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Birth Injury Meconium Aspiration Syndrome
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Meconium Aspiration Syndrome Medical Malpractice

What Is Meconium Aspiration Syndrome?

Meconium aspiration syndrome (MAS) occurs when a newborn inhales a combination of the surrounding amniotic fluid (bag of water) and meconium while still inside the uterus or immediately after birth. Meconium is a newborns first bowel movement or discharge that consists of intestinal cells, mucus, fetal hair, secretions such as bile, proteins, fats, and water. Meconium normally comes out after the baby is born. Its appearance is tarry, greenish in nature, and has a sticky consistency. It has no bacteria which differentiates it from the normal stool.

Approximately 8-25% of all births after 34 weeks of gestation have meconium-stained amniotic fluid, but only 10% of those develop MAS. The incidence is going down in developed countries due to improved prenatal care and birthing facilities. Meconium-stained amniotic fluid is more common in babies at or beyond their due date and those in breech (feet first) positions.

Causes of Meconium Aspiration Syndrome (MAS)

Factors that increase the risk of meconium passage in the uterus are:

  • Placental dysfunction
  • Maternal hypertension
  • Preeclampsia known as “toxemia” which is high blood pressure and kidney dysfunction that leads to protein in the urine 
  • Low amniotic fluid
  • Maternal drug abuse such as cocaine or cigarettes
  • Maternal infection/ Fetal hypoxia (lack of oxygen)
  • Acidosis (low pH in the blood) from lack of oxygen

How Does MAS Affect the Baby?

It is the lack of oxygen that triggers the nerves to relax the anal sphincter which releases the meconium. Meconium in the amniotic fluid is toxic to the skin and lowers the bacterial resistance. The most severe complication is when a baby inhales or aspirates the stained fluid into their lungs. This limits the oxygen intake into the blood via four mechanisms:

  1. Obstruction of the airway such as would occur with choking, which may lead to lung rupture with trapping of air around the heart or other nearby tissues.
  2. Dysfunction of the surfactant that coats the air sacs to allow them to expand with oxygen. This causes the air sacs to collapse, which leads to lowered oxygen and respiratory distress.
  3. Chemical-induced pneumonitis—a form of pneumonia. Enzymes in the meconium act much like gastric acid and harm the developing air sacs by causing massive inflammation. The ability to exchange carbon dioxide for oxygen is greatly diminished.
  4. Elevated blood pressure in the lung vessels, which causes thickening of the walls. This further diminishes the oxygen levels in the blood pumped from the heart.

Signs and Symptoms

Symptoms of respiratory distress include the following:

  • Grunting
  • Nasal flaring
  • Rib cage breathing
  • Fast breathing
  • Blue lips and nail beds (due to low oxygen)
  • Abnormal lung sounds heard on the stethoscope
  • Yellow-green tinge to the skin, nails, and umbilical cord
  • Green urine


The laboratory tests reveal an abnormal level of acid in the blood and require continuous monitoring of oxygen levels by a process and device called pulse oximetry. Blood levels of electrolytes such as sodium, potassium and calcium, are measured because kidney dysfunction may occur in MAS. A complete blood count is collected to measure the levels of hemoglobin which is the substance responsible for carrying oxygen in the blood, platelets, and white blood cells. 

A condition known as polycythemia is when the blood is thickened with extra red blood cells and may indicate that there was diminished oxygen chronically or in the past that may have caused MAS earlier in the pregnancy rather than during labor and delivery. 

Chest x-ray confirms the diagnosis, locate the areas of lung collapse, leakage, and confirm that all devices such as endotracheal tubes are in their correct location. An ultrasound of the heart (echocardiography) is performed to ensure there are no anatomic defects and that the heart is functioning normally. It can also measure the degree of lung hypertension. A lung ultrasound in MAS can show the severity of the lung collapse, fluid collections around the lungs, and other disturbances consistent with MAS.

A brain CT or MRI may be administered once the baby is stable or if there are neurologic changes that occur. 


The best way to prevent MAS is to identify risk factors such as fetal distress and take preventative action. Conditions such as placental insufficiency, low amniotic fluid, and high blood pressure are also contributing risk factors for fetal distress. Continuous fetal monitoring is the best way to detect fetal distress in labor. 

Amnioinfusions used to be commonly employed to make the meconium less thick. They entail inserting a soft, hollow tube into the uterus after the water is broken and infusing warm saline into the cavity. Theoretically, less thick or chunky material would be better tolerated, if aspirated. Studies have failed to prove its usefulness in preventing MAS.

Routine suctioning after birth is no longer recommended nor is inserting a finger into the mouth. This behavior can trigger the gag reflex, which could make matters worse. Gentle bulb suctioning is sufficient to clear secretions. Likewise, the chest of the baby should not be squeezed to force meconium out of the lungs, esophagus, or mouth.  

The American Academy of Pediatrics (AAP) Neonatal Resuscitation Program Steering Committee and the American Heart Association (AHA) recommend the following guidelines for the management of meconium stained fluid. 

  • If the baby is vigorous as in good muscle tone and normal breathing efforts, only bulb suction is needed.
  • If the baby is not vigorous as in poor tone and breathing efforts; warm the baby, clear secretions with bulb suction, dry, stimulate movement, and reposition the head.
  • The principles are the same as for a newborn without meconium

Management and Treatment Guidelines

Neonatal intensive care unit (NICU)

The principals for optimal care include:

  • Maintain body temperature
  • Minimize handling to reduce agitation
  • Sedation may be needed
  • Continuous monitoring of oxygen status and pH
  • Continuous oxygen supplied via a hood or by positive pressure ventilation
  • Mechanical ventilation may be needed in up to 30% of babies with MAS
  • Consider surfactant supplementation as it has been shown to decrease the severity of the disease, need for more invasive procedures and shortens the hospital stay.
  • If there is pulmonary (lung) hypertension, inhaled nitric oxide can open up the air ways
  • Maintain blood pressure in other organs with infused fluid, transfusions, or drugs that tighten up the arteries.
  • Antibiotic use is controversial if there is no evidence of infection
  • Consultations with cardiologists and neurologists are helpful
  • Transfer to a regional Level III NICU may be necessary
  • No feeding in the early stages of MAS

Surgical Care is rarely needed unless severe air leakage or fluid collections cannot be managed with draining tubes or fibrin glue.

Medication Summary

  • Surfactant to replace that which was stripped by the meconium and because it acts as a deterrent to break up meconium particles
  • Drugs to raise blood pressure and open airways called vasoconstrictors consist of dobutamine, dopamine, and epinephrine. 
  • Sedative drugs reduce oxygen requirements and improve ventilation
  • Analgesics such as morphine, fentanyl, and phenobarbital may be helpful for agitation.
  • If sedatives fail, skeletal muscle paralysis may be needed to improve ventilation by the addition of drugs, pancuronium or vecuronium


The overall complication rate in the United States for MAS is approximately 1.2%, but the mortality rate for severe residual lung disease and pulmonary hypertension is high at a rate of 20%. Air leak syndromes and emphysema can occur in 10-30% of babies with MAS. The neurologic disabilities, if present, are not due to the MAS itself, but from the underlying cause such as chronic oxygen deprivation and pH changes that can occur well in advance of the labor process. Fetal distress can occur before labor or during the labor and birthing process. 


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