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Malignant hyperthermia (reaction to anesthesia)

Also called: Malignant hyperthermia

A rare inherited reaction to some anesthesia drugs causing high fever, muscle rigidity, and a fast heartbeat during or after surgery.

TreatmentDantrolene
FamilyTell surgeons about family history

Overview

Some anesthesia gases trigger a fast rise in body heat.

Dantrolene treats it.

Symptoms

Common signs:

  • High fever during surgery
  • Muscle rigidity

Less common

  • Muscle stiffness

When to get medical care

Call 911Call 911 now for: high fever during surgery, muscle rigidity.
Get care todayMilder symptoms that could be early signs.
See a doctor soonQuestions about lowering your risk.

Causes

Gene change.

Does it spread or run in families?

  • It isn't contagious. You can't catch it from someone else.
  • It can run in families. Tell your doctor if a parent, brother, or sister has it.

Who is more likely to get it

  • Family history

Diagnosis

This is diagnosed in the emergency room or hospital.

The exam

A physical exam.

Tests

Tests, if needed:

  • Genetic test:

Treatment

Emergency care is needed. While waiting for help:

Self-care

  • Treated in the operating room

Prevention

To lower your risk or prevent problems:

  • Tell your team about family reactions

Which doctor treats this

  • Emergency doctors treat it first, in the ER.
  • They may send you to an anesthesiologist, before any future surgery.

Living with it

Support groups and helplines

Back to school, work, or sports

  • Recovery time varies. Ask your care team when you can drive, lift, work, and exercise.

Children, pregnancy, and older adults

  • Families: Relatives should tell anesthesia teams before surgery.

Pregnancy and breastfeeding

  • If you're pregnant or planning to be, tell your prenatal provider about this condition.
  • Don't start or stop any medicine on your own. Some are safe in pregnancy and some need to be changed.
  • Ask before taking any pain reliever. The FDA advises avoiding ibuprofen and naproxen after 20 weeks unless your doctor says to.
  • Breastfeeding: Most medicines are fine, but ask. The NIH LactMed database lists what's known about each one.

For caregivers

  • Go to visits when you can and take notes.
  • Keep a list of medicines, allergies, and doctors in one place.
  • Learn the warning signs that need fast care.
  • Learn CPR. Many hospitals and the Red Cross offer classes.
  • Take breaks and ask for help. Caregivers need care too.

Outlook

Fast treatment saves lives.

Getting ready for your visit

Bring a list of your symptoms and medicines.

What to bring

  • A list of your medicines and supplements
  • Notes on when symptoms started and what makes them better or worse

Questions to ask

  • What follow-up care do I need?
  • How can I prevent this from happening again?

Research studies

Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.

Search ClinicalTrials.gov for studies on Malignant hyperthermia (reaction to anesthesia)

Sources

Last updated 2026-11-12.