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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. (See the section below on Testing for MH Susceptibility.)
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, Pittsburgh, PA by calling 888-274-7899.
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 Associated Conditions.
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.