Meconium aspiration syndrome — formative SAQs

Question 1

A term male infant is born at 41 weeks' gestation via emergency caesarean section for fetal distress through thick, pea-soup meconium-stained amniotic fluid. At 1 minute he has poor tone, is gasping, and has a heart rate of 70/min. He is intubated and ventilated; by 2 hours of age his FiO2 requirement is 0.7, with pre-ductal SpO2 90 per cent and post-ductal SpO2 72 per cent. Chest radiograph shows coarse bilateral infiltrates with hyperinflation. [7]

(a) Describe your immediate delivery-room management and justify it. (6 marks) [1]

(b) What is the most likely cause of the wide pre- to post-ductal saturation gradient, and how would you confirm it? (4 marks) [6]

(c) Outline the stepwise escalation of respiratory support for this infant. (6 marks) [2]

(d) State four important elements of supportive care. (4 marks) [7]

Model Answer

(a) The infant is non-vigorous (poor tone, gasping, heart rate below 100). Per current NRP/ILCOR guidance, the presence of meconium does not mandate tracheal suctioning; a non-vigorous infant receives standard NRP resuscitation with positive-pressure ventilation (here via intubation). Routine intubation-with-suction was abandoned in 2015 (no benefit, harmful delay), and intrapartum oronasal suctioning before the shoulders was abandoned after the Vain et al. trial of 2004 [1].

(b) The likely cause is persistent pulmonary hypertension of the newborn (PPHN) with right-to-left ductal shunting, producing post-ductal desaturation disproportionate to the radiographic infiltrates. Confirmation is by echocardiography showing elevated pulmonary pressures with right-to-left ductal or foramen-ovale shunt, after excluding structural congenital heart disease [6].

(c) Stepwise escalation: warmed humidified oxygen titrated to SpO2 90 to 95 per cent, then CPAP if FiO2 above about 30 per cent, then intubation and lung-protective ventilation for respiratory failure, then exogenous surfactant for moderate-to-severe MAS (meconium inactivates surfactant), then inhaled nitric oxide 20 ppm for PPHN (oxygenation index above 15 to 25), then ECMO referral if OI above 40 and refractory [2][6].

(d) Empiric broad-spectrum antibiotics pending cultures (sepsis indistinguishable); normoglycaemia and normothermia; correction of acidosis (target pH above 7.25) with permissive hypercapnia rather than hyperventilation; adequate sedation and analgesia to avoid pulmonary hypertensive crises; fluid and electrolyte management [7].

Question 2

A 40-week infant develops respiratory distress at 1 hour of age after delivery through moderately meconium-stained liquor. He is tachypnoeic (RR 75) with grunting and recessions in 30 per cent oxygen. [7]

(a) Define meconium aspiration syndrome. (3 marks) [7]

(b) Outline the pathophysiology of MAS under four mechanisms. (8 marks) [7]

(c) Why is surfactant therapy beneficial in moderate-to-severe MAS, and what is the evidence? (4 marks) [2]

(d) What determines the long-term neurodevelopmental prognosis? (5 marks) [4]

Model Answer

(a) MAS is respiratory distress in an infant born through meconium-stained amniotic fluid, with characteristic chest radiograph changes (coarse infiltrates, hyperinflation), once other causes of neonatal respiratory distress are excluded [7].

(b) Four parallel mechanisms: (1) airway obstruction — particulate meconium and mucus produce a ball-valve effect causing air trapping, hyperinflation and air leak, with distal atelectasis; (2) surfactant inactivation — bile salts and enzymes inhibit endogenous surfactant, producing an RDS-like physiology; (3) chemical pneumonitis — inflammatory cascade with neutrophil influx, oedema and epithelial injury; (4) infection risk — meconium is a bacterial growth medium. In severe cases, hypoxaemia and acidosis drive PPHN with right-to-left shunting [7][6].

(c) Meconium inactivates endogenous surfactant; exogenous surfactant restores surface-tension lowering. Cochrane systematic review evidence shows improved oxygenation and reduced need for ECMO in moderate-to-severe MAS [2].

(d) Long-term neurodevelopmental outcome is determined predominantly by whether the infant sustained hypoxic-ischaemic encephalopathy, since the same fetal hypoxia that causes meconium passage and gasping injures the brain. Uncomplicated MAS without HIE generally has a normal neurological outcome. Mortality (about 3 to 5 per cent) is confined largely to the severe/PPHN subset [4][7].