Meconium Aspiration Syndrome

Introduction

• Meconium is a viscous green-black substance composed of swallowed amniotic fluid, gastrointestinal epithelial cells, and intestinal secretions produced by the fetus.¹
• MSAF occurs when fetal colonic activity is stimulated before delivery, leading to the passage of meconium in utero.
  • MSAF is present in 10–15% of all deliveries, most commonly among term and postterm infants.¹
• General risk factors include thick meconium, fetal distress, postterm pregnancy, rupture of membranes ≥ 18 hours, chorioamnionitis, shoulder dystocia, oligohydramnios, vaginal breech delivery, and intrauterine growth restriction.^5,6
  • Antenatal and intrapartum factors—such as chronic placental insufficiency, postterm pregnancy, and intrauterine stress—can increase the likelihood of in-utero meconium passage and aspiration.^5,6
• MAS occurs when meconium-containing fluid is aspirated into the fetal or neonatal airway, typically during gasping or agonal respirations in response to hypoxia or distress.²
  • MAS develops in approximately 2–9% of neonates born through MSAF and represents a form of chemical pneumonitis with airway obstruction, inflammation, and surfactant inactivation.
  • Pathophysiologic effects include airway obstruction, alveolar inflammation, surfactant washout, decreased compliance, and pulmonary vasoconstriction leading to persistent pulmonary hypertension of the newborn (PPHN).^1,3,4
  • Clinical severity ranges from mild respiratory distress to severe hypoxemia with PPHN requiring mechanical ventilation or extracorporeal membrane oxygenation.
  • MAS is now recognized as a multifactorial disorder involving both antenatal inflammation and intrapartum hypoxia rather than purely postnatal aspiration1.
• Complications may include air leak syndromes (pneumothorax, pneumomediastinum), long-term reactive airway disease, and neurodevelopmental impairment following severe hypoxia.^1,2
• Systemic inflammatory response: Meconium in the airways and gastrointestinal tract can trigger cytokine release, correlating with disease severity.^1,4
• Mortality remains up to 5%, with higher rates associated with thick meconium, fetal distress, and delayed resuscitation1.

Management

• General Principles
  • MAS is no longer considered a purely postnatal aspiration event; aspiration often occurs in utero in the setting of fetal hypoxia or distress.
  • Routine intrapartum oropharyngeal or nasopharyngeal suctioning does not prevent MAS and is not recommended.²
  • Management focuses on supportive ventilation, oxygenation, and treatment of pulmonary hypertension, rather than aggressive airway suctioning.²
• Initial delivery room management
  • All infants born through MSAF should receive standard neonatal resuscitation per Neonatal Resuscitation Program (NRP) 2021.³
  • Vigorous infants (good tone, spontaneous respirations, HR more than 100 bpm)^1,3,4:
    • Routine tracheal or oropharyngeal suctioning → not indicated.
    • Provide routine care and observation.
  • Nonvigorous or depressed infants (poor tone, inadequate breathing)^1,3,4:
    • Prioritize initial steps of resuscitation — warming, drying, positioning, and clearing secretions as needed.
    • If airway obstruction is suspected, consider tracheal suctioning before initiating positive pressure ventilation.
  • Amnioinfusion for meconium dilution is not recommended.
• Historical perspective:
  • Earlier management presumed that meconium aspiration occurred after birth with the onset of breathing.
  • This led to routine suctioning of the oropharynx and trachea at delivery, including suctioning after head delivery and again after visualization by the resuscitation team.
  • Subsequent studies showed these techniques did not reduce the incidence or severity of MAS.
  • MAS is now understood to result from in utero aspiration in the setting of fetal hypoxia, rather than a purely postnatal event.
• Routine oropharyngeal suctioning is no longer recommended, as it may cause several adverse effects.^1-4
  • Vagal bradycardia
  • Mucosal irritation and increased secretions
  • Airway trauma and infection risk
  • Apnea

Anesthetic Management

• Anesthesia providers may be called to assist with neonatal resuscitation when pediatric or neonatal teams are not immediately available.
• Familiarity with NRP guidelines is essential; many obstetric anesthesiologists maintain NRP certification.
• During deliveries complicated by MSAF, anesthesia personnel can contribute expertise in:
  • Airway management (e.g., mask ventilation, endotracheal intubation, suctioning if indicated).
  • Vascular access and medication administration during neonatal resuscitation
  • Maternal support during emergency interventions, including emergent cesarean delivery or postpartum complications.
• Delivery room considerations for an anesthesiologist include:
  • Anesthesia presence is often requested for high-risk deliveries, especially in settings where neonatology support is not immediately available, including:
    • Thick meconium or nonreassuring fetal heart tracing.
    • Operative vaginal or emergent cesarean delivery.
    • Known fetal distress or depression at delivery.
  • Providers should ensure:
    • Immediate availability of airway equipment suitable for neonatal resuscitation (mask, laryngoscope, endotracheal tube, suction).
    • Coordination with obstetric and pediatric teams to clarify roles before delivery.
    • Rapid transition to neonatal or neonatal intensive care unit personnel once initial stabilization is achieved.
• Anesthetic Implications for the Parturient
  • Maternal anesthesia choice (neuraxial vs general) generally does not alter MAS risk, but:
    • Emergent cesarean delivery for fetal distress may necessitate rapid-sequence induction, requiring anticipation of neonatal depression.
    • Maternal hypotension or hypoxemia should be minimized, as these contribute to fetal hypoxia and possible meconium passage.
  • When general anesthesia is required, ensure neonatal resuscitation personnel are present and prepared for potential airway intervention.

Conclusion and Guidelines

• Routine tracheal suctioning is not indicated in vigorous infants, but anesthesia teams may assist with tracheal intubation and suction in nonvigorous neonates if obstruction is suspected.
• Communication and preparation between obstetric, anesthesia, and pediatric teams are critical for optimal outcomes.
• NRP certification and familiarity with neonatal airway management are strongly encouraged for obstetric anesthesia providers.
• American College of Obstetricians and Gynecologists, American Academy of Pediatrics, and International Liaison Committee on Resuscitation have provided statements about suctioning and resuscitation.