Meconium aspiration syndrome

Background

• May cause meconium aspiration syndrome (MAS) in a newborn infant that was born through meconium-stained amniotic fluid (MSAF)
• The presentation can range from mild respiratory distress to life-threatening respiratory failure and to make the diagnosis the symptoms cannot be better explained otherwise.
• Incidence is 2-10% of infants born through MSAF
• 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

• Tachypnea
• Cyanosis
• Accessory muscle use (intercostal/subxiphoid retractions, paradoxical breathing, grunting, nasal flaring)
• Barrel-shaped chest
• Rales and rhonchi on lung auscultation
• Pneumothorax
• Pneumomediastinum
• Usually develop symptoms immediately after birth, but sometimes are born asymptomatic and develop symptoms as meconium moves into lower tracheobronchial tree

Differential Diagnosis

• Transient tachypnea of the newborn
• Sepsis
• Pneumonia
• Delayed transition from fetal circulation
• Pneumothorax
• Pulmonary edema
• Blood aspiration

Evaluation

• Clinical diagnosis based on the following:
  • Evidence of meconium on infant
  • Respiratory distress shortly after birth
  • Characteristic CXR findings
    • Initially, streaky, linear densities
    • Next, development of hyperinflated lungs and flattened diaphragm
    • Finally, diffuse patchy opacities (may appear similar to ARDS if severe)
  • If intubation required, meconium visualized in trachea