Chapter 33. Anesthesia in the Surgical Intensive Care Unit
A previously healthy 24-year-old, 75-kg woman developed hypertension, hypercarbia, and hyperthermia after induction of anesthesia with midazolam, fentanyl, propofol, and succinylcholine. Malignant hyperthermia (MH) was suspected, and she was given an initial intravenous (IV) bolus dose of dantrolene. An intraoperative creatinine kinase was measured as 23,000 U/L, and potassium was measured as 5.7 mEq/L. After the patient was stabilized, she was transported to the intensive care unit (ICU) for monitoring. Which of the following statements about MH is correct?
A. Patients with MH should be monitored for 12 hours in the postoperative period.
B. MH is caused by an abnormality in ryanodine receptors in skeletal muscle.
C. One should monitor for hypokalemia in MH.
D. A negative screen of the RYR1 and CACNA1S genes rules out MH susceptibility.
B. Malignant hyperthermia (MH) is an autosomal dominant disease of hypermetabolism in the skeletal muscle that is triggered by all potent volatile anesthetics and depolarizing muscle relaxants. MH is caused by abnormalities in ryanodine receptors in skeletal muscle that cause an abnormal buildup of myoplasmic calcium, which leads to an immense metabolic reaction. This could result in increased metabolic acidosis, increased carbon dioxide production, increased heart rate, hyperthermia, hyperkalemia, increased creatine kinase, myoglobinemia, myoglobinuria, and muscle rigidity. Multisystem organ failure can also develop. The most common initial signs of MH are hypercarbia, masseter muscle rigidity, and sinus tachycardia. The most frequent clinical signs include hyperthermia, sinus tachycardia, and hypercarbia. The caffeine halothane contracture assays done on muscle biopsies remain the most reliable tests for MH. Molecular genetic testing that identifies mutations in the RYR1 and CACNA1S genes confirms the diagnosis of susceptibility to MH; however, a negative screen of the RYR1 and CACNA1S genes does not rule out MH susceptibility.
When MH is suspected, all potent halogenated anesthetics and depolarizing muscle relaxants should be discontinued, and the patient should be hyperventilated. Further administration of succinylcholine should be avoided. General anesthesia should be maintained with IV nontriggering anesthetics. An IV dantrolene bolus of 2.5 mg/kg should be given through a large-bore IV. A blood gas should be obtained to determine the degree of metabolic acidosis and to determine serum potassium concentration. When the patient has stabilized, he or she should be transferred to the ICU for monitoring for at least 24 hours. The maintenance dose of dantrolene should be 1 mg/kg every 4 to 6 hours for at least 24 hours or to maintain an infusion of dantrolene at 0.25 mg/kg/h for at least 24 hours. Dantrolene may be needed for more than 24 hours, if clinically indicated.
A 33-year-old man with a 4-day history of third-degree ...