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