Malignant Hyperthermia

💪 Definition: Malignant Hyperthermia (MH) is a rare, life-threatening pharmacogenetic disorder of skeletal muscle, triggered by certain anaesthetic agents (volatile agents, suxamethonium), leading to uncontrolled intracellular calcium release and a hypermetabolic crisis.

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🪨 Triggers:

• Volatile anaesthetic agents (e.g. sevoflurane, desflurane)

• Succinylcholine (suxamethonium)

🤔 Pathophysiology:

• Mutation in RYR1 (ryanodine receptor) gene → excess calcium release from sarcoplasmic reticulum

• Sustained muscle contraction, ATP depletion, heat and lactic acid production

Clinical Features:

Feature	Notes
🔢 EtCO₂ ↑	Early sign; rises despite hyperventilation
🌡️ Hyperthermia	| Often a late sign
❤️ Tachycardia	Often first cardiovascular sign
🧱 Muscle rigidity	Generalised or masseter spasm
📉 Acidosis	Metabolic ± respiratory
✨ Hyperkalaemia	May lead to arrhythmias
💳 Myoglobinuria	Risk of AKI
📅 CK ↑	Rhabdomyolysis marker

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📉 Key Investigations:

• Arterial blood gas (ABG): Acidosis, hyperkalaemia, lactate

• CK, serum myoglobin, renal function

• Core temperature

• Urinalysis for pigment

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📅 Management: Use "S.A.F.E.R."

Step	Action
🔴 S	Stop the trigger: Cease volatile agent/suxamethonium, remove vaporiser
🪂 A	Airway + 100% O₂: Hyperventilate to clear CO₂ and reduce acidosis
🧪 F	First-line therapy: Give Dantrolene 2.5 mg/kg IV, repeat q5-10 min (max 10 mg/kg)
📢 E	Escalate: Call for help, delegate dantrolene prep (2 staff), notify retrieval/ICU early
🚁 R	Rescue planning: Insert IDC, cool patient, monitor for complications, prep transfer

Supportive Measures:

• Active cooling: IV cold fluids, ice packs, fan

• Treat hyperkalaemia: Calcium chloride/gluconate, insulin + dextrose

• Insert arterial line, urinary catheter

• Serial monitoring: ABG, CK, renal function

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🏥 Post-Event Management:

• Do NOT extubate early

• ICU admission mandatory

• Refer for confirmatory testing (e.g. caffeine halothane contracture test (CHCT) or genetic RYR1 testing)

• Family screening + documentation

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🌍 Scenarioville Context Considerations:

• Check MH kit weekly (stock dantrolene and protocol)

• At least 2 staff required for reconstituting traditional dantrolene (20 mg/vial)

• Maintain up-to-date MH policy and liaise with centralised retrieval service early

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💡 Pro Tip for Viva:

"I would apply the SAFE-R mnemonic to structure my response, emphasise early dantrolene, team delegation, supportive care, and prompt ICU retrieval from Scenarioville."