Malignant hyperthermia is a rare, inherited reaction to certain anesthesia drugs and gases. In people who are susceptible, it can cause the body’s muscles to work too hard, body temperature to rise fast, and the heart rate to become irregular. It can be life-threatening if it is not treated quickly.

It is usually triggered by halogenated inhaled anesthetics and succinylcholine, a muscle relaxant used during anesthesia. The problem comes from too much calcium being released inside muscle cells, which leads to sustained muscle contraction, extra heat, and muscle breakdown.

Common warning signs include:

• fast heart rate
• fast breathing or rising carbon dioxide
• muscle rigidity or jaw tightness
• high body temperature
• acidosis, which means too much acid in the blood
• high potassium and muscle breakdown

If MH is suspected, the triggering drugs are stopped and dantrolene is given right away.