Malignant Hyperthermia

Malignant hyperthermia (MH) is a pharmacogenetic disorder in which skeletal muscle releases calcium abnormally when exposed to a triggering anesthetic. The two established triggers are volatile inhalational anesthetics and the depolarizing muscle relaxant succinylcholine. In a susceptible person, the trigger causes uncontrolled calcium release inside skeletal-muscle cells. The muscles remain activated, consuming large amounts of oxygen and adenosine triphosphate while producing excess carbon dioxide, acid, and heat. Muscle-cell breakdown then releases potassium and creatine kinase; myoglobin can enter the urine. The resulting combination of hyperkalemia, acidosis, hypoxia, and myocardial irritability can progress to dysrhythmia, shock, renal injury, and cardiac arrest. The name can mislead. A rapidly rising temperature is dangerous, but it may be a later finding. An unexplained rise in end-tidal CO₂ despite adequate ventilation is often the first visible sign that the patient’s metabolism has accelerated. A family history of an anesthesia-related crisis, a previous unexplained reaction during anesthesia, or known MH susceptibility increases risk. A previous uneventful anesthetic does not exclude susceptibility.