Active URI and asthma for MRI under GA3-year-old boy, 15 kg, for elective MRI brain under general anaesthesia in the radiology suite

The patient

The examiner asks

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1. Consider

   What are your concerns?

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   • A feverish 3-year-old with a cold and asthma, booked for elective MRI under general anaesthesia. Patient
   • At 3 he uses more oxygen per kilo than an adult, so he desaturates fast in any airway event.
   • Fever, green discharge and wheeze make this a significant URI with a high airway-event risk. Disease
   • His asthma and his father's smoking each add to that risk.
   • MRI is remote: monitoring lags, nothing ferromagnetic near the magnet, and help is far away. Surgery

2. Prepare

   Do you go ahead today?

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   • No: an elective scan in a febrile child with green discharge and wheeze, so I postpone. Stem trigger
   • Rebook about two weeks after his symptoms settle; six weeks isn't required.
   • He keeps using his budesonide meanwhile, and comes back with a clear chest. Disease
   • If the scan were urgent, an experienced paediatric anaesthetist would give it, as experience lowers airway events. Stem trigger

3. Plan

   Three weeks later he is well and his chest is clear. How do you anaesthetise him?

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   • Inhaled salbutamol before induction; it prevents bronchospasm in reactive children like him. Disease
   • Oral midazolam 0.2–0.5 mg/kg so he is settled for a cannula. Patient
   • Propofol IV induction, up to 3 mg/kg in a child; fewer airway events than gas. Airway
   • Laryngeal mask rather than a tube, which lowers his respiratory complications.
   • MR-safe monitor, pumps and machine; I expect the capnograph to lag in the scanner. Surgery
   • Propofol, adrenaline, atropine and suxamethonium drawn up before he goes into the scanner. Crisis
   • Mask removed awake: deep removal means less coughing but more obstruction, far from help. Airway

4. Crisis

   In the MRI recovery bay, as the laryngeal mask comes out, he has stridor then silence; SpO2 82%. What do you do?

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   • Laryngospasm: call for help; tight mask, 100% oxygen, CPAP 15–20 cmH2O and a firm jaw thrust. (Crisis)
   • Suction his pharynx if secretions or blood set it off.
   • Not breaking: propofol 1–2 mg/kg IV to deepen him.
   • Still complete with falling saturation: suxamethonium 1–2 mg/kg IV, or 4–5 mg/kg IM without a cannula.
   • Then mask-ventilate until he breathes, and check his chest for bronchospasm.

5. Crisis

   Before the relaxant works, SpO2 is 60% and HR falls to 50 with weak pulses. What now?

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   • PALS bradycardia with a pulse: HR 50 and poor perfusion, caused by his hypoxia. Crisis
   • Oxygenation first: 100% oxygen and effective bag-mask ventilation; intubate if the mask fails.
   • If his rate stays below 60 and he's poorly perfused despite good ventilation: CPR.
   • Bradycardia persisting once oxygenated: adrenaline 0.01 mg/kg IV.
   • Atropine 0.02 mg/kg only for a vagal cause, such as suxamethonium; it won't fix hypoxic bradycardia.
   • Once recovered, he stays on oximetry in recovery until fully awake. After surgery