Meconium aspiration syndrome is respiratory distress in a newborn who has breathed (aspirated) meconium into the lungs before or around the time of birth.
Meconium is the dark green, sterile fecal material that is produced in the intestine before birth. Normally, meconium is expelled only after birth when newborns start to feed. However, in response to stress, such as an inadequate level of oxygen in the blood, the fetus may pass meconium into the amniotic fluid. Stress may also cause the fetus to take forceful gasps, so that the meconium-containing amniotic fluid is breathed (aspirated) into the lungs. After delivery, the aspirated meconium may block the airways and cause regions of the lungs to collapse. Sometimes airways are only partially blocked, allowing air to reach the parts of the lung beyond the block but preventing it from being breathed out. Thus, the involved lung may become over-expanded. Progressive over-expansion of a portion of the lung can result in rupture and then collapse of the lung. Air may then accumulate within the chest cavity around the lung (pneumothorax).
Meconium aspirated into the lungs also causes inflammation of the lungs (pneumonitis) and increases the risk of lung infection.
Meconium aspiration syndrome is often most severe in postmature newborns because they have a smaller volume of amniotic fluid so the meconium is concentrated in a smaller amount of amniotic fluid (see see Postmaturity). Newborns with meconium aspiration syndrome are also at increased risk of persistent pulmonary hypertension (see below).
Symptoms and Diagnosis
Affected newborns have respiratory distress, in which they breathe rapidly, draw in their lower chest wall while breathing in, and grunt during breathing out. Their skin may be bluish (cyanotic) if the blood levels of oxygen are reduced, and they may also develop low blood pressure.
Doctors base the diagnosis based on the presence of meconium in the amniotic fluid at the time of birth, respiratory distress in the newborn, and abnormal chest x-ray results.
At delivery, if the newborn is covered with meconium and is limp and not breathing, doctors immediately suction the mouth, nose, and throat to remove any meconium. They then place a breathing tube into the windpipe (trachea) to suction out any meconium there.
Newborns are treated with antibiotics because of the risk of an infection and are given supplemental oxygen and are placed on a ventilator if necessary. Sometimes repeated suctioning is done to try to remove more of the meconium. Newborns on a ventilator are observed closely for serious complications, such as pneumothorax or persistent pulmonary hypertension.
Most newborns with meconium aspiration syndrome survive. However, if the disorder is severe, especially if it leads to persistent pulmonary hypertension, it can be fatal.
Last full review/revision February 2009 by Arthur E. Kopelman, MD