Meconium aspiration syndrome: historical aspects

The meconium aspiration syndrome (MAS) is a common problem that continues to concern perinatologists and neonatologists. MAS is defined as respiratory distress in an infant born through meconium-stained amniotic fluid (MSAF) whose symptoms cannot be otherwise explained. This disorder may be life threatening, complicated by respiratory failure, pulmonary air leaks and persistent pulmonary hypertension. Approaches to the prevention of MAS have changed over time with collaboration between obstetricians and pediatricians forming the foundations for care.
The first strategy for MAS prevention was the routine endotracheal intubation. In particular, the first recommendation to reduce the incidence and severity of MAS was intubation and suctioning for all the babies born through thick meconium. However, this approach was based on anecdotal evidence and remained the standard of care only until its verification by a series of prospective randomized trials.
For term babies who are vigorous at birth, endotracheal intubation may be both difficult and unnecessary. These clinical observation was confirmed in an observational study, conducted in 1988, which showed no differences in outcome with and without routine intubation. Similar findings were obtained in a prospective controlled trial, conducted in the same year on 572 infants: none of 264 expectantly managed infants developed MAS and 2 of 308 intubated infants developed MAS. Even if some methodological concerns may limit, at least in part, the validity of this study, the authors concluded that intubation may be superfluous in a vigorous infant born through MSAF, thus inducing a change in clinical practice.
A decade later, the results of an international prospective, randomized, controlled trial assessing need for intubation in more than 2000 apparently vigorous meconium-stained infants randomized to either intubation and suctioning or to expectant management, disclosed no significant differences in either MAS or any respiratory disorders supporting the concept that it was not necessary to intubate vigorous term infants irrespective of the nature of the MSAF (thick or thin). In 2001, Halliday conducted a meta-analysis of four randomized controlled trials of endotracheal intubation at birth in vigorous term meconium-stained babies. Overall, the results did not support routine use of endotracheal intubation at birth in vigorous meconium-stained babies to reduce mortality, MAS, other respiratory symptoms or disorders, pneumothorax, oxygen need, stridor, and convulsions. However, the rate of many of these outcomes is low in the reported trials making reliable estimates of treatment effect impossible. Last, in 2004, Vain et al. reported that routine intrapartum oropharyngeal and nasopharyngeal suctioning of term-gestation infants born through MSAF does not prevent MAS.
In conclusion, meconium aspiration syndrome remains a challenging condition. Despite optimal perinatal management, infants born through MSAF may still develop MAS and have morbid or even fatal outcomes. Whereas there is inconclusive evidence as to the optimal ventilator strategy for MAS, surfactant replacement therapy has been beneficial and surfactant lavage is still being explored. Inhaled nitric oxide has significantly enhanced the treatment of pulmonary hypertension and substantially reduced the need for extracorporeal membrane oxygenation (ECMO).

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