Malignant hyperthermia (MH) is a rare reaction to certain medicines used for general anesthesia. This problem runs in families (genetic). This means it's passed down from parents to children. The problem is severe and life-threatening. But it can be treated. You can take steps to help prevent it in the future. It's vital for your family members to know that they may also be likely to have MH.
Causes and symptoms of malignant hyperthermia
MH happens in people who have a gene that causes abnormal proteins in the muscles. Certain anesthesia medicines react with these proteins. This leads to sudden and severe symptoms. These include:
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Increased heart rate.
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Severe muscle contractions.
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Very high body temperature.
These symptoms appear soon after the medicines are given. They may also appear soon after surgery has ended. This is less common.
Treatment for malignant hyperthermia
Any person being given anesthesia is closely watched for signs of MH. The surgery and medicines are stopped if you develop signs of MH. Steps are taken to cool your body. You may get an antidote medicine called dantrolene. This medicine is given for 24 to 48 hours. Medical staff will watch you closely during that time.
Possible complications
The problem can lead to the breakdown of muscle tissues if it's not treated quickly. The result may be cardiac arrest, brain damage, kidney failure, or even death.
When to contact your doctor
Get emergency medical care right away if you are likely to get MH and have any of the following symptoms:
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Dark brown urine
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Fever of 105°F (40.6°C) or higher, or as advised by your health care provider
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Muscle rigidity and stiffness
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Unexplained bleeding
Also tell your surgeon and anesthesiologist before you get anesthesia if you or anyone in your family has had MH during or after a past procedure.
Tell your health care providers
People who are likely to have this problem can still have surgery if they take precautions. If you have had MH, tell all health care providers before you have any dental work or surgery. Carry a wallet card or medical alert bracelet. Your family members may also have the gene for MH. Even if they had surgery without problems in the past, they should not assume they couldn’t get MH in the future. All your close family members should tell their providers that they might be likely to get MH and consider getting tested.
To learn more
Author: Michels, Karen
© 2000-2026 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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