Meconium Aspiration (MAS) and Birth Injury*

Under normal circumstances, the baby’s meconium (excretory matter) is stored in the intestines until after delivery. If the baby is in distress during labor, it passes this stool into the amniotic fluid and breathes it in. This blocks the airways, decreases oxygen supply and causes pneumonia. The medical team must work quickly to re-establish proper breathing and prevent and treat complications. This is one of the most common birth injuries and is classified as an emergency.

Meconium aspiration syndrome (MAS) is a serious medical condition in which a baby breathes a mixture of meconium (the baby’s first stool) and amniotic fluid into her lungs around the time of delivery.  Meconium is the early, thick, green feces of the baby.  It normally is stored in the baby’s intestines until after birth.  Sometimes, however, while the baby is still inside the uterus, the meconium is expelled into the amniotic fluid, either right before or during labor.  This usually happens when the baby is experiencing fetal distress, especially when the baby is past the due date. Once the baby has passed meconium into the surrounding amniotic fluid, she may inhale meconium deep into her lungs.  This can cause airway blockage and constriction, a decrease in oxygen in the baby’s body, inflamed airways and pneumonia.  Meconium aspiration also can happen after labor, when a baby inhales meconium and amniotic fluid that is covering her body.

When meconium aspiration occurs, it is essential that the medical team act quickly to try and restore normal breathing and prevent or minimize meconium aspiration complications.  Often, emergency resuscitation efforts are required to restore the baby’s breathing and, sometimes, the baby’s heartbeat.  It is very important that the medical staff know how to spot the potential for meconium aspiration, and be equipped and prepared to handle this type of emergency.  MAS is one of the leading causes of severe birth injuries in newborn babies, and it occurs in about 5 – 10 % of births.  Failure to properly manage meconium aspiration can cause the baby to experience respiratory distress, hypoxic ischemic encephalpathy (HIE), seizures and cerebral palsy.

Medical Explanations

Causes of Meconium Aspiration Syndrome

If a baby is in distress around the time of labor, this can cause the baby’s intestines to contract and the anal sphincter to relax, which allows meconium to pass into the amniotic fluid and contaminate it.  A baby may be under stress if he or she is not receiving enough oxygen or blood.  Causes of meconium aspiration include the following:

  • It may be the baby’s response to a stressor that is caused by the baby being past her due date.  When babies are past due, there may be problems with the umbilical cord and placenta, which can cause the baby to be deprived of adequate oxygen, blood and nutrients.
  • It may be a response to an event whereby the baby is severely deprived of oxygen for a period of time (hypoxia, birth apshyxia).
  • It may be a response to the baby having low oxygen levels over a long period of time (chronic intrauterine hypoxia).

Risk Factors for Meconium Aspiration Syndrome

  • The baby is overdue; the baby’s gestational age is more than 40 weeks (postmaturity).
  • “Aging” of the placenta if the pregnancy goes far past the due date (placental insufficiency).
  • Decreased oxygen (fetal hypoxia) to the baby while in the uterus.
  • Diabetes in the pregnant mother (gestational diabetes).
  • Difficult delivery or prolonged labor.
  • The pregnant mother develops high blood pressure and protein in her urine after the 20th week of pregnancy (preeclampsia).
  • Drug abuse by the pregnant mother (tobacco or cocaine use).

Signs and Symptoms of Meconium Aspiration Syndrome

  • Fast heart rate on the electronic fetal monitor.
  • Slow heart rate on the electronic fetal monitor that occurs at or after the peak of a uterine contraction (late decelerations / non-reassuring heart tracings).
  • Greenish or yellowish appearance of the amniotic fluid.
  • The baby’s skin, umbilical cord, and / or nailbeds are stained green.
  • The baby is not breathing, or has fast or labored breathing after birth.
  • Bluish skin color (cyanosis).
  • Slow heartbeat (bradycardia).
  • A  larger than normal chest and rib cage (barrel chest).
  • Low Apgar score. (An Apgar score is an assessment of the newborn the first few minutes of life that considers factors such as the baby’s skin color / complexion, pulse rate, reflexes, muscle tone and breathing.)
  • The baby’s blood at the moment of birth, umbilical cord blood, is acidic (has a low pH).
  • Meconium in the baby’s trachea.
  • At birth, the baby appears weak, with a loss of muscle and body mass (hypotonia).
  • The baby is limp at birth.

