Meconium aspiration syndrome (MAS)
Meconium is the first feces (stool) of the newborn. It is thick, sticky, and greenish-black in color. Aspiration means the newborn inhales a mixture of the meconium and amniotic fluid, either in the uterus or just after delivery.
Causes, incidence, and risk factors
The possibility of inhaling meconium occurs in about 5-10% of births. It typically occurs when the fetus is stressed during labor, especially when the infant is past its due date. The condition is serious - meconium aspiration is a leading cause of severe illness and death in the newborn.
During a stressful labor, an infant may suffer a lack of oxygen. This can cause increased movement of the infant’s intestines and relaxation of the anal sphincter, causing meconium to pass into the amniotic fluid surrounding the unborn baby. The amniotic fluid and meconium mix to form a green-stained fluid of various thickness. Meconium itself is thick, sticky, and greenish-black in color.
If the infant breathes while still in the uterus or while still covered by this fluid after birth, the mixture of meconium and amniotic fluid can be inhaled into the lungs. The inhaled meconium can partially or completely block the infant’s airways. The infant has difficulty breathing and poor gas exchange in the lungs. In addition, the substance is irritating and causes inflammation in the airways and, potentially, chemical pneumonia.
About one-third of the infants with meconium aspiration will require some type of assisted breathing. Risk factors include maternal diabetes, maternal hypertension, difficult delivery, fetal distress, and intra-uterine hypoxia (decreased oxygen to the infant while it is still in the uterus).
- Dark, greenish staining or streaking of the amniotic fluid or the obvious presence of meconium in the amniotic fluid
- Infant’s skin stained greenish (occurs if meconium passed a long period before delivery)
- Infant appears limp at birth
- Bluish skin color in the infant
- Rapid breathing
- Labored breathing (the infant needs to work hard to breathe)
- Absence of breathing
- Signs of post-maturity such as Weight loss, peeling skin
Signs and tests
Before birth, the fetal monitor may show a slow heart rate. At birth, meconium is visible in the amniotic fluid. The infant may have a low Apgar score.
The physical examination of the infant may involve:
- Directly looking for meconium staining on the vocal cords with a laryngoscope in the delivery room. This is the most accurate evaluation for possible meconium aspiration.
- Listening to the infant’s chest with a stethoscope and hearing abnormal breath sounds, especially coarse, crackly sounds.
Tests performed on the infant may include:
- Blood gas analysis showing low blood pH (acidosis, an acidic condition of the blood), decreased pO2 and increased pCO2
- A Chest x-ray showing patchy or streaky areas on lungs
The newborn’s mouth should be suctioned as soon as the head is delivered. Further treatment is necessary if there is thick meconium staining and fetal distress. A tube is placed in the infant’s trachea and suction is applied as the endotracheal tube is withdrawn. This procedure is repeated until meconium is no longer seen in the suction contents.
If there have been no signs of prenatal fetal distress, and the baby is a vigorous term-birth newborn, experts now recommend NO deep suctioning of the trachea for fear of causing aspiration pneumonia. Occasionally, a saline solution is used to wash the airway of particularly thick meconium.
After delivery, the infant is observed carefully. The infant may be placed in the special care nursery or newborn intensive care unit. Other treatments may include chest physiotherapy (tapping on the chest to loosen secretions), antibiotics to treat infection, use of a radiant warmer to maintain body temperature and mechanical ventilation to keep the lungs inflated.
Breathing problems generally subside in 2 to 4 days, although Rapid breathing may persist for days. An infant with severe aspiration who requires mechanical ventilation may have a more guarded outcome. Lack of oxygen in the uterus 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
- Pneumothorax (collapsed lung)
- Persistent fetal circulation
- Residual brain damage due to lack of oxygen
- Persistent respiratory distress (breathing difficulty) lasting for several days
Calling your health care provider
If the baby is born outside of the hospital and exhibits any signs of distress, immediate emergency help should be sought.
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 dark 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 aspiration.
by Martin A. Harms, M.D.
All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.