Malignant hyperthermia


  • Inherited disorder of skeletal muscles triggered most often by anesthesia inhalation agents, succinylcholine, heat or exercise[1]
  • Results in hypermetabolism, skeletal muscle damage, hyperthermia, and death if not treated quickly
  • GENERALIZED rigidity NOT always present; if it occurs, MH is almost certain

Likelihood of Complications

  • Increased time from 1st sign to 1st dantrolene
    • For every 30 minute increase in the interval, complication likelihood increases x 1.6
  • Increased maximal temperature
    • For every 2°C increase in max temp, complication likelihood increases x 2.9

Clinical Features

  • Muscle contraction
  • Fever
  • May have dark colored urine from myoglobinuria
  • First signs
    • Hypercarbia
    • Sinus tachycardia
    • Masseter spasm
    • Temperature abnormalities (may be early)
  • Most common pattern
    • Respiratory acidosis and muscular abnormalities


Watch for it with succinylcholine use.


  • Fulminant MH
    • muscle rigidity, high fever, increased HR shortly after induction of anesthesia
  • Masseter muscle rigidity
    • jaw muscle rigidity after succinylchoine
    • More common in children
    • Presages MH in 20-30% cases
    • All patients demonstrate elevated CK and often gross myoglobinuria
    • CK >20,000IU = high likelihood of MH
  • Late onset MH
    • Uncommon, may begin shortly after anesthesia termination (usually within first hour)

Differential Diagnosis

Altered mental status and fever


  • Core temperature
  • CBC
  • Chem 7
  • Total CK
  • PT/PTT
  • ABG


  • Discontinue Triggering Agents
  • 100% Oxygen at High Flow
  • Give Dantrolene
  • Provide bicarbonate for metabolic acidosis temporization
  • Actively cool the patient
  • Treat any dysrhythmia


  • 60ml sterile water into each vial of dantrolene may need up to 36 vials
  • If using Dantrium® (20mg/vial), each vial contains 3 g of mannitol (renal vasodilation); newer nanocrystalline dantrolene (250mg/vial) has 250mg mannitol per vial and requires mannitol supplementation
  • 2.5mg/kg IV push
  • Titrate to effect; may need more than 10mg/kg
  • Call MHAUS Hotline if needed: 1-800-644-9737
  • Continued Care
    • Dantrolene 1mg/kg every 4-6 hours for 24–48 hours
    • Monitor for recrudescence (rate is 25%)
    • Follow electrolytes, blood gases, CK, core temperature, urine output and color, coagulation studies


  • 1-2 mEQ/kg if blood gas values not yet available

Cooling Measures

  • Most patietns will have a core temperature >39 deg C (102.2 deg F)
  • Stop cooling when temperature reaches 100.4

Dysrhythmic therapy

  • Dysrhythmias usually respond to treatment of acidosis and hyperkalemia
  • AVOID CA CHANNEL BLOCKERS as they may cause hyperkalemia or cardiac arrest in presence of dantrolene


  • Not always present but can occur
  • Treat hyperkalemia with standard treatment, remember to check glucose levels q1h after treatment with insulin/glucose


Stable to Transfer Criteria

  • ETCO2 is declining or normal
  • HR is stable or decreasing
  • No ominous dysrhythmias
  • Temperature is declining
  • Generalized muscular rigidity is resolving (if present)
  • IV dantrolene administration has begun


  • Consciousness Level Change/Coma
  • Cardiac Dysfunction
  • Pulmonary Edema
  • Renal Dysfunction
  • Disseminated Intravascular Coagulation
  • Hepatic Dysfunction
  • Relapse
  • Death


  1. Denborough, M. (1998) ‘Malignant hyperthermia’, The Lancet, 352(9134), pp. 1131–1136. doi: 10.1016/s0140-6736(98)03078-5

See Also