Diagnosing Meconium Aspiration Syndrome

Inhalation of meconium can be confirmed by one or more of the following tests:

  • The health care team listen’s to the baby’s chest with a stethoscope and hears abnormal breath sounds, especially coarse, crackly sounds.
  • An analysis of the baby’s blood shows acidic blood (low pH), decreased oxygen, and increased carbon dioxide.
  • A chest x-ray shows patchy or streaky areas in the baby’s lungs.  The lungs appear overinflated, and the x-ray shows collapse of multiple small areas of the lung.  In addition, the heart appears larger than normal.

Treating Meconium Aspiration Syndrome

If a baby is at risk for MAS, foetal monitoring should be done in order to prevent dangerous complications.  If the baby is not receiving enough blood or oxygen, or if the baby’s heart rate is slow, doctors must act quickly to restore blood flow and oxygen supply.  If oxygen and blood supply cannot be restored, an emergency delivery, usually a C-section, should be performed.  It is essential that a team skilled at reviving newborn babies be present at the delivery if meconium staining is found in the amniotic fluid.  A failure to adequately monitor the baby, or a delay in emergency delivery can cause significant brain damage, injury, or even death of the baby.

Treatment of MAS includes the following:

  • Airway clearance: Deep airway clearing, called suctioning, is recommended only for non-vigorous / depressed babies who have a risk for MAS.  A depressed baby has absent or slow breathing (apnea or bradypnea), a slow heart rate (bradycardia), and low muscle tone (hypotonia).  Initial suctioning should not exceed five seconds. If no meconium is retrieved, repetitive suctioning is not required. However if meconium is retrieved and no bradycardia is present, it is recommended that the baby be suctioned again, with oxygen being given right before and after suctioning.
  • Neonatal Intensive Care Unit: A baby at risk for MAS who shows signs of respiratory distress should be admitted to the neonatal intensive care unit (NICU).  Close monitoring of the baby is essential since he or she can deteriorate very quickly.  Once the baby develops MAS, maintenance of good oxygenation, ventilation and blood pressure, and correction of acidic blood, low blood sugar and other metabolic disorders is the main focus of treatment.
  • Breathing machine (ventilator): About 30% – 50% of babies with MAS require a machine, called a ventilator, to help them breathe.  One reason for this is because their lungs have areas of collapsed lung tissue, as well as airflow obstruction and inflammation throughout.  The ventilator controls the oxygen and carbon dioxide levels within the baby’s blood, and makes it easier and safer to suction meconium, mucus and other secretions that are common in babies with MAS.
  • Supplemental oxygen: Some babies with MAS do not need a machine to help them breathe, they just need a little extra oxygen.  The oxygen can be delivered through an oxygen hood, nasal cannula or face mask.
  • Surfactant therapy: Surfactant is a substance that occurs naturally in the lungs.  Surfactant decreases the tension in the lungs and helps make the lungs compliant (easy to expand).  When babies have meconium in their lungs, the meconium interferes with the the function of the surfactant, which can make it very difficult for the baby to breathe and  for the baby’s lungs to function properly.  Surfactant in drug form often is given to babies with MAS to help improve their lung function, reduce the severity of respiratory distress and decrease the likelihood of respiratory failure.
  • Steroid therapy: Meconium in the lungs causes an inflammatory response in the airways.  Providing steroid treatment for babies with MAS may help reduce the inflammation and inflammation side-effects of meconium, thereby improving the baby’s lung function.
  • Nitric oxide: A condition called persistent pulmonary hypertension (PPHN) often accompanies MAS.  PPHN occurs when the newborn baby’s circulation does not adapt to breathing outside the womb.  PPHN causes the blood pressure in the arteries of the lungs to be very high, and a large portion of the baby’s blood bypasses the lungs and this blood, therefore does not receive oxygen.  This can be life-threatening.  Inhalation of nitric oxide causes the dilation (relaxation) of the vessels in the lungs and improves oxygenation of the baby.
  • Extracorporeal membrane oxygenation (ECMO): In extracorporeal membrane oxygenation (ECMO), a machine that takes blood from the body, oxygenates it using an artificial lung, and pumps it back into the body using an artificial heart, is used. ECMO is similar to a heart/lung bypass machine used in open heart surgery, but can be used for a longer period of time.  ECMO is used for babies whose low oxygen levels (hypoxia) cannot be corrected with other treatments, such as by putting them on a ventilator and giving them extra oxygen to breathe.
  • Radiant warmer to maintain body temperature

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