A 3-week-old with poor feeding and a murmur
A 3-week-old term male, born at home to a 32-year-old primigravida, is brought to the emergency department at 2 a.m. by his grandmother because he has fed poorly for 24 hours and is 'breathing fast.' Birth weight was 3.1 kg; he now weighs 2.7 kg. He has been exclusively breastfed, with feeds reduced from 8 to 4 per day. Examination: axillary temperature 36.4 °C, respiratory rate 72/min, heart rate 190/min, capillary refill 4 seconds, mottled extremities. Femoral pulses are barely palpable; brachial pulses are normal. There is a soft systolic murmur at the left sternal edge. The liver edge is 4 cm below the costal margin. Preductal SpO2 is 92% on room air, postductal 88%. Capillary glucose is 2.1 mmol/L. A venous blood gas shows pH 7.24, lactate 6.8 mmol/L.
1. State your leading diagnosis and the immediate resuscitative priorities in order.
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Leading diagnosis: duct-dependent systemic circulation - critical coarctation of the aorta or interrupted aortic arch - now presenting in cardiogenic shock with possible ductal closure.
Immediate priorities (in order):
- Airway/breathing: high-flow oxygen; be ready to intubate for respiratory failure; avoid hyperoxia but do not withhold oxygen in shock.
- Circulation: secure IV/IO access, draw blood cultures and glucose before antibiotics if no delay. Start a prostaglandin E1 infusion (0.01–0.05 microgram/kg/min) empirically - do not wait for echocardiography in a shocked neonate with weak femoral pulses. Expect apnoea; have a bag-mask ready.
- Glucose: treat the 2.1 mmol/L with 2 mL/kg 10% dextrose bolus, then maintenance glucose-containing fluid.
- Volume and inotropy: cautious 10 mL/kg crystalloid bolus with reassessment; start inotrope (e.g., adrenaline or milrinone per local protocol) for myocardial dysfunction.
- Correct acidosis and electrolytes after perfusion is addressed; avoid bicarbonate as first-line.
- Urgent echocardiography and transfer to a cardiac centre once stabilised.
2. Explain why the preductal and postductal saturations differ and what the difference does and does not tell you.
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In coarctation or interrupted arch, the descending aorta is supplied by the ductus arteriosus from the pulmonary artery. When pulmonary vascular resistance is still high, desaturated pulmonary arterial blood flows right-to-left through the duct into the descending aorta, lowering postductal saturation relative to the preductal (right arm) value. A difference of ≥3–5% or a postductal saturation <90% is a recognised red flag.
What it tells you: it supports a duct-dependent systemic lesion with right-to-left ductal shunting, and it is a reason to start prostaglandin urgently.
What it does not tell you: it is not specific - the same pattern is seen in persistent pulmonary hypertension of the newborn and in some other duct-dependent lesions. A normal gradient does not exclude critical coarctation, because if the duct has closed or the shunt is predominantly left-to-right, saturations may be equal. The diagnosis rests on pulses, blood pressure in all four limbs, and echocardiography.
3. The family asks why the baby was not detected earlier, given that he was born at home and had no newborn screening. Outline the examination findings at the newborn check that should have raised suspicion, and the ethical and practical issues in this presentation.
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Findings that should prompt referral at any newborn check:
- Weak or absent femoral pulses with normal brachial pulses, or a palpable radial–femoral delay.
- Four-limb blood pressure difference: systolic in the right arm >90th centile with lower limb pressure lower than arm pressure.
- A systolic murmur at the left sternal edge or back, and hepatomegaly.
- Poor feeding, tachypnoea, or a fall in weight >10% from birth weight.
- Pre/postductal saturation difference.
Ethical and practical issues:
- The absence of newborn screening and of a documented newborn examination is a systems failure, not simply a family failing; the response should be non-judgemental and focused on the child's interests.
- The baby is in a time-critical emergency; consent for prostaglandin and transfer should be obtained from the grandmother if a parent cannot be reached, under the emergency doctrine, and parental consent sought as soon as possible.
- Explain honestly that the condition may have been undetectable at birth and that late presentation is well described; avoid assigning blame.
- Involve a social worker and the primary care team to support the family, and document the discussion. Report concerns through the appropriate child-protection pathway only if there are other indicators of neglect.