Respiratory Distress Syndrome
Respiratory distress syndrome is a breathing disorder of premature newborns in which the air sacs (alveoli) in a newborn's lungs do not remain open because the production of surfactant is absent or insufficient.
For a newborn to be able to breathe easily, the air sacs in the lungs must be able to remain open and filled with air. Normally, the lungs produce a mixture of lipids (fats) and proteins called surfactant. Surfactant acts as a wetting agent and lines the surface of the air sacs, where it lowers the surface tension and allows the air sacs to remain open throughout the respiratory cycle. Usually, production of surfactant begins after about 34 weeks of pregnancy. The more premature the newborn, the greater the likelihood that respiratory distress syndrome will develop after birth. Respiratory distress syndrome occurs almost exclusively in premature newborns and is more common in those whose mother has diabetes.
Symptoms and Diagnosis
In an affected newborn, the lungs are stiff and the air sacs tend to collapse completely, emptying the lungs of air. In some very premature newborns, the lungs may be so stiff that the newborn is unable to begin breathing at birth. More commonly, the newborn tries to breathe, but because the lungs are so stiff, severe respiratory distress occurs. Respiratory distress is manifested by visibly labored breathing, including retractions of the chest below the rib cage, flaring of the nostrils during breathing in, and "grunting" during breathing out. Because a good portion of the lung is airless, the newborn has low blood oxygen levels, which cause a bluish discoloration to the skin (cyanosis). Over a period of hours, the respiratory distress tends to become more severe, as the small amount of surfactant in the lungs is used up and increasing numbers of air sacs collapse and also as the muscles used for breathing tire and become weak. Eventually, without treatment, the newborn may suffer damage to the brain and other organs from a lack of oxygen or may die.
Diagnosis of respiratory distress syndrome is based on the symptoms and on abnormal chest x-ray results in a premature newborn.
Prevention and Treatment
The risk of respiratory distress syndrome is greatly reduced if delivery can be safely delayed until the fetal lungs have produced sufficient surfactant. The obstetrician can perform amniocentesis, in which some amniotic fluid is withdrawn into a syringe and analyzed for the adequacy of surfactant production. If production is not adequate but premature delivery cannot be avoided, the obstetrician may give the mother injections of a corticosteroid drug (betamethasone or dexamethasone). The corticosteroid crosses the placenta into the fetus and accelerates the production of surfactant. Within 48 hours of starting the injections, the fetal lungs mature to the point that respiratory distress syndrome will not develop after delivery or, if it does, is likely to be milder.
After delivery, a newborn with mild respiratory distress syndrome may require only supplemental oxygen, which is given through an oxygen hood or through a tube placed in the nose. A newborn with severe respiratory distress syndrome may require oxygen delivered by continuous positive airway pressure (CPAP --breathing spontaneously against positive pressure oxygen or air administered through tubes placed in both nostrils). In a very sick infant, a tube may need to be passed into the windpipe (intubation), and the infant's breathing supported with mechanical ventilation.
Use of a surfactant preparation can be lifesaving and reduces complications, such as rupture of the lungs (pneumothorax). The surfactant preparation acts in the same way that natural surfactant does. Surfactant may be given immediately after birth in the delivery room to attempt to prevent respiratory distress syndrome or in the early hours after birth to a premature newborn who already has symptoms of this disorder. A newborn who is intubated can receive surfactant through the tube in the windpipe.
Surfactant treatments may be repeated several times over the first days until respiratory distress syndrome resolves.
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