Understanding Respiratory Distress Syndrome in Infants

Posted on Mar 2, 2025 in Biology

Respiratory Distress Syndrome (RDS)

Respiratory distress syndrome (RDS) is the most common cause of respiratory failure in preterm infants. Over the past several decades, a number of names have been used to identify infants with RDS. A common thread running through most names is the term “Respiratory Distress,” which characterizes an immature lung disorder in a preterm infant caused by inadequate pulmonary surfactant.

Names Used to Identify RDS

  • Infant respiratory distress syndrome
  • Idiopathic respiratory distress syndrome
  • Neonatal respiratory distress syndrome
  • Respiratory distress syndrome of the newborn
  • Hyaline membrane disease

Anatomic Alterations of the Lungs

  • Interstitial and intra-alveolar edema and hemorrhage
  • Alveolar consolidation
  • Alveolar hyaline membrane
  • Pulmonary surfactant deficiency
  • Atelectasis
  • Hypoxia-induced pulmonary vasospasm and vasoconstriction
  • Transient pulmonary hypertension (right-to-left shunting)
  • Left-to-right shunting (in cases lasting longer than 24 hours)
  • Worsening hypoxia
  • Hyperperfusion (in cases lasting longer than 24 hours, leading to excessive lung fluid and pulmonary edema)

Etiology

Although the exact cause of RDS is controversial, the most popular theory suggests the disorder develops as a result of:

  • A pulmonary surfactant abnormality or deficiency
  • Pulmonary hypoperfusion evoked by hypoxia

About 30,000 cases of RDS are reported each year in the USA. RDS is the leading cause of death in preterm infants. RDS occurs more often in males and is usually more severe compared to females. RDS is also more commonly seen in:

  • Infants of diabetic mothers
  • White preterm babies compared to Black preterm infants
  • Infants delivered by Cesarean section

RDS is also associated with:

  • Low birth weight
  • Multiple births
  • Prenatal asphyxia
  • Prolonged labor
  • Maternal bleeding
  • Second-born twins

Diagnosis

  • Lecithin to Sphingomyelin ratio (L:S Ratio)
  • Phosphatidylglycerol (PG)
  • Surfactant to albumin ratio (S:A ratio)

Clinical Data Obtained at Patient’s Bedside

  • Increased respiratory rate (RR): During the early stages of RDS, the RR is generally well over 60 breaths per minute. The respiratory pattern of the RDS baby is commonly described as hard, fast, and deep breathing.
  • Increased heart rate (HR)
  • Increased blood pressure
  • Apnea

Clinical Manifestations Associated with Negative Intrapleural Pressure During Inspiration

  • Intercostal retractions
  • Substernal retraction/abdominal distention
  • Cyanosis of the dependent portion of the thoracic and abdominal areas
  • Flaring nostrils
  • Chest Assessment Finding: Bronchial or harsh breath sounds, fine crackles, expiratory grunting, and cyanosis.

Radiological Findings

Increased Opacity (ground-glass appearance).

General Management of RDS

During the early stages, CPAP is the treatment of choice. CPAP:

  • Increases the functional residual capacity
  • Decreases the work of breathing
  • Works to increase the PaO2 through alveolar recruitment while the infant is receiving a lower FIO2.

A PaO2 between 40 to 70 mmHg is normal for newborn infants. No effort should be made to get an infant’s PaO2 within the normal adult range (80 to 100 mmHg). Special attention should be given to the thermal environment of the infant with RDS. Exogenous surfactant preparations include Beractant (Survanta), Calfactant (Infasurf), and Poractant alfa (Curosurf).

Respiratory Care Treatment Protocols

  • Oxygen therapy protocol
  • Lung expansion therapy protocol
  • Mechanical ventilation protocol

Early Stages of RDS

↓Pulmonary Surfactant – Atelectasis – ↓Lung compliance – ↓Alveolar Ventilation – ↓Alveolar oxygen tension – Reflex pulmonary vasoconstriction – Blood bypasses lungs via fetal pathways – Lung hypoperfusion – Lung ischemia – ↓Lung metabolism.