Respiratory distress syndrome (RDS) is a relatively common condition that occurs in preterm neonates resulting from insufficient production of surfactant.
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Terminology
Respiratory distress syndrome is also known as hyaline membrane disease (this term is not favored as it reflects non-specific histological findings), neonatal respiratory distress syndrome, lung disease of prematurity (both non-specific terms), or surfactant deficiency disorder 2.
Epidemiology
The incidence is estimated at 6 in 1000 births 2. It is uncommon after 36 weeks gestation due to the development of pneumocyte surfactant production around 35 weeks 5.
Risk factors
Risk factors include:
greater prematurity
perinatal asphyxia
multiple gestations
Associations
Associated conditions are those that can occur in prematurity:
delayed developmental milestones
hypothermia
hypoglycemia
Clinical presentation
Respiratory distress syndrome presents in the first few hours of life in a premature baby. Signs include tachypnea, expiratory grunting, and nasal flaring. The infant may or may not be cyanosed. Substernal and intercostal retractions may be evident.
Pathology
Immature type II pneumocytes cannot produce surfactant. The lack of surfactant increases the surface tension in alveoli causing them to collapse. Patients have a decreased lecithin to sphingomyelin ratio. Damaged cells, necrotic cells, and mucus line the alveoli.
Although most cases are related to prematurity alone, patients may rarely have genetic disorders of surfactant production and can present in a similar clinical and radiological manner 6.
As the alveoli are collapsed (microscopically), the lungs are collapsed macroscopically as well. It is a diffuse type of adhesive atelectasis.
Radiographic features
Plain radiograph
low lung volumes
diffuse, bilateral and symmetrical granular opacities
bell-shaped thorax
air bronchograms may be evident
Hyperinflation makes the diagnosis less likely, unless the patient is intubated.
If treated with surfactant therapy, there may be an asymmetric improvement as more surfactant may reach certain parts of the lungs than others.
Ultrasound
On transabdominal ultrasound, retrodiaphragmatic hyperechogenicity can be seen. If this hyperechogenicity does not resolve by day 9-18 on follow-up ultrasound, it helps in the prediction of the risk of development of bronchopulmonary dysplasia ref.
Treatment and prognosis
Exogenous surfactant administration is an effective treatment, traditionally administered via endotracheal tube, though less invasive methods of surfactant administration such as via laryngeal mask airway are becoming more common 7. Supportive oxygen therapy is typically required for a period of time.
Complications
Acute
persistent patent ductus arteriosus (PDA) due to reduced oxygen stimulus
pulmonary interstitial emphysema or air leak (secondary to mechanical ventilation)
oxygen toxicity (from treatment)
Chronic
recurrent pulmonary infection
subglottic stenosis (secondary to intubation)
Differential diagnosis
Consider:
neonatal pneumonia (particularly group B Streptococcus)
transient tachypnea of the newborn (TTN): lung volumes are normal to slightly hyperinflated in transient tachypnea of the newborn and decreased in respiratory distress syndrome
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