Meconium aspiration syndrome (MAS, alternatively "Neonatal aspiration of meconium") is a medical condition affecting newborn infants. It occurs when meconium is present in their lungs during or before delivery. Meconium is the first stool of an infant, composed of materials ingested during the time the infant spends in the uterus.
Meconium is normally stored in the infant's intestines until after birth, but sometimes (often in response to fetal distress) 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.
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. This can cause breathing difficulties due to swelling (inflammation) in the baby's lungs after birth. Treatment may include suctioning the newborn's mouth as soon as the head emerges during delivery, deep suctioning of the windpipe, antibiotics to treat infection, oxygen to keep blood levels normal, and radiant heat to maintain body temperature. In severe cases, the baby may need assistance breathing (ventilator).
The most obvious sign that meconium has been passed during or before labor is the greenish or yellowish appearance of the amniotic fluid. The infant's skin, umbilical cord, or nailbeds may be stained green if the meconium was passed a considerable amount of time before birth. These symptoms alone do not necessarily indicate that the baby has inhaled in the fluid by gasping in utero or after birth. After birth, rapid or labored breathing, cyanosis, slow heartbeat, a barrel-shaped chest 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 (diffuse crackles and rhonchi), performing blood gas tests to confirm a severe loss of lung function, and using chest X-rays to look for patchy or streaked areas on the lungs. Infants who have inhaled meconium may develop respiratory distress syndrome often requiring ventilatory support. Complications of MAS include pneumothorax and persistent pulmonary hypertension of the newborn.
Meconium is the term used for the early feces passed by a newborn soon after birth. In some cases, the baby passes the meconium while still inside the uterus. This most often 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 immediately following birth. Some of the factors that may cause stress on the baby before birth include:
- Decreased oxygen immediately before or during the birthing process
- Difficult or lengthy labor and delivery
- Delivery that occurs past the due date
- High blood pressure in the pregnant mother
- Diabetes in the pregnant mother
High risk infants may be identified by fetal tachycardia, bradycardia or absence of fetal accelerations upon CTG in utero, at birth the infant may look cachexic and show signs of yellowish meconium staining on skin, nail and the umbillical cord, these infants usually progress onto Infant Respiratory distress syndrome within 4 hours. Investigations which can confirm the diagnosis are fetal chest x-ray, which will show hyperinflation, diaphragmatic flattening, cardiomegaly and pathy atelectasis, and ABG samples, which will show decreased oxygen levels.
The mortality rate of meconium-stained infants is considerably higher than that of non-stained infants; meconium aspiration used to account for a significant proportion of neonatal deaths. Residual lung problems are rare but include symptomatic cough, wheezing, and persistent hyperinflation for up to 5-10 yr. The ultimate prognosis depends on the extent of CNS injury from asphyxia and the presence of associated problems such as pulmonary hypertension.
Amnioinfusion, a method of thinning thick meconium that has passed into the amniotic fluid through pumping of sterile fluid into the amniotic fluid, has not shown a benefit in treating MAS. Until recently it had been recommended that the throat and nose of the baby be suctioned by the delivery attendant as soon as the head is delivered. However, new studies have shown that this is not useful and the revised Neonatal Resuscitation Guidelines published by the American Academy of Pediatrics no longer recommend it.When meconium staining of the amniotic fluid is present and the baby is born depressed, it is recommended by the guidelines that an individual trained in neonatal intubation use a laryngoscope and endotracheal tube to suction meconium from below the vocal cords.
If the condition worsens to a point where treatments are not affecting the newborn as they should, extracorporeal membrane oxygenation (ECMO) can be necessary to keep the infant alive.
Lucinactant (Surfaxin) is used as a treatment of MAS. Albumin-lavage has not demonstrated to benefit outcomes of MAS. Steroid use has not demonstrated to benefit the outcomes of MAS.