Malignant hyperthermia is a life-threatening skeletal muscle disorder

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A 59-year-old man is evaluated for tachycardia and hypertension six hours after undergoing an uncomplicated open cholecystectomy under general anesthesia. The patient had intraoperative high blood pressure and was treated postoperatively with metoprolol, 5 mg every 4 hours by intravenous bolus. The patient underwent repair of a laceration of the liver 5 years ago and had an uncomplicated intraoperative and postoperative course. He has a history of essential hypertension, and his medications are hydrochlorothiazide and metoprolol.

On physical examination, the temperature is 39.2 °C (102.5 °F), the blood pressure is 190/110 mm Hg, and the pulse rate is 115/min. There is significant rigidity of all his extremities.

Which of the following is the most appropriate therapy for this patient?

A) Alcohol sponge baths
B) Ampicillin-sulbactam
C) Corticosteroids
D) Dantrolene
E) Sodium nitroprusside

MKSAP Answer and Critique

The correct answer is D) Dantrolene. This item is available to MKSAP 15 subscribers as item 26 in the Pulmonary and Critical Care Medicine section. MKSAP 16 will release Part A on July 31. More information is available online.

This patient likely has malignant hyperthermia, an inherited skeletal muscle disorder characterized by a hypermetabolic state precipitated by exposure to volatile inhalational anesthetics (halothane, isoflurane, enflurane, desflurane, sevoflurane) and the depolarizing muscle relaxants succinylcholine and decamethonium. Although malignant hyperthermia usually occurs at the time of exposure intraoperatively, it can occur several hours after the initial exposure and can develop in patients who were previously exposed to the drug without any effect. Increased intracellular calcium leads to sustained muscle contractions with skeletal muscle rigidity and masseter spasm, tachycardia, hypercarbia, hypertension, hyperthermia, tachypnea, and cardiac arrhythmias.

Malignant hyperthermia is life-threatening unless treated promptly and aggressively. Supportive measures include hydration and decreasing the fever. Dantrolene, a skeletal muscle relaxant, is given as a bolus of 1 mg/kg intravenously and then 2 mg/kg every 5 to 10 minutes until the symptoms resolve. Response to dantrolene is not diagnostic of the disorder but is supportive if signs and symptoms resolve quickly. For those patients with a known history, pretreatment with dantrolene before the anesthetic agent is administered prevents the development of symptoms.

Alcohol sponge baths are generally not recommended as an augmentation of evaporative cooling in any hyperthermic patient, including malignant hyperthermia, owing to the possibility of substantial alcohol absorption through the skin. Furthermore, augmented cooling (typically accomplished with water misting and forced air circulation by fans) may result in shivering which can increase body temperature unless it is suppressed with benzodiazepine administration. Ampicillin-sulbactam might be a consideration if acute ascending cholangitis were suspected; however, this is unlikely only hours after an elective cholecystectomy. Furthermore, an infection cannot account for the patient’s muscular rigidity. Corticosteroids would be effective treatment for an allergic reaction, but there are no symptoms suggesting an allergic reaction such as rash, urticaria, angioedema, or wheezing. Sodium nitroprusside is indicated in patients with hypertensive emergencies. However, this patient’s blood pressure is elevated secondary to malignant hyperthermia, and treatment of the underlying disorder is the preferred therapy.

Key Point

Malignant hyperthermia is a life-threatening skeletal muscle disorder characterized by a hypermetabolic state precipitated by exposure to volatile inhalational anesthetics or depolarizing muscle relaxants.

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