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Respiratory Distress Syndrome

Also called hyaline membrane disease, respiratory distress syndrome (RDS) is the most common cause of neonatal mortality. In the United States alone, it causes the death of 40,000 neonates every year. If untreated, RDS is fatal within 72 hours of birth in up to 14% of neonates weighing less than 5½ Ib (2,500 g).

RDS occurs almost exclusively in neonates born before the 37th week of gestation (in 60% of those born before the 28th week). It occurs more often in neonates of diabetic mothers, those delivered by cesarean section, and those delivered suddenly after antepartum hemorrhage.

Aggressive management using mechanical ventilation can improve the prognosis, but a few neonates who survive have bronchopulmonary dysplasia. Mild RDS slowly subsides after 3 days.

Causes

Although the airways and alveoli of a neonate's respiratory system are present by the 27th week of gestation, the intercostal muscles are weak and the alveoli and capillary blood supply are immature. In RDS, the premature neonate develops widespread alveolar collapse because of lack of surfactant, a lipoprotein present in alveoli and respiratory bronchioles.

Signs and symptoms

The following are the most common symptoms of HMD. However, each baby may experience symptoms differently. Symptoms may include:

• respiratory difficulty at birth that gets progressively worse
• cyanosis (blue coloring)
• flaring of the nostrils
• tachypnea (rapid breathing)
• grunting sounds with breathing
• chest retractions (pulling in at the ribs and sternum during breathing)
  

The symptoms of HMD usually peak by the third day, and may resolve quickly when the baby begins to diurese (excrete excess water in urine) and begins to need less oxygen and mechanical help to breathe.

The symptoms of HMD may resemble other conditions or medical problems. Always consult your baby's physician for a diagnosis.

Diagnosis

Although signs of respiratory distress in a premature neonate during the first few hours of life strongly suggest RDS, the following tests are necessary to confirm the diagnosis:

• Chest X-ray may be normal for the first 6 to 12 hours (in 50% of neonates with RDS) but later shows a fine reticulonodular pattern.
• Arterial blood gas (ABG) analysis shows decreased partial pressure of arterial oxygen (Pao2); normal, decreased, or increased partial pressure of arterial carbon dioxide (Paco2); and decreased pH (from respiratory or metabolic acidosis or both).
• Chest auscultation reveals normal or diminished air entry and crackles (rare in early stages).

When a cesarean section is necessary before the 36th week of gestation, amniocentesis allows determination of the lecithin-sphingomyelin ratio, which helps to assess prenatal lung development and the risk of RDS.

Treatment

An infant with RDS requires vigorous respiratory support. Warm, humidified, oxygen-enriched gases are administered by oxygen hood or, if such treatment fails, by mechanical ventilation. Severe cases may require mechanical ventilation with PEEP or continuous positive airway pressure (CPAP), administered by a tightly fitting face mask or, when necessary, endotracheal (ET) intubation.

Treatment also includes:

• a radiant infant warmer or isolette for thermoregulation
• I.V. fluids and sodium bicarbonate to control acidosis and maintain fluid and electrolyte balance
• tube feedings or total parenteral nutrition if the neonate is too weak to eat .
• administration of surfactant by an ET tube.

Prevention

The best way of preventing RDS is to delay delivery until the fetal lungs have matured and are producing enough surfactant--generally at about 37 weeks of pregnancy. If delivery cannot be delayed, the mother may be given a steroid hormone, similar to a natural substance produced in the body, which crosses the barrier of the placenta and helps the fetal lungs to produce surfactant. The steroid should be given at least 24 hours before the expected time of delivery. If the infant does develop RDS, the risk of bleeding into the brain will be much less if the mother has been given a dose of steroid.

If a very premature infant is born without symptoms of RDS, it may be wise to deliver surfactant to its lungs. This may prevent RDS, or make it less severe if it does develop. An alternative is to wait until the first symptoms of RDS appear and then immediately give surfactant. Pneumothorax may be prevented by frequently checking the blood oxygen content, and limiting oxygen treatment under pressure to the minimum needed.