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Intubation and Tracheal Suctioning for Meconium Aspiration

Overview

Background

Meconium is a viscous green-black substance that consists of denuded intestinal epithelial cells, ingested lanugo hair, mucus, digestive enzymes, bile acids, and water. The term meconium is derived from the Greek word mekonion, which means poppy juice or opium, presumably either because of its tarry appearance or because of Aristotle’s belief that it induced sleep in the fetus.

Meconium constitutes the first stool of a newborn infant. The passage of meconium typically occurs within 48 hours after birth; however, it can occur in utero. Postterm fetus may pass the meconium physiologically. Intrauterine meconium passage has been linked to fetal hypoxia and is associated with fetal acidosis, abnormal fetal heart tracings, and low Apgar scores.

In preterm pregnancies, intrauterine meconium passage has been associated with fetomaternal stress and infection.
In term and postterm infants without fetal distress, intrauterine meconium passage may result from normal gastrointestinal (GI) maturation or from vagal stimulation caused by head or cord compression.
Meconium staining of the amniotic fluid occurs in approximately 13% of live births; this percentage increases with increasing gestational age at delivery.

Meconium aspiration syndrome (MAS) occurs when meconium-stained amniotic fluid (MSAF) is aspirated into the lungs of an infant before, during, or immediately after birth (see the image below). Intrauterine gasping, resulting in aspiration of meconium, has been demonstrated in animal models exposed to hypoxia.
MAS occurs in approximately 5% of infants born through MSAF.
Even with modern neonatal intensive care, mortality from MAS remains high, in the range of 3-5%.

Pathophysiology of meconium aspiration. Image adap

Pathophysiology of meconium aspiration. Image adapted from Wiswell T, Bent RC. Meconium staining and the meconium aspiration syndrome. Pediatr Clin North Am. 1993;40(5):955-981.

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Many perinatal risk factors have been associated with meconium aspiration, including placental insufficiency, maternal hypertension, maternal diabetes mellitus, preeclampsia, oligohydramnios, and maternal tobacco use.
 Perhaps the most significant risk factor, however, is postterm delivery. In a prospective clinical study, a decrease in the incidence of MAS from 5.8% to 1.5% over an 8-year period was attributed to a reduction in births at more than 41 weeks’ gestation.

MAS occurs along a continuum from mild to severe.
Mild MAS is seen in infants born through MSAF who have mild respiratory symptoms; it probably reflects mild parenchymal irritation from aspirated meconium. Moderate MAS presents with more pronounced pulmonary symptoms, including moderately high oxygen requirements and a possible need for mechanical ventilation; it may reflect a more significant meconium load or the aspiration of thicker meconium into the lungs.

Infants with severe MAS require mechanical ventilation with high settings and may need alternative therapies, such as inhaled nitric oxide (NO) and, possibly, extracorporeal membrane oxygenation (ECMO).
These cases probably represent a combination of meconium aspiration and persistent pulmonary hypertension of the newborn (PPHN). PPHN in these cases is thought to arise from chronic fetal compromise (hypoxia) with resultant pulmonary vascular remodeling.

There is evidence to suggest that chronic in utero hypoxia with resultant PPHN, rather than the aspiration of meconium per se, may be the primary pathologic problem in newborn infants diagnosed with severe MAS.

Revised ACOG Recommendations

See the list below:

Infants with meconium-stained amniotic fluid, regardless of whether they are vigorous or not, should no longer routinely receive intrapartum suctioning. However, meconium0stained amniotic fluid is a condition that requires the notification and availability of an appropriately credentialed team with full resuscitation skills, including endotracheal intubation.

Resuscitation should follow the same principles for infants with meconium-stained fluid as for those with clear amniotic fluid.

Routine intubation and tracheal suctioning are no longer required.

If the infant is vigorous with good respiratory effort and muscle tone, the infant may stay with the mother to receive the initial steps of newborn care.  Gentle clearing of meconium from the mouth and nose with a bulb syringe may be done if necessary.

If the infant born through meconium-stained amniotic fluid presents with poor muscle tone and inadequate breathing efforts, the initial steps of resuscitation should be completed under the radiant warmer. Appropriate intervention to support ventilation and oxygenation should be initiated as indicated for each infant and, if the airway is obstructed, this may include intubation and suction.

This new recommendation to no longer routinely suction nonvigorous infants arose from an emphasis on prevention of harm (ie, delays in providing bag-mask ventilation and potential consequences of unnecessary interventions) instead of the unknown benefit of the interventions of routine tracheal intubation and suctioning.

Technical Considerations

Best practices

Several procedures have been used in the past to prevent MAS; none are supported by strong evidence of proven benefit.

Several other preventive measures that were commonly used in the past to prevent MAS, including amnioinfusion and intrapartum oronasopharyngeal suctioning, have now been largely abandoned as a result of findings from randomized, controlled trials.

Amnioinfusion involves the infusion of isotonic fluid (either normal saline or lactated Ringer solution) into the amniotic cavity via a transcervical intrauterine pressure catheter in an attempt to dilute the MSAF. The results of previous trials using amnioinfusion to prevent MAS have been mixed. However, given the heterogeneity of the studies and the small number of patients in each study, results must be interpreted with caution.

A 2002 Cochrane review concluded that amnioinfusion was effective in reducing the incidence of MAS, especially in centers where perinatal surveillance was limited.
; however, a 2010 update of this study found that substantive improvements in perinatal outcome were restricted to settings where facilities for perinatal surveillance are limited.
In a multinational, multicenter, randomized controlled trial involving 1998 women with thick MSAF, amnioinfusion had no significant effect on the incidence of MAS or death.

These findings and the supposition that a large number of infants born through MSAF will have aspirated meconium before amnioinfusion can be performed prompted an ACOG opinion stating that “routine prophylactic amnioinfusion for the dilution of meconium-stained amniotic fluid should be done only in the setting of additional clinical trials.”
In this same statement, however, the ACOG noted that “amnioinfusion remains a reasonable approach in the treatment of repetitive variable decelerations, regardless of amniotic fluid meconium status.”

In a randomized controlled trial involving 2514 full-term women with MSAF, Vain et al did not find intrapartum suctioning with a suction catheter to have a beneficial effect on need for endotracheal intubation, incidence of MAS, need for mechanical ventilation, and neonatal mortality.
The ACOG now recommends that “infants with MSAF should no longer receive intrapartum suctioning.

Because meconium aspiration can occur before delivery as a consequence of chronic asphyxia and infection, perhaps the most important strategy for preventing MAS is good prenatal care, including the detection and prevention of fetal hypoxemia and the avoidance of postterm deliveries.

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