What Is Malignant Hyperthermia, and What Causes It?

The idea of getting anesthesia can be anxiety provoking. Although anesthesia is safer now than ever before, sometimes complications happen. One rare complication is called malignant hyperthermia. Malignant hyperthermia happens in 1 out of every 100,000 surgeries involving adults and in 1 out of every 30,000 surgeries involving children.

Some people are at higher risk of developing malignant hyperthermia during anesthesia. Let’s take a closer look at malignant hyperthermia and what it can mean for you. 

Why does malignant hyperthermia happen?

Certain anesthesia medicines cause muscle cells to release calcium. This causes a chain reaction where muscles contract uncontrollably, use up their energy stores, and die. During this reaction, waste products like potassium, carbon dioxide, and lactic acid are released into the bloodstream. The process also generates a lot of heat. Our bodies can handle this process when it happens slowly. But with malignant hyperthermia, the process happens so fast that it overwhelms the body and causes organ damage. 

Do certain drugs have a higher association with malignant hyperthermia?

Certain drugs are more likely to cause malignant hyperthermia, including:

• Desflurane 

• Enflurane 

• Halothane 

• Isoflurane 

• Methoxyflurane 

• Sevoflurane 

• Succinylcholine

What are the symptoms of malignant hyperthermia?

The symptoms of malignant hyperthermia include: 

• Increased body temperature: Temperatures as high as 110 F have been recorded.

• Increased heart rate and breathing rate.

• Muscle stiffness — especially the jaw muscles.

Is malignant hyperthermia life-threatening?

Malignant hyperthermia is life-threatening and, if left untreated, leads to death. Rapid treatment is crucial. For each 10-minute delay in the treatment, the rate of complications, including heart failure or kidney failure, increases substantially. 

How is malignant hyperthermia treated?

A medication called dantrolene treats malignant hyperthermia by stopping muscles from contracting. Dantrolene treatment is lifesaving. Hospitals and surgery centers have to have it available within 10 minutes of when malignant hyperthermia is diagnosed. 

Besides giving dantrolene, healthcare providers will: 

• Stop anesthesia medications.

• Stop the surgery — or, if surgery cannot be stopped, different anesthesia medications are used.

• Give oxygen.

• Put a cooling blanket over the person.

• Give fluids through the vein, to lower body temperature.

Who’s most at risk of experiencing malignant hyperthermia?

Some people are more at risk of developing malignant hyperthermia, including those with:

• Medical conditions that affect the muscles.

• Genetic mutations in the ryanodine receptor.

About two-thirds of people at risk for malignant hyperthermia have a genetic mutation in their ryanodine receptor. This receptor controls the movement of calcium in muscle cells. In normal situations, this mutation doesn’t cause any problems. So, most people with the mutation have no idea they are at risk for developing malignant hyperthermia.

Which other conditions put people at risk of malignant hyperthermia?

People with conditions that affect muscles can develop either malignant hyperthermia or a reaction similar to malignant hyperthermia. People with the following conditions are most at risk:

• Inherited myopathies: Especially central core myopathy, multiminicore myopathy, and King Denborough syndrome.

• Rhabdomyolysis: Including conditions associated with rhabdomyolysis.

• Muscular dystrophy: Including Duchenne and Becker muscular dystrophy.

Is there any way to know if you’ll have a bad reaction to drugs used for anesthesia?

Here are some questions to ask yourself:

• Do I have an inherited myopathy or muscular dystrophy?

• Do I have a history of severe muscle weakness?

• Do I have a history of muscle breakdown or rhabdomyolysis?

• Has anyone in my family ever had malignant hyperthermia?

• Has anyone in my family ever had a serious reaction to anesthesia? 

• Has anyone in my family ever died during anesthesia?

If you answered “yes” to any of these questions, you could be at risk for malignant hyperthermia. Talk to your healthcare provider about getting genetic testing for the mutation in the gene that codes for the ryanodine receptor. 

What should I do if I am at risk for having malignant hyperthermia?

Remember that malignant hyperthermia is only an issue if you’re having anesthesia. The rest of the time, being at risk doesn’t affect your life. 

If you need anesthesia, you should ask to speak to the anesthesia team before the day of your procedure. At that meeting, you should:

• Ask them to complete this patient safety checklist.

• Give them this templated letter to keep in your patient file.

• Ask how quickly they can administer dantrolene.

• Ask if they have a malignant hyperthermia response poster in the procedure room.

• Give them the American Association of Nurse Anesthesiology’s Malignant Hyperthermia hotline number (800-644-9737).

You can also get a medical alert bracelet. These can be helpful in situations where you might need emergency surgery and don’t have time to talk to the anesthesia team. 

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Written by:

Ronald W. Dworkin, MD, PhD

Ronald W. Dworkin, MD, is a board-certified anesthesiologist who has been practicing anesthesiology in a community hospital for 30 years. He has taught in the honors program at George Washington University for over 10 years and works as a senior fellow at the Hudson Institute.

Edited by:

Patricia Pinto-Garcia, MD, MPH

Patricia Pinto-Garcia, MD, MPH, is a medical editor at GoodRx. She is a licensed, board-certified pediatrician with more than a decade of experience in academic medicine.

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