Meconium

Meconium

The term meconium derives from ancient Greek meconium-arion, or "opium-like." Aristotle developed the term because he believed that it induced foetal sleep. The contents of the foetal intestine, meconium is a sterile admixture of numerous chemicals, including mucous glycoprotiens, swallowed vernix caseosa , gastrointestinal secretions, bile, pancreatic and liver enzymes, plasma proteins, minerals, and lipids. Mucopolysaccharides compose 80% of meconium's dry weight. The concentration of pancreatic and liver enzymes vary with gestational age.

Meconium Aspiration Syndrome

Meconium Aspiration Syndrome (MAS) is a common problem faced by paediatricians and obstetricians. In the U.S., there are an estimated 520,000 births (12% of live births) complicated by meconium stained amniotic fluid (MSAF). Of these, 35% will develop MAS (approximately 4% of all live births). 30% of babies with MAS will require mechanical ventilation, 10% develop pneumothoraces, and 4% die. As many as 66% of all cases of persistent pulmonary hypertension (PPHN) are related to meconium aspiration syndrome.

Meconium aspiration syndrome should be suspected in any neonate with a history of meconium-stained amniotic fluid and respiratory distress .  MAS is most strictly defined as the presence of any meconium below the vocal cords.
MAS can present mildly as transient respiratory distress or severely as respiratory failure with hypoxemia, acidosis, and pulmonary hypertension.  Classically, these babies are postmature and show signs of weight loss and yellow-stained nails, skin, and cord.  Rarely, MAS occurs before 38 weeks of gestation. 

Risk Factors

Risk factors have been developed to predict which babies will develop MAS. These include maternal admission of labour induction with nonreassuring foetal heart tracings, need for suctioning of the baby's trachea, one-minute Apgar score of 4 or less, and caesarean-section delivery. The presence of at least one of these risk factors had a positive predictive value of 8% and a negative predictive value of 99%.

The syndrome of meconium aspiration can be identified by its clinical hallmarks: history of meconium aspiration and hypoxemia without structural heart disease. To the right is a flow diagram describing this syndrome's pathophysiology, compiled from currently available literature:

Therapy begins in the delivery room, aimed at preventing the neonate who has been exposed to MSAF from aspirating that fluid.

Amnioinfusion :  This involves infusing normal saline into the amniotic space, which dilutes the meconium and/or decompresses the umbilical cord and the placenta. May ameliorate respiratory distress, acidosis, and the incidence of meconium aspiration syndrome or it may increase incidence of foetal heart rate abnormalities and increased incidence of Caesarean deliveries and operative vaginal deliveries.
Tracheal Intubation and Suctioning . A tube is placed into the neonate's mouth, nose and throat and any meconium is suctioned out.
Antibiotics . The use of antibiotics in patients with MAS has stemmed from three rationale:  meconium produces segmental atelectasis which may mimic bacterial pneumonia, foetal bacterial infection may have been the stress that caused meconium passage and subsequent MAS, and there has been evidence of in vitro enhancement of bacterial growth by meconium.

For further, more detailed information on this topic, please refer to the reference source for this page.

The information in this page is presented in summarised form and has been taken from the following source(s):
1. picuBOOK: An on-line resource for pediatric critical care