Meconium aspiration syndrome
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Meconium aspiration syndrome (MAS) occurs when infants take meconium into their lungs during delivery. Meconium is the first stool of an infant, composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, aminotic fluid, bile, and water. Meconium is sterile, unlike later feces, and has no odor.
Meconium is normally stored in the infant's intestines until after birth, but sometimes it is expelled into the amniotic fluid prior to birth, or during labor. If the baby then inhales the contaminated fluid, respiratory problems may occur.
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Causes and risk factors
MAS occurs in about five to ten percent of all births. Frequently, fetal distress during labor causes intestinal contractions, as well as a relaxation of the anal sphincter, which allows meconium to contaminate the amniotic fluid. Amniotic fluid is normally clear, but becomes greenish if it is tinted with meconium. If the infant inhales this mixture before, during, or after birth, it may be sucked deep into the lungs. Three main problems occur if this happens:
- the material may block the airways
- efficiency of gas exchange in the lungs is lowered
- the meconium-tainted fluid is irritating, inflaming airways and possibly leading to chemical pneumonia
About a third of those infants who experience MAS require breathing assistance.
Symptoms and signs
The most obvious sign that meconium may have been aspirated is the greenish appearance of the amniotic fluid. The infant's skin may be stained green if the meconium was passed a considerable amount of time before birth. Rapid or labored breathing, slow heartbeat, or low Apgar score are all signs of the syndrome. Inhalation can be confirmed by one or more tests such as using a stethoscope to listen for abnormal lung sounds, performing blood gas tests, and using chest X-rays to look for patchy or streaked areas on the lungs. A quick and reliable way to verify MAS is to use a laryngoscope to look for meconium stains on the vocal cords.
Treatment
One of the most common treatments for MAS is the suctioning of the airways as soon as the head is delivered. Deeper suctioning of the trachea may be called for if thick meconium is present, or if there are signs of fetal distress. Infants who have inhaled meconium may be started on antibiotic treatment. If complications develop, breathing assistance may be called for.
Prevention
MAS is difficult to prevent. Ensuring that the infant is born before 42 weeks of gestation may lessen the risk. Amnioinfusion is a method of thinning thick meconium that has passed into the amniotic fluid. In this procedure, a tube is inserted into the uterus through the vagina, and sterile fluid is pumped in to dilute thick meconium.
External links
- eMedicine's article about meconium aspiration syndrome (http://www.emedicine.com/ped/topic768.htm)nl:Meconium