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Cardiac · Core07 / 22

Unrepaired tetralogy of Fallot for MRI2-year-old girl, 11 kg, for MRI brain under general anaesthesia in the radiology suite

Cyanotic congenital lesion: balancing shunt flow with systemic and pulmonary resistance

From memory: the diagnosis and the notes are hidden. Answer each question aloud, then press Show.

Know this first

  • Spells follow crying, stress and dehydration, and falling systemic resistance.
  • Raising SVR pushes blood back through her lungs.
  • Short fasting and a calm child prevent spells.
  • No ferromagnetic equipment inside the scanner room.

The patient

2-year-old girl, 11 kg, for MRI brain under general anaesthesia in the radiology suite, investigating seizures. Unrepaired tetralogy of Fallot awaiting repair; two previous spells; haematocrit 58%. Drugs: propranolol. Vitals: HR 110, BP 88/50, SpO2 82% on air, RR 28.

The examiner asks

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  1. Consider

    What are your concerns?

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    • A 2-year-old with unrepaired tetralogy and past spells, needing GA for MRI far from theatre. Patient
    • At 2 she can't be reasoned with; crying itself can trigger her spell.
    • Her saturation of 82% reflects right-to-left flow past a narrowed outflow tract. Disease
    • Haematocrit 58% makes dehydration dangerous: thrombosis and stroke.
    • MRI suite: remote, magnetic, with delayed monitoring and little help nearby. Surgery

  2. Prepare

    How will you prepare?

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    • Keep her fasting to the minimum so she isn't dry and hypotensive. Patient
    • Oral midazolam 0.2–0.5 mg/kg so she arrives calm, not crying.
    • She takes her propranolol this morning. Disease
    • MR-safe monitor, pumps and machine; nothing ferromagnetic goes into the room. Surgery
    • Vasopressor, ketamine and fluid drawn up; cardiac team told she's here. Crisis

  3. Plan

    How do you induce and maintain anaesthesia?

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    • Gas induction with sevoflurane while she is calm, then IV access straight away. Disease
    • No IV and too upset for the mask: ketamine 4–5 mg/kg IM.
    • Once IV is in, ketamine 1–2 mg/kg IV suits her; it keeps systemic resistance up.
    • Keep her SVR up and PVR down: no hypotension, hypoxia or high airway pressures.
    • Every line de-aired; air can cross her shunt to the brain.
    • IV fluid running throughout to keep her filled.
    • Recover her in a monitored area with full resuscitation kit. After surgery

  4. Crisis

    During gas induction she screams, SpO2 falls to 55% and HR rises to 165. What do you do?

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    • Hypercyanotic spell: call for help, 100% oxygen. Crisis
    • Fold her knees to her chest to raise her systemic resistance.
    • Get IV access and give a fluid bolus.
    • If positioning and fluid fail, phenylephrine to raise SVR.
    • Deepen her or give an opioid to settle infundibular spasm; a short-acting beta-blocker if it persists.
    • Not settling: cardiac team for an urgent shunt or repair, ECMO team alerted. After surgery

Fatal mistakes

  • An inotrope during a spell.
  • No vasopressor drawn up before induction.
  • Long fasting that leaves her dehydrated.

Checked against: Stoelting 8e · Miller 10e · Barash 9e

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