The preterm infant who stops weaning — a haemodynamically significant PDA

Clinical information for the examiner

Setting: Tertiary NICU, day 5 of life. The infant is ventilated on volume-targeted ventilation (PIP 16, PEEP 5, rate 30, FiO₂ 0.42) for respiratory distress syndrome; antenatal steroids were given and one dose of surfactant administered at birth. The creatinine has risen from 78 to 102 µmol/L. [13]

On your arrival:

• Heart rate 158, SpO₂ 92%, blood pressure 52/24 (mean 34), widened pulse pressure 28. [13]
• Pulses bounding at the brachial and femoral arteries; precordium hyperdynamic. [13]
• Soft systolic murmur at the upper left sternal border. [13]
• Urine output 0.8 mL/kg/h (was 2.5). [13]

Functional echocardiogram (provided): structurally normal heart; duct diameter 2.1 mm with left-to-right flow; left atrial-to-aortic root ratio 1.7; diastolic flow reversal in the descending aorta; increased left ventricular output. [13]

Task 1 — Assess haemodynamic significance (3 marks)

The candidate should integrate the bedside and echocardiographic findings. [13]

1. Bedside shunt signature: bounding pulses, hyperdynamic precordium, widened pulse pressure with a low diastolic (52/24). [13]
2. End-organ compromise: oliguria and rising creatinine (systemic steal), escalating oxygen need (pulmonary over-circulation). [13]
3. Echo constellation: duct 2.1 mm, LA:Ao 1.7, diastolic flow reversal in the descending aorta. [13]

Pass criterion: candidate states that significance is a constellation integrating the clinical end-organ signs with the echo, not a single threshold, and names the key markers. [13]

Task 2 — Expectant management first (3 marks)

The candidate must lead with expectant, supportive care, not the drug cupboard. [13]

• Correct hypoxia and acidosis (both relax the ductal smooth muscle); treat anaemia to preserve oxygen delivery. [13]
• Lung-protective ventilation with permissive hypercapnia; avoid fluid overload and modestly restrict intake. [13]
• Support the circulation with a vasoconstrictor if hypotension persists (volume boluses rarely help the steal); reduce or pause feeds to protect the gut. [13]
• Trend the urine output, creatinine, blood pressure and ventilator needs serially. [13]

Pass criterion: candidate frames expectant management as an evidence-based strategy, not inaction, and cites that most ducts close spontaneously. [13]

Task 3 — Pharmacological closure and doses (3 marks)

If the end-organ compromise progresses despite supportive care, pharmacological closure is indicated. [2]

• Ibuprofen: 10 mg/kg then 5 mg/kg at 24 and 48 hours (first-line). [2]
• Paracetamol: 15 mg/kg every six hours — preferred here given the rising creatinine, avoiding the renal vasoconstriction of the cyclo-oxygenase inhibitors. [4]
• Indomethacin: 0.2 mg/kg every 12 to 24 hours for three doses. [2]

Pass criterion: candidate gives correct doses and chooses paracetamol with a renal-sparing rationale, citing the Mitra network meta-analysis that all three beat placebo with ibuprofen and paracetamol favoured over indomethacin for safety. [2]

Task 4 — Evidence, safety and the ligation debate (2 marks)

Safety check: before any closure, confirm a structurally normal heart and exclude a duct-dependent circulation — closing a duct-dependent lesion is catastrophic. [13]

Evidence: the BeNeDuct trial (NEJM 2023) showed early ibuprofen was no better than expectant care, and PDA-TOLERATE showed treating at one week did not reduce death or bronchopulmonary dysplasia — anchoring the treat-the-infant approach. [1] [6]

Ligation: reserved for failure or contraindication; the association with adverse outcomes is confounded by indication (causality or bias). [10]