What is respiratory distress syndrome?

Causes and Symptoms

Respiratory distress syndrome (RDS) is a condition observed mainly in premature infants and children born to diabetic patients. It is also known as premature lungs, pulmonary immaturity, hyaline membrane
disease, and surfactant deficiency syndrome. In 1959, researchers discovered that surfactant deficiency is the cause of RDS in premature infants; this discovery has been the basis for treatment since that time.

The main symptom is a rapid respiratory rate involving the use of accessory muscles to increase the amount of air taken into the lungs. The forceful closure of the vocal cords while contracting the abdominal muscles and diaphragm causes a particular grunting sound. The premature rib cage is very flexible, and affected infants must use extra effort to maintain expanded lungs.

A diagnosis of RDS is made on a clinical basis, including a history of premature delivery and the symptoms listed above. A chest x-ray is also useful; in RDS, a reticulogranular pattern and air bronchograms are observed together with a whited-out appearance in the lung fields. Respiratory function is determined by measuring the amount of oxygen and carbon dioxide in the arterial blood. The samples are obtained using a catheter inserted in an arterial vessel and analyzed in a blood gas machine. In newborns, the catheter is usually placed in one of the umbilical arteries, but samples from radial, posterior tibial, or dorsal pedis arteries are acceptable for analysis. Respiratory failure is defined as the inability of the lungs to perform adequate gas exchange, resulting in insufficient oxygen absorption and carbon dioxide elimination to sustain life.

Treatment and Therapy

Initially, the treatment for RDS was nonspecific. Physicians used various methods to maintain open airways and waited until the infant’s lungs matured on their own. The treatment of RDS was one of the main areas of research that helped in the development of the subspecialty of neonatology.

At present, the pregnant patient who is in imminent danger of delivering a child prematurely, between twenty-four and thirty-six weeks of gestation, is given antenatal steroids. The use of prenatal steroids has been associated with accelerated maturity of the lungs in infants born prematurely. Once a premature infant is born, endotracheal intubation, mechanical ventilation, and natural or artificial surfactants are used in order to maintain open airways and to prevent the development of atelectasis, the defective expansion of the alveoli.

Mechanical ventilation became a standard of care across the United States in teaching institutions. It has helped decrease mortality rates for premature infants and has evolved into a fine art assisted by advanced technology. Mechanical ventilation uses a variety of techniques to maximize lung expansion and to minimize the damage to lung tissues caused by high concentration of oxygen and pressures. Pressure, volume, and high-frequency ventilators are among the current equipment available to neonatologists for use with infants suffering from RDS.

In 1980, a report was published concerning the use of bovine surfactant mixed with saline solution administered endotracheally in infants with RDS. This treatment offered significant improvement in the outcome of this disease. Natural surfactants have been extracted from the lung tissues of calves and pigs, and surfactant has even been harvested from amniotic fluid in humans. The main difference between natural and artificial surfactants is the presence of surfactant-associated proteins. Surfactant-associated proteins function as dispersing agents for the lipid components that line the internal surface of the alveoli, thus preventing the collapse of these air sacs. Artificial surfactants are pure chemicals mixed in the laboratory without surfactant-associated proteins; other chemical substances are used as dispersing agents.

At least seven different types of surfactant have been tested in humans in clinical trials; controversy still exists regarding the proper timing of surfactant replacement, either as prophylaxis or as a rescue treatment. In addition, concern remains about the possible increased incidence of two major complications, pulmonary hemorrhage and intraventricular hemorrhage, in premature infants with RDS following the use of surfactant treatment.

Overall, the use of surfactants and mechanical ventilation has decreased mortality and complications in premature infants, but the number of patients with long-term complications, such as chronic lung disease with oxygen dependency, has increased considerably.

Perspective and Prospects

In 1960, the infant son of John Fitzgerald Kennedy, then president-elect of the United States, died of respiratory distress syndrome. Since then, significant advances in the understanding and treatment of this condition have been made, but the elimination of this disease will be achieved only when premature births are prevented. Until then, RDS will continue to exist in nurseries everywhere.

Bibliography

Bradford, Nikki. Your Premature Baby: The First Five Years. Toronto, Ont.: Firefly Books, 2003.

Martin, Richard J., Avroy A. Fanaroff, and Michele C. Walsh, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 9th ed. 2 vols. Philadelphia: Mosby/Elsevier, 2011.

Rosenbaum, Laurie. "Respiratory Distress Syndrome in Newborns." Health Library, September 10, 2012.

Turner, Joan, Gwendolyn J. McDonald, and Nanci L. Larter, eds. Handbook of Adult and Pediatric Respiratory Home Care. St. Louis, Mo.: Mosby, 1994.

West, John B. Pulmonary Pathophysiology: The Essentials. 8th ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, 2012.

"What Is Respiratory Distress Syndrome?" National Heart, Lung, and Blood Institute, January 24, 2012.