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.
MAS; Meconium pneumonitis (inflammation of the lungs)
Causes, incidence, and risk factors
Meconium is the term used for 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 stools (meconium) while still inside the uterus. This usually happens when babies are under stress because they are not getting enough blood and oxygen.
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 difficulties due to swelling (inflammation) in the baby's lungs after birth.
Risk factors that may cause stress on the baby before birth include:
- 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
- Passing the due date
- Bluish skin color (cyanosis) in the infant
- Breathing problems
- Difficulty breathing (the infant needs to work hard to breathe)
- No breathing
- Rapid breathing
- 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 immediately after birth, and therefore 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 blood pH (acidic), decreased oxygen, and increased carbon dioxide.
A chest x-ray may show patchy or streaky areas in the infant's lungs.
The delivering obstetrician or midwife should suction the newborn's mouth as soon as the head emerges during delivery.
Further treatment is necessary if the baby is not active and crying immediately after delivery. A tube is placed in the infant's trachea and suction is applied as the endotracheal tube is withdrawn. This procedure may be repeated until meconium is no longer seen in the suction contents.
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 lungs inflated
- Oxygen to keep blood levels normal
- Radiant warmer to maintain body temperature
If there have been no signs of fetal distress during pregnancy and the baby is an active full-term newborn, experts do not recommend deep suctioning of the windpipe, because it carries a risk of causing a certain type of pneumonia.
Meconium aspiration syndrome is a leading cause of severe illness and death in newborns.
In most cases, the outlook is excellent and there are no long-term health effects.
In more severe cases, breathing problems may occur. They generally go away in 2 - 4 days. However, rapid breathing may continue for days.
An infant with severe aspiration who needs a breathing machine may have a more guarded outcome. Lack of oxygen before birth, or from complications of meconium aspiration, may lead to brain damage. The outcome depends on the degree of brain damage.
Meconium aspiration rarely leads to permanent lung damage.
- Aspiration pneumonia
- Brain damage due to lack of oxygen
- Breathing difficulty that lasts for several days
- Collapsed lung (pneumothorax)
- Persistent pulmonary hypertension of the newborn (inability to get enough blood into the lungs to take oxygen to the rest of the body)
Risk factors 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 recognized 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.
Committee on Obstetric Practice, American College of Obstetricians and Gynecologists. ACOG Committee Opinion No. 379: Management of delivery of a newborn with meconium-stained amniotic fluid. Obstet Gynecol. 2007;110:739.
ACOG Committee Obstetric Practice. ACOG Committee Opinion Number 346, October 2006: amnioinfusion does not prevent meconium aspiration syndrome. Obstet Gynecol. 2006;108:1053.
Greenough A. Respiratory disorders in the newborn. In: Chernick V, Boat T, Wilmott R, Bush A, eds. Kendig's Disorders of the Respiratory Tract in Children. 7th ed. Philadelphia, Pa: Saunders Elsevier;2006:chap 18.
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.
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