Meconium Aspiration Syndrome

Pathogenesis and risk groups

The passage of meconium into amniotic fluid can occur even during a normal pregnancy—this is observed in approximately 10% of cases. However, true aspiration does not always develop. Post-term infants, full-term infants who have suffered intrauterine hypoxia, and newborns with intrauterine growth restriction (IUGR) are at the greatest risk.

The triggering mechanism is intrauterine stress (asphyxia). Oxygen deprivation stimulates fetal bowel peristalsis, leading to premature passage of meconium. Upon inhalation, these viscous masses enter the respiratory tract, causing mechanical obstruction. Concurrently with the blockage, a pronounced inflammatory response is triggered in the lung tissue, which together leads to severe respiratory failure.

Clinical and radiographic presentation

If meconium penetrates the distal airways without complete obstruction, the infant develops respiratory distress syndrome (RDS). Due to partial bronchial blockage and air trapping, the shape of the chest changes: it becomes barrel-shaped (increased anteroposterior diameter).

Auscultation of the lungs reveals the following changes:

• Coarse crackles over the entire surface.
• Fine crepititation.
• Prolonged (intensified) expiration.

Radiological signs of MAS are quite specific. The images show an alternation of large irregular opacities with areas of increased lucency (indicating emphysematous changes in the lung tissue). Flattening of the diaphragmatic domes due to lung overinflation is also characteristic.

Management tactics: from the delivery room to the ICU

The neonatologist's actions in cases of thick meconium aspiration must be lightning-fast and strictly algorithmic.

1. During labor: immediate suctioning (cleaning) of the nose and oropharynx is performed right after the fetal head crowns, even before the delivery of the body.
2. Immediately after birth: mandatory endotracheal intubation is indicated for tracheal suctioning. Suctioning of contents continues until the fluid is completely clear. Critically important: tracheal suctioning must be performed before initiating mechanical ventilation. Ignoring this rule sharply increases the risk of mortality, as ventilation will push the masses deeper.
3. Prevention of re-aspiration: mandatory gastric tube insertion and removal of swallowed meconium from the stomach.
4. Pharmacotherapy: broad-spectrum antibacterial drugs are prescribed to all infants with MAS.

In mild cases of the syndrome, oxygen therapy is sufficient. In severe cases, prolonged mechanical ventilation is required, and general management tactics are similar to the treatment of classic RDS.

Differential diagnosis: milk aspiration

In addition to meconium, newborns may aspirate milk. Preterm infants fall into the risk group here. Predisposing factors include a small stomach capacity and delayed gastric emptying. This risk persists for several weeks after birth.

Clinically, milk aspiration manifests as apnea episodes, cyanosis, and signs of airway obstruction. Emergency care consists of immediate suctioning of the nasal passages, oropharynx, and stomach. For prevention, such infants are fed strictly in a side-lying position. If radiological evidence confirms the development of extensive bronchopulmonary changes, empirical broad-spectrum antibiotic therapy is indicated.

Note: in recurrent aspirations, persistent choking, or coughing during feeding, congenital malformations—such as a tracheoesophageal fistula or posterior cleft palate—must be ruled out.

Class and exam questions

What else to study on this topic

• Pathophysiology of the inflammatory response of lung tissue to meconium components.
• Principles of selecting mechanical ventilation parameters in severe MAS.
• Empirical antibiotic therapy in newborns: drug selection and dosages.
• Anatomical features and diagnosis of tracheoesophageal fistulas.

Other topics in «Chapter 2. Neonatology»

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