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Crisis Card

Malignant Hyperthermia

Hypermetabolic crisis triggered by halogenated volatiles or succinylcholine.

Call MHAUS — 1-800-MH-HYPER (1-800-644-9737)

Recognize

  • Unexplained ↑↑ EtCO₂ (most sensitive & specific early sign)
  • Tachycardia, tachypnea
  • Muscle rigidity (esp. masseter after sux)
  • Mixed metabolic / respiratory acidosis
  • Hyperthermia — LATE sign (1–2 °C every 5 min)
  • Dark urine (myoglobinuria), hyperkalemia

Doses

Dantrolene
2.5 mg/kg IV bolus q5 min
Up to 10–30 mg/kg total
Calcium chloride
1 g IV (central)
Or Ca gluconate 1–2 g peripheral
Insulin + D50
10 U IV + 25 g D50
Bicarbonate
1–2 mEq/kg IV
Cooling
Cold saline + surface ice
Stop at 38 °C

Sequenced Actions

  1. 1
    STOP triggers
    • Stop all volatile anesthetics and succinylcholine
    • Switch to TIVA (propofol + opioid + non-depolarizing NMBA)
    • High-flow O₂ 10 L/min via clean circuit (or charcoal filter); change CO₂ absorbent
  2. 2
    Hyperventilate
    • 100% FiO₂, increase minute ventilation 2–3× to blow off CO₂
  3. 3
    Call for help
    • Call MHAUS hotline: 1-800-MH-HYPER (1-800-644-9737)
    • Mobilize additional staff (need many hands to mix old dantrolene)
    • Get the MH cart to the room
  4. 4
    Dantrolene
    • 2.5 mg/kg IV bolus every 5 min until reaction abates
    • Often need 10 mg/kg total; up to 30 mg/kg possible
    • Ryanodex (250 mg vial in 5 mL sterile water) — fast prep
    • Old dantrolene: 20 mg vial + mannitol in 60 mL sterile water — slow prep, need help
    • Continue 1 mg/kg IV q6h × 24–48 h after acute event
  5. 5
    Cool the patient
    • Cold saline IV (avoid LR)
    • Ice packs to axillae, groin
    • Lavage open cavities, NG, bladder with cold fluid
    • Stop cooling at 38 °C to avoid overshoot hypothermia
  6. 6
    Treat hyperkalemia
    • Calcium chloride 1 g IV (central) or Ca gluconate 1–2 g (peripheral)
    • Insulin 10 units IV + D50 25 g
    • Sodium bicarbonate 50–100 mEq IV
    • Albuterol nebulized
    • AVOID calcium channel blockers with dantrolene — risk of cardiovascular collapse
  7. 7
    Treat dysrhythmias & acidosis
    • Standard antiarrhythmics (avoid CCBs)
    • Sodium bicarbonate for acidosis
    • Maintain UOP > 1 mL/kg/h (consider mannitol, furosemide) to prevent myoglobinuria-induced AKI
  8. 8
    ICU transfer
    • 24–48 h ICU monitoring — recrudescence in ~25%
    • Repeat CK, K⁺, myoglobin, BUN/Cr, coags
    • Refer for MH testing; counsel family (first-degree relatives 50% risk)
    • Add to MHAUS registry, issue MedicAlert

Common Pitfalls

  • Confusing late hyperthermia with normal heat retention — CO₂ rises first.
  • Giving verapamil or other CCB with dantrolene → cardiovascular collapse.
  • Failing to mobilize enough staff to mix old dantrolene formulation quickly.
  • Missing recrudescence in PACU/ICU — must monitor 24–48 h.

References & Further Reading

  1. 1
    SocietyOpen source

    Malignant Hyperthermia Association of the United States (MHAUS). Recognition and Treatment of MH. Hotline 1-800-MH-HYPER. mhaus.org.

  2. 2
    WebOpen source

    Stanford Anesthesia Cognitive Aid Group. Stanford Anesthesia Emergency Manual. emergencymanual.stanford.edu.

  3. 3
    Textbook

    Gropper MA, Miller RD, Cohen NH, et al., eds. Miller's Anesthesia. 9th ed. Philadelphia: Elsevier; 2020.

  4. 4
    Textbook

    Flood P, Rathmell JP, Shafer S. Stoelting's Pharmacology and Physiology in Anesthetic Practice. 5th ed. Philadelphia: Wolters Kluwer; 2015.

  5. 5
    Textbook

    Adriano A, Morris R, eds. 2021 CA-1 Tutorial Textbook (15th Ed.). Stanford University Medical Center, Department of Anesthesiology.

Citations are provided to direct further study. Always check the most current edition of guidelines and society recommendations — the information in this chapter is a teaching summary, not primary source material.

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