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24-HOUR MH HOTLINE: 800-644-9737

Frequently Asked Questions

Frequently Asked Questions

A list of the most frequently asked questions that we receive from both Medical Professionals and Patients.

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The most frequent questions of all: Which anesthetics are safe?  Which ones trigger MH? Are there other drugs that can trigger MH?  See our Safe and Unsafe Anesthetics page for full, regularly updated details.

Safe and Unsafe Anesthetics
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 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?
What is MH / MHAUS?

Learn about Malignant Hyperthermia, and the mission and goals of the Malignant Hypertermia 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
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
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
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 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
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
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.

How Does The Antidote Dantrolene Work?

Dantrolene is the only currently accepted specific treatment for MH. In an episode of MH, muscle metabolism is dramatically increased secondary to an increase in calcium within the muscle. This causes muscles to contract, ATP hydrolysis, and heat production. Dantrolene directly interferes with muscle contraction; decreasing calcium in muscle cells.

Dantrolene does not block neuromuscular transmission nor interfere with reversal of muscle relaxants. Although it does not block neuromuscular transmission, the mechanical response to nerve stimulation will be depressed, with subsequent potentiation of the non-depolarizing neuromuscular blockade. When dantrolene is used with non-depolarizing muscle relaxants, care should be taken to ensure muscle strength has returned prior to extubation.

Dantrolene may cause significant muscle weakness in patients with pre-existing muscle disease and should be used with extreme caution in those patients. Sterile phlebitis may follow administration of dantrolene, and should be infused through the largest possible vein. The sterile phlebitis can be later treated with warm soaks and elevation. When used with calcium channel blockers (verapamil or diltiazem), dantrolene may produce life-threatening hyperkalemia and myocardial depression. Otherwise there does not appear to be significant negative interaction with other drugs.

Once a patient has been successfully treated for 48 hours with intravenous dantrolene may be stopped and the blood tested daily until the CK level is trending down.

Who Should Stock Dantrolene?

All facilities, including ambulatory surgery centers and offices, where MH triggering anesthetics (isoflurane, desflurane, and sevoflurane) and depolarizing muscle relaxants (succinylcholine) are administered, should stock dantrolene as indicated below, along with the other drugs and devices necessary to treat an MH reaction. If none of these agents are ever in use in the facility, then dantrolene need not be kept on hand.<

Succinylcholine is a potentially life-saving medication used to treat upper airway obstruction, and should be immediately available in any facility that administers anesthesia or sedative agents that have the potential to cause airway obstruction. In the absence of succinylcholine, practitioners should be prepared to administer an immediate-acting paralytic agent to treat life-threatening airway obstruction.

Watch this video FAQ for more information.

FAQ Video: Temperature Range For Refrigerated Supplies
FAQ Video: Temperature Range For Refrigerated Supplies

Does MHAUS state a specific temperature range for refrigerated supplies for an MH event?

Where Should Dantrolene Be Kept?

Dantrolene should be kept in or very close to the operating room, so that it is available immediately if MH occurs. Dantrolene may be stored at room temperature. A supply of sterile water for injection USP (without a bacteriostatic agent) should be kept nearby to mix with dantrolene before injection (60 ml/vial); the water for diluting dantrolene should not be stored in a refrigerator; it may be stored in a warming cabinet designed to maintain fluid temperatures between 35-40° C. All anesthesia and surgical team members should be aware of this location. NOTE: Dantrolene should not be mixed with any other diluent other than sterile water. The drug will not completely dissolve in crystalloid-containing solutions.

How Quickly Must Dantrolene Be Accessible?

Dantrolene must be available for all anesthetizing locations within 10 minutes of the decision to treat for MH. Dantrolene must be available for all anesthetizing locations where MH trigger agents are used.” This is a slight modification of the current recommendation that the drug be available within five minutes because the five minute recommendation was not made based on consensus discussion and it is often not practical to have a large supply of dantrolene in every area where anesthesia is administered. For example anesthesia administration is now common in locations far from the operating rooms such as interventional radiology suites. This comment and others were made at the MH Hotline – Professional Advisory Council meeting held on May 14, 2011.

