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A 45-year-old woman undergoes an open cholecystectomy for multiple gallstones. Her medical history is significant only for alcohol abuse, and she is not taking any medications. At the conclusion of the operative procedure, the anesthesiologist notices that her end-tidal carbon dioxide has increased and her peak airway pressures have increased. Her temperature has abruptly increased to 39.2 °C (102.5 °F). Her heart rate increases to 110/min and blood pressure increases to 190/110 mm Hg. The endotracheal tube position is unchanged, and her lungs are clear to auscultation.
Which of the following is the most appropriate next step in her management?
A Inform the surgeon the patient may be bleeding
B Lower the blood pressure with sodium nitroprusside
C Continue hydration and administer intravenous dantrolene.
D Administer a neuromuscular blocker
E Administer intravenous corticosteroids
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Answer and Critique (Correct Answer = C)
Malignant hyperthermia is 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. It usually occurs on exposure to the drug but can occur several hours after the initial exposure and can develop in patients who were previously exposed to the drug without effect. Increased intracellular calcium leads to sustained muscle contractions with skeletal muscle rigidity and masseter spasm, tachycardia, hypercarbia, hypertension, hyperthermia, tachypnea, and cardiac arrhythmias. The clinician should have a high index of suspicion in patients with a family history of problems during anesthesia. Increased end-tidal carbon dioxide and peak airway pressures may be the presenting signs intraoperatively.
Malignant hyperthermia is life-threatening if not treated immediately, and the mortality rate is estimated at 10%. Supportive treatment includes discontinuing the drug, hydration, oxygen, and cooling measures. Dantrolene sodium, 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 symptoms resolve. Response to dantrolene is not pathognomonic, but the diagnosis is supported if signs and symptoms resolve rapidly and completely. Pretreatment of susceptible patients with dantrolene prior to the anesthetic administration will prevent the development of malignant hyperthermia.
There is no evidence that the patient is bleeding. Lowering the blood pressure acutely will not affect the underlying problem. A neuromuscular blocking agent will not prevent or treat seizures. She is intubated and has no evidence of laryngospasm.
Key Point
Malignant hyperthermia is a life-threatening inherited skeletal muscle disorder characterized by a hypermetabolic state precipitated by exposure to volatile inhalational anesthetics and depolarizing muscle relaxants.
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CONTINUE HYDRATION AND DANTROLENE
