OVERVIEW: What every practitioner needs to know
Are you sure your patient has respiratory distress syndrome? What are the typical findings for this disease?
Patients with Respiratory Distress Syndrome (RDS) are typically preterm (born at less than 37 weeks gestation). The most common signs are respiratory distress in the first minutes to hours after birth, including tachypnea, retractions of the chest wall, nasal flaring, and expiratory grunting. Babies with RDS are usually cyanotic in room air. In a preterm baby with these symptoms, RDS is the most common cause.
What other disease/condition shares some of these symptoms?
Respiratory distress in infants can be caused by a variety of other conditions. These include pneumonia (such as that caused by group B streptococcus), sepsis, retained fetal lung fluid (transient tachypnea of the newborn), or heart failure due to congenital heart disease.
Surfactant protein deficiency
A newborn with unexplained severe respiratory failure consistent with surfactant deficiency, but not responsive to surfactant, may have surfactant protein deficiency. These life-threatening conditions that present in the newborn period are rare and due predominantly to mutations in the genes encoding for surfactant protein B or the ABC binding cassette transporter protein (ABCA3 protein).
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What caused this disease to develop at this time?
RDS is caused by pulmonary surfactant deficiency. Surfactant is critical for maintaining end-expiratory inflation of the lungs; thus, surfactant deficiency results in diffuse atelectasis of the alveoli. Prematurity is the biggest risk factor for surfactant deficiency at birth.
What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?
Arterial blood gas may show carbon dioxide retention and respiratory acidosis. Hypoxemia is usually present in the absence of supplemental oxygen. A complete blood count and differential may be helpful in distinguishing RDS from sepsis or pneumonia.
Would imaging studies be helpful? If so, which ones?
A chest radiograph helps confirm the diagnosis. Infants with RDS typically have small lung volumes (although late preterm infants have sufficient respiratory muscle strength to maintain normal lung volumes early in the course of the disease) and a reticular granular pattern (“ground glass”) appearance of the lung fields with air bronchograms (Figure 1).
Figure 1.
Typical pattern of RDS. Note atelectatic lungs, “ground-glass” appearance, low lung volumes, and air bronchograms.
If you are able to confirm that the patient has respiratory distress syndrome, what treatment should be initiated?
Provide supplemental oxygen to maintain percent arterial oxygen saturation in the low 90s. Provide continuous positive airway pressure (CPAP) at 5 to 7 cm H2O to maintain end-expiratory lung volume. CPAP is usually administered via nasal prongs.
In infants with severe respiratory distress, or a supplemental oxygen requirement of greater than 40%–50% on CPAP, treat with exogenous surfactant after intubation and initiation of mechanical ventilation. Exogenous surfactant will lead to a rapid improvement in lung compliance. Several different exogenous surfactants are available, each with different dosing regimens.
Ventilatory support should be weaned as tolerated. Rapid extubation to CPAP after surfactant administration is tolerated by many infants. Prolonged mechanical ventilation may be necessary for the most immature infants. Nasal CPAP started right after delivery may obviate the need for surfactant administration in all but the most immature infants and those with severe disease.
Consider prophylactic surfactant administration (immediate intubation with surfactant administration in the delivery room prior to the development of respiratory distress) in babies less than 27 weeks gestation, given the high likelihood of surfactant deficiency in this gestational age group. Prophylactic surfactant has been shown to decrease the risk of death in this population of infants. Table I gives dosing levels for the administration of exogenous surfactant.
Table I.
| Beractant (Survanta®) | 4 mL/kg/dose | Divide in 4 aliquots, with up to 4 total doses, Q 6 hours as needed |
| Poractant (Curosurf®) | Initial dose: 2.5 mL/kg/dose; subsequent doses: 1.25 mL/kg/dose | Divide in 2 aliquots, with up to two additional doses Q 12 hours as needed |
| Calfactant (Infasurf®) | 3 mL/kg/dose | Divide in 2 aliquots, with up to two additional doses Q12 hours as needed |
What are the adverse effects associated with each treatment option?
Mechanical ventilation is a risk factor for the development of bronchopulmonary dysplasia (chronic lung disease of prematurity). Air leak (e.g., pneumothorax) may complicate the use of both CPAP and mechanical ventilation in infants with RDS. Surfactant treatment requires intubation, but reduces the risk of complications such as air leak.
What are the possible outcomes of respiratory distress syndrome?
