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Malignant Hyperthermia


David Tanen

, MD, David Geffen School of Medicine at UCLA

Reviewed/Revised Mar 2023

Malignant hyperthermia is a rare, life-threatening rise in body temperature that occurs in susceptible people who are given certain muscle-relaxing drugs plus an anesthetic gas for surgery.

  • Malignant hyperthermia can occur when the anesthesia is given or during or soon after surgery.

  • Muscle cells become overactive, causing sustained muscle contractions that produce heat and raise body temperature extremely high.

  • Symptoms include muscle rigidity, rapid heart rate, and rapid breathing

  • Doctors diagnose malignant hyperthermia based on symptoms in people who have just had surgery.

  • Treatment is rapid cooling.

Malignant hyperthermia usually develops after a person receives a muscle relaxant (most often succinylcholine) along with an anesthetic gas (most often halothane) for surgery. Although malignant hyperthermia may develop after the first use of these drugs, people usually develop the condition only after about three exposures. Susceptibility to malignant hyperthermia is an inherited genetic trait that runs in families.

Malignant hyperthermia may cause imbalances in body salts (electrolytes) and blood clotting. Excessive blood clotting (disseminated intravascular coagulation Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation is a condition in which small blood clots develop throughout the bloodstream, blocking small blood vessels. The increased clotting depletes the platelets... read more ) causes organ damage, followed by excessive bleeding when the body runs out of clotting factors.

Malignant hyperthermia can also cause significant muscle damage. Damaged muscles release the protein myoglobin, which turns the urine brown or bloody. This condition (myoglobinuria) can lead to acute kidney injury Acute Kidney Injury Acute kidney injury is a rapid (days to weeks) decline in the kidneys’ ability to filter metabolic waste products from the blood. Causes include conditions that decrease blood flow to the kidneys... read more or even kidney failure. Death may occur.

Symptoms of Malignant Hyperthermia

Malignant hyperthermia may develop during anesthesia or shortly after surgery. Often, the first signs are rapid breathing, a fast heart rate, and muscle rigidity, especially in the jaw. Temperature usually becomes extremely high (usually over 104° [40° C] and sometimes higher than 109° F [43° C]). Abnormal heart rhythms, nausea, and vomiting may occur. Urine may appear brown or bloody.

Diagnosis of Malignant Hyperthermia

  • Typical symptoms developing after anesthesia is given

Doctors suspect malignant hyperthermia when typical symptoms and signs occur within a few minutes to a few hours after anesthesia is given.

Blood is tested to detect organ damage and to exclude other possible causes. Urine is tested for myoglobinuria.

People with a family history of the disorder or a previous serious side effect during anesthesia can be tested to see whether they are susceptible to malignant hyperthermia. A sample of muscle tissue is tested to see whether it contracts in response to caffeine and halothane (caffeine halothane contracture test).

Genetic testing can also be done. However, because many gene abnormalities may be involved, genetic testing does not detect all (or even most) susceptible people and is not always available.

Treatment of Malignant Hyperthermia

  • Rapid cooling of the body

  • Giving dantrolene

People with malignant hyperthermia are cooled as quickly as possible, usually by removing the clothes and covering the skin with water or occasionally ice. To speed evaporation and body cooling, a fan may be used to blow air on the body. Body temperature is measured frequently, often continuously, in an intensive care unit. Dantrolene, a muscle relaxant, is usually given. By relaxing the muscles, fever and muscle damage are also reduced.

Abnormal blood clotting and symptoms related to organ malfunction may also need treatment. As with neuroleptic malignant syndrome Neuroleptic Malignant Syndrome Neuroleptic malignant syndrome is confusion or unresponsiveness, muscle rigidity, high body temperature, and other symptoms that occur when certain antipsychotic (neuroleptic) drugs or anti-vomiting... read more , doctors may try to prevent kidney damage from myoglobinuria by giving large amounts of intravenous fluid that contains added sodium bicarbonate.

Many people with malignant hyperthermia die even when they receive early and intensive treatment.

Prevention of Malignant Hyperthermia

Doctors try to prevent malignant hyperthermia in people who are high risk, which includes those with

  • Previous episodes of malignant hyperthermia

  • Positive genetic markers

  • Family members who have had problems with anesthesia

In these instances, doctors use local or regional anesthesia when possible. When general anesthesia must be used, doctors select those anesthetics that are least likely to cause a reaction.

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