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MALIGNANT HYPERTHERMIA

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MALIGNANT HYPERTHERMIA

Malignant hyperthermia is a type of severe reaction to certain drugs used as anesthesia for surgery and other invasive procedures.

  • People at increased risk are said to have a malignant hyperthermia susceptibility
  • Except for susceptibility to triggering agents, affected people are usually not distinguishable from the general population
  • Susceptible people are usually recommended to avoid potential triggers
  • Malignant hyperthermia occurs in 1 in 5,000 to 50,000 cases on exposure to anesthetic gases
  • Without treatment, the complication of malignant hyperthermia can be fatal
  • With proper treatment, the risk of death is about 5%. Without proper treatment, the risk of death is about 75%
  • Men are more likely to have an episode than women

CAUSES

The cause of malignant hyperthermia is exposure to volatile anesthetics (such as halothane) or depolarizing muscle relaxant (such as succinylcholine) in those who are susceptible.

Susceptibility can occur from mutations in different genes. Researchers have identified at least six forms of malignant hyperthermia susceptibility, caused by different gene mutations. The most common is a mutation in the RYRI gene which is responsible for a form of the condition known as MHS1. Others include mutations in the CACNA1S gene which is responsible for a form of the condition known as MHS5 and the CACNAD21 gene which has been linked to a form of the condition known as MHS3.

Susceptibility is usually inherited in an autosomal dominant manner which means only one copy of the mutant gene is necessary for an individual to inherit the disorder.

There are numerous reports of susceptible people who have developed symptoms in association with the biological stress of physical exercise and/or heat exposure.

The disorder may also occur with some inherited muscle diseases, such central core disease

Before you have surgery, it is very important to inform your doctor if you are aware of any malignant hyperthermia susceptibility in your family

SYMPTOMS

  • A very high temperature
  • Muscle rigidity
  • Rhabdomyolysis (the breakdown of muscle fibers)
  • A rapid heart rate and abnormally rapid breathing
  • Acidosis (an increased acid level in the blood and other tissues)
  • Increased carbon dioxide production

These symptoms can develop any time during the administration of the anesthetic triggering agents

DIAGNOSIS AND TREATMENT

Diagnosis is suspected by the appearance of typical symptoms a few minutes or several hours following administration of anesthesia. Earliest symptoms may include muscle rigidity, unexplained fast heart rate, and abnormally elevated carbon dioxide in the blood.

Those with a personal history of a severe adverse effect to general anesthesia or with a close relative who has suffered an episode of the disorder are usually recommended for testing. The standard procedure is the caffeine halothane contracture (CHCT). This test measures the response of a muscle tissue sample to caffeine and halothane and can be done only at certain referral centers.

Genetic testing may also be performed to determine susceptibility.

TREATMENT

Treatment options include:

  • Intravenous administration of dantrolene. Dantrolene remains the only drug known to be effective in the treatment of malignant hyperthermia
  • Rapid cooling
  • Discontinuation of triggering agents
  • Supportive therapy directed at correcting organ dysfunction and acidosis