Chronic Lung Disease

I. Etiology

BPD is multifactorial, resulting from the interaction between an immature lung and environmental insults (the "Multiple Hit" hypothesis).

1. Prematurity (Primary Factor): Incidence is inversely proportional to gestational age.
2. Ventilator-Induced Lung Injury (VILI):
   • Barotrauma: High peak pressures.
   • Volutrauma: Overdistension from large tidal volumes (most damaging).
   • Atelectotrauma: Repeated alveolar collapse and reopening.
3. Oxygen Toxicity: Production of Reactive Oxygen Species (ROS) causing free radical damage.
4. Infection/Inflammation: Chorioamnionitis (antenatal) or postnatal sepsis stimulating proinflammatory cytokines.
5. Patent Ductus Arteriosus (PDA): Pulmonary overcirculation and edema.
6. Fluid Overload: excessive fluid administration in the first week of life.

II. Pathogenesis

The pathology has evolved from "Old BPD" (intense fibrosis/injury) to "New BPD" (developmental arrest).

1. Arrest of Alveolarization: The hallmark of New BPD.
   • Insults occur during the Saccular Stage (26–36 weeks).
   • Interference with septation leads to fewer, larger, and simplified alveoli.
   • Result: Reduced surface area for gas exchange.
2. Dysregulated Angiogenesis: Abnormal pulmonary vasculature growth leading to increased pulmonary vascular resistance (PVR).
3. Inflammation: Influx of neutrophils and macrophages releases elastases and cytokines (IL-1, IL-6, IL-8), disrupting the extracellular matrix.
4. Fibrosis: Variable degrees of interstitial fibrosis (less prominent in New BPD than Old BPD).

III. Clinical Presentation

1. Respiratory Features:
   • Oxygen Dependence: Need for supplemental oxygen >36 weeks corrected gestational age (CGA).
   • Work of Breathing: Tachypnea, intercostal/subcostal retractions.
   • Exacerbations: "BPD Spells" – episodes of cyanosis and agitation due to bronchospasm or pulmonary edema.
2. Growth & Systemic:
   • Failure to Thrive: Poor weight gain despite adequate calories (increased metabolic demand of breathing).
   • Pulmonary Hypertension: Signs include loud P2 or desaturation with handling.
3. Radiology (Chest X-Ray):
   • Diffuse haziness evolving into coarse reticular opacities.
   • Cystic lucencies (in severe cases) and hyperinflation.

IV. Management

Management is multidisciplinary, focusing on minimizing injury and supporting growth.

A. Prevention (Antenatal & Delivery Room)

• Antenatal Steroids: Accelerate lung maturation.
• Surfactant Therapy: Early rescue.
• Gentle Ventilation: Use of CPAP or Volume-Targeted Ventilation (to limit volutrauma).

B. Respiratory Management

• Target SpO2: 90–95% (Avoid hyperoxia).
• Weaning: Gradual weaning of CPAP/ventilator to prevent atelectasis.
• Permissive Hypercapnia: Tolerating higher $PaC{O}_2$ (55–65 mmHg) to minimize aggressive ventilation.

C. Nutrition (Critical)

• High Caloric Goals: 120–150 kcal/kg/day.
• Fluid Restriction: Mild restriction (130–140 ml/kg/day) to prevent pulmonary edema.
• Supplements: Human Milk Fortifiers (HMF), Calcium, Phosphorus, and Vitamin D to prevent osteopenia.

D. Pharmacotherapy

1. Diuretics (Thiazides/Furosemide): For pulmonary edema/fluid overload (symptomatic relief).
2. Caffeine: Reduces apnea and facilitates extubation (proven to reduce BPD rates).
3. Vitamin A (IM): High dose supplementation reduces BPD risk (modest benefit).
4. Corticosteroids:
   • Systemic: Dexamethasone (DART Protocol - low dose, short course) used only for those unable to wean from ventilator due to risk of CP.
   • Inhaled: Routine use is not recommended.
5. Bronchodilators: Only if clinical response (wheeze) is documented.

E. Infection Control

• Palivizumab: Monthly prophylaxis against RSV during RSV season for high-risk infants.
• Immunization: Timely Influenza and Pneumococcal vaccines.

F. Long-term Follow-up

• Monitor for Neurodevelopmental delay (CP) and Pulmonary Hypertension.