What is Malignant Hyperthermia?

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  • Written By: J.M. Willhite
  • Edited By: Heather Bailey
  • Last Modified Date: 18 September 2019
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Malignant hyperthermia (MH), also known as malignant hyperthermia syndrome (MHS), is a rare genetic condition that presents following the administration of a general anesthetic. Treatment for this potentially fatal condition is centered on the immediate alleviation of episodic symptoms to prevent complications that may include organ damage and impaired brain function. If left untreated, malignant hyperthermia can result in organ failure and premature death.

Individuals with malignant hyperthermia experience an adverse physiological reaction to the administration of certain general anesthetic drugs, such as desflurane, methoxyflurane, and sevoflurane. Generally administered as an inhalant, such anesthetics can induce an elevated or irregular heartbeat once the drugs enter the individual’s system. In most cases, the adverse reaction is not discovered until after the anesthetic has been given. Some individuals with malignant hyperthermia may develop an extremely high temperature following anesthetic administration that requires the immediate application of cooling materials to bring down their fever and prevent brain damage. Additional signs of MH include rigidity of the muscles and urine discoloration resulting from impaired kidney function.


Many who develop this serious condition have a family history of the disorder or anesthetic-induced death. Those who are diagnosed with MHS generally have at least one parent who is a carrier for the disease. Individuals with MH possess a genetic cell mutation that triggers the unrestrained release of calcium and potassium when he or she is exposed to certain anesthetic drugs or, in some cases, physiological stress as induced by extreme temperatures or extreme physical strain.

The rapid release of calcium from the muscles during an MH episode essentially causes muscular seizure and stiffening while depleting the energy needed for proper muscle function. Lost cellular energy triggers the onset of muscle decay and the unregulated release of potassium into the bloodstream. The introduction of potassium is further compounded by the loss of myoglobin pigmentation released by the decaying muscle tissues. The combination of the two adversely affects cardiovascular and renal function.

If an individual is suspected of having the genetic mutation responsible for malignant hyperthermia or is aware of a family history, he or she may undergo genetic testing to verify the presence of the ryanodine receptor 1 (RYR1) gene that is responsible for the presentation of MH. Though the condition is most often diagnosed following the administration of an anesthetic drug, there are tests that may be administered to evaluate the individual’s condition following his or her MH episode. A urine myoglobin may be performed to evaluate the condition of the muscles and check for any deterioration as indicated by the presence of myoglobin in the urine. Additionally, a metabolic panel may be conducted to evaluate the individual’s liver and kidney function.

Treatment for MH is entirely dependent on symptom presentation and severity. Most individuals present with an extremely high temperature that necessitates immediate measures to reduce it to prevent permanent organ damage. In such cases, a cool towel or blanket may be placed over the individual to help lower his or her body temperature. Muscle relaxant and nerve blocker medications, such as dantrolene and beta-blockers, may be administered to alleviate muscle spasms and regulate the individual’s heart rhythm. Additional fluids may be intravenously administered to prevent dehydration and support proper organ function.

Malignant hyperthermia episodes may be prevented through awareness about one’s family medical history. Those with relatives who have been diagnosed with MHS or died due to complications associated with this disorder should inform their doctor. There are anesthetic drugs that may be administered in the presence of malignant hyperthermia that are completely safe and will not trigger an MH episode, such as vecuronium, nitrous oxide, and propofol.


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