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Malignant Hyperthermia

Kristin Barkley, DNP, CRNA

Quick Facts
Clinical Progression
Signs
Procedure
Workstation Preparation
Differential Diagnosis
Scope Guide

Quick Facts

  • What: Malignant Hyperthermia (MH) is a rare, life-threatening hypermetabolic crisis triggered by certain anesthetic agents.
  • How: Autosomal dominant genetic disorder of the RYR1 receptor gene. Defective skeletal muscle calcium channels allow uncontrolled calcium release from the sarcoplasmic reticulum, causing sustained muscle contraction and hypermetabolism.
  • Triggers: Volatile anesthetic gases and succinylcholine.
  • Who: Occurs in genetically susceptible patients (may present despite prior uneventful anesthetics). Over 80 genetic defects identified; associated with:
    • King Denborough syndrome (congenital myopathy)
    • Central core disease (skeletal muscle weakness)
    • Carnitine palmitoyl transferase deficiency
    • Muscular dystrophies (mimic MH, not true crisis — avoid succinylcholine)
  • When: MH may occur immediately after trigger administration or several hours later.
  • Incidence: ~1:100,000 adult anesthetics.

 

Clinical Progression

  • Excessive calcium release → sustained muscle rigidity
  • Hypermetabolic state → increased heat production
  • Marked increase in CO₂ production → metabolic & respiratory acidosis
  • Increased O₂ consumption, tachycardia, tachypnea, sweating
  • Muscle breakdown → rhabdomyolysis:
    • Myoglobinemia/Myoglobinuria → acute renal failure
    • Hyperkalemia → arrhythmias
    • Elevated creatine kinase

 

Signs

Early Signs

  • Increased ETCO₂ (2–3x normal)
  • Masseter muscle spasm (after succinylcholine)
  • Tachycardia
  • Generalized muscle rigidity
  • Tachypnea
  • Profuse sweating

Late Signs

  • Rapidly rising temperature (1–2°C every 5 minutes)
  • Dark urine (myoglobinuria)
  • Skin mottling, cyanosis, hypoxemia

 

Procedure

Treatment Mnemonic: “Some Hot Dude Better Get Iced”

  1. S – Stop triggering agents
    • Call for help; bring MH cart
    • Convert to TIVA if needed
  2. H – Hyperventilate
    • High fresh gas flow with 100% O₂
    • Increase minute ventilation
    • Add activated charcoal filters if available (replace hourly)
  3. D – Dantrolene (RYR1 antagonist)
    • Initial dose: 2.5 mg/kg IV (up to 10 mg/kg as needed)
    • Mix 20 mg vial with 60 ml sterile water until clear
    • Ryanodex: 250 mg/vial, mix with 5 ml sterile water
    • Continue dosing until symptoms resolve
    • Blocks further calcium release (not neuromuscular transmission)
  4. B – Bicarbonate
    • Treat metabolic acidosis: Sodium Bicarbonate 1–2 mEq/kg IV
  5. G – Glucose & Insulin
    • Treat hyperkalemia
    • Calcium chloride may also be given (avoid calcium channel blockers)
  6. I – Iced
    • Active cooling if temperature >39°C
    • Cool IV fluids, ice packs (groin, axilla, neck), cooling blanket
    • Lavage stomach, bladder, or open cavities with cold saline
    • Stop cooling when patient reaches 38°C

Other Treatment Measures

  • Treat arrhythmias (beta blockers, lidocaine; avoid calcium channel blockers)
  • Draw labs: ABG, electrolytes, CK, urine myoglobin, coagulation panel, LDH
  • Insert Foley → monitor UOP (if <0.5 ml/kg/hr, give Lasix for diuresis)
  • Secure extra IV access; consider central line & arterial line
  • Insert central temperature probe

Post-Event

  • Admit to ICU for ≥24 hours
  • Ongoing dantrolene therapy, close monitoring, and labs

 

Prep Anesthesia Workstation

  1. Remove vaporizers (or tape off).
  2. Place new circuit and bag.
  3. Flush anesthesia machine:
    • High fresh gas flow (10 L/min O₂/air), vent on, TV 700, RR 12
    • New machines: ~104 min; older: ~20 min
    • GE machines:
      • Aisys – 35 min
      • Aestiva – 40 min
      • Avance/Aespire – 30 min
  4. Charcoal filters:
    • High FGF for 90 sec before filters placed
    • Apply to inspiratory and expiratory limbs
  5. Change out circuit and CO₂ absorber after flush.
  6. Flush 10 sec before connecting patient.

 

Differential Diagnosis

  • Neuroleptic malignant syndrome
  • Serotonin syndrome
  • Light plane anesthesia
  • Pheochromocytoma
  • Thyroid storm
  • Hypoventilation / CO₂ insufflation

Tip: All may cause hypermetabolic signs; not all present with rigidity, fever, rhabdomyolysis. When in doubt, call the MH Hotline.

 

SCOPe Guide

Clinical Optimization

  • Early recognition is critical — rising ETCO₂ is the most sensitive sign.
  • Temperature rise is late.
  • Call for help early; grab MH cart.

Pearls

  • Remember mnemonic: Some Hot Dude Better Get Iced
  • Stop triggering agents immediately, give dantrolene promptly.
  • Use sterile water only for mixing dantrolene or Ryanodex.

Resources

 

References

  1. Malignant Hyperthermia Association of the United States (MHAUS). Available at: https://www.mhaus.org.
  2. GE Healthcare. Preparing Anesthesia Systems for MH-Susceptible Patients. 2021. Available at: <a href=”https://www.gehealthcare.com/-/media/b19b04665517

License

Icon for the Creative Commons Attribution-NonCommercial 4.0 International License

The Scope Copyright © by Bailey Freeman, DNP, CRNA; Angela Mordecai, DNP, CRNA; Brian Cornelius, DNP, CRNA; and Kristin Barkley, DNP, CRNA is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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