Q&A: Malignant Hyperthermia




Q: What drugs trigger MH and are not safe?

A: The potent/volatile gaseous inhalation anesthetics are MH triggers. Examples are:

  • sevoflurane
  • desflurane
  • isoflurane
  • halothane
  • enflurane
  • methoxyflurane

Also not safe is the depolarizing muscle relaxant: succinylcholine

Q: What drugs are safe?

A: The non-triggering anesthetic agents/drugs include the following:

  • propofol
  • barbiturates
  • narcotics
  • benzodiazepines
  • ketamine
  • etomidate
  • nitrous oxide (not a potent inhalation anesthetic)
  • local/regional anesthetics
  • monitored anesthesia care (local anesthesia plus sedation)

Non-depolarizing muscle relaxants (used to temporarily produce muscle paralysis are also safe:

  • pancuronium
  • cisatracurium
  • vecuronium
  • rocuronium
  • atracurium
  • mivacurium

Q: Can MH symptoms be induced by stress, overheating or excessive exercise?

A: The symptoms of heat exertion and heat stroke are remarkably similar to MH. However, the vast majority of patients who suffer heat-related illness are not MH susceptible. In a few cases, MH susceptibility has been diagnosed by muscle biopsy in patients who have suffered from heat stroke (non-fatal), and some experts believe heat stroke may occur more often in MH-susceptible individuals. This is an area of intense interest and investigation. The general advice for MH-susceptibles is to be prudent in their exposure to excessive heat and exercise in hot environments, although that same advice holds true for non-MH-susceptible patients.

Q: Are MH-susceptible individuals at risk for symptoms/episode if exposed to triggering agents while working in an operating room or similar environment?

A: There are no cases reported of MH patients having problems on exposure to waste anesthetic gases while working in the OR. The usual operating room procedures maintain low, trace amounts of the potent volatile anesthetics in the air. During a mask induction, someone within two feet or so of the face of the patient may be exposed to somewhat greater concentrations, but that is easily avoided. Further, the volatile agents are heavier than air and drift down to the floor, where the excellent ventilation systems efficiently clear the vapors.

Heredity and Links

Q: Is MH always hereditary?

A: MH is considered a dominantly inherited disorder in humans. All closely related members of a family in which MH has occurred must also be considered MH susceptible and managed accordingly, unless proven otherwise. It should be noted that those who have had previous anesthetics without problem cannot be certain they are not at risk; MH related deaths have occurred even though patients have undergone multiple prior uneventful surgeries. Certainly any family with a history of anesthetic deaths or complications should make this known to the anesthesiologist before undergoing surgery. Additionally, they should register their MH susceptibility with the North American MH Registry of MHAUS

Q: If I have had an episode of malignant hyperthermia, who else is at risk?

A: Malignant hyperthermia is inherited in humans in a pattern termed “autosomal dominant.” This means 50 percent of the offspring of an MH-susceptible and 50 percent of siblings would be MH-susceptible. The risk of MH susceptibility diminishes further out on the family tree, proportional to the dilution of the relationship. For example, an aunt or an uncle would have a 25 percent risk of MH-susceptibility. Muscle biopsy testing is the only way to determine for certain the susceptibility status. Hence, when an acute MH episode occurs in a family member, all family members, including cousins, should be alerted to their potential risk as well.

Q: Is MH linked to other serious medical problems?

A: MH itself is not usually associated with other serious medical problems, such as hypertension, diabetes or similar diseases. MH or MH-like events however, have occurred in patients with underlying muscle diseases, such as muscular dystrophy and myotonia. Such patients typically display muscle weakness. MH has been linked to a rare disorder of muscle called Central Core Disease and King Denborough Syndrome, a rarer muscle syndrome. Additionally, patients with certain forms of muscular dystrophy may develop life-threatening disturbances and muscle destruction on exposure to the triggering agents for MH. The clinical event may resemble MH in many ways, but is not considered “true” MH. In patients with Duchenne muscular dystrophy (the classic muscular dystrophy), succinylcholine, a trigger agent for MH, should always be avoided or muscle breakdown (rhabdomyolysis) may occur. Potent volatile agents may produce rhabdomyolysis in time, but most believe that brief exposure is a small risk. Patients with muscle disorders should be carefully evaluated by their anesthesiologist prior to surgery.

