What is the treatment approach for meconium aspiration syndrome (MAS)?

Treatment and Diagnosis of Meconium Aspiration Syndrome

Immediate Delivery Room Management

For nonvigorous infants born through meconium-stained amniotic fluid, do NOT perform routine tracheal intubation and suctioning—instead, immediately initiate positive pressure ventilation as needed. 1, 2

Initial Assessment at Birth

• Determine infant vigor immediately: A vigorous infant has strong respiratory effort, good muscle tone, and heart rate >100 bpm 1, 2
• Vigorous infants: Allow to remain with mother for routine newborn care; gentle bulb syringe clearing of mouth/nose only if necessary 1
• Nonvigorous infants: Proceed directly to standard resuscitation without routine laryngoscopy or tracheal suctioning 3

Critical Rationale for Avoiding Routine Suctioning

• Tracheal suctioning has NOT been shown to reduce mortality or incidence of MAS in nonvigorous infants 3
• Routine suctioning delays initiation of ventilation, which is the priority intervention 3, 2
• Suctioning can cause vagal-induced bradycardia, prolonged hypoxia, and lower oxygen saturation 2
• Exception: Consider intubation and suctioning ONLY if there is clear evidence of airway obstruction preventing effective ventilation 1

Resuscitation Protocol

Standard Resuscitation Steps

• Provide warmth under radiant heat source—hypothermia increases mortality 3, 1
• Position airway in "sniffing" position 3
• Dry and stimulate the infant 3
• Initiate positive pressure ventilation within the first minute if infant is not breathing or breathing ineffectively 3

Oxygen Management

• Start resuscitation with room air (21% oxygen) for term infants 3, 1
• Use pulse oximetry to guide oxygen therapy—attach probe to right upper extremity (preductal site) 3, 1
• Titrate oxygen to achieve normal saturation targets (70-80% in first few minutes, gradually increasing to 85-95% by 10 minutes) 3

Treatment of Established MAS

Respiratory Support Strategy

Approximately 30-50% of infants with MAS will require mechanical ventilation or CPAP. 4, 5

Conventional Mechanical Ventilation

• Use higher ventilator pressures than typical for neonatal respiratory distress to overcome poor lung compliance 4
• Employ relatively long inspiratory time and slow ventilator rate to achieve adequate oxygenation 4
• Apply positive end-expiratory pressure (PEEP) to establish and maintain functional residual capacity 1, 4

High-Frequency Ventilation

• Consider for infants with refractory hypoxemia despite conventional ventilation 4, 6
• May benefit those with significant gas trapping 4

Adjunctive Therapies

Inhaled Nitric Oxide (iNO)

• FDA-approved and effective for MAS with pulmonary hypertension 7, 4
• Significantly reduces need for ECMO (31% vs 57% in placebo, p<0.001) 7
• Dose: Start at 20 ppm, wean to 5 ppm when PaO2 >60 mmHg and pH <7.55 7
• MAS represented 49% of patients in the NINOS trial and 35% in the CINRGI trial 7
• Monitor methemoglobin levels (discontinue if >4%) 7

Surfactant Therapy

• Should be considered in selected cases with severe MAS and surfactant dysfunction 4, 8, 6
• Particularly useful when there is evidence of surfactant inhibition by meconium 4

Lung Lavage

• Consider in selected severe cases with thick meconium obstruction 4

Supportive Care

• Maintain normothermia strictly—avoid both hypothermia and hyperthermia 1
• Provide adequate oxygenation and ventilation to prevent secondary pulmonary hypertension 4
• Monitor for complications: pneumothorax (from gas trapping), persistent pulmonary hypertension, secondary infection 4, 8

Diagnosis of MAS

Clinical Criteria

MAS is diagnosed when an infant born through meconium-stained amniotic fluid develops:

• Respiratory distress (tachypnea, grunting, retractions, cyanosis) 8
• Hypoxemia requiring supplemental oxygen 4
• Radiographic findings consistent with aspiration (patchy infiltrates, hyperinflation, atelectasis) 8
• Exclusion of other causes of respiratory distress 8

Epidemiology

• Meconium-stained amniotic fluid occurs in 5-15% of deliveries 2
• Only 3-5% of infants born through MSAF develop MAS 2
• More common in post-term pregnancies (≥42 weeks) 2

Common Pitfalls to Avoid

• Delaying positive pressure ventilation to perform suctioning in nonvigorous infants leads to prolonged hypoxia 2
• Focusing on meconium presence rather than infant vigor leads to inappropriate interventions 2
• Using 100% oxygen routinely when room air is appropriate for term infant resuscitation 3, 1
• Inadequate ventilator pressures in established MAS—these infants often need higher pressures than typical 4
• Missing pulmonary hypertension component—consider iNO early if oxygenation remains poor despite adequate ventilation 7, 4

Preparedness Requirements

• Skilled personnel capable of tracheal intubation should be present at delivery when MSAF is identified 1, 2
• Equipment for advanced resuscitation must be immediately available 3