Malignant Hyperthermia - 6
Clinical Presentation(s)
Malignant hyperthermia may occur in an MHS patient exposed to triggering agents. So far, the only known triggers are:
  • all major inhalational anesthetic agents, including
    • desflurane
    • enflurane
    • halothane
    • isoflurane
    • sevoflurane
  • succinylcholine
MH Triggers
All other agents are "safe." Safe agents include N2O, all intravenous anesthetics, all local anesthetics, and all nondepolarizing muscle relaxants.
Malignant hyperthermia may present in a dramatic, fulminant form or an insidious, relatively mild, "abortive" form. Early detection and prompt treatment are important in minimizing morbidity and mortality.
Nonspecific indicators of increased metabolism are seen first. The following may represent the minimal group of clinical signs (in a patient not previously known to be MHS) for which a trial of dantrolene is indicated:
  • tachycardia +
  • tachypnea (or apparent "mechanical hyperventilation") +
  • ETCO2 increasing +
  • metabolic acidosis =
Dantrolene indicated because malignant hyperthermia possible.

Other clinical events that may develop during an MH episode:

  • masseter muscle rigidity (MMR) (also referred to as masseter muscle spasm, MMS)
  • VO2 increasing, sometimes to 8-10 times normal
  • sweating, mottled and cyanotic skin
  • fever (usually relatively late) perhaps to greater than 105 degrees Fahrenheit
  • muscle rigidity (may be severe) of extremities or entire body
  • rhabdomyolysis (with myoglobinemia and myoglobinuria)
  • hyperkalemia
  • cardiac arrhythmias (PVC's, ventricular tachycardia and fibrillation)
  • renal failure
  • DIC

Differential Diagnosis

The differential diagnosis of unexplained increasing ETCO2 includes
  • hyperthermia associated with sepsis
  • iatrogenic warming
  • faulty equipment (e.g., machine valve malfunction)
  • rebreathing
Hyperthermia, acidosis, rhabdomyolosis with myoglobinura, arrhythmias and cardiac arrest may also be features of:
  • cocaine toxicity
  • exertional heat stroke
  • hypoxic encephalopathy
  • idiosyncratic drug reaction (e.g., MAO inhibitors and meperidine interaction)
  • neuroleptic malignant syndrome (NMS)
  • pheochromocytoma
  • serotonin syndrome
  • status epilepticus
  • thyrotoxicosis
  • water soluble contrast agents in CSF
No clinical syndrome is entirely specific for malignant hyperthermia. Increasing ETCO2 despite apparent increasing ventilation is very suggestive of MH. If reasonable suspicion exists, especially in the presence of an unexplained tachycardia, increasing ETCO2 plus a moderately severe combined (respiratory and metabolic) acidosis: give dantrolene. A venous blood gas will usually be satisfactoy. Other confirmatory laboratory data would include elevated CPK, myoglobin, lactate, and potassium.

Greg Gordon MD