in the past, the prophylactic use of dantrolene was recommended for mh-susceptible patients undergoing general anesthesia. however, multiple retrospective studies have demonstrated the safety of trigger-free general anesthesia in these patients in the absence of prophylactic dantrolene administration. the largest of these studies looked at the charts of 2214 patients who underwent general or regional anesthesia for an elective muscle biopsy. about half (1082) of the patients were muscle biopsy positive for mh. only five of these patients exhibited signs consistent with mh, four of which were treated successfully with parenteral dantrolene, and the remaining one recovered with only symptomatic therapy. after weighing its questionable benefits against its possible adverse effects (including nausea, vomiting, muscle weakness and prolonged duration of action of nondepolarizing neuromuscular blocking agents), experts no longer recommend the use of prophylactic dantrolene prior to trigger-free general anesthesia in mh-susceptible patients. anesthesia machine preparation anesthesia for people with known mh susceptible requires avoidance of triggering agent concentrations above 5 parts per million (all volatile anesthetic agents and succinylcholine). most other drugs are safe (including nitrous oxide), as are regional anesthetic techniques. where general anesthesia is planned, it can be provided safely by either flushing the machine or using charcoal filters. to flush the machine, first remove or disable the vaporizers and then flush the machine with 10 l/min or greater fresh gas flow rate for at least 20 minutes. while flushing the machine the ventilator should be set to periodically ventilate a new breathing circuit. the soda lime should also be replaced. after machine preparation, anesthesia should be induced and maintained with non-triggering agents. the time required to flush a machine varies for different machines and volatile anesthetics. this prevention technique was optimized to prepare older generation anesthesia machines. modern anesthetic machines have more rubber and plastic components which provide a reservoir for volatile anesthetics, and should be flushed for 60 minutes. charcoal filters can be used to prepare an anesthesia machine in less than 60 seconds for people at risk of malignant hyperthermia. these filters prevent residual anesthetic from triggering malignant hyperthermia for up to 12 hours, even at low fresh gas flows. prior to placing the charcoal filters, the machine should be flushed with fresh gas flows greater than 10 l/min for 90 seconds. treatment dantrolene sodium, the only available medical treatment for malignant hyperthermia the current treatment of choice is the intravenous administration of dantrolene, the only known antidote, discontinuation of triggering agents, and supportive therapy directed at correcting hyperthermia, acidosis, and organ dysfunction. treatment must be instituted rapidly on clinical suspicion of the onset of malignant hyperthermia. dantrolene dantrolene is a muscle relaxant that appears to work directly on the ryanodine receptor to prevent the release of calcium. after the widespread introduction of treatment with dantrolene, the mortality of malignant hyperthermia fell from 80% in the 1960s to less than 5%. dantrolene remains the only drug known to be effective in the treatment of mh. the recommended dose of dantrolene is 2.5 mg/kg, repeated as necessary. it is recommended that each hospital keeps a minimum stock of 36 dantrolene vials (720 mg), sufficient for four doses in a 70-kg person. training this is a mixed modality medical simulation of the treatment of malignant hyperthermia by anesthesia residents. the residents are managing care, mixing dantrolene and utilizing a cognitive aid at the bedside. fast recognition and treatment of mh utilizes skills and procedures that are utilized with a low-frequency and high-risk. conducting mh crisis training for perioperative teams can identify system failures as well as improve response to these events. simulation techniques to include the use of cognitive aids have also been shown to improve communication in clinical treatment of mh. prognosis prognosis is poor if this condition is not aggressively treated. in the 1970s, mortality was greater than 80%; however, with the current management mortality is now less than 5%. epidemiology it occurs in between 1:5,000 and 1:100,000 in procedures involving general anaesthesia. this disorder occurs worldwide and affects all racial groups. in the manawatu region of new zealand, up to 1 in 200 people are at high risk of the condition. history the syndrome was first recognized in royal melbourne hospital, australia in an affected family by denborough et al. in 1962. denborough did much of his subsequent work on the condition at the royal canberra hospital. similar reactions were found in pigs. the efficacy of dantrolene as a treatment was discovered by south african anesthesiologist gaisford harrison and reported in a 1975 article published in the british journal of anaesthesia. after further animal studies corroborated the possible benefit from dantrolene, a 1982 study confirmed its usefulness in humans. in 1981, the malignant hyperthermia association of the united states (mhaus) hotline was established to provide telephone support to clinical teams treating patients with suspected malignant hyperthermia. the hotline became active in 1982 and since that time mhaus has provided continuous access to board-certified anesthesiologists to assist teams in treatment. other animals other animals, including certain pig breeds, dogs, and horses, are susceptible to malignant hyperthermia. in dogs its inheritance is autosomal dominant. the syndrome has been reported in pointers, greyhounds, labrador retrievers, saint bernards, springer spaniels, bichon frises, golden retrievers, and border collies. in pigs its inheritance is autosomal recessive. in horses its inheritance is autosomal dominant, and most associated with the american quarter horse although it can occur in other breeds. research azumolene is a 30-fold more water-soluble analog of dantrolene that also works to decrease the release of intracellular calcium by its action on the ryanodine receptor. in mh-susceptible swine, azumolene was as potent as dantrolene. it has yet to be studied in vivo in humans, but may present a suitable alternative to dantrolene in the treatment of mh.