Chapter 66 Respiratory Distress Syndrome
PATHOPHYSIOLOGY
Respiratory distress syndrome (RDS) results from the absence, deficiency, or alteration of the components of pulmonary surfactant. Surfactant, a lipoprotein complex, is an ingredient of the filmlike surface of each alveolus that prevents alveolar collapse. It is secreted from type II respiratory cells in the alveoli. When surfactant is inadequate, alveolar collapse occurs and hypoxia results. Pulmonary vascular constriction and decreased pulmonary perfusion then occur, which lead to progressive respiratory failure.
INCIDENCE
1. The incidence of RDS shows an inverse relationship to gestational age: the younger the infant, the greater the risk of RDS. However, the occurrence of RDS appears to be more dependent on lung maturity than on actual gestational age.
2. The severity of RDS is decreased in infants whose mothers received corticosteroids 24 to 48 hours before delivery. There appears to be an additive effect in improved lung function when antenatal steroid therapy is combined with postnatal surfactant administration.
3. RDS occurs twice as often in males as in females.
4. Incidence increases in full-term infants in the presence of certain factors:
CLINICAL MANIFESTATIONS
The following symptoms are observed in the first 2 to 8 hours of life. Symptoms are progressive as atelectasis increases:
1. Tachypnea (more than 60 breaths/min)
2. Intercostal and sternal retractions
3. Audible expiratory grunting
5. Cyanosis as hypoxemia increases
6. Decreasing lung compliance (paradoxic seesaw respirations)
7. Systemic hypotension (peripheral pallor, edema, capillary filling delayed by more than 3 to 4 seconds)
RDS is a self-limiting disease. Improvement is typically seen 48 to 72 hours after birth, when type II alveolar cell regeneration occurs and surfactant is produced. Presentation and duration of symptoms can be altered with surfactant replacement therapy.
COMPLICATIONS
1. Metabolic: acid-base imbalance
2. Pulmonary: air leaks (pneumothorax, pneumomediastinum, pneumopericardium, pneumoperitoneum, subcutaneous emphysema, pulmonary interstitial emphysema), pulmonary hemorrhage, chronic lung disease of infancy (in 5% to 10% of infants, see Chapter 13), apnea
3. Cardiovascular: systemic hypotension
5. Infection: pneumonia, septicemia—transplacental or nosocomial
6. Developmental: altered infant development and parenting behaviors
