Neonatal respiratory distress — diagnostic approach — formative SAQs

SAQ 1 — Differentiating RDS, TTN and MAS in the first hour (20 marks, ~15 minutes)

Three newborns are admitted to the neonatal unit within the same hour: a 28-week preterm infant with grunting and rising oxygen need; a term infant born by elective caesarean with mild tachypnoea at 2 hours; and a term post-dates infant born through meconium-stained liquor with coarse respiratory distress. [1]

Questions

1. For each infant, state the most likely diagnosis and the single most discriminating risk factor or feature. (6 marks) [1]
2. Describe the expected chest X-ray pattern for each infant and explain how it confirms the mechanism. (6 marks) [5]
3. Outline the first-line management for each infant, naming the threshold for surfactant in the preterm infant and the evidence supporting it. (5 marks) [1] [3]
4. State one critical differential that must be excluded in the term infant whose saturations do not improve with oxygen, and the immediate action. (3 marks) [5]

Model answer (must-hit)

1. Preterm infant: respiratory distress syndrome (RDS), discriminated by gestation below 34 weeks and surfactant deficiency. Term caesarean infant: transient tachypnoea of the newborn (TTN), discriminated by elective caesarean before labour (bypassed catecholamine-driven lung liquid clearance). Post-dates infant: meconium aspiration syndrome (MAS), discriminated by meconium-stained liquor. [1]
2. RDS: symmetric reticulogranular (ground-glass) pattern with air bronchograms and low lung volumes, reflecting diffuse alveolar collapse. TTN: perihilar streaking, fluid in the minor fissure, and mild hyperinflation, reflecting retained fetal lung liquid. MAS: coarse patchy infiltrates with hyperinflation and possible pneumothorax, reflecting airway obstruction (ball-valve) and chemical pneumonitis. [5]
3. RDS: start CPAP 5–6 cm H₂O; give exogenous (animal-derived) surfactant by a less invasive technique (LISA/INSURE) when FiO₂ exceeds 0.30, supported by the 2022 European Consensus Guidelines and the SUPPORT trial showing CPAP-first is non-inferior to prophylactic intubation. TTN: supportive oxygen titrated to target, minimal handling, expect resolution in 24–72 hours. MAS: ventilation for the depressed infant, no routine tracheal suctioning, consider surfactant for severe disease and inhaled nitric oxide for PPHN. [1] [3] [4]
4. A term infant with refractory hypoxaemia and a normal chest X-ray must be assumed to have a duct-dependent congenital heart lesion; check pre/post-ductal saturations, start an intravenous prostaglandin E1 infusion at 0.01–0.05 microgram/kg/min, and obtain urgent echocardiography. [5] [6]