Respiratory Distress Syndrome
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.
- 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.
- Low birth weight
- Maternal diabetes
- Delivery without labor
- Absence of antenatal steroid administration
- Male gender
- Caucasian race
- Perinatal depression
- Prevention of prematurity
- Maternal antenatal steroids
- 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.
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