Meconium aspiration syndrome — clinical reasoning case

Clinical Presentation

A 3.8 kg male infant is delivered at 41+4 weeks' gestation by emergency caesarean section for fetal bradycardia and thick, pea-soup meconium-stained amniotic fluid. Apgar scores are 2, 4, and 6 at 1, 5 and 10 minutes. Pregnancy was complicated by gestational hypertension and reduced fetal movements in the preceding 24 hours. [7]

At delivery the infant is floppy, apnoeic and centrally cyanosed with heart rate 70/min. He is resuscitated with positive-pressure ventilation via mask then intubated; heart rate rises to 140. Cord blood gases show arterial pH 7.02, base excess minus 12 [7].

Progression

By 2 hours of age he is in 50 per cent oxygen with marked subcostal retractions, grunting and a barrel-shaped chest. Auscultation reveals coarse bilateral crackles. Pre-ductal SpO2 is 92 per cent; post-ductal SpO2 is 70 per cent. Chest radiograph shows coarse, fluffy bilateral infiltrates with hyperinflation and a small right pneumothorax. [7]

By 4 hours, on mean airway pressure 13 cmH2O and FiO2 0.95, pre-ductal SpO2 is 88 per cent, post-ductal 64 per cent. Pre-ductal PaO2 is 38 mmHg. [6]

Questions

1. What is the diagnosis and what two major complications has he developed?
2. Calculate the oxygenation index and state its significance.
3. Outline the complete management plan from this point. [6]

Model Answers

1. The diagnosis is meconium aspiration syndrome (MSAF + early distress + characteristic CXR, excluding other causes). The two major complications are persistent pulmonary hypertension of the newborn (PPHN) — indicated by the wide pre-/post-ductal gradient and disproportionate hypoxaemia — and a right pneumothorax (air-leak complication of ball-valve obstruction). Coexisting hypoxic-ischaemic encephalopathy is also likely given the cord pH 7.02 and low Apgars [7][6].

2. Oxygenation index equals (mean airway pressure multiplied by FiO2 multiplied by 100) divided by PaO2, which is (13 times 0.95 times 100) divided by 38, approximately 32.5. This exceeds the threshold (above 15 to 25) for inhaled nitric oxide and is approaching the ECMO threshold (above 40); he warrants urgent iNO and preparation for possible ECMO [6].

3. Management plan:

• Drain the pneumothorax — needle aspiration followed by chest drain given clinical significance and the need for positive-pressure ventilation [7].
• Echocardiography to confirm PPHN, estimate pulmonary pressures, demonstrate right-to-left shunt and exclude structural CHD.
• Inhaled nitric oxide 20 ppm as the selective pulmonary vasodilator [6].
• Surfactant administration (meconium inactivates endogenous surfactant; Cochrane-supported for moderate-to-severe MAS) [2].
• Lung-protective ventilation — low tidal volume, permissive hypercapnia, target pH above 7.25, avoid hyperventilation.
• Empiric broad-spectrum antibiotics pending cultures.
• Supportive care — normoglycaemia, normothermia, careful fluid and electrolyte management, adequate sedation and analgesia.
• Assess for therapeutic hypothermia within the 6-hour window given cord pH 7.02 and likely HIE.
• Early transfer to a tertiary NICU with iNO and ECMO capability; activate ECMO pathway if OI climbs past 40 [6].
• Counsel parents regarding severity, the role of HIE in prognosis, and the likely need for neurological follow-up.

Discussion Points

• Why vigour — not meconium — governs delivery-room management [1].
• The rationale and evidence for surfactant in MAS [2].
• Why long-term outcome is determined by HIE rather than the lung disease itself [7].