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.
MAS; Meconium pneumonitis (inflammation of the lungs)
Causes, incidence, and risk factors
Meconium is the early feces (stool) passed by a newborn soon after birth, before the baby has started to digest breast milk (or formula).
In some cases, the baby passes meconium while still inside the uterus. This usually happens when babies are "under stress" because their supply of blood and oxygen decreases, often due to problems with the placenta.
Once the meconium has passed into the surrounding amniotic fluid, the baby may breathe meconium into the lungs. This may happen while the baby is still in the uterus, or still covered by amniotic fluid after birth. The meconium can also block the infant's airways right after birth.
This condition is called meconium aspiration. It can cause breathing problems due to swelling (inflammation) in the baby's lungs after birth.
Risk factors that may cause stress on the baby before birth include:
"Aging" of the placenta if the pregnancy goes far past the due date
Decreased oxygen to the infant while in the uterus
Diabetes in the pregnant mother
Difficult delivery or long labor
High blood pressure in the pregnant mother
Bluish skin color (cyanosis) in the infant
Difficulty breathing (the infant needs to work hard to breathe)
Limpness in infant at birth
Signs and tests
Before birth, the fetal monitor may show a slow heart rate. During delivery or at birth, meconium can be seen in the amniotic fluid and on the infant.
The infant may need help with breathing or heartbeat right after birth, and may have a low Apgar score.
The health care team will listen to the infant's chest with a stethoscope and may hear abnormal breath sounds, especially coarse, crackly sounds.
A blood gas analysis will show low (acidic) blood pH, decreased oxygen, and increased carbon dioxide.
A chest x-ray may show patchy or streaky areas in the infant's lungs.
A team that is skilled at reviving newborn infants should be at the delivery if meconium staining is found in the amniotic fluid. If the baby is active and crying, no treatment is needed.
If the baby is not active and crying right after delivery, a tube is placed in the infant's trachea and suction is applied as the tube is pulled out. This procedure may be repeated until meconium is no longer seen in the suction contents.
If the baby is not breathing or has a low heart rate, the team will help the baby breathe using a face mask attached to a bag and an oxygen mixture to inflate the baby's lungs.
The infant may be placed in the special care nursery or newborn intensive care unit for close observation. Other treatments may include:
Antibiotics to treat infection
Breathing machine (ventilator) to keep the baby's lungs inflated
Extracorporeal membrane oxygenation (ECMO) for babies with severe persistent pulmonary hypertension of the newborn (PPHN)
Oxygen to keep blood levels normal
Radiant warmer to maintain body temperature
In most cases, the outlook is excellent and there are no long-term health effects.
In more severe cases, breathing problems may occur. They usually go away in 2 - 4 days. However, rapid breathing may continue for several days.
An infant with severe aspiration who needs a breathing machine may have more problems. A lack of oxygen before and right after birth may lead to brain damage. Many problems can develop while the child is using a breathing machine.
Meconium aspiration rarely leads to permanent lung damage.
A serious problem with the blood circulation to and from the lungs may occur. This is called persistent pulmonary hypertension of the newborn (PPHN). As a result, the baby may not be able to get enough blood into the lungs and out to the rest of the body.
Risk factors for this condition should be identified as early as possible. If the mother's water broke at home, she should tell the health care provider whether the fluid was clear or stained with a greenish or brown substance.
Fetal monitoring is started so that any signs of fetal distress can be found early. Immediate intervention in the delivery room can sometimes help prevent this condition. Health care providers who are trained in newborn resuscitation should be present.
Singh BS, Clark RH, Powers RJ, Spitzer AR. Meconium aspiration syndrome remains a significant problem in the NICU: outcomes and treatment patterns in term neonates admitted for intensive care during a ten-year period. J Perinatol. 2009;29:497-503.
Kattwinkel J, Perlman JM, et al. Part 15: neonatal resuscitation: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122:S909-S919.
Kimberly G. Lee, MD, MSc, IBCLC, Associate Professor of Pediatrics, Division of Neonatology, Medical University of South Carolina, Charleston, SC. Review Provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.