Merck Manual

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Pet Owner Version

Malignant Hyperthermia in Cats


Hui-Chu Lin

, DVM, DACVAA, Department of Clinical Sciences, Auburn University

Reviewed/Revised Aug 2018 | Modified Oct 2022

Malignant hyperthermia is seen mostly in pigs, but it has also been reported in dogs, cats, and horses. This syndrome is characterized by abnormally high body temperature and muscle contractions that can potentially lead to death. A rapid and sudden increase in body temperature can be followed by muscle rigidity, a very rapid and irregular heartbeat, increased breathing rate, a bluish tinge to the skin and mucous membranes, unstable blood pressure, fluid buildup in the lungs, impaired blood coagulation, kidney failure, and death.

Malignant hyperthermia is triggered in susceptible animals by excitement, apprehension, exercise, or environmental stress. Giving certain anesthetics or specific drugs that affect the neurologic and muscular systems also consistently triggers malignant hyperthermia in these animals.

Diagnosis is based on the development of signs in an animal that has been given an anesthetic agent or is participating in a stressful event. Signs can develop slowly or rapidly. Animals that are not under anesthesia may show open-mouthed breathing and an increased breathing rate, followed by a temporary break in breathing. Blanching and redness of the skin followed by blotchy blue tinges can be seen in light-colored animals. Body temperature increases rapidly and can reach 113°F (45°C).

Usually, malignant hyperthermia episodes occur suddenly and are severe. If the condition is recognized early in an animal under anesthesia, supportive measures may be able to save the animal. A drug called dantrolene may also be effective. Unfortunately, regardless of treatment, malignant hyperthermia is often fatal.

Stress must be minimized to prevent malignant hyperthermia episodes in susceptible animals. If a cat that is suspected to be susceptible to malignant hyperthermia (or that has survived a previous episode) needs anesthesia and surgery, certain precautions should be taken. These include administering dantrolene before anesthesia and avoiding certain anesthetic agents. Certain local anesthetics are also safe to use. All procedures must be kept as short as possible because malignant hyperthermia happens most often when the animal has been under anesthesia for longer than 1 hour. Although these precautions cannot prevent malignant hyperthermia, they can reduce the chances of a crisis developing.

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