Meconium aspiration syndrome

Background

  • Presentation ranges from mild respiratory distress to life-threatening respiratory failure
  • Incidence is 2-10% of infants born through MSAF (meconium-stained amniotic fluid)
  • Thought to be associated with fetal hypoxia and post-term delivery
  • Causes hypoxemia and acidosis via airway obstruction, chemical irritation/inflammation, infection, and surfactant inactivation
  • Associated with persistent pulmonary hypertension of the newborn (PPHN)

Clinical Features

  • Usually develop symptoms within 15 minutes after birth
  • Tachypnea
  • Cyanosis
  • Accessory muscle use (intercostal/subxiphoid retractions, paradoxical breathing, grunting, nasal flaring)
  • Barrel-shaped chest
  • Rales and rhonchi on lung auscultation
  • Pneumothorax
  • Pneumomediastinum

Differential Diagnosis

Newborn Problems

Evaluation

Workup

  • CXR
  • ABG
  • Echocardiogram
  • Blood and sputum cultures

Diagnosis

  • Clinical diagnosis based on the following:
    • Evidence of meconium on infant
    • Respiratory distress shortly after birth
    • Characteristic CXR findings
      • Streaky, linear densities
      • Hyperinflated lungs and flattened diaphragm
      • Diffuse patchy opacities (may appear similar to RDS if severe)
    • If intubation required, meconium visualized in trachea
  • Ways to differentiate between other causes of respiratory distress in a neonate:
    • TTN is more common in late preterm infants (34-37 weeks) and RDS in preterm infants, whereas MAS more common in postmature infants (>41 weeks)
    • Delayed transition from fetal circulation symptoms improve more quickly than those of MAS
    • Congenital cyanotic heart disease is differentiated by physical exam (murmurs, hepatomegaly), CXR (cardiac size/shape), and echocardiogram (cardiac anatomy and function)

Management

  • Supportive care: see newborn resuscitation
    • Adequate oxygenation and ventilation
      • Supplemental oxygen to keep saturation >99% and PaO2 55-90
      • Assisted ventilation with CPAP if FiO2 exceeds 0.4 to 0.5
      • High frequency oscillatory ventilation or ECMO for those who fail conventional mechanical ventilation
      • Goal PaCO2 50-55 mmHg
    • Maintain blood pressure and perfusion
      • Umbilical lines to monitor blood gases and BP
    • Correct metabolic abnormalities
  • Empiric antibiotics while awaiting culture results (because of difficulty differentiating between pneumonia initially)
  • Surfactant administration for severe disease requiring mechanical ventilation, FiO2>0.5, and mean airway pressure >10-12

Disposition

  • Admit to NICU

Prevention

  • Fetal heart rate monitoring intrapartum to reduce risk of fetal hypoxia
  • Induction of labor after 41 weeks gestation to reduce postmature delivery
  • Amnioinfusion with isotonic fluid to dilute thick meconium is NOT routinely recommended

See Also

External Links

References