Frequently Asked Questions

Category: Malignant Hyperthermia

What Is MH?

The sudden unexpected death of a healthy individual undergoing minor surgery is a tragedy almost beyond comprehension in this day of modern medical miracles. Yet this still happens to patients susceptible to malignant hyperthermia (MH). Even when treated properly, the syndrome known as the MH crisis can cause death. Survivors might be left with brain damage, failed kidneys, muscle damage or impaired function of other major organs.

The MH crisis is a biochemical chain reaction response, “triggered” by commonly used general anesthetics and the paralyzing agent succinylcholine (a neuromuscular blocker), within the skeletal muscles of susceptible individuals. The general signs of the MH crisis include increased heart rate, greatly increased body metabolism, muscle rigidity and/or fever that may exceed 110 degrees F along with muscle breakdown, derangements of body chemicals and increased acid content in the blood. Severe complications include: cardiac arrest, brain damage, internal bleeding or failure of other body systems. Thus, death, primarily due to a secondary cardiovascular collapse, can result.

What is MH / MHAUS?

Learn about Malignant Hyperthermia, and the mission and goals of the Malignant Hyperthermia Association of the United States.

Who Is Susceptible To MH?

There has been dramatic improvement in our understanding of what causes MH and who is at risk. Over 80 genetic defects have been associated with MH. MH susceptibility is inherited with an autosomal dominant inheritance pattern. This means that children and siblings of a patient with MH susceptibility usually have a 50% chance of inheriting a gene defect for MH, and hence would also be MH susceptible. They, therefore, may develop an MH reaction upon exposure to triggers.

Nevertheless, those who are carriers for susceptibility may be completely unaware of this risk unless they or a family member developed a life-threatening crisis during anesthesia. It is important to know that not everyone who has a gene defect linked to MH develops the MH crisis upon each exposure to the triggering anesthetics.

Testing for Malignant Hyperthermia

Information on Genetic and Muscle Biopsy testing for MH.

What Drugs Trigger MH? What Drugs Are Safe?

Please see our Safe and Unsafe Anesthetics page for complete details.

Safe and Unsafe Anesthetics

A comprehensive list of anesthetics that are safe for MH susceptible patients, and those that are known triggers for MH

What Is The Incidence Of MH?

The exact incidence of MH is unknown. Epidemiologic studies reveal that MH complicates one in about 100,000 surgeries in adults and one in about 30,000 surgical procedures in children. The incidence varies depending on the concentration of MH families in a given geographic area. High incidence areas in the United States include Wisconsin, Nebraska, West Virginia and Michigan. However, the prevalence of genetic change that predisposes to MH is much higher. About one in 2,000 patients harbor a genetic change that makes them susceptible to MH.

What Causes An MH Episode?

MH-susceptible persons have a mutation that results in the presence of abnormal proteins in the muscle cells of their body. Although normal in everyday life, when these patients are exposed to certain anesthetic agents, or in rare cases when exposed to high environmental heat or strenuous exercise, it causes an abnormal release of calcium from the sarcoplasmic reticulum (a storage site for calcium) in the muscle cell, which results in a sustained muscle contraction and thus an abnormal increase in metabolism and heat production. The muscle cells eventually are depleted of adenosine triphosphate (ATP) the source of cellular energy, and die, releasing large amounts of potassium into the bloodstream, causing hyperkalemia, followed by ventricular (cardiac) arrhythmias. The muscle pigment myoglobin is also released from the muscle cells and may be toxic to the kidney. Left untreated, these changes can cause cardiac arrest, kidney failure, blood coagulation problems, internal hemorrhage, brain injury, liver failure, and may be fatal. A more detailed explanation of the biochemical changes in MH may be found on the MHAUS website.

How Is MH Treated?

Treatment is predicated upon preparation for a rare event. Every anesthetic must be associated with a plan for treatment of unanticipated MH. With the plan in place, treatment can be prompt and lifesaving. Prompt recognition of the signs of MH is essential to an optimal outcome. Preparedness is essential to prevent death from MH.

In addition to an anesthesia machine (if used), ECG monitor, pulse oximeter and capnometer, all locations where general anesthesia is administered should contain:

• A plan to treat MH, such as the poster and MH Procedure Manual available from MHAUS. For immediate emergency consultation with a volunteer anesthesiologist MH Hotline consultant, contact the MH Hotline.
• A means to continuously monitor end-tidal carbon dioxide levels, blood oxygen saturation and core body temperature.
• A means to actively cool a patient; e.g., a hypothermia blanket(s) (over and under the patient) and a refrigerator containing cold isotonic saline for IV infusion and for gastric, peritoneal or rectal irrigation, as appropriate. Ice is much more effective at cooling, though core cooling using iced saline intravenously may be effective (0.5°C. /liter in a 70 kg adult). The volume of IV saline that should be rapidly infused limits maximum effect.

Beware of unintentional hypothermia! Stop cooling measures when temperature falls to 38°C

An MH cart or kit containing the required drugs, equipment, supplies and forms should be immediately accessible to operating rooms.

Healthcare Professionals

Information for Healthcare Professionals, including MH Hotline

How Can MH-Susceptible Patients Be Identified?

Because MH is a dominantly inherited disorder, 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 anesthesiolgist before undergoing surgery. Additionally, they should register their MH susceptibility with the North American Registry of MHAUS.

The North American Malignant Hyperthermia Registry of MHAUS

The North American MH Registry (NAMHR) was established in 1987 and merged with the Malignant Hyperthermia Association of the United States (MHAUS) in 1995 so that data on MH could be stored in a site that is supported by one organization to offer greater support for research initiatives. 

Can MH-Susceptible Patients Have Surgery?

Yes! Surgery can be safely performed in the known MH-susceptible patients. However, only those anesthetics that do not trigger the MH reaction must be used. In addition, close monitoring of appropriate vital functions is necessary. When dealing with an MH susceptible, the anesthesiologist should:

• Avoid the use of MH-triggering anesthetics.
• Be familiar with the signs and treatment of MH, e.g., re-review the routine information.
• Continuously monitor the patient’s exhaled carbon dioxide concentration and minute ventilation.
• Continuously monitor the patient’s temperature (also during recovery). Skin temperature is not optimal in this situation.
• Have an MH kit or cart within the operating room suite stocked with an adequate supply of dantrolene.

Watch this video FAQ for more information.

FAQ Video: MH Susceptible Patients and Surgery

Are MHS patients candidates for surgery? Watch this video for details.

Can MH Occur Outside Of The Operating Room?

Yes. While most cases of MH occur during general anesthesia, the one-hour period immediately following surgery (including the recovery room) is also a critical time. In addition, MH can occur if trigger anesthetics and/or succinylcholine are used in any location, such as emergency rooms, dental surgeries, surgeon’s offices or intensive care units.

Can Anything Other than Anesthetic Drugs Trigger MH?

Studies have shown that a small percent of people who develop muscle breakdown following exercise only, or after heat stroke, harbor the genetic changes associated with MH susceptibility. It is still unclear if the muscle breakdown and other changes result from these non-anesthetic incidences.  In the absence of a personal or family history of heat stroke or exercise-induced muscle breakdown or evidence of muscle disorders, ask your personal physician to consult with an MH expert.

Are There Links Between MH And Other Conditions?

Please see our Associated Conditions page.

Associated Conditions

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.

Is MH always hereditary?

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.

The North American Malignant Hyperthermia Registry of MHAUS

The North American MH Registry (NAMHR) was established in 1987 and merged with the Malignant Hyperthermia Association of the United States (MHAUS) in 1995 so that data on MH could be stored in a site that is supported by one organization to offer greater support for research initiatives.