Home > Encyclopedia of Nursing & Allied Health > Respiratory Distress Syndrome

Definition

Respiratory distress syndrome (RDS) of the newborn, known as infant RDS, is an acute lung disease present at birth. RDS usually affects premature babies who weigh less than 5.5 pounds (2.5 kg). In these babies, the lack of a pulmonary substance called surfactant allows layers of tissue called hyaline membranes to develop in the lungs. This development prevents the oxygen that is inhaled from passing into the blood vessels (capillaries) and thereby into the bloodstream. The lungs are said to be airless. Untreated, the infant will die within a few days after birth. RDS in newborns used to be called hyaline membrane disease.

Description

To breathe properly, the alveoli (small air sacs in the lungs) of a newborn infant must remain open so that oxygen in the air can enter the capillaries that surround the alveoli. Normally, during the last months of pregnancy, cells in the alveoli produce a substance called surfactant that maintains a low surface tension inside the alveoli. This allows the sacs to expand at the moment of birth, enabling the infant to breathe. Surfactant is produced starting at about 34 weeks of pregnancy and, by the time the fetal lungs mature at 37 weeks, a normal amount is present; after this point, it can be detected in the amniotic fluid.

When an infant is born prematurely without enough surfactant in the alveoli, the lungs may collapse, making it very difficult for the baby to get enough oxygen. Sometimes a layer of glassy, fibrous tissue called a hyaline membrane forms in the air sacs, making it even harder for oxygen to pass through the membrane to the capillaries.

Causes and symptoms

RDS nearly always occurs in premature infants, and the earlier the birth, the greater the chance that RDS will develop. The syndrome is also seen in some infants whose mothers have diabetes. Paradoxically, RDS is less likely to occur in the presence of conditions that are equally harmful: abnormally slow fetal growth, toxemia, and early rupture of the amniotic sac.

An infant with RDS may struggle to breathe as soon as it is born, or difficulty may develop within a few hours. Breathing becomes rapid and shallow, the nostrils flare, and the infant grunts with each breath. Muscles around the ribs and structures in the neck strain inward with each breath, showing the extreme effort that is being exerted. Before long, the intercostal muscles that move the ribs and diaphragm to draw air into the lungs become fatigued, making the breaths even more shallow. This shallow breathing diminishes the oxygen level in the blood so severely that the infant becomes cyanotic (the skin turns bluish). Tiny, very premature infants may not even have signs of trouble breathing. Their lungs may be so filled with hyaline membrane that when they are born they cannot even start breathing without assistance.

There are two major complications of RDS. One is pneumothorax, which means "air in the chest." When the infant itself or a ventilator breathing for the infant forces air into the lungs in an attempt to expand them, a lung may rupture, causing air to leak into the chest cavity. This air puts pressure on the lung, collapsing it and making breathing even more labored. Because pneumothorax interferes with blood flow in the pulmonary arteries, the infant's blood pressure may drop suddenly, diminishing blood supply to the brain. The other complication is intraventricular hemorrhage (bleeding into the ventricles of the brain), which can be fatal.

Diagnosis

When a premature infant has obvious trouble breathing at birth or within a few hours of birth, RDS is a possible diagnosis. If premature birth is expected, or there is some condition that calls for delivery prior to term, the amount of surfactant in the amniotic fluid indicates the extent to which the lungs have matured. If little surfactant is found in an amniotic fluid sample obtained via amniocentesis, then there is a definite risk of RDS. In some cases where delivery is essential to maternal or fetal survival, amniocentesis is performed at regular intervals so that the infant may be delivered as soon as the lungs are sufficiently mature. If the amniotic sac has ruptured, surfactant levels may be easily measured using a sample of vaginal fluid.

---

KEY TERMS

---

Alveoli—The small air sacs located at the ends of the breathing tubes of the lung, where oxygen normally passes from inhaled air through the membranes into the capillaries and the bloodstream.

Amniocentesis—Analysis of amniotic fluid, extracted surgically by a hollow needle from the uterus of a pregnant woman, to determine the health or other characteristics of a fetus.

Amniotic fluid—The fluid cushioning the fetus inside the uterus, which may be sampled to determine whether the fetus is making enough surfactant to breathe independently.

Endotracheal tube—A metal or plastic tube inserted in the windpipe, which may be attached to a ventilator. It may also be used to deliver such medications as surfactant.

