Summary

Meconium Aspiration Syndrome (MAS) is a severe respiratory distress caused by the inhalation of meconium-stained amniotic fluid (MSAF) before or during birth. It is a "chemical pneumonitis" combined with mechanical obstruction. The meconium deactivates surfactant, plugs airways (ball-valve effect), and triggers intense inflammation. The most dangerous complication is Persistent Pulmonary Hypertension of the Newborn (PPHN), which causes severe hypoxemia refractory to oxygen.

Key Facts

• Definition: Respiratory distress in an infant born through MSAF with radiological changes and no other cause.
• Timing: Usually term or post-term (>40 weeks). Rare in preterms (<34 weeks).
• Mechanism: "Triple Hit": 1. Obstruction 2. Inflammation 3. Surfactant Inactivation.
• Critical Complication: PPHN (20% of cases).
• Prevention: Do NOT routinely suction vigorous babies at birth. Only suction if non-vigorous (and even then, NRP guidelines have evolved).

Clinical Pearls

The "Ball-Valve" Effect: Meconium is sticky. It lets air IN during inspiration (when airways dilate) but traps air OUT during expiration (when airways collapse). This causes massive air trapping -> Pneumothorax. Never turn the PEEP up too high blindly.

The "Honeymoon" Phase: A baby with MAS might look okay for the first hour, then rapidly deteriorate as the chemical pneumonitis sets in (6-12 hours). Never discharge a meconium baby early if they have any grunting.

Satellites of Doom: If you see "Differential Cyanosis" (Right hand sat > Foot sat by >10%), start iNO (Nitric Oxide) early. PPHN kills.

Why This Matters Clinically

MAS is a preventable cause of neonatal death. The management requires a sophisticated understanding of ventilator physiology (Time constants, HFOV) and pulmonary vascular resistance. It is the classic indication for ECMO in neonates.

Assessment

1. Inspection: "Barrel chest" (AP diameter increased). Green staining.
2. Auscultation: Coarse crackles ("wet lungs"). Diminished breath sounds if pneumothorax.
3. Circulation: Poor perfusion? (PPHN causes Right Ventricular failure -> low cardiac output).

Prognostic Factors

Follow-up

• Respiratory review at 6 months (wheeze?).
• Neurodevelopmental check at 2 years (if HIE/Seizures occurred).

Psychological Support: The Traumatic Birth

• The Father/Partner: Often witnesses the emergency "crash" delivery, the flat baby, and the resuscitation. Rates of PTSD in partners are high.
• The Mother: Often separate from the baby (Mother on postnatal ward, Baby in NICU).
• Bonding: Delayed. Promote "hand hugs" even if intubated.
• Breastfeeding: Stress delays lactogenesis II (milk coming in). Support pumping early (within 6 hours).

Discharge Checklist (Going Home)

• Oxygen Requirement: Stable in air for 48 hours?
• Feeding: Sucking well (full oral feeds)? (Hypotonia/poor suck common after illness).
• Growth: Gaining weight consistently?
• Cranial Ultrasound: Normal? (If HIE suspected).
• Parental Education: CPR training completed? (Standard for NICU grads).
• Follow-up: Appointments booked for 6 weeks and 6 months?

Long-Term Follow-Up Schedule

For severe MAS / ECMO survivors.

Key Guidelines

1. NRP 8th Edition (2021): No routine tracheal suctioning for non-vigorous infants.
2. AAP Clinical Report: Management of MAS.

Landmark Trials

Cochrane Review: Surfactant for MAS (El Shahed et al)

• Population: 326 Infants in 4 trials.
• Intervention: Bolus Surfactant vs Standard Care.
• Outcome:
  • ECMO Requirement: Significant reduction (RR 0.64). Number Needed to Treat (NNT) = 6.
  • Pneumothorax: No significant difference.
  • Mortality: No significant difference (likely due to successful ECMO salvage).
• Conclusion: Give surfactant early in moderate-severe MAS (Oi > 15) to prevent ECMO.

Wiswell Trial (Resuscitation)

• Finding: Intubation and suctioning of vigorous infants caused more harm (vocal cord injury, delay) than benefit. Changed practice instantly.

Q: Did the baby poop because they were stressed? A: Sometimes. In post-term babies, it can just be because the gut is mature. But often, a stressful event (lack of oxygen) causes the sphincter to relax. This is why we monitor them so closely for brain issues too.

Q: Will he have asthma? A: There is a slightly higher risk of wheezing in the first few years of life, as the lungs heal from the inflammation. Most children grow out of it.

Q: Why does he need the oscillator (shaking machine)? A: Traditional ventilators push big breaths in, which can pop the fragile air-trapped lungs. The oscillator vibrates air in and out gently, which protects the lungs while getting oxygen in.

Q: What is "Cooling"? A: If the baby also suffered lack of oxygen at birth (HIE), we might cool their body temperature for 72 hours to protect the brain.