Meconium aspiration syndrome

Overview

Meconium Aspiration Syndrome (MAS) is a serious respiratory condition that occurs when a newborn inhales a mixture of meconium (the baby’s first feces) and amniotic fluid into the lungs around the time of delivery. This aspiration can cause airway obstruction, inflammation, infection, and impaired gas exchange, leading to respiratory distress shortly after birth. MAS is a common cause of respiratory illness in term and post-term neonates, particularly those who experience fetal distress during labor.

While most babies exposed to meconium-stained amniotic fluid do not develop MAS, a small percentage—especially those who are stressed or asphyxiated in utero—can inhale the contaminated fluid, leading to potentially severe respiratory complications that may require intensive care.

Causes

The underlying cause of Meconium Aspiration Syndrome is the passage of meconium into the amniotic fluid followed by the aspiration of this meconium-stained fluid before, during, or immediately after birth. Key contributing factors include:

• Fetal distress: Hypoxia (lack of oxygen) during labor stimulates increased intestinal activity, leading to the release of meconium into the amniotic fluid.

• Post-term pregnancy: Babies born after 40 weeks are more likely to pass meconium before delivery.

• Complicated labor and delivery: Conditions like prolonged labor, umbilical cord compression, or maternal hypertension increase the risk of fetal hypoxia and subsequent meconium passage.

• Intrauterine infections: Can contribute to early meconium passage and increased aspiration risk.

Once meconium is present in the amniotic fluid, the fetus may gasp or breathe in utero due to stress, allowing the meconium-laden fluid to enter the lungs.

Symptoms

Signs of Meconium Aspiration Syndrome typically appear within minutes to hours after birth. Common symptoms include:

• Respiratory distress: Rapid breathing (tachypnea), grunting, nasal flaring, and use of accessory muscles

• Cyanosis: Bluish discoloration of the skin, lips, or fingernails due to low oxygen levels

• Barrel-shaped chest: Due to overinflated lungs from air trapping

• Decreased breath sounds: On auscultation, indicating partial obstruction or atelectasis (collapsed lung segments)

• Greenish staining: Meconium-stained amniotic fluid may be present on the skin, umbilical cord, or fingernails

• Poor feeding and lethargy

The severity of symptoms can range from mild breathing difficulty to life-threatening respiratory failure, depending on the extent of aspiration and lung involvement.

Diagnosis

Diagnosis of Meconium Aspiration Syndrome is based on clinical history, physical examination, and supportive diagnostic tests. The key diagnostic components include:

• Clinical history:

  • Presence of meconium-stained amniotic fluid at delivery

  • Signs of fetal distress before or during labor

• Physical examination:

  • Respiratory distress shortly after birth in a term or post-term infant

• Chest X-ray:

  • Patchy infiltrates, hyperinflation, and areas of lung collapse (atelectasis)

• Arterial blood gas analysis:

  • Shows hypoxemia (low oxygen) and possibly respiratory acidosis

• Pulse oximetry:

  • Continuous monitoring of oxygen saturation levels

MAS should be differentiated from other neonatal respiratory conditions such as transient tachypnea of the newborn (TTN), neonatal pneumonia, and respiratory distress syndrome (RDS).

Treatment

The treatment of Meconium Aspiration Syndrome depends on the severity of the condition and involves supportive care, respiratory support, and close monitoring. Management strategies include:

1. Immediate Post-Delivery Management

• Routine suctioning of the mouth and nose is no longer recommended for vigorous infants with meconium-stained fluid.

• For non-vigorous infants (poor tone, weak breathing), endotracheal suctioning may be performed by trained personnel to clear the airways.

2. Respiratory Support

• Oxygen supplementation: For mild cases with low oxygen levels

• Continuous Positive Airway Pressure (CPAP): Helps keep airways open in moderately affected infants

• Mechanical ventilation: Required for infants with severe respiratory distress or respiratory failure

• High-frequency oscillatory ventilation (HFOV): May be used in severe cases unresponsive to conventional ventilation

3. Additional Therapies

• Surfactant therapy: Administered in some cases to improve lung function

• Inhaled nitric oxide: Used to treat pulmonary hypertension, a complication of MAS

• Antibiotics: Empiric antibiotics are often started due to difficulty distinguishing MAS from infection, and discontinued if cultures are negative

• Extracorporeal Membrane Oxygenation (ECMO): Used in rare, life-threatening cases where conventional ventilation fails

Prognosis

The prognosis of Meconium Aspiration Syndrome depends on the severity of lung involvement and associated complications. Most infants with mild to moderate MAS recover fully with appropriate care. Prognostic factors include:

• Severity of aspiration: Infants with large amounts of meconium in the lungs may require prolonged ventilation

• Presence of complications: Such as persistent pulmonary hypertension of the newborn (PPHN) or secondary infection

• Promptness of treatment: Early identification and supportive care improve outcomes significantly

Long-term complications are rare but may include chronic lung disease or reactive airway disease, especially in infants who required prolonged mechanical ventilation. Most infants recover fully with no long-term consequences.