Except for the most immature infants, almost all infants with RDS will recover completely after a few days. More severe cases may result in complications, including air leak, development of bronchopulmonary dysplasia, or death.
What causes this disease and how frequent is it?
RDS is most commonly seen in preterm babies. Over half of babies at 28 weeks gestation or less will have RDS. Less than one-third of babies at 32 to 36 weeks will have RDS.
The risk of RDS is greater in infants with: lower gestational age, Caucasian race, male sex, previous sibling with RDS, cesarean delivery, perinatal asphyxia, infant of a diabetic mother, cold stress after birth, multiple births, and perinatal infection.
How do these pathogens/genes/exposures cause the disease?
N/A
Other clinical manifestations that might help with diagnosis and management
N/A
What complications might you expect from the disease or treatment of the disease?
Bronchopulmonary dysplasia develops more commonly in extremely preterm infants (< 27 weeks gestation) with RDS. CPAP or mechanical ventilation may result in air leak, including pneumothorax, pneumomediastinum, pneumopericardium, or pulmonary interstitial emphysema.
Persistent pulmonary hypertension may develop in some infants with RDS, typically those who are late preterm (34 to 36 weeks gestational age) or in some severely growth restricted infants. Pulmonary hypertension causes shunting of blood right to left either through the patent ductus arteriosus or foramen ovale, resulting in more severe hypoxemia.
Are additional laboratory studies available; even some that are not widely available?
Echocardiography should be performed in infants suspected of having congenital heart disease (such as infants with profound cyanosis despite substantial supplemental oxygen, persistent loud heart murmur, or large cardiac silhouette on chest radiograph). Echocardiography is also useful in infants in whom persistent pulmonary hypertension is suspected. Prenatal testing of lung maturity may be performed on amniotic fluid if preterm delivery is anticipated.
How can respiratory distress syndrome be prevented?
Prenatal administration of glucocorticoids to women if preterm delivery is anticipated reduces the incidence and severity of RDS. All mothers expected to deliver between 23 to 24 weeks and 34 weeks gestation should receive a full course of betamethasone if possible.
What is the evidence?
Soll, RF, Morley, CJ. “Prophylactic versus selective use of surfactant in preventing morbidity and mortality in preterm infants”. Cochrane Database Syst Rev. vol. 2. 2001. pp. CD000510(Excellent meta-analysis of use of surfactant in treatment of RDS comparing prophylactic to rescue dosing after the diagnosis of RDS.)
Finer, NN, Carlo, WA, Walsh, MC. “Early CPAP versus surfactant in extremely preterm infants”. N Engl J Med. vol. 362. 2010. pp. 1970-9. (This reports the randomized trial conducted by the Eunice Shriver NICHD Neonatal Network of early CPAP in the delivery room versus intubation for surfactant administration in infants born at 24 to 27 weeks gestation. The primary outcome was the occurrence of bronchopulmonary dysplasia (BPD) or death. Early CPAP was at least as effective as early surfactant at preventing BPD or death, with no additional adverse effects. CPAP reduced the need for mechanical ventilation and surfactant administration.)
Morley, CJ, Davis, PG, Doyle, LW. “Nasal CPAP or intubation at birth for very preterm infants”. N Engl J Med. vol. 358. 2008. pp. 700-8. (This reports a randomized trial of CPAP versus intubation and mechanical ventilation at 5 minutes of age in infants born at 25 to 28 weeks. CPAP reduced the need for mechanical ventilation, but did not reduce the incidence of BPD or death. There was a higher incidence of pneumothorax in the infants assigned to CPAP, which was initiated at 8 cm H2O.)
Ongoing controversies regarding etiology, diagnosis, treatment
Differences in interpretation of the available evidence result in different early management practices among centers. Our practice is initial use of CPAP; infants who meet the criteria for intubation and mechanical ventilation are given surfactant, and ventilation is continued until the criteria for extubation are met. Although this practice may avoid the need for mechanical ventilation in all but the most premature infants, it has not been proven to prevent the development of BPD or death from RDS.
Another approach is to limit use of early CPAP to infants 28 weeks or more gestation; more immature infants are intubated and given prophylactic surfactant. Some centers treat all infants at risk for RDS (below 32 weeks, for example) with prophylactic surfactant. In infants treated with prophylactic surfactant, centers differ in whether infants remain mechanically ventilated until they meet criteria for extubation or are extubated to CPAP immediately after surfactant treatment.
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