Description

Respiratory distress syndrome (RDS) is an acute, developmental lung disease affecting primarily premature infants. Disease is characterized by alveolar collapse due to a lack of pulmonary surfactant owing to lung immaturity that results in increased work of breathing, hypoxemia, and respiratory acidosis. The term hyaline membrane disease (HMD) is often used synonymously.

Epidemiology

• RDS is the most common lung disease in premature infants, affecting approximately 60,000 to 80,000 infants per year in the United States.
• Risk increases with the degree of prematurity; nearly 100% of infants born at <26 weeks’ gestation affected
• For near-term infants delivered operatively without benefit of labor, the risk of developing RDS increases roughly 2-fold for every week <39 weeks’ gestation.

Risk Factors

• Prematurity
• Low birth weight
• Maternal diabetes
• Delivery without labor
• Absence of antenatal steroid administration
• Male gender
• Caucasian race
• Perinatal depression

General Prevention

• Prevention of prematurity
• Maternal antenatal steroids

Pathophysiology

• Insufficient or dysfunctional surfactant results in alveolar instability and atelectasis, causing hypoventilation and ventilation–perfusion mismatch, leading to hypoxemia and respiratory acidosis.
• The lack of surfactant in conjunction with pulmonary immaturity also leads to transudation of fluid and alveolar edema.
• Surfactant inactivation from transudation of proteins or other substances into the alveolus
• Increased work of breathing generates high negative intrathoracic pressures to overcome alveolar collapse. Retractions result from the highly compliant newborn rib cage combined with poorly compliant lungs.
• Expiratory grunting is due to glottic closure at the end of expiration to prevent end-expiratory atelectasis and maintain functional residual capacity.
• Infants with a well-developed pulmonary arterial muscular bed can develop secondary pulmonary hypertension, with hypoxemia leading to pulmonary vasoconstriction.