Respiratory Distress Syndrome

Respiratory distress syndrome (RDS) - also called hyaline membrane disease - is the most common cause of neonatal death. The syndrome occurs almost exclusively in infants born before the 37th gestational week (and in about 60% of those born before the 28th week). It's most common in infants of diabetic mothers, those delivered by cesarean section, and those delivered suddenly after antepartum hemorrhage.

In RDS, the premature infant develops widespread alveolar collapse from a deficiency of surfactant. Untreated, the syndrome causes death within 72 hours of birth in up to 14% of infants weighing less than 5½ Ib (2,500 g). Aggressive management assisted by mechanical ventilation can improve the prognosis. A few patients who survive are left with bronchopulmonary dysplasia. Mild cases of the syndrome slowly subside after about 3 days.

Causes and pathophysiology

The immediate cause of RDS is lack of surfactant, a lipoprotein present in alveoli and respiratory bronchioles. In these structures, surfactant helps to lower surface tension, maintain alveolar patency, and prevent collapse, particularly at end expiration.

Although neonatal airways are developed by the 27th gestational week, the intercostal muscles are weak, and the alveoli and the capillary blood supplies are immature. Surfactant deficiency then leads to widespread atelectasis, which leads, in turn, to inadequate alveolar ventilation and shunting of blood through collapsed lung areas. The results are hypoxia and acidosis.

Signs and Symptoms

• Shortness of breath
• Labored, rapid breathing
• Low blood pressure or shock (low blood pressure accompanied by organ failure)

Often, persons affected by ARDS are so sick they are unable to complain of symptoms.

Diagnostic tests

Despite warning signs suggesting RDS, the diagnosis must be confirmed by chest X-rays and arterial blood gas (ABG) analysis.

Chest X-ray findings may be normal for the first 6 to 12 hours in 50% of patients. However, later films show a fine reticulonodular pattern and dark streaks, indicating air-filled, dilated bronchioles.

ABG values show a diminished level of partial pressure of arterial oxygen (Pa02); normal, decreased, or increased level of partial pressure of arterial carbon dioxide; and reduced pH (a combination of respiratory and metabolic acidosis).

Treatment

The neonate with RDS requires vigorous respiratory support. Warm, humidified, oxygen-enriched gases are administered by oxygen hood or, if such treatment fails, by mechanical ventilation. The neonate with severe RDS may require mechanical ventilation with PEEP or continuous positive airway pressure (CPAP) administered by a tight-fitting face mask or, when necessary, endotracheal tube.

If the neonate can't maintain adequate gas exchange, high-frequency oscillation ventilation may be initiated to provide satisfactory minute volume (the total volume of air breathed in 1 minute) with lower airway pressures.

Treatment also may include:

• a radiant warmer or an Isolette for thermoregulation
• I.V. fluids and sodium bicarbonate to control acidosis and maintain fluid and electrolyte balance
• tube feedings or total parenteral nutrition to maintain adequate nutrition if the neonate is too weak or unable to eat
• drug therapy with pancuronium bromide (which paralyzes muscles to prevent spontaneous respirations during mechanical ventilation), prophylactic antibiotics, diuretics (to reduce pulmonary edema), and synthetic surfactant (to prevent atelectasis)
• alternative drug therapy - for example, with vitamin E to prevent complications associated with oxygen therapy, and corticosteroids administered maternally to stimulate surfactant production in fetuses at high risk for preterm birth.

Prevention

To help reduce your chances of getting ARDS, seek timely treatment for any direct or indirect injury to the lungs.