Sick neonate — duct-dependent collapse and parallel differentials

This is a well-then-sick neonate at the classic 24–72 hour ductal-closure window. The pre/post-ductal saturation gap, weak femorals and four-limb BP differential make duct-dependent left-sided obstructive congenital heart disease (e.g. coarctation, HLHS, interrupted arch) the leading reversible diagnosis until proven otherwise.^[1][4] In parallel, neonatal sepsis remains mandatory cover because the presentations overlap and fever is often absent.^[2] Metabolic crises (including salt-wasting CAH at 1–3 weeks) and hypoglycaemia are also on the checklist even when glucose is currently acceptable.

Immediate parallel actions

1. Resuscitation bay, warm, monitor, airway support; target age-appropriate saturations with oxygen/CPAP while recognising pure cyanotic shunt may not correct.
2. IV/IO access; bloods including gas, lactate, FBC, cultures; do not delay therapy for imaging.
3. Prostaglandin E1 (alprostadil) 0.05 µg/kg/min (standard starting dose) IV started on clinical suspicion — never wait for echo.^[1][3][4]
4. Pre-empt PGE1 apnoea: prepare intubation; strongly consider elective intubation before retrieval — respiratory depression occurred in 28 per cent with 8 per cent needing ventilation.^[3]
5. Empiric antibiotics after cultures if no delay: cefotaxime 50 mg/kg IV + ampicillin 50 mg/kg IV (not ceftriaxone); add aciclovir 20 mg/kg if HSV plausible.^[2]
6. Cautious fluid: 5 mL/kg balanced crystalloid aliquots if cardiogenic physiology suspected (not blind 20 mL/kg boluses).
7. Urgent echo after PGE1 starts; activate NETS/paediatric cardiac retrieval with ventilated transfer capability.
8. Full septic workup when stable (LP, SPA/catheter urine — never bag urine).