Define Meconium Aspiration Syndrome. Describe its pathophysiology, clinical features, investigations and management.

Definition

• Meconium Aspiration Syndrome is respiratory distress in a newborn born through meconium-stained amniotic fluid (MSAF), whose symptoms cannot otherwise be explained, together with characteristic radiological changes.
• It occurs mainly in term and post-term infants and is a marker of intrauterine stress.

Pathophysiology

Intrauterine hypoxia / stress → increased gut peristalsis + anal sphincter relaxation → meconium passage; fetal gasping causes aspiration of meconium into the airways, which produces:

• Airway obstruction — a 'ball-valve' effect → air trapping, hyperinflation, and pneumothorax.
• Chemical pneumonitis — an inflammatory lung injury.
• Surfactant inactivation → atelectasis.
• Persistent Pulmonary Hypertension of the Newborn (PPHN) — right-to-left shunting → severe, refractory hypoxaemia.

Clinical Features

• Meconium staining of the skin, nails and cord; a post-term, growth-restricted appearance.
• Respiratory distress (tachypnoea, grunting, retractions, cyanosis) soon after birth.
• Barrel-shaped chest from air trapping; coarse crepitations and rhonchi.

Investigations

• Chest X-ray: patchy, coarse, non-homogeneous opacities with areas of hyperinflation; may show a pneumothorax.
• ABG — hypoxaemia, hypercapnia, acidosis.
• Echocardiography — to assess for PPHN and cardiac function.

Management

• At birth: a non-vigorous meconium-stained baby who is not breathing → begin PPV (routine tracheal suctioning is no longer recommended); a vigorous baby needs only routine care.
• Supportive: oxygen, maintain temperature, glucose and perfusion; minimal handling; correct acidosis.
• Respiratory: CPAP / mechanical ventilation as required; surfactant for severe disease; drain a pneumothorax.
• PPHN: optimal oxygenation, inhaled nitric oxide (iNO), sildenafil, and ECMO in refractory cases.
• Antibiotics until sepsis is excluded.

Complications

• Air leaks (pneumothorax), PPHN, hypoxic organ injury.
• Secondary infection; chronic lung disease in ventilated babies.