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pencilMalignant 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.

🪨 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

📉 Key Investigations:

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

  • CK, serum myoglobin, renal function

  • Core temperature

  • Urinalysis for pigment

📅 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

🏥 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

🌍 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

💡 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."

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