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.
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.
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.
Please see our Safe and Unsafe Anesthetics page for complete details.
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.
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.
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:
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.
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.
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:
Watch this video FAQ for more information.
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.
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.
Please see our Associated Conditions page.
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.
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.
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.
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.
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.
Newer formulations of dantrolene are more soluble, making the warming of the sterile water unnecessary.
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.
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.
* Lidocaine or procainamide should not be given if a wide-QRS complex arrhythmia is likely due to hyperkalemia; this may result in asystole.