Alternate Names: Meconium aspiration syndrome (MAS)
Causes and Risks: Meconium aspiration typically occurs when the fetus is stressed during labor. The infant is often post term (more than 40 weeks gestation).
During labor, the infant may suffer a lack of oxygen. This can cause increased movement of the intestines (peristalsis) and relaxation of the anal sphincter, resulting in passage of meconium into the amniotic fluid surrounding the unborn baby. The amniotic fluid and meconium mix to form a green stained fluid of various thickness (viscosity). If the infant breathes while still in the uterus or when the baby takes its first breath, the meconium/amniotic fluid mixture can be inhaled into the lungs. The inhaled meconium can cause a partial or complete blockage of the airways, causing difficulty breathing and poor gas exchange in the lungs. In addition, it is irritating and causes inflammation in the airways and a chemical pneumonia.
Meconium staining of the amniotic fluid with possibility of aspiration occurs in approximately 5% to 10% of births. About one third of the infants with meconium aspiration will require some type of assisted breathing. Meconium aspiration is a leading cause of severe illness and death in the newborn. Risk factors include: post-term pregnancy, preeclampsia, maternal diabetes, maternal hypertension, difficult delivery, fetal distress and intra-uterine hypoxia (decreased oxygen to the infant while still in the uterus).
Prevention: Risk factors should be identified as early as possible. If the mother’s membranes ruptured (water broke) at home, she should be asked if the fluid was clear or stained with a dark substance. Fetal monitoring is started to allow early recognition of fetal distress. Immediate intervention in the delivery room can sometimes help prevent aspiration. (See the Treatment section.)
Symptoms:
- 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 (cyanosis)
- rapid breathing (tachypnea)
- labored breathing (the infant needs to work hard to breathe)
- absence of breathing (apnea)
- the infant may show signs of post-maturity (weight loss, peeling skin)
Signs and Tests: Before birth, the fetal monitor may show a slow heart rate (bradycardia). At birth, there is meconium in the amniotic fluid (dark staining or streaking). The infant may have a low Apgar score.
PHYSICAL EXAMINATION OF THE INFANT:
- Direct visualization of the vocal cords for meconium staining with a laryngoscope in the delivery room is the most accurate evaluation for possible meconium aspiration.
- The diagnosis may be aided by listening to the infant’s chest with a stethoscope (auscultation) 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 pC02
- a chest X-ray showing patchy or streaky areas on lungs
Treatment: The newborn’s mouth should be suctioned as soon as the head is delivered. Further intervention 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 has been no signs of prenatal fetal distress, and the baby is a vigorous term birth newborn and there is meconium staining of the skin, some authorities recommend no deep suctioning of the trachea for fear of causing an 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.
Prognosis: Respiratory distress generally subsides in 2 to 4 days, although rapid breathing may persist for days. Infants with severe aspiration that require mechanical ventilation have a more guarded outcome. Hypoxia in the uterus or hypoxia from complications of meconium aspiration may lead to brain damage (hypoxic or anoxic brain damage). The outcome depends on the degree of brain damage. Meconium aspiration rarely leads to permanent lung damage.
Complications:
If the baby is born outside of the hospital and exhibits any signs of distress, immediate emergency help should be sought.
