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Malignant Hyperthermia (MH)

Hypermetabolic crisis triggered by volatile anesthetics or succinylcholine in genetically susceptible patients (RYR1, CACNA1S). Treat with dantrolene immediately.

Recognition

  • •Unexplained ↑EtCO₂ unresponsive to ↑MV (often the earliest sign)
  • •Tachycardia, tachypnea, masseter rigidity after sux
  • •Mixed acidosis on ABG (respiratory + metabolic)
  • •Late: hyperthermia (a late sign — do not wait for it)
  • •Hyperkalemia, myoglobinuria, peaked T waves

Steps

  1. 1
    Call for help + MH cart + MHAUS hotline
    1-800-MH-HYPER (1-800-644-9737)
  2. 2
    Stop all triggers
    Discontinue volatile + sux. Switch to TIVA (propofol).
  3. 3
    Hyperventilate 100% O₂ at ≥10 L/min
    Flush circuit; do not change machine if delays ventilation.
  4. 4
    Dantrolene 2.5 mg/kg IV bolus
    Repeat q5 min until symptoms resolve. Max ~10 mg/kg, often more.
  5. 5
    Active cooling
    Ice packs to groin/axilla, cold IV NS, gastric/bladder lavage. Stop at 38°C.
  6. 6
    Treat hyperkalemia + arrhythmias
    Calcium, insulin/dextrose, bicarb. Avoid CCBs (interaction with dantrolene).
  7. 7
    Foley + alkalinize urine
    Bicarb + furosemide; goal UOP > 2 mL/kg/hr to prevent ARF from myoglobin.
  8. 8
    ICU x 24+ h, refer for genetic counseling

Drugs + doses

DrugDoseNote
Dantrolene (Ryanodex preferred)2.5 mg/kg IV, repeat q5 minRyanodex 250 mg/vial reconstitutes in 5 mL — fast. Standard dantrolene 20 mg/vial in 60 mL water — slow.
Sodium bicarbonate1–2 mEq/kg titrated to ABG
Calcium chloride10 mg/kg IV for hyperkalemia
Insulin + D5010 U regular insulin + 25 g dextrose
Furosemide0.5–1 mg/kg IV

Pitfalls

  • !Calcium channel blockers + dantrolene → severe hyperkalemia. Avoid.
  • !Mannitol is in the dantrolene vial — track total mannitol load.
  • !Hyperthermia is LATE; rising EtCO₂ comes first.

Sources

  • MHAUS guidelines
  • ASA Practice Advisory 2024
  • Larach Anesthesiology 2014

Anatomy reference

Sourced reference images. 4 matches for "muscle skeletal sarcoplasmic reticulum".

fig-ch04_04_01abc
OpenStax · CC BY 4.0
fig-ch10_02_02
OpenStax · CC BY 4.0
fig-ch10_02_03
OpenStax · CC BY 4.0
fig-ch11_01_02
OpenStax · CC BY 4.0
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Education only — not a substitute for facility protocols, MOC certification, or clinical judgment. Always follow your institutional crisis algorithm and confirm doses against current package inserts.