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12.09.25 Respiratory Distress Syndrome

Embryology
  • <16 weeks: Pseudoglandular
  • 16-24 weeks: Canalicular
    • Some primitive gas exchange possible
  • 24-36 weeks: Saccular
    • Beginning of surfactant production
  • >36 weeks: Alveolar

CXR
  • Hazy lung fields throughout
  • Stuff obscured
    • Heart borders
    • Diaphragm if severe


Chronic lung disease (CLD)

  • Used to be called bronchopulmonary dysplasia (BPD)
  • Results from physical damage to lungs, by repeated forced opening
  • Develops within 15 mins of birth
  • => Usefulness of HFOV


Factors decreasing surfactant production

  • Acidosis
    • pH <7.25
  • Cold
    • < 35 degrees
  • Asphyxia
    • Damages vasculature
  • C-section
    • Esp. elective


Prevention

  • Betamethasone 12 mg q. 24 hr to mum, for all deliveries <35 weeks
  • Ideally for 7 days pre-delivery


Management

  • Steroids to mum pre-delivery if possible
  • Don't give multiple courses of steroids to baby
    • Decreases myelination
    • Decreases head circumference
  • Judicious O2
    • Beware:
      • ROP
      • Cerebral apoptosis
      • Reduced blood flow
  • Surfactant
    • Reduces death (NNT 20)
    • Reduces pneumothorax (NNT 50)
    • Do it within 15 mins
    • 2 doses better than 1
  • Caffeine
  • Extubate early, or use non-invasive CPAP


Prevalence

  • 90% at 26 weeks
  • 70% at 30 weeks
  • 20% at 35 weeks
  • 1-2% at term


Differentials

  • Congenital pneumonia
  • Congenital heart disease
  • Lung malformation


Notes
  • RDS is a resp rate of >60 at birth
  • Key respiratory parameter to change is functional reserve capacity (FRC)
    • i.e. can't establish the "open state" to breath over
  • More than six anterior ribs in the mid-clavicular line shows hyperinflation
  • Grunting serves the same purpose as pursed-lips breathing - keeps airways open
  • Reduced CO2 causes cerebral vasoconstriction
    • cf Over-ventilation
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