Hyaline membranes—A fibrous layer that develops in the alveoli of many premature infants, which prevents oxygen from passing through the alveolar sac into the capillaries.

Pneumothorax—Air in the chest outside the lung, which compresses the lung. It occurs as a result of the lung rupture, often caused by oxygen delivered under too high a pressure.

Steroids—Also known as corticosteroids or glucocorticoids, these naturally occurring substances are often given to women before they deliver a very premature infant to stimulate the fetal lungs to produce surfactant; this treatment is intended to prevent or minimize RDS.

Surfactant—A substance normally produced in fetal lungs after the 34th week of pregnancy that helps the air sacs to open up at the time of birth so that the infant can breathe independently.

Toxemia—A disease of pregnancy in which the mother's blood pressure is elevated; it is associated with both maternal and fetal complications, and sometimes with fetal death.

Ventilator—A machine that breathes for an infant with RDS until its lungs are producing enough surfactant and are able to function normally.

---

RDS can also be diagnosed by chest x ray. The syndrome has a recognizable radiologic image, and an x ray will also reveal pneumothorax (if this has occurred), as well. This test may be ordered if the infant suddenly becomes worse while on ventilation.

Treatment

If only a mild degree of RDS is present at birth, then placing the infant in an oxygen hood may be sufficient to sustain them until they can breathe independently. Nurses must closely monitor infants receiving oxygen, however, to prevent excessive oxygen saturation, which can damage the retina. This condition, called retinitis of prematurity, causes blindness. The oxygen level in the blood may be tested by analyzing the levels of arterial gases present, or more easily, by using a device called a pulse oximeter, which is clipped to an earlobe. A laboratory technologist usually performs all necessary blood work.

In more severe cases, a drug that mimics the action of natural surfactant (Exosurf Neonatal or Survanta), may be dripped into the lungs through an endotracheal tube. Typically, the infant will be able to breathe more easily within a few days, and such complications as lung rupture are less likely to occur. The drug is continued until the infant starts producing its own surfactant. There is a risk of bleeding into the lungs from surfactant treatment; this affects about 10% of the smallest infants.

Infants with severe RDS may also be placed on a ventilator, a machine that delivers air under pressure through a tracheal tube to the lungs. This is performed as an emergency procedure for infants who do not breathe when born. Assisted ventilation must be closely supervised, as too much pressure can cause further lung damage, injure vocal cords, and increase the baby's risk of pulmonary infection. A gentler way to assist breathing is continuous positive airway pressure (CPAP), which delivers an oxygen mixture through nasal prongs or a tube placed through the nose rather than an endotracheal tube. CPAP may be tried before resorting to a ventilator, or after an infant placed on a ventilator begins to improve. Drugs that stimulate breathing may speed the recovery process.

Pneumothorax, which is a possible complication of assisted ventilation, is a medical emergency requiring immediate intervention. Air may be removed from the chest using a needle and syringe. A tube is then inserted into the lung cavity, and suction applied.

Prognosis

If an infant born with RDS is not treated promptly, lack of an adequate oxygen supply will damage the body's organs. They will eventually stop functioning, after which death follows. The central nervous system in particular—made up of the brain and spinal cord—is very dependent on a steady oxygen supply and is one of the first organ systems to feel the effects of RDS. On the other hand, if the infant's breathing is supported immediately after birth until the lungs mature and make their own surfactant, complete recovery within three to five days is the rule.

Health care team roles

Premature infants with respiratory disorders are usually cared for in a neonatal intensive care unit by a neonatologist, certified neonatal intensive care nurse specialist, anesthesia provider (to maintain the airway), and respiratory therapist. Once the infant has recovered, a pediatrician, family practice physician, and a pediatric nurse practitioner may provide continuing medical care. Parents and siblings of critically ill newborns may require additional support from social workers, pastoral counselors, self-help support groups, or other mental health professionals.

Prevention

The best way to prevent RDS is to delay delivery until 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 placental barrier and helps the fetal lungs produce surfactant. The steroid should be given at least 24 hours before the expected delivery. If the infant does develop RDS, this treatment sharply reduces the risk of cerebral hemorrhage.

If a very premature infant is born without symptoms of RDS, it may be wise to deliver surfactant to its lungs anyway. This treatment 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 give surfactant immediately. Pneumothorax may be prevented by frequently monitoring blood oxygen content, and limiting oxygen treatment under pressure to the minimum.

Barbara Wexler