The cause of malignant hypehermia is unknown, but it is associated with inhalational anesthetic agents and succinylcholine. It may develop in an otherwise healthy person who has tolerated previous surgery without incident. It should be suspected in the presence of a history of unexplained fever, muscle or connective tissue disorder, or a positive family history (evidence suggests an autosomal dominant inheritance pattern). In addition to fever during anesthesia, the syndrome includes tachycardia, increased O2 consumption, increased CO2 production, increased serum K+ , myoglobinuria, and acidosis. Rigidity rather than relaxation following succinylcholine injection may be the first clue to its presence. Treatment of malignant hypehermia should include prompt conclusion of the operative procedure and cessation of anesthesia, hyperventilation with 100% O2 , and administration of intravenous dantrolene. The urine should be alkalinized to protect the kidneys from myoglobin precipitation. If reoperation is necessary, the physician should premedicate heavily, alkalinize the urine, and avoid depolarizing agents such as succinylcholine. Pretreatment for 24 hours with dantrolene is helpful; it is thought to act directly on muscle fiber to attenuate calcium release.