Dantrolene Should Be Readily Available Wherever Malignant Hyperthermia Triggering Drugs Are Stocked

To the Editor We read with concern the special article by Urman et al,1 Malignant hyperthermia-susceptible adult patient and ambulatory surgery center: Society for Ambulatory Anesthesia and the Ambulatory Surgical Care Committee of the American Society of Anesthesiologists Position Statement. We agree that adult malignant hyperthermia (MH)-susceptible patients can safely undergo a procedure in a freestanding ambulatory surgery center (ASC) assuming that proper precautions for preventing, identifying, and managing MH are taken. However, we disagree with the position statement’s caveat “dantrolene should also be immediately available when triggering agents are routinely used.”1 The professional advisory council, hotline consultants, and board of directors of the Malignant Hyperthermia Association of the United States (MHAUS) recommend that dantrolene should be available within 10 minutes of a clinician’s decision to treat MH wherever the MH triggering drugs succinylcholine and/or volatile anesthetics “may” be used.2 If succinylcholine or volatile anesthetics are stocked by a freestanding ASC, then dantrolene must be stocked unless dantrolene can be obtained within 10 minutes. Why does MHAUS take this position? Succinylcholine without volatile anesthetics triggers MH. A recent analysis of 3 large databases (Multicenter Perioperative Outcomes Group, Anesthesia Closed Claims Project, and North American MH Registry of MHAUS) combined with a systematic review of 65 studies examined succinylcholine use and dantrolene availability. This study found “succinylcholine given without volatile anesthetics triggered 24 malignant hyperthermia events, 13 of which were treated with dantrolene. Fourteen patients experienced substantial complications, and one died.”3 MH events are associated with significant morbidity and mortality. “Among 310 anesthetic-triggered MH cases, morbidity was 20 to 37%.” Complications included pulmonary edema, disseminated intravascular coagulation, and heart, liver, kidney, and brain dysfunction. “Complications increased substantially with every 10-min delay in initiating dantrolene treatment… If clinicians waited more than 50 min, complications increased to 100%... Fifteen US patients died, including 4 after anesthetics administered in freestanding facilities.”3 Which patients will benefit most from dantrolene stocking? ASC patients who have not been identified as MH-susceptible because they have not yet experienced an MH event and may be unfamiliar with their own family medical history. North American Malignant Hyperthermia Registry of MHAUS studies showed “7.2% (24/332) of positive family histories were discovered after anesthetics triggered MH events. Three of these 24 patients died.”3 The median number of prior unremarkable general anesthetics before 152 MH events was 2 (first quartile, 1; third quartile, 2; range, 0–30) underscoring the unreliability of previous uneventful anesthetic history in determining MH susceptibility.3 A multicenter case-control study of 229 MH-susceptible patients showed the probability of developing MH on exposure to MH anesthetic triggers was 0.25 among all ryanodine receptor 1 (RYR1) mutation carriers and 0.76 in MH event survivors. Given a prevalence of all known MH-causative mutations of 1:2750 individuals, the number of expected MH events is not insignificant. Also, this study showed that succinylcholine use was a nongenetic risk factor for increasing the likelihood of an MH reaction.4 Therefore, we urge all freestanding ASCs that stock succinylcholine and/or volatile anesthetic agents to stock dantrolene. Be prepared to rapidly treat life-threatening MH events. Marilyn Green Larach, MD, FAAPThe North American Malignant Hyperthermia Registry of the Malignant Hyperthermia Association of the United StatesDepartment of AnesthesiologyUniversity of Florida College of MedicineGainesville, FloridaMalignant Hyperthermia Association of the United StatesSherburne, New York[email protected] Sheila Riazi, MSc, MD, FRCPCDepartment of Anesthesia and Pain ManagementUniversity Health NetworkUniversity of Toronto, Toronto, CanadaBoard of Directors and Professional Advisory CouncilMalignant Hyperthermia Association of the United StatesSherburne, New York Henry Rosenberg, MD, CPEBoard of Directors and Professional Advisory CouncilMalignant Hyperthermia Association of the United StatesSherburne, New York