Malignant Hyperthermia

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Malignant Hyperthermia (MH) is a rare but potentially life-threatening condition that affects individuals undergoing general anesthesia. It is characterized by a hypermetabolic response to certain triggering agents, leading to muscle rigidity, high fever, tachycardia, acidosis, elevated creatine kinase, hyperkalemia, respiratory and metabolic acidosis, dark urine, rhabdomyolysis, and in severe cases, cardiac arrest. Understanding the symptoms, causes, and treatment options for MH is crucial for healthcare professionals and patients alike.

Muscle Rigidity: The First Sign

One of the earliest signs of malignant hyperthermia is muscle rigidity. This rigidity can occur in various muscle groups, including the jaw, neck, and extremities. It is often accompanied by an increase in body temperature and heart rate. The muscle rigidity is a result of abnormal calcium release from the sarcoplasmic reticulum in skeletal muscle cells.

High Fever and Tachycardia: Alarming Symptoms

As the condition progresses, individuals with malignant hyperthermia may experience a rapid increase in body temperature, leading to a high fever. This fever is often accompanied by tachycardia, an abnormally fast heart rate. These symptoms can be alarming and require immediate medical attention.

Acidosis and Elevated Creatine Kinase: Metabolic Imbalance

Malignant hyperthermia can lead to metabolic acidosis, a condition characterized by an imbalance in the body’s pH levels. This occurs due to the excessive production of lactic acid as a result of increased muscle activity. Additionally, individuals with MH may exhibit elevated levels of creatine kinase, an enzyme released during muscle breakdown.

Hyperkalemia: Electrolyte Disturbance

Hyperkalemia, an elevated level of potassium in the blood, is another common feature of malignant hyperthermia. This electrolyte disturbance can have serious implications for cardiac function and requires prompt intervention to prevent complications.

Respiratory and Metabolic Acidosis: Breathing Difficulties

As the metabolic imbalance worsens, individuals with malignant hyperthermia may experience respiratory acidosis. This occurs when the body’s ability to remove carbon dioxide from the bloodstream is compromised, leading to an accumulation of carbonic acid. The combination of respiratory and metabolic acidosis can result in severe breathing difficulties.

Dark Urine and Rhabdomyolysis: Kidney Involvement

Dark urine is a common symptom of rhabdomyolysis, a condition characterized by the breakdown of muscle tissue. In individuals with malignant hyperthermia, rhabdomyolysis can occur due to the excessive muscle activity and subsequent release of myoglobin into the bloodstream. This can lead to kidney damage and further complications.

Cardiac Arrest: A Life-Threatening Complication

In severe cases, malignant hyperthermia can progress to cardiac arrest, a life-threatening condition where the heart stops beating. Prompt recognition and treatment of MH are crucial to prevent this potentially fatal complication.

Treatment and Prevention

While there is no cure for malignant hyperthermia, prompt treatment can help manage the condition and prevent complications. The primary treatment for MH is the administration of dantrolene, a medication that inhibits calcium release in skeletal muscle cells. Dantrolene helps reverse the hypermetabolic state and restore normal muscle function.

In addition to dantrolene, other supportive measures may be necessary to stabilize the patient. These may include cooling measures to reduce body temperature, administration of intravenous fluids to maintain hydration, and correction of electrolyte imbalances.

Prevention of malignant hyperthermia is crucial, especially for individuals with a known susceptibility to the condition. Prior to undergoing general anesthesia, patients with a family history of MH or a personal history of adverse reactions to anesthesia should inform their healthcare providers. This allows for appropriate precautions to be taken, such as using alternative anesthetic agents or monitoring the patient closely for signs of MH.


Malignant hyperthermia is a rare but potentially life-threatening condition that can occur during general anesthesia. Understanding the symptoms and treatment options for MH is essential for healthcare professionals to ensure prompt recognition and management. Patients with a known susceptibility to MH should inform their healthcare providers before undergoing anesthesia to prevent complications. With early intervention and appropriate treatment, the prognosis for individuals with malignant hyperthermia can be significantly improved.

Haroon Rashid, MD
Rate author
Urgent Care Center of Arlington, VA
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