MH is a syndrome that should be diagnosed early and dantrolene, when given promptly, can prevent complications associated with MH. (Image source: Thinkstock)

MH is a syndrome that should be diagnosed early and dantrolene, when given promptly, can prevent complications associated with MH. (Image source: Thinkstock)

Despite the current focus on determining the precise genetic mutations responsible for malignant hyperthermia, there is still a lot that can be learned by conventional epidemiologic analysis. Dr. Sheila Riazi, Malignant Hyperthermia Investigation Unit, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada, and colleagues describe nationwide epidemiology on malignant hyperthermia in Canada over a period of nearly 20 years.  Their findings are discussed in the article “Malignant Hyperthermia in Canada: Characteristics of Index Anesthetics in 129 Malignant Hyperthermia Susceptible Probands,” which was  published in the February 2014  issue of Anesthesia & Analgesia.

Of almost 400 individuals who had an adverse anesthetic reaction, 129 patients who had an anesthetic record the authors could examine, survived the anesthetic, and then underwent a caffeine-halothane contracture test that was positive for malignant hyperthermia (MH) were included in the study.  MH was triggered by use of succinylcholine, an inhalation agent, or both.  Eight patients had an adverse reaction that first appeared in the postanesthesia care unit (PACU), though no one had such a reaction after leaving the PACU.  As others have found, hyperthermia, sinus tachycardia, and hypercarbia were the most common clinical signs; masseter muscle rigidity, sinus tachycardia, and hypercarbia were the most common presenting signs.  About 1/5 of patients (a total of 26 or 20.1%) experienced complications, the most common of which were renal and cardiac dysfunction.  Fewer than 50% of patients received dantrolene after an adverse reaction, a lower rate than seen by others, and the group who most commonly received dantrolene consisted of patients who received a volatile anesthetic without succinylcholine.  As also observed by others, when the time between onset of first clinical signs and dantrolene administration was longer, the incidence of complication was higher.

Perhaps the most interesting finding is that roughly 15% of the MH episodes were triggered only by use of succinylcholine. Indeed, 4 of these patients had their reaction while undergoing electroconvulsive therapy, a procedure with almost no chance of exposure to a volatile anesthetic. Every patient with MH triggered only by succinylcholine had biopsy-proven MH.  There has been some controversy as to whether succinylcholine could trigger MH in the absence of a volatile anesthetic. The answer is yes.

Though MH is uncommon, reports such as these help remind us the diagnosis must be rapid, and that dantrolene must be given early. The other take-home message is that dantrolene must be rapidly accessible to any location that stocks succinylcholine.