Nutrition Parentérale et Risque de Dysplasie Bronchopulmonaire chez les Nourrissons Prématurés

1. Importance of Understanding BPD Complications

• BPD is a leading cause of mortality and disability in children under five years of age.
• Preterm infants are at risk for developing a range of perinatal complications, including respiratory distress syndrome (RDS), nosocomial infections, necrotizing enterocolitis, intraventricular hemorrhage, and retinopathy of prematurity.
• RDS can precede the development of bronchopulmonary dysplasia (BPD), the most frequent and severe complication in extremely preterm infants.

2. Alveolar Development: Phases and Regulation

• Alveolar development begins around 36 weeks of gestation and continues till early adulthood.
• The process is characterized by a dramatic increase in the gas exchange surface area.
• The time line of this process is relatively long; starting around 36 weeks of gestation and continuing till early adulthood.
• During the first 2 years of life, the number of alveoli in a human lung increases very rapidly and recent human studies demonstrated an increase with slower rate throughout adolescence.
• At the cellular level, there is marked interstitial fibroblast proliferation and differentiation with increased collagen, elastin, and fibronectin deposition.
• Both type I and type II alveolar cells rapidly increase in number, but type II cells are the ones proliferating actively suggesting that type II cells are progenitor cells for type I cells.
• While type II alveolar cells represent two thirds of all alveolar epithelial cells in human adult lung, it only represents about 7% of total alveolar surface while the larger squamous type I cells account for the rest of the surface area.

3. Role of Steroids in Lung Development

• Steroids have significant short and long-term effects on the lung development as demonstrated in cases of antenatal and post-natal administration for fetus and preterm infants.

4. Thyroid Hormone and Lung Maturation

• The thyroid hormone plays an important role in lung maturation and alveolarization.
• Compared to control mice and euthyroid offspring of hypothyroid mother, postnatal hypothyroid mice offspring of hypothyroid mothers had decreased postnatal alveolarization due to decreased alveolar septation resulting in fewer large saclike alveoli.

5. Structural Changes in Iodine Deficiency

• In a model of iodine deficiency in female Sprague Dawley rats’ pups were compared to iodine sufficient mothers matched age pups.
• Structurally wise, larger and irregularly shaped alveoli were documented in the iodine deficient pups.

6. Deficiency of Surfactant Protein

• Preterm infants who are born before late third trimester are at high risk of developing hyaline membrane disease or respiratory distress syndrome due to surfactant deficiency that leads to alveolar collapse and increased work of breathing.

7. Pulmonary Preparation for Term Delivery

• The goal of the morphological maturation that is described in the previous section is to increase the surface area for gas exchange and to decrease to the minimum the thickness of the alveolar-capillary membrane.

8. BPD Definition

• In the original paper that described BPD, the disease was characterized by prolonged cyanosis, O2 requirements clinically and by radiologic changes resulting from a chronic lung disease that represents prolonged healing of RDS under the effect of O2 toxicity and mechanical ventilation.

9. BPD Incidence

• Recent studies reported different incidences of BPD depending on the population used.