MECONIUM ASPIRATION SYNDROME

MECONIUM Meconium is the first feces (stool) of the newborn. Meconium is composed of amniotic fluid, mucus, lanugo (the fine hair that covers the baby's body), bile, and cells that have been shed from the skin and the intestinal tract. Meconium is thick, greenish black, and sticky.

MECONIUM ASPIRATION SYNDROME Meconium aspiration syndrome is a serious condition in which a newborn breathes a mixture of Meconium and amniotic fluid into the lungs around the time of delivery.

ETIOLOGY Physiologic stress at the time of labor and delivery (eg, due to hypoxia caused by umbilical cord compression or placental insufficiency or caused by infection) may cause the fetus to pass Meconium into the amniotic fluid before delivery. Meconium passage is noted in about 8 to 15% of births. During delivery, perhaps 5% of neonates with Meconium passage aspirate the Meconium, triggering lung injury and respiratory distress, termed Meconium aspiration syndrome. Post term infants delivered through reduced amniotic fluid volume are at risk of more severe disease because the less dilute Meconium is more likely to cause airway obstruction.

PATHOPHYSIOLOGY The aspiration of Meconium causes injury by mechanical obstruction of the small airways, by causing a chemical pneumonitis, and by inactivation of surfactant.   The Meconium triggers an inflammatory response in the lung parenchyma, which results in a patchy infiltrate seen on chest radiographs. The inflammatory response is a type of chemical pneumonitis.   The mechanical obstruction by Meconium results in air trapping. Bile salts in the Meconium inactivate surfactant. The resulting clinical picture is one of respiratory distress. 10-15% of deliveries demonstrate Meconium-stained amniotic fluid, and 5-15% of those go on to develop Meconium aspiration syndrome.

SIGNS AND SYMPTOMS Symptoms Signs Tachypnea, Nasal flaring, Neonates with air trapping may have a barrel-shaped chest. Pneumothorax. Pulmonary interstitial emphysema. Pneumomediastinum. Signs Tachypnea, Nasal flaring, Retractions, Cyanosis or Desaturation Rales, Rhonchi Greenish yellow staining of the umbilical cord, Nail beds, or skin

DIAGNOSIS The presence of Meconium in a mother's amniotic fluid is key to diagnosing Meconium aspiration. Diagnosis is suspected when a neonate shows respiratory distress in the setting of Meconium-tinged amniotic fluid and is confirmed by chest x-ray showing hyperinflation with variable areas of atelectasis and flattening of the diaphragm.

X-Ray Findings Pneumomediastinum from gas trapping and air leak. Air trapping and hyperexpansion from airway obstruction. Acute Atelectasis. Diffuse chemical pneumonitis from constituents of Meconium. Left Pneumothorax with depressed diaphragm and minimal mediastinal shift because of noncompliant lungs

COMPLICATIONS Pulmonary air leaks. Pulmonary interstitial emphysema. Pneumothorax. Pneumomediastinum. Pneumonia.

TREATMENT Suctioning at birth before the first breath. Endotracheal intubation. Mechanical ventilation. Supplemental O2. IV antibiotics to treat infection. Nitric oxide Treatment.

TREATMENT Immediate treatment, indicated for all neonates delivered through Meconium, is vigorous suctioning of the mouth and nasopharynx using a De Lee suction apparatus as soon as the head is delivered and before the neonate breathes and cries.

ADDITIONAL TREATMENTS Surfactant for mechanically ventilated neonates with high O2 requirements, which can decrease the need for extracorporeal membrane oxygenation, and antibiotics (usually ampicillin and an aminoglycoside). Inhaled nitric oxide in the range of 5 to 20 ppm and high-frequency ventilation are other therapies that are used if refractory hypoxemia develops; they also may decrease need for extracorporeal membrane oxygenation

PROGNOSIS Some infants with MAS experience delayed neurologic function and cerebral palsy. Survivors often acquire chronic respiratory disease.

QUESTIONS?