Q: I've heard a lot about malignant hyperthermia (MH). What is it and what warning signs should I be alert to?
A: MH is a rare, genetic, life-threatening response to anesthesia characterized by skeletal muscle contractions and excessively high body temperatures that can reach 105 to 108° F (40.6 to 42.2° C). Metabolic acidosis—pH below 7.35 and a bicarbonate level below 22 mEq/L—can also occur, resulting in mental status changes and, potentially, coma. Dysrhythmias and cardiac arrest may also ensue if MH is left untreated.
An autosomal dominant gene (RYR1) causes calcium abnormalities when the patient is exposed to succinylcholine, a powerful muscle relaxant used to temporarily paralyze the respiratory muscles during emergent or operative procedures. Although succinylcholine is the most common offender, MH may be caused by other anesthetics. MH has also been linked to patients with multiminicore myopathy—an inherited skeletal muscle disorder characterized by hypertonia—and central core disease.
The patient with MH presents with a multitude of symptoms. Muscle rigidity and fasciculation are most commonly observed; however, be alert for hyperthermia, tachycardia, tachypnea, diaphoresis, arrhythmias, and cyanosis.
Left untreated, secondary signs of MH include cardiac arrest, disseminated intravascular coagulation (DIC), acute renal failure, myoglobinuria, and rhabdomyolysis. Acid-base and electrolyte imbalances, such as hyperkalemia and hypercalcemia, may also occur.
Various blood tests, diagnostic procedures, and clinical presentations can detect the severity of MH. Vital signs will reveal tachycardia, tachypnea, hyperthermia, and fluctuating BP. Respiratory and/or metabolic acidosis can be seen through arterial blood gases. A comprehensive metabolic panel will show electrolyte and kidney function abnormalities, such as an increase in blood urea nitrogen and creatinine, hyperkalemia, and hypercalcemia. Coagulation studies aid in detecting DIC, and urinalysis aids in detecting myoglobinuria. Dysrhythmias can be seen with continuous cardiac monitoring.
Upon detection of MH, anesthesia and the concomitant surgery must be stopped. The surgical procedure is postponed and the trigger agent removed. Immediately administer dantroline sodium—a skeletal muscle relaxant—as a reversal agent. Hyperventilate the patient with 100% oxygen and administer I.V. fluids for hydration and dilution of the trigger agent/succinylcholine.
When hyperthermia occurs, apply cooling blankets; ice to the groin, axilla, and neck areas; or chilled I.V. fluids. During the use of cooling agents, frequently monitor the patient's temperature and perform frequent skin assessments. Continuous telemetry is essential for monitoring potential arrhythmias and tachycardia.
A thorough preoperative history may prevent MH. It's imperative to inquire about a history of reactions to or complications from anesthesia in the patient or family. Genetic testing for RYR1 defects is available to pinpoint familial tendencies of MH. Instruct the patient with a known history of or potential for MH to wear a medical-alert bracelet.