Meconium Aspiration Syndrome (MAS) is a respiratory condition affecting newborns. This syndrome develops when a baby inhales meconium, their first stool, into the lungs. The presence of meconium can lead to breathing difficulties. MAS affects a small percentage of deliveries.
What is Meconium Aspiration Syndrome
Meconium is a thick, sticky, greenish-black substance that accumulates in the fetal gastrointestinal tract during the third trimester of pregnancy. It is composed of intestinal secretions, amniotic fluid, bile, mucus, and cellular debris. While typically passed within the first 48 hours after birth, some infants pass meconium into the amniotic fluid before or during delivery.
When meconium is released into the amniotic fluid, a baby may inhale this mixture into their lungs. This aspiration can cause mechanical obstruction of the airways. Meconium also irritates lung tissue, causing inflammation and chemical pneumonitis.
The presence of meconium can inactivate surfactant, a substance that helps keep the tiny air sacs in the lungs open. This inactivation reduces the lung’s ability to expand and exchange oxygen efficiently. Consequently, the baby experiences reduced oxygen uptake and increased carbon dioxide levels.
Factors Contributing to MAS
Meconium passage in utero often occurs when a fetus experiences stress, which can stimulate intestinal peristalsis and relax the anal sphincter. Conditions causing fetal distress, such as decreased oxygen supply (hypoxia), can prompt this early passage. This reduced oxygen can result from issues like problems with the placenta or umbilical cord.
Several factors increase the likelihood of meconium passage and subsequent aspiration. Post-term pregnancy, after 40 to 42 weeks of gestation, is a common risk factor because the placenta may show signs of “aging.” Difficult or prolonged labor can also contribute to fetal stress.
Maternal health conditions, including high blood pressure (preeclampsia or maternal hypertension) and diabetes, are associated with a higher risk of meconium passage. Intrauterine growth restriction (IUGR) and certain infections during pregnancy can also induce fetal distress, potentially leading to the early release of meconium into the amniotic fluid.
Identifying MAS
The presence of meconium-stained amniotic fluid, which appears greenish or yellowish, is the first indication that a baby may be at risk for MAS. Upon birth, newborns with MAS exhibit signs of respiratory distress. These signs include rapid breathing (tachypnea), grunting sounds during exhalation, and flaring of the nostrils.
Observing chest retractions, where the chest wall pulls inward with each breath, is another common symptom. The baby’s skin may appear bluish (cyanosis) due to low oxygen levels, or in infants of color, the skin may change to colors such as yellow-gray, gray, or white. Limpness at birth and a low Apgar score can also suggest MAS.
Medical professionals confirm the diagnosis through a physical examination, listening for abnormal breath sounds like crackles or rhonchi in the lungs with a stethoscope. A chest X-ray can reveal characteristic findings such as hyperinflation of the lungs with patchy or streaky areas of density and flattened diaphragms. Blood gas analysis, which measures oxygen and carbon dioxide levels and pH, can further support the diagnosis by showing low oxygen, high carbon dioxide, and increased blood acidity.
Managing MAS
Initial management of MAS involves supportive care to help the newborn breathe more easily. If thick meconium is present and the baby is not vigorous, a healthcare provider may suction the baby’s mouth, nose, and throat with a bulb syringe or a tube inserted into the airway. However, routine deep suctioning of the windpipe is not recommended for vigorous infants born through meconium-stained fluid.
Oxygen therapy is a primary treatment, with oxygen saturation targets ranging from 90% to 95%. Depending on the severity of respiratory distress, a baby might receive continuous positive airway pressure (CPAP) to help keep airways open, or require mechanical ventilation to support breathing. Approximately 40% of infants with MAS may need mechanical ventilation.
Management strategies for MAS include:
- Surfactant administration: Used to improve lung function, particularly for intubated infants needing higher oxygen.
- Antibiotics: May be given to prevent or treat bacterial infections, though studies on their effectiveness vary.
- Inhaled nitric oxide: For severe cases, helps relax pulmonary blood vessels and improve lung blood flow, especially with persistent pulmonary hypertension (PPHN).
- Extracorporeal membrane oxygenation (ECMO): A heart-lung bypass machine used in the most severe instances for temporary support.
- Neonatal intensive care unit (NICU) care: Close monitoring and supportive care are essential for managing MAS.
Prognosis and Follow-Up
Most infants with Meconium Aspiration Syndrome recover well, with breathing problems resolving within two to four days. Rapid breathing, however, may persist for several days beyond this initial period. Severe cases, particularly those requiring mechanical ventilation, may have a more guarded outcome.
Potential short-term complications include persistent pulmonary hypertension of the newborn (PPHN), where blood bypasses the lungs, and air leak syndromes such as pneumothorax. While MAS rarely leads to permanent lung damage, some infants with severe aspiration may experience chronic coughing and wheezing for up to 5 to 10 years.
A lack of oxygen in the uterus or from severe complications of MAS can, in rare instances, lead to brain damage or developmental abnormalities. Follow-up medical appointments are important to monitor the child’s respiratory development and overall health after discharge.