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RDS

Definition
Risk Factors
  • Prematurity
  • Male
  • Hypothermia
  • Maternal diabetes
  • Cesarian
  • Perinatal asphyxia
  • Multiple pregnancy
  • FHx of RDS
Differential diagnosis
Epidemiology
  • Affects about 1% of newborn infants and is the leading cause of death in preterm infants
  • Incidence decreases with advancing gestational age
    • About 50% in babies born at 26–28 weeks
    • About 25% at 30–31 weeks
    • > 90% at 28 weeks?
    • 50% at 32 weeks?
  • More frequent in infants of diabetic mothers and in the second born of premature twins
Aetiology
  • Surfactant deficiency
  • => full lung closure on expiration
Clinical features
  • tachypnea
  • tachycardia
  • chest wall retractions (recession)
  • expiratory grunting
    •  breath against a partially closed glottis
  • flaring of the nostrils
  • cyanosis
  • Progression over 2-3 days
    • More O2 required
    • Either => death or recovery by 72 h
Pathophysiology
  • Deficit in surfactant
    • Complex system of lipids, proteins and glycoproteins
    • Produced in specialized lung cells called Type II cells or Type II pneumocytes
    • Packaged by the cell in structures called lamellar bodies, and extruded into the air-spaces
      • Unfold into a complex lining of the air-space
    • Reduces the surface tension of the fluid that lines the air-space
      • Surface tension is responsible for approximately 2/3 of the elastic recoil forces
    • Prevents the air-spaces from completely collapsing on exhalation
    • Allows re-opening of the air-space with a lower amount of force
  • Without adequate amounts of surfactant, the air-spaces collapse and are very difficult to expand
  • Lungs are characterized by collapsed air-spaces alternating with hyper-expanded areas, vascular congestion and, in time, hyaline membranes.
  • As a result, blood passing through the lungs is unable to pick up oxygen and unload carbon dioxide
  • Structural immaturity, as manifest by decreased number of gas-exchange units and thicker walls, also contributes to the disease process
  • Therapeutic oxygen and positive-pressure ventilation, while potentially life-saving, can also damage the lung
Investigations
  • Fetal lung maturity may be tested by sampling the amount of surfactant in the amniotic fluid, obtained by inserting a needle through the mother's abdomen and uterus
  • Blood gases
    • respiratory and metabolic acidosis along with hypoxia
  • CXR
  • Pulmonary mechanics testing (PMT)
    • Reduced complience

Management

http://eng.mapofmedicine.com/evidence/map/respiratory_distress_syndrome1.html

a) conservative

b) medical
  • Pre-term glucocorticoids speed the production of surfactant
  • Ventilation
    • High frequency oscillatory ventilation
    • Continuous positive airway pressure (CPAP)
    • High-speed mechanical ventilation (> 40 breaths per min)
  • Oxygen
  • Intravenous fluids to stabilize the blood sugar, blood salts, and blood pressure
  • Extracorporeal membrane oxygenation (ECMO)
    • Not appropriate for premature babies
  • Exogenous surfactant
    • Pig better than synthetic
c) surgical

Prognosis
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