Malignant Hyperthermia

Malignant hyperthermia is a rare genetic disorder. It causes sudden, life-threatening problems such as a high fever and a rapid, irregular heart rate. The disorder occurs during or right after a person is in a sleep-like state of non-feeling produced by medicines (general anesthesia).


The disorder is caused by a sudden increase in the body's breakdown and use of food and energy (metabolism). It is almost always triggered by a type of medicine that makes you sleep (general anesthetic) and is inhaled, or it is triggered by a medicine that relaxes your muscles (muscle relaxant).


  • Rapid, irregular heart rate.

  • Difficulty breathing.

  • Excessive sweating, often with clamminess.

  • Stiff muscles in all of the large muscle groups, not just where the surgery was.

  • Excessive bleeding from the nose or where the surgical cut (incision) was made.  

  • Blood in the urine.

  • Dark brown urine.

  • Rapidly increasing fever.


Your caregiver will be able to diagnose the disorder from your signs and symptoms.


It is not always known why the disorder develops in some people and not others. However, tests can show if a person is at risk of developing the disorder. Usually, testing is only done if there is a family history of problems under general anesthesia. To be tested, a muscle tissue sample (muscle biopsy), urine sample, or blood sample may be taken.

If a close relative has been diagnosed with malignant hyperthermia or has had significant problems with anesthesia in the past, tell all caregivers who treat you. Carry a wallet card, bracelet, or medical identification tag that indicates this. Always keep it with you. If you are in an accident or have a medical emergency and cannot communicate, this item may prevent caregivers from giving you the medicines that trigger the disorder.


Treatment should begin immediately. Treatment may involve:

  • Receiving medicines through an intravenous (IV) tube.

  • Being wrapped in a cooling blanket.

  • Receiving fluids through a vein and by mouth.


  • You have any symptoms of malignant hyperthermia. These may occur up to 24 hours after waking up from general anesthesia.

  • You have persistent vomiting.

  • You have decreased urine output.

  • You have unexplained muscle pain.