Abstract
Malignant hyperthermia (MH) is a rare and life-threatening pharmacogenetic disorder triggered by volatile anesthetics, the depolarizing muscle relaxant succinylcholine, and rarely by strenuous exercise or environmental heat. The exact prevalence of MH is unknown, and it varies from 1:16 000 in Denmark to 1:100 000 in New York State. The underlying mechanism of MH is excessive calcium release from the sarcoplasmic reticulum (SR), leading to uncontrolled skeletal muscle hyper-metabolism. Genetic mutations in ryanodine receptor type 1 ( RYR1) and CACNA1S have been identified in approximately 50% to 86% and 1% of MH-susceptible (MHS) individuals, respectively. Classic clinical symptoms of MH include hypercarbia, sinus tachycardia, masseter spasm, hyperthermia, acidosis, muscle rigidity, hyperkalemia, myoglobinuria, and etc. There are two types of testing for MH: a genetic test and a contracture test. Contracture testing is still being considered as the gold standard for MH diagnosis. Dantrolene is the only available drug approved for the treatment of MH through suppressing the calcium release from SR. Since clinical symptoms of MH are highly variable, it can be difficult to establish a diagnosis of MH. Nevertheless, prompt diagnosis and treatments are crucial to avoid a fatal outcome. Therefore, it is very important for anesthesiologists to raise awareness and understand the characteristics of MH. This review summarizes epidemiology, clinical symptoms, diagnosis and treatments of MH and any new developments.
Highlights
Malignant hyperthermia (MH) is a rare and lifethreatening pharmacogenetic disorder of skeletal muscle
The clinical effect of dantrolene therapy in MH is dramatic. It was reported the case fatality rate of MH was 70% in the 1970s[9]. This number had dropped to 9.5% according to a report from the Malignant Hyperthermia Association of the United States (MHAUS)[10]
MH is a rare and life-threatening anesthesia complication. It is caused by Ca2+ release from the sarcoplasmic reticulum (SR) leading to uncontrolled skeletal muscle hypermetabolism
Summary
Malignant hyperthermia (MH) is a rare and lifethreatening pharmacogenetic disorder of skeletal muscle. Not all susceptible individuals have events upon exposure to triggering agents This explains the discrepancy between reported clinical incidence and genetic prevalence. The main clinical presentations of MH are unexplained increased ETCO2 concentration, tachycardia, muscular rigidity, combined metabolic and respiratory acidosis, hyperthermia, cardiac arrhythmia and renal failure. For about 30 years, the gold standard for diagnosing MHS individuals have been the in vitro measurement of contracture response of biopsied muscle to graded concentrations of caffeine and the anesthetic halothane Two protocols of this test have been used currently, one is the caffeine/halothane contracture test (CHCT) established by the MHAUS, and the other is in vitro contracture test (IVCT) established by the European Malignant Hyperthermia Group (EMHG)[60,61,62]. ·Elevated creatine kinase >20 000 IU after anesthetic that included succinylcholine ·Elevated creatine kinase >10 000 IU after anesthetic without succinylcholine ·Cola colored urine in perioperative period ·Myoglobin in urine >60 μg/L ·Myoglobin in serum >170 μg/L ·Blood/plasma/serum K+ >6 mEq/L (in absence of renal failure) ·PETCO2 >55 mmHg with appropriately controlled ventilation ·Arterial PaCO2 >60 mmHg with appropriately controlled ventilation ·PETCO2 >60 mmHg with spontaneous ventilation ·Arterial PaCO2 >65 mmHg with spontaneous ventilation ·Inappropriate hypercarbia (in anesthesiologist's judgment) ·Inappropriate tachypnea
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