods lasting less than 10 to 15 seconds. Management of apnea and periodic breathing includes use of medications or ventilatory support until the CNS is de­veloped and able to sustain adequate ventilatory drive.¹²,²¹