What is Malignant Hyperthermia?
Malignant hyperthermia (MH) is a genetic condition that affects the muscles. It usually causes an overactive response to certain types of anesthetic gases commonly used in surgeries, or a muscle relaxant called succinylcholine. An overactive response means the body starts to break down substances too quickly, causing a rapid increase in body temperature and other complications.
What Causes Malignant Hyperthermia?
Malignant hyperthermia is a potentially dangerous reaction to certain medications or treatments. This can happen in people who have a genetic predisposition to it. Common triggers are specific types of anesthetic gases (known as halogenated anesthetic gases) or a drug called succinylcholine. These are often used during surgeries.
However, it’s not exclusive to surgery – it can happen in response to intense physical activity or exposure to high temperatures. It’s important to note that not all anesthetic gases cause this reaction. For instance, Nitrous Oxide and Xenon, which are also inhaled anesthetics, are not associated with malignant hyperthermia as they are not halogenated (they don’t contain halogens).
Risk Factors and Frequency for Malignant Hyperthermia
Malignant hyperthermia is a condition where the exact occurrence is uncertain. Research indicates that it affects 1 in 100,000 adults and 1 in 30,000 children. The geographical area can influence how often malignant hyperthermia occurs. High occurrences have been found in families in Wisconsin and the upper Midwest region. Despite proper treatment, the death rate due to malignant hyperthermia is between 3% and 5%.
Malignant hyperthermia can also develop in association with other disorders such as central core disease and King-Denborough syndrome. Central core disease is a rare, non-evolving muscle disease that causes muscle weakness and low muscle tone. King-Denborough syndrome is another rare muscle disease associated with several distinct physical characteristics.
Historically, there have been rarely recorded instances of stress provoked “awake malignant hyperthermia.” Notably, a particular case of exercise-induced malignant hyperthermia led to the death of a 13-year-old boy. Studies later revealed the presence of the causative RYR1 mutation in both the boy and his family members.
The susceptibility to malignant hyperthermia is not limited to humans. It has been observed in other species as well, especially pigs, which significantly contributed to the initial research into this disease and available treatments.
Signs and Symptoms of Malignant Hyperthermia
Malignant hyperthermia is a severe reaction to certain medications used during anesthesia. If someone has this condition, they might show signs like a fast heart rate (tachycardia), rapid breathing (tachypnea), low oxygen levels in the blood (hypoxemia), high levels of carbon dioxide in the blood (hypercarbia), metabolic and respiratory acidosis, high levels of potassium in the blood (hyperkalemia), abnormal heart rhythms (cardiac dysrhythmias), low blood pressure (hypotension), muscle stiffness, and a high body temperature (hyperthermia).
Usually the first signs to appear are a fast heartbeat and an increase in carbon dioxide, because the body is producing more than usual. Not everyone will show all these symptoms, and the diagnosis sometimes may be missed if not highly suspected. Malignant hyperthermia can happen anytime during or after surgery.
Sometimes, patients prone to this condition might also experience stiff jaw muscles. This condition needs to be considered if there are signs of increased metabolism, such as an increase in the acid levels in the body or a rise in body temperature.
- Fast heart rate (tachycardia)
- Rapid breathing (tachypnea)
- Low oxygen (hypoxemia)
- High carbon dioxide (hypercarbia)
- Metabolic and respiratory acidosis
- High potassium (hyperkalemia)
- Abnormal heart rhythms (cardiac dysrhythmias)
- Low blood pressure (hypotension)
- Muscle stiffness
- High body temperature (hyperthermia)
Testing for Malignant Hyperthermia
Diagnosing malignant hyperthermia, a potentially life-threatening reaction to certain drugs used during general anesthesia, usually involves a specific type of test called the caffeine halothane contracture test (CHCT). The test studies how a small sample of live muscle fibers reacts when exposed to certain chemicals, like halothane and caffeine, which are types of anesthetics. This reaction can hint at how your muscles might respond to these drugs under anesthesia.
Genetic testing is another approach that’s becoming increasingly common and valuable. This kind of test looks for certain changes in the RYR1 gene, or other related genes, that are known to be linked with malignant hyperthermia.
However, these tests can be costly and are not offered everywhere. Thus, when a patient needs surgery urgently or in an emergency situation, and there’s some reason to suspect they or a close relative could be at risk of malignant hyperthermia, doctors like anesthesiologists will typically choose a “non-triggering anesthetic”. This is a specific combination of drugs that is much less likely to cause a malignant hyperthermia reaction.
It’s important to note, though, that malignant hyperthermia’s symptoms can look similar to several other unrelated health conditions, such as neuroleptic malignant syndrome, pheochromocytoma (a rare tumor of the adrenal glands), sepsis (a life-threatening infection), thyroid storm (a severe and sudden increase in thyroid hormone levels), serotonin syndrome (caused by an excess of serotonin, a chemical your neurons produce), or even simply overheating due to some other cause such as certain medications.
