Diseases & Conditions


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Meconium Aspiration Syndrome


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 fecal material that is produced in the intestines before birth. Normally, meconium is expelled after birth when a newborn starts to feed. However, in response to stress, such as an inadequate blood oxygen level, the fetus may pass meconium into the amniotic fluid. The same stress causes the fetus to take forceful gasps, so that the meconium-containing amniotic fluid may be breathed into the lungs. After delivery, the aspirated meconium may block the airways leading to portions of the newborn's lungs, which may cause them to collapse. Alternatively, when some airways are only partially blocked, air may be able to reach the parts of the lung beyond the block but may be prevented from being breathed out. Thus, the involved lung may become over-expanded. Progressive over-expansion of a portion of the lung can eventually result in rupture and then collapse of the lung. Air may then accumulate within the chest cavity around the lung (pneumothorax). Meconium breathed into the lungs may also cause inflammation of the lungs (pneumonitis).

Meconium aspiration syndrome is often most severe in postmature newborns because the meconium is very concentrated in a smaller amount of amniotic fluid and it causes more irritation than in a term newborn (see Problems in Newborns: Postmaturity ). Newborns with meconium aspiration syndrome are also at increased risk for developing persistent pulmonary hypertension.

An affected newborn suffers from respiratory distress, in which he breathes rapidly, draws in his lower chest wall while breathing in, and grunts during breathing out. The newborn's skin may be bluish (cyanotic) if the blood levels of oxygen are reduced.

A doctor makes the diagnosis based on the observation of thick 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, the newborn's mouth, nose, and throat are immediately suctioned to remove any meconium. If the newborn is lethargic or unresponsive, a tube may need to be passed into the windpipe to suction as much meconium as possible from the respiratory tract.

The newborn is treated with oxygen and placed on a ventilator if necessary. If the newborn needs intubation, then repeated suctioning is performed to try to remove more of the meconium. A newborn on a ventilator is 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 and especially if it leads to persistent pulmonary hypertension, it can be fatal.

Last full review/revision February 2003

Source: The Merck Manual Home Edition

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