A 28-week preterm infant born to a mother with incomplete antenatal corticosteroid coverage presents with respiratory distress within 2 hours of birth. Chest X-ray shows a ground-glass appearance with air bronchograms. Regarding the pathophysiology and management of Respiratory Distress Syndrome (RDS), all of the following are true EXCEPT:

Question

Accepted Answer

C. Exogenous surfactant replacement therapy is most effective when administered after 72 hours of life. ## Pathophysiology of RDS

**Key Point:** Respiratory Distress Syndrome (RDS), formerly called Hyaline Membrane Disease, is caused by surfactant deficiency in preterm infants, leading to increased alveolar surface tension and progressive atelectasis.

### Surfactant and Alveolar Mechanics

**High-Yield:** Surfactant is a lipoprotein complex (90% lipid, 10% protein) synthesized by type II pneumocytes. It reduces surface tension at the air-liquid interface, preventing alveolar collapse and reducing the work of breathing.

- **Deficiency mechanism:** Immature lungs (especially <32 weeks gestation) produce insufficient surfactant, causing:
  - Increased alveolar surface tension
  - Progressive atelectasis (collapse)
  - Ventilation-perfusion mismatch
  - Hypoxemia and hypercapnia

### Antenatal Corticosteroids

**Clinical Pearl:** Maternal corticosteroids (betamethasone or dexamethasone) given 24 hours to 7 days before preterm delivery significantly reduce RDS incidence and severity by:
  1. Accelerating surfactant synthesis in fetal lungs
  2. Promoting type II pneumocyte maturation
  3. Reducing intraventricular hemorrhage and necrotizing enterocolitis

**Mnemonic: CRIB** — **C**orticosteroids **R**educe **I**ncidence of **B**irth complications

### Exogenous Surfactant Replacement

**Key Point:** Surfactant therapy is MOST EFFECTIVE when administered **early** — ideally within the **first 6–12 hours of life**, and certainly before 72 hours. Early treatment:
  - Prevents further alveolar damage
  - Reduces need for mechanical ventilation
  - Decreases mortality and morbidity (BPD, IVH)

**Warning:** The statement "most effective after 72 hours" is **FALSE**. Surfactant given after 72 hours has diminished benefit because:
  - Hyaline membranes have already formed
  - Secondary surfactant deficiency develops
  - Lung injury is more established

### PEEP and Mechanical Ventilation

**High-Yield:** Positive End-Expiratory Pressure (PEEP) is a cornerstone of RDS management:
  - Maintains alveolar patency during expiration
  - Prevents repetitive opening-closing of alveoli (atelectotrauma)
  - Reduces intrapulmonary shunting
  - Improves oxygenation and reduces FiO~2~ requirement

**Clinical Pearl:** Even gentle ventilation with PEEP (5–6 cm H~2~O) is superior to no PEEP in RDS.

## Summary Table: RDS Management Principles

| Intervention | Timing | Mechanism | Effectiveness |
| --- | --- | --- | --- |
| Antenatal corticosteroids | 24 hrs–7 days before delivery | Accelerate surfactant synthesis | ↓ RDS incidence by ~50% |
| Exogenous surfactant | **First 6–12 hours of life** | Replace deficient surfactant | ↓ Mortality, BPD |
| PEEP/CPAP | Immediately on presentation | Prevent alveolar collapse | ↑ Oxygenation, ↓ FiO~2~ |
| Oxygen therapy | Titrate to SpO~2~ 90–95% | Correct hypoxemia | Avoid hyperoxia (ROP) |

Answer

A. Antenatal corticosteroids accelerate fetal lung maturity by inducing surfactant synthesis

Answer

B. Deficiency of pulmonary surfactant is the primary cause of increased alveolar surface tension

Answer

D. Mechanical ventilation with positive end-expiratory pressure (PEEP) prevents alveolar collapse during expiration

Explanation

Pathophysiology of RDS

Surfactant and Alveolar Mechanics

Antenatal Corticosteroids

Exogenous Surfactant Replacement

PEEP and Mechanical Ventilation

Summary Table: RDS Management Principles

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Intervention	Timing	Mechanism	Effectiveness
Antenatal corticosteroids	24 hrs–7 days before delivery	Accelerate surfactant synthesis	↓ RDS incidence by ~50%
Exogenous surfactant	First 6–12 hours of life	Replace deficient surfactant	↓ Mortality, BPD
PEEP/CPAP	Immediately on presentation	Prevent alveolar collapse	↑ Oxygenation, ↓ FiO₂
Oxygen therapy	Titrate to SpO₂ 90–95%	Correct hypoxemia	Avoid hyperoxia (ROP)