Congenital heart disease presenting in the newborn — formative SAQs

SAQ 1 — The day-three collapsed neonate (20 marks, ~15 minutes)

A term infant was well at discharge on day 2 with normal pulses and a passed pulse-oximetry screen. He returns on day 3 with poor feeding, mottled cool peripheries, tachypnoea, weak femoral pulses and a capillary gas showing a metabolic acidosis. ^[6]

Questions

1. State the most likely diagnosis category and why the timing and signs point to it. (4 marks) ^[6]
2. Give your immediate first-hour management, naming the key drug, its dose and the principle that governs its timing. (6 marks) ^[9]
3. Outline the bedside assessment and first-line investigations that confirm the direction of the diagnosis, and state why the definitive test does not delay treatment. (5 marks) ^[9]
4. Explain to the parents, in plain language, why a baby who looked well and passed screening can still collapse on day three. (5 marks) ^[7]

Model answer (must-hit)

1. This is a duct-dependent obstructive lesion until proven otherwise — classically coarctation of the aorta or interrupted aortic arch. The baby was well while the ductus arteriosus supplied the lower body; as the duct functionally closes at 24 to 48 hours, systemic flow falls and the baby shocks with weak femoral pulses and metabolic acidosis. The weak femoral pulses and the day-three timing are the decisive clues. ^[6]
2. Stabilise the ABCs, establish access, correct hypoglycaemia, hypocalcaemia and acidosis, give empiric antibiotics to cover sepsis, and start prostaglandin E1 (alprostadil) 0.01 to 0.05 mcg/kg/min intravenously to reopen the duct. The governing principle is that prostaglandin is started the moment a duct-dependent lesion is suspected — before the echocardiogram — because the echo confirms but does not treat. Anticipate prostaglandin-induced apnoea and have intubation equipment ready, with a low threshold for elective intubation before retrieval. ^[9]
3. Assess colour, palpate right brachial and femoral pulses simultaneously (brachio-femoral delay or absent femorals), measure four-limb blood pressure (a gradient suggests coarctation), examine for hepatomegaly and a murmur, and run pre/post-ductal oximetry. Send a capillary gas with lactate, glucose, ionised calcium, cultures and a chest radiograph. The definitive test — echocardiography — defines the anatomy but is obtained in parallel; it never delays prostaglandin, because the diagnosis is clinical at the point of action. ^[9]
4. The ductus arteriosus is a fetal blood vessel that was keeping the lower body supplied; it closes over the first day or two. While it was open the baby looked well and passed the oxygen screen, because blood was still reaching the body. As it closed, the body lost that blood supply and the baby became sick. Screening is designed to catch most babies before this happens, but it cannot catch every lesion, which is why we watch for warning signs after going home. ^[7]