Neonatal cyanosis and collapsed neonate — formative SAQs

SAQ 1 — The day-3 term infant with sudden cyanosis (20 marks, ~15 minutes)

A 3-day-old term infant, previously feeding well and discharged home, is brought to the emergency department dusky and limp. The tongue and lips are blue. The respiratory rate is 65 with mild recession. The right-arm oxygen saturation is 82% and the right-leg saturation is 80%. There is no murmur. The antenatal scans and the newborn pulse-oximetry screen were reportedly normal. ^[3]

Questions

1. State whether this is central or peripheral cyanosis, and name the most likely diagnostic category, justifying your answer from the clinical features. (5 marks) ^[3]
2. Describe your immediate management, including a specific drug, its dose and the timing of its administration relative to echocardiography. (6 marks) ^{[3] [6]}
3. Describe the hyperoxia test and the PaO2 cut-points that distinguish cyanotic heart disease from a pulmonary cause. (5 marks) ^[3]
4. State the sepsis consideration and the empiric antibiotic regimen you would give alongside the cardiac work-up. (4 marks) ^[8]

Model answer (must-hit)

1. This is central cyanosis: the tongue and lips are blue, signalling arterial desaturation (peripheral acrocyanosis alone has a pink tongue). The most likely diagnostic category is cyanotic or duct-dependent congenital heart disease. The day-3 onset in a previously well term infant with cyanosis and relatively little respiratory distress is the classic presentation of a duct-dependent lesion as the ductus closes; the normal antenatal scan and passed pulse-oximetry screen do not exclude critical congenital heart disease. ^[3]

2. Immediate management is ABCDE stabilisation — airway, oxygen to target saturations, glucose and temperature, IV access — with simultaneous pre-/post-ductal oximetry, blood gas, cultures, FBC/CRP and chest X-ray. The time-critical drug is prostaglandin E1 (alprostadil), started NOW at 0.01 to 0.05 mcg/kg/min IV continuous, titrating up to 0.1 to 0.4 mcg/kg/min to the lowest effective dose, BEFORE the echocardiogram. The principle is absolute: if a duct-dependent lesion is possible, re-open the ductus first; the risk of an unnecessary infusion is far lower than the risk of a closed duct. ^{[3] [6]}

3. The hyperoxia test places the infant in 100% oxygen for about 10 minutes and measures the arterial PaO2. A PaO2 that rises above 150 mmHg argues strongly against cyanotic heart disease and points to a pulmonary, neurological, metabolic or septic cause. A PaO2 that stays below 100 mmHg supports a right-to-left shunt and cyanotic heart disease. The 100 to 150 mmHg grey zone includes PPHN, mixed lesions and severe lung disease — treat the patient, not the number. ^[3]

4. The cyanotic neonate is septic until proven otherwise, so blood cultures are taken and empiric antibiotics given alongside the cardiac work-up. The typical regimen is benzylpenicillin plus an aminoglycoside such as gentamicin, adjusted to local antimicrobial guidance and weight. Sepsis is both a direct cause of cyanosis and a cause of collapse, and covering it must never be omitted. ^[8]