Are There Any Advantages In Sharing A Supply of Dantrolene?

No. Minutes count in an MH emergency.

The Professional Advisory Council of MHAUS strongly recommends that an adequate supply of dantrolene be available wherever general anesthesia is administered. Responsibility for treatment rests with the facility where the surgery is performed. Sharing is not a good alternative.

Can Warming the Sterile Water Facilitate Mixing?

Newer formulations of dantrolene are more soluble, making the warming of the sterile water unnecessary.

What Is The Cost Of Dantrolene?

The cost of maintaining dantrolene in stock is a tiny fraction of most facility budgets and a very small price to pay for patient safety. By analogy, a cardiac defibrillator, a necessary emergency tool in all OR suites, is seldom used, and is paid for in time by each patient’s charges. In fact, many hospitals have 30-50 such units deployed at all times. Dantrolene, an emergency drug that is kept in only one location within most institutions, is an appropriate parallel to that situation and is relatively inexpensive when prorated.

*Contact manufacturer for current pricing. Although fulminant MH episodes are unusual, they do happen, and patients still die form MH. Remember that dantrolene is like a defibrillator; it is kept ready for use at all times, even though the need is rare. The cost can be prorated among all patients.

What Should Be On An MH Cart?


Therapy should be aimed at prompt administration of dantrolene, treatment of hyperkalemia, hyperventilation, and cooling to a target core temperature of no more than 38°C.

  1. Dantrolene – To treat an MH episode, an initial dose of dantrolene at 2.5 mg/kg is recommended. There are two formulations now available. DANTRIUM®/REVONTO® are the older formulation, which provides 20 mg dantrolene sodium/60 mL after reconstitution in sterile water. The second formulation, RYANODEX® (dantrolene sodium), is a new formulation that is an injectable suspension of dantrolene sodium providing 250 mg of dantrolene sodium/5 mL after reconstitution. RYANODEX® is manufactured by Eagle Pharmaceuticals, Inc. and was approved by the FDA in 2014.
    1. DANTRIUM®/REVONTO® – 36 vials should be available in each institution where MH can occur, each vial to be diluted at the time of use with 60 ml sterile water, USP (without a bacteriostatic agent). There are 3 grams of mannitol in each vial of 20 mg of dantrolene (0.15 g mannitol/ 1 mg dantrolene).
    2. RYANODEX® – 3 vials should be available in each institution where MH can occur, each to be diluted at the time of use with 5 ml of sterile water for injection, USP (without a bacteriostatic agent). There are 0.125 grams of mannitol in each vial of 250 mg of Ryanodex® (0.0005 grams mannitol/1 mg dantrolene).
  2. Sterile water for injection USP (without a bacteriostatic agent) – It is mandatory to get dantrolene sodium to its effective site, the skeletal muscle.
    1. DANTRIUM®/REVONTO® – Each 20 mg vial should be reconstituted by adding 60 ml of sterile water for injection, USP (without a bacteriostatic agent) and the vial shaken until the solution is clear. If the MH episode is proceeding rapidly, simply mix and inject. We advise that the sterile water be stored in 100 ml vials, not bags, to avoid accidental IV administration of this hypotonic solution.
    2. RYANODEX® – Each 250 mg vial should be reconstituted with 5 ml of sterile water for injection, USP (without a bacteriostatic agent) and shaken to ensure an orange-colored uniform, opaque suspension. RYANODEX® should be administered by intravenous push. Five percent dextrose injection, USP, 0.9% sodium chloride injection, USP, and other acidic solutions are NOT compatible with RYANODEX® and should not be used. The contents of the vial must be used within 6 hours after reconstitution.
  3. Sodium bicarbonate (8.4%) – 50 ml x 5
  4. Dextrose 50% – 50 ml vials x 2
  5. Calcium chloride (10%) – 10 ml vial x 2
  6. Regular insulin – 100 units/ml x 1 (refrigerated)
  7. Lidocaine* for injection (2%) – 100 mg/5 ml or 100 mg/10 ml in preloaded syringes (3). Amiodarone is also acceptable. ACLS protocols, as prescribed by the AHA, would be followed when treating all cardiac derangements caused by MH.
  8. Refrigerated cold saline solution – A minimum of 3,000 ml for IV cooling

