Meconium aspiration syndrome
Meconium aspiration syndrome (MAS, alternatively "Neonatal aspiration of meconium") is a medical condition affecting newborn infants. It occurs when meconium
Meconium is the earliest stools of an infant. Unlike later feces, meconium is composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. Meconium is almost sterile, unlike later feces, is viscous and...

 is present in their lungs during or before delivery. Meconium is the first stool
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...

 of an infant
A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

, composed of materials ingested during the time the infant spends in the uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...


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.

Signs and symptoms

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
Apgar score
The Apgar score was devised in 1952 by the eponymous Dr. Virginia Apgar as a simple and repeatable method to quickly and summarily assess the health of newborn children immediately after birth...

 are all signs of the syndrome. Inhalation can be confirmed by one or more tests such as using a stethoscope
The stethoscope is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to lung and heart sounds. It is also used to listen to intestines and blood flow in arteries and veins...

 to listen for abnormal lung sounds (diffuse crackles and rhonchi), performing blood gas
Blood gas
Blood gas is a term used to describe a laboratory test of blood where the purpose is primarily to measure ventilation and oxygenation. The source is generally noted by an added word to the beginning; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood...

 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
Respiratory distress syndrome
There are two forms of respiratory distress syndrome:* ARDS, which is acute respiratory distress syndrome* Infant respiratory distress syndrome , which is a complication of premature birth, also known as hyaline membrane disease Also, respiratory distress can mean:* Shortness of breath*...

 often requiring ventilatory support
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...

. Complications of MAS include pneumothorax
Pneumothorax is a collection of air or gas in the pleural cavity of the chest between the lung and the chest wall. It may occur spontaneously in people without chronic lung conditions as well as in those with lung disease , and many pneumothoraces occur after physical trauma to the chest, blast...

 and persistent pulmonary hypertension of the newborn.


Fetal distress
Fetal distress
In medicine , the term fetal distress refers to the presence of signs in a pregnant woman—before or during childbirth—that suggest that the fetus may not be well...

 during labor causes intestinal contractions, as well as relaxation of the anal sphincter, which allows meconium to pass into the amniotic fluid and contaminate the amniotic fluid. Meconium passage into the amniotic fluid occurs in about 5-20 percent of all births and is more common in overdue births. Of the cases where meconium is found in the amniotic fluid, meconium aspiration syndrome develops less than 5 percent of the time. Amniotic fluid is normally clear, but becomes greenish if it is tinted with meconium.

Pathophysiology and Mechanism

The pathophysiology of MAS is due to a combination of primary surfactant deficiency and surfactant inactivation as a result of plasma proteins leaking into the airways from areas of epithelial disruption and injury.

The leading three causes of MAS are
  1. Due to physiologic maturational event,
  2. A response to acute hypoxic events, and
  3. A response to chronic intrauterine hypoxia.

If an 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 (pneumonitis
    Pneumonitis or pulmonitis is a general term that refers to inflammation of lung tissue.Pneumonia is pneumonitis combined with consolidation and exudation...

    ) and possibly leading to chemical pneumonia
    Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...


These can lead to possibly fatal or long term health problems for the infant.


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.

Prevention and Screening

MAS is difficult to prevent. The risk of MAS increases after the 40th week of pregnancy.


Amnioinfusion is a method of thinning thick meconium that has passed into the amniotic fluid.It can increase fetal space.It has been used to reduce meconium aspiration syndrome, though evidence of benefit is mixed....

, 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
Neonatal Resuscitation Program
The Neonatal Resuscitation Program was developed and is currently maintained by the American Academy of Pediatrics. This program focuses on the teaching and maintaining basic skills for the resuscitation of neonates. NRP's didactic portion includes nine lessons modules along with 5 skills...

 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
Tracheal intubation, usually simply referred to as intubation, is the placement of a flexible plastic or rubber tube into the trachea to maintain an open airway or to serve as a conduit through which to administer certain drugs...

 use a laryngoscope
Laryngoscopy is a medical procedure that is used to obtain a view of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during general anesthesia or cardiopulmonary resuscitation or for procedures on the larynx or other parts of the upper...

 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
Extracorporeal membrane oxygenation
In intensive care medicine, extracorporeal membrane oxygenation is an extracorporeal technique of providing both cardiac and respiratory support oxygen to patients whose heart and lungs are so severely diseased or damaged that they can no longer serve their function...

 (ECMO) can be necessary to keep the infant alive.

Surfaxin is a liquid medication used to treat Infant Respiratory Distress Syndrome in infants. It is currently under investigation by the FDA and not licensed for general use.-History:...

(Lucinactant) 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.


In a study conducted between 1995 and 2002, MAS occurred in 1061 of 2,490,862 live births, reflecting an incidence of 0.43 of 1000. MAS requiring intubation occurs at higher rates in pregnancies beyond 40 weeks. 34% of all MAS cases born after 40 weeks required intubation compared to 16% prior to 40 weeks.

External links

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