Treatment Options for Malignant Hyperthermia
When treating malignant hyperthermia, a severe reaction to certain medications used for anesthesia during surgery, it’s crucial to act fast. The moment this condition is suspected, all medications triggering it should be stopped immediately. The patient will be given 100% oxygen and non-triggering anesthetic agents for their care while preparations are made to finish the surgery as soon as safely possible.
In response to this medical emergency, the doctors administer dantrolene, a special medication, intravenously (which means directly into a vein). This medicine is key in treating malignant hyperthermia. In tandem with the administration of dantrolene, doctors also work on correcting a variety of related complications, such as excessively high body temperature (hyperthermia), acidic blood (acidosis), low oxygen levels in blood (hypoxemia), irregular heartbeats (arrhythmias), and kidney function preservation.
Irregular heartbeats can be regulated with antiarrhythmic medication, and kidney function can be protected through maintaining a urine flow of at least 2 ml/kg/hr with a medication called furosemide. This step is important because it protects the kidneys from possible severe damage due to a condition called acute tubular necrosis, which might happen because of harmful substances (myoglobin) released from the affected skeletal muscles.
The plan of action during this medical emergency usually follows these steps:
- Stop the triggering medications.
- Call for medical help.
- Administer dantrolene until the reaction subsides.
- Ramp up ventilation to decrease the concentration of carbon dioxide in exhaled air.
- Apply cooling methods (like cold IV fluids and ice packs).
- Treat irregular heartbeats.
- Perform certain lab tests, including a blood gas analysis (to measure the oxygen, carbon dioxide, and pH levels in the blood), electrolytes (especially potassium), checking the amount of myoglobin in the blood and urine, and how well the blood is clotting.
- Keep administering dantrolene every 4 hours for 24 to 48 hours.
- Ensure urine output is maintained.
Patients generally experience better outcomes the quicker the condition is diagnosed, treated with dantrolene, and cooled down to prevent a rapid rise in core body temperature.
Once the patient is stabilized, they need to be moved to the intensive care unit for at least 24 hours. This enables doctors to continue monitoring the patient and watch for any signs that the condition could be returning. The highest risk for the condition recurring tends to be in patients with a large muscle mass or those who were under anesthesia for an extended period before the condition was triggered.
In the past, it was common to pretreat patients who were susceptible to malignant hyperthermia with dantrolene, but this is no longer recommended. Instead, these patients should receive anesthetic that doesn’t trigger the condition.
What else can Malignant Hyperthermia be?
When a doctor is trying to figure out if a patient has malignant hyperthermia, they would also consider the following possible conditions and factors:
- Reactions to contrast dye
- Cystinosis, a condition that affects the body’s cells
- Diabetic coma
- Drug toxicity or overdose
- Exposure to environmental heat
- Equipment malfunction during treatment
- Exercise-induced hyperthermia
- Freeman-Sheldon syndrome, a genetic disorder
- Heatstroke
- Hyperthyroidism, an overactive thyroid gland
- Hypokalemic periodic paralysis, a muscle disorder
- The presence of blood inside the skull
- Multiple organ dysfunction syndrome
- Muscular dystrophy, a group of genetic diseases
- Myotonia, a condition that causes muscle stiffness
- Osteogenesis imperfecta, also known as brittle bone disease
- Pheochromocytoma, a rare tumor of the adrenal glands
- Prader-Willi syndrome, a genetic disorder
- Rhabdomyolysis, a breakdown of muscle tissue
- Thyrotoxicosis, a condition caused by an excess of thyroid hormone
- Problems with ventilation
- Wolf-Hirschhorn syndrome, a genetic disorder
What to expect with Malignant Hyperthermia
Full recovery is possible if the symptoms of malignant hyperthermia – a severe reaction to certain drugs used during general anesthesia – are detected early and appropriate treatment is started swiftly. However, despite quick treatment, serious complications like multiple organ failure and even death can still happen. Nonetheless, the death rate is less than 5%.
Possible Complications When Diagnosed with Malignant Hyperthermia
The complications from an episode of malignant hyperthermia can be severe. These might consist of:
- Brain damage, where the brain cells are harmed
- Cardiac arrest, which means the heart stops beating suddenly
- Death can occur as the most severe outcome
- Heart failure, where the heart is unable to pump blood efficiently
- Internal bleeding that takes place inside the body
- Kidney failure, resulting in the kidneys unable to filter waste from the blood
- Pulmonary edema, causing fluid to accumulate in the lungs
- Skeletal muscle degeneration, indicating a breakdown in your body’s muscle tissue
Preventing Malignant Hyperthermia
If your family member has malignant hyperthermia, which is a severe reaction to certain drugs used during general anesthesia, you should know that it can run in families. The Malignant Hyperthermia Association of the United States (MHAUS) is a useful resource for those wanting to learn more about this condition. Founded in 1981, MHAUS provides a wealth of information about malignant hyperthermia. They even have a 24-hour hotline, at (800) MH-HYPER or (800) 644-9737, where you can reach out for more information or assistance anytime.
