Malignant Hyperthermia — FRCA Final MCQ

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ModerateGeneral AnaesthesiaMalignant HyperthermiaFRCA Final

A 42-year-old man develops masseter spasm following suxamethonium during an emergency appendicectomy. His temperature rises from 36.5°C to 39.2°C over 20 minutes, end-tidal CO2 increases from 4.5 to 9.0 kPa despite increasing minute ventilation, and his heart rate is 145 beats/min. Arterial blood gas analysis shows pH 7.15, PaCO2 10.2 kPa, K+ 6.2 mmol/L and lactate 8.5 mmol/L. What is the initial dose of intravenous dantrolene?

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Correct answer: B — 2.5 mg/kg

The correct answer is B: dantrolene 2.5 mg/kg intravenously. Masseter spasm after suxamethonium, rapidly increasing end-tidal CO2 despite increased ventilation, tachycardia, hyperthermia, mixed acidosis and hyperkalaemia indicate a malignant hyperthermia crisis. Dantrolene should be given immediately while triggering agents are stopped and supportive treatment proceeds. It inhibits abnormal RYR1-mediated calcium release from the skeletal-muscle sarcoplasmic reticulum, reducing sustained contraction and hypermetabolism. Doses of 0.5 or 1 mg/kg are inadequate as the initial treatment. Five and 10 mg/kg may resemble cumulative doses used during an ongoing crisis but are not the recommended initial bolus. Further dantrolene is administered according to clinical response and the applicable preparation and local malignant-hyperthermia protocol; treatment should not be withheld solely because the cumulative dose reaches 10 mg/kg.

Reference: Dantrium IV 20 mg powder for solution for injection, Summary of Product Characteristics, section 4.2 Posology and method of administration (eMC, current version). https://www.medicines.org.uk/emc/product/1097/smpc