Q: Can an MH susceptible person donate blood or organs?

A: Yes. MH is not "carried" in the blood or organs.

Hospitals and MH

Q: How aware are hospitals and ER personnel of MH? If I went to a hospital other than my normal one, could I feel confident?

A: No answer can be given to this question, since we do not have specific information about every hospital. Major medical centers and teaching hospitals are likely to be prepared to respond to MH. Anesthesiologists and nurse anesthetists are more likely to be aware of MH than other medical specialists. If you are malignant hypothermia susceptible (MHS), you should carry information with you, such as the MHS wallet card and the MH Hotline number, etc. In addition, wear a medical ID tag (available from North American MH Registry of MHAUS) and notify health care givers of your susceptibility.

I.D. Tags for MH

Q: I know adults susceptible to MH should wear a medical ID tag. Should my children wear medical I.D. tags as well?

A: The safest approach for MHS children is to wear an I.D. bracelet. In an emergency situation, the parent might not be available and the child might not be able to provide the necessary information to medical personnel.

North American MH Registry of MHAUS (NAMHR)

Q: What is the purpose for the North American MH Registry of MHAUS?

A: The North American MH Registry is a division of MHAUS. The purpose of the Registry is to collect specific information regarding an MH episode and to analyze data from such episodes in order to better understand the patterns of manifestation of MH and to provide information to family members as to the susceptibility status of relatives when known. The primary aims of MHAUS are to provide information and education regarding malignant hyperthermia to health care providers and patients in order to reduce the risk of an MH tragedy. MHAUS also supports research into the preventive diagnosis and treatment of malignant hyperthermia.

Oral Surgery and MH

Q: Should an MHS be hospitalized for oral surgery?

A: Minor oral surgery performed on an outpatient basis under local anesthesia has been shown to be safe for MHS patients. General anesthesia using intravenous medications and nitrous oxide only also is safe. However, any facility that performs surgery or anesthesia using MH trigger agents should be prepared to monitor the patient and treat an MH crisis, including having an adequate supply of dantrolene.

Testing for MH

Q: How accurate is the muscle biopsy?

A: The accuracy (sensitivity and specificity of the muscle biopsy) has been evaluated at various biopsy centers. The test is extremely sensitive in detecting MH (i.e., no false negatives). Specificity is somewhat less accurate. Up to 15 percent of patients who are diagnosed as MH positive are not MH susceptible. However, the sensitivity and specificity is compatible with other known tests in medicine and it is the most accurate diagnostic test available.

Q: How important is it to have a muscle biopsy if someone has MH in the family?

A: The muscle biopsy is the only reliable diagnostic test for MH at the present time. If it is not possible to perform this test, members of the family should be considered MH susceptible and managed accordingly. The muscle biopsy is important for ruling out MH susceptibility in various family members and their offspring because if a patient is MH negative, their offspring will also be MH negative. However, if they are MH positive, their offspring will have a 50 percent likelihood of being MH susceptible.

Q: What is the progress/status of a simple blood test vs. a muscle biopsy?

A: Muscle biopsy is presently the only reliable test of MH susceptibility. Our hope, by understanding the genetics of malignant hyperthermia at a molecular level, is to be able to determine whether a patient harbors the gene(s) for malignant hyperthermia. Such a test would be very specific, accurate and would employ blood cells. The genetics of malignant hyperthermia is very complicated and, so far, there are at least 40 genes involved in MH susceptibility. MHAUS is diligently doing research in this area in an effort to establish a lab for the development of a molecular genetic test for susceptibility to MH.

Content Courtesy of the Malignant Hyperthermia Association of the United States

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