Malignant Hyperthermia

Epidemiology

  • Probably the leading cause of anesthesia-related death in healthy patients
  • Incidence
    • Anesthetized Adults: 1 in 50k-100k patients
    • Anesthetized Children: 1 in 3k-15k patients
  • Inheritance: autosomal dominant

Etiology

Halogenated Inhalational Anesthetics

  • Enflurane
  • Halothane
  • Isoflurane

Aminoamide Local Anesthetics (less clearly etiologic)

  • Lidocaine
  • Prilocaine
  • Etidocaine
  • Mepivacaine
  • Bupivacaine

Other

  • Succinylcholine
  • Surgical Stress: reported to be etiologic in some cases

Physiology

  • Sarcoplasmic Reticulum Calcium Channel Defect: impaired ability of skeletal muscle to uptake myoplasmic calcium released from sarcoplasmic reticulum (SR)
  • Elevated Myoplasmic Calcium During Event: causes increased muscle metabolism and contraction
  • Intact Hypothalamic Thermoregulation

Diagnosis

  • ABG: may demonstrate hypoxemia and hypercapnia
    • May demonstrate metabolic acidosis (due to lactate)
  • CHEM
    • Hyperglycemia
    • Hyperkalemia
    • Hypernatremia
    • Hypercalcemia
    • Hypermagnesemia
    • Hyperphosphatemia
  • Lactate: may be elevated
  • CK: may be elevated

Clinical Manifestations

Timing of Onset

  • Symptom onset usually within 30 min of start of anesthesia (or may occur several hours later), with rapid progression

Neuro Manifestations

  • Muscle Stiffness
  • Rigidity

Other Manifestations

  • Fever (see Fever, [[Fever]]): may rise as fast as 1°C q5min
  • Hypotension (see Hypotension, [[Hypotension]])
  • Tachypnea
  • Tachycardia

Treatment

  • Immediately Discontinue Offending Agent
  • Supportive Care
    • Cooling/Ventilation
    • Antipyretics
    • Hemodynamic Support
    • Electrolyte Replacement
    • Correction of Acidosis
  • Dantrolene (see Dantrolene, [[Dantrolene]]): drug of choice
    • Mechanism: inhibits release of calcium from muscle sarcoplasmic reticulum and antagonizes calcium effect on muscle contraction
    • Administration: 2.5 mg/kg IV, repeat q5 min to max 10 mg/kg or until improvement/then maintenance q 5-8 hrs
  • Calcium Channel Blockers: used in animal models, but not found to be useful in humans

Prognosis

  • Mortality: <10% with early recognition and therapy

References

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