Meconium aspiration syndrome: pathophysiology and prevention.

BACKGROUND Despite the common occurrence of intrauterine meconium passage and resultant meconium aspiration syndrome (MAS), controversies regarding the pathophysiology and use of appropriate preventive strategies abound. METHODS Databases from MEDLINE, MD Consult, and the Science Citation Index were searched from 1964 to the present to find relevant sources of information. RESULTS AND CONCLUSIONS Meconium passage occurs by three distinct mechanisms: (1) as a physiologic maturational event, (2) as a response to acute hypoxic events, and (3) as a response to chronic intrauterine hypoxia. Meconium passage might merely be a marker of chronic intrauterine hypoxia or can predispose to aspiration of meconium and resultant inflammatory pneumonitis, surfactant inactivation, and mechanical airway obstruction. Aspiration can occur in utero with fetal gasping, or after birth with the first breaths of life. Many cases of MAS can be prevented by the strategies addressed in this article, but some will occur despite appropriate preventive techniques. There is not enough evidence to support the use of amnioinfusion as a standard of care for all pregnancies complicated by meconium. Pharyngeal suctioning before delivery of the shoulders is an effective preventive intervention, as is the combination of pharyngeal suctioning followed by intubation and tracheal suctioning. Suctioning of the trachea may be done on a selective basis depending on fetal vigor and consistency of meconium.