Meconium aspiration syndrome: current concepts [editorial]

Aspiration of meconium causes considerable perinatal morbidity and mortality. Meconium-stained amniotic fluid (MSAF) is present in 7-22% of all deliveries. Gastrointestinal secretions bile bile acids mucus pancreatic juice cellular debris amniotic fluid swallowed vernix caseosa lanuge and blood comprise meconium. Passage of meconium occurs most often in deliveries after 42 weeks gestation (30%) because of high levels of the hormone motilin. This hormone is responsible for bowel peristalsis defecation and maturation of the innervation of the intestinal tract associated with vagal stimulation. It tends to be a marker of pre/intrapartum asphyxia. MSAF is also a sign of fetal hypoxia or acidosis. It appears that meconium aspiration is predominantly an intrauterine event. The definition of meconium aspiration syndrome (MAS) is respiratory distress in a meconium-stained newborn compatible radiographic findings (e.g. coarse irregular pattern of increased density throughout the lung) and symptoms that can not otherwise be explained. MAS occurs in 1-4% of infants with MSAF and up to 10% of those with thick meconium. Mortality ranges from 6% to 40%. Initially meconium particles mechanically obstruct the small airways. Later chemical pneumonitis and interstitial edema are responsible for small airway obstruction. As many as 66% of persistent pulmonary hypertension of the newborn cases are associated with MAS. Clinical signs and symptoms of MAS include frothy yellow-green secretions from the mouth; very rapid breathing; intercostal retractions; cyanosis; overinflated chest due to air trapping; rales; and rattling in the throat. Transcervical amnio-infusion of warmed normal saline may be an obstetric intervention in cases of MSAF. Intrapartum oropharyngeal suctioning and postpartum intratracheal suctioning has reduced the incidence of MAS. Routine care of MAS infants includes monitoring and correcting of the thermal environment and blood glucose and calcium levels. Chest physiotherapy saline lavage management of hypoxemia surfactant therapy and systemic steroid treatment are MAS therapies.