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 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