* Lidocaine or procainamide should not be given if a wide-QRS complex arrhythmia is likely due to hyper­kalemia; this may result in asystole.

General Equipment

  1. Charcoal Filters - Two pairs of activated charcoal filters (Vapor-Clean, Dynasthetics, Salt Lake City, UT). Attach activated charcoal filters to inspiratory and expiratory ports of the anesthesia machine to quickly reduce the concentration of gas (<5ppm) from the anesthesia machine. In this situation, even though the anesthetic gas has been discontinued when MH was first suspected, the Vapor-Clean filter may become saturated after one hour; therefore, a replacement set of filters should be substituted after each hour of use.
  2. Syringes – (60 ml x 5) to dilute Dantrium®/Revonto® and (5 ml x 3) for Ryanodex®
  3. Intravenous catheters – 16G, 18G, 20G, 2-inch; 22G, 1-inch; 24G, 3/4-inch (4 each) (for IV access and arterial line)
  4. NG tubes – (sizes appropriate for your patient population)
  5. Toomey irrigation syringes – (60 ml x 2) with adapter for NG irrigation

Monitoring Equipment

  1. Esophageal or other core (e.g., nasopharyngeal, tympanic membrane, rectal, bladder, pulmonary artery catheter) temperature probes
  2. CVP kits (sizes appropriate to your patient population).  We recommend these are used in patients who are critically ill.
  3. Transducer kits for arterial and central venous cannulation

Nursing Supplies

  1. Large sterile Steri-Drape (for rapid drape of wound)
  2. Urine meter x 1
  3. Irrigation tray with piston (60cc irrigation) syringe
  4. Large clear plastic bags for ice x 4
  5. Small plastic bags for ice x 4
  6. Bucket for ice
  7. Test strips for urine hemoglobin

Laboratory Testing Supplies

  1. Syringes (3 ml) for blood gas analysis or ABG kits x 6 or point of care monitors; ISTAT with TB syringes (the point of care ISTAT device has replaced lab blood gene and electrolyte measurement).
  2. Blood specimen tubes for CK, myoglobin, SMA 19 (LDH, electrolytes, thyroid studies), PT/PTT, fibrinogen, fibrin split products; and lactate, CBC, platelets. If no immediate laboratory analysis is available, samples should be kept on ice for later analysis. This may well prove useful on retrospective review and diagnosis. Blood cultures are very useful and should be included to rule out bacteremia.
  3. Urine collection container for myoglobin level. Pigrnenturia (e.g , brown or red urine and heme positive dipstick) indicates that renal protection is mandated, when the urine is centrifuged or allowed to settled, and the sample shows clear supernatant, i.e., the coloration is due to red cells in the sample.
    1. Sodium bicarbonate (8.4%) – 50 ml x 5
    2. Dextrose 50% – 50 ml vials x 2
    3. Calcium chloride (10%) – 10 ml vial x 2
    4. Regular insulin – 100 units/ml x 1 (refrigerated)
    5. Lidocaine* for injection (2%) – 100 mg/5 ml or 100 mg/10 ml in preloaded syringes (3). Amiodarone is also acceptable. ACLS protocols, as prescribed by the AHA, would be followed when treating all cardiac derangements caused by MH.
    6. Refrigerated cold saline solution – A minimum of 3,000 ml for IV cooling 
The mission of MHAUS is to promote optimum care and
scientific understanding of MH and related disorders.