Neonatal cyanosis and collapsed neonate — branching viva

Station opening

Examiner: "Define neonatal cyanosis and tell me the first bedside decision in a blue newborn." [3]

Strong candidate (must-hit)

• Defines cyanosis as the blue discolouration that appears when deoxyhaemoglobin exceeds about 3 g/dL; notes it is a late and unreliable sign of hypoxaemia and that an anaemic infant may never look blue. States that the first decision is to distinguish central cyanosis (blue tongue and mucous membranes — pathological, arterial desaturation) from benign peripheral acrocyanosis (blue hands and feet, pink tongue) — and that the tongue is the single site that settles it. [3]

Weak candidate

• "Cyanosis is being blue, usually from a lung problem." [3]

Branch A — The day-3 sudden collapse (duct-dependent lesion)

Examiner: "A 3-day-old term infant, previously well, is now dusky with blue tongue and lips but little respiratory distress. The right-arm saturation is 82%. The antenatal scans and the pulse-oximetry screen were normal. What is your immediate management, and what drug do you not delay?" [3]

Strong

• States that a term infant collapsing on day 2 to 7 has a duct-dependent cardiac lesion until proven otherwise; the normal scans and passed screen do not exclude it. Immediate management is ABCDE stabilisation, simultaneous pre-/post-ductal oximetry, blood gas, cultures, FBC/CRP and chest X-ray, and empiric antibiotics (benzylpenicillin plus an aminoglycoside) because the cyanotic neonate is septic until proven otherwise. The drug that is NOT delayed is prostaglandin E1 (alprostadil), started now at 0.01 to 0.05 mcg/kg/min IV continuous, titrating to 0.1 to 0.4 mcg/kg/min, BEFORE the echocardiogram — because re-opening the ductus is life-saving and the risk of an unnecessary infusion is far lower than the risk of a closed duct. [3] [6]

Weak

• "Send for an echocardiogram and start oxygen while waiting for cardiology." [3]

Branch B — The oxygen-refractory blue infant

Examiner: "A 12-hour-old term infant stays cyanotic in 100% oxygen. The PaO2 is 130 mmHg, the pulse oximeter reads 85% and will not climb, and the blood looks chocolate-brown. What is the diagnosis, the mechanism, and the treatment with its caution?" [10]

Strong

• Diagnoses methaemoglobinaemia: the iron in haemoglobin is locked in the ferric state and cannot bind oxygen, so the blood carries less oxygen regardless of the inspired concentration, and raising FiO2 cannot help. The pulse oximeter reads falsely high around 85% because methaemoglobin absorbs at both oximetry wavelengths and is misread. Confirms with a methaemoglobin level (co-oximetry). Treats a symptomatic infant with methylene blue 1 to 2 mg/kg IV, with specialist input, and names the caution of glucose-6-phosphate dehydrogenase deficiency, in which methylene blue is ineffective and may cause haemolysis. [10]

Weak

• "It must be a heart problem — start prostaglandin E1." [10]

Branch C — The shocky infant with weak femoral pulses

Examiner: "A 5-day-old term infant presents in shock with weak femoral pulses, a capillary refill of 5 seconds, and a metabolic acidosis. The blood pressure is lower in the legs than the arms. Which duct-dependent lesion category is this, and why does it present this way?" [2]

Strong

• Identifies an obstructive duct-dependent LEFT-heart lesion — coarctation of the aorta, interrupted arch, hypoplastic left heart, or critical aortic stenosis — in which systemic blood flow depends on the ductus arteriosus. As the duct closes (under prostaglandin withdrawal and rising oxygen after birth), systemic flow collapses and the infant presents in shock with weak femoral pulses, a blood-pressure gradient between the upper and lower limbs, hepatomegaly and a metabolic acidosis, typically on day 2 to 7. The management is prostaglandin E1 to re-open the ductus, fluids and inotropes for shock, and empiric antibiotics while the work-up proceeds. [2] [3]

Weak

• "This is septic shock — give fluids and antibiotics." [2]

Branch D — The apnoea trap on prostaglandin

Examiner: "An infant on prostaglandin E1 for a confirmed duct-dependent lesion develops episodic apnoea with a rising CO2. The team suggests stopping the infusion. What do you do?" [6]

Strong

• States that apnoea is a recognised side-effect of prostaglandin E1 but is anticipated, not feared: the infant is intubated and ventilated as needed, but the infusion is NOT stopped, because stopping sacrifices the ductal rescue keeping the infant alive. The infusion is held at the lowest effective dose to minimise side-effects, and definitive surgery or catheter intervention is expedited. Names that gastrointestinal adverse effects also rise with the cumulative dose, reinforcing the lowest-effective-dose principle. [6]

Weak

• "Stop the prostaglandin — the apnoea is dangerous." [6]

Close

Examiner: "Summarise your approach to the cyanotic or collapsed neonate in one sentence." [3]

Strong

• "I confirm central cyanosis by checking the tongue; I treat a day-2-to-7 collapse as duct-dependent until proven and start prostaglandin E1 before the echo; I read the pre-/post-ductal difference and run the hyperoxia test to decide whether the heart is the problem; I cover sepsis empirically; and when cyanosis is oxygen-refractory with an SpO2 stuck at 85%, I think methaemoglobinaemia and send a methaemoglobin level." [3] [6] [10]