Malignant Hyperthermia Clinical Presentation

Malignant hyperthermia (MH) may occur either in the operating room (OR) or in the early postoperative period. The earliest sign is an increase in end-tidal carbon dioxide.

A fulminant reaction is obvious, with very high end-tidal carbon dioxide (>100 mm Hg), a low pH with a metabolic component, tachycardia and dysrhythmias, rigidity (in some cases), rapidly increasing temperature, a mottled skin color, hyperkalemia, myoglobinuria, muscle edema, sympathetic hyperactivity with eventual metabolic exhaustion, increased cellular permeability, whole body edema, disseminated intravascular coagulopathy (DIC), and cardiac and renal failure.

Early diagnosis and treatment with dantrolene can improve the outcome. Fortunately, fulminant reactions are rare; most reactions are slower and display more subtle changes. Larach et al devised an MH grading scale based on points given to various signs and laboratory tests to help with the diagnosis of MH. ^[8]

The hotline run by the Malignant Hyperthermia Association of the United States (MHAUS) can be consulted for assistance in treatment. Many calls to the hotline are for high carbon dioxide values that are not reduced by increasing the minute ventilation, tachycardia, rigidity, masseter rigidity after succinylcholine administration, or postoperative fever. Other calls involve questions about safe technique for a patient with known MH.

Often, the hotline consultant will refer the patient to an MH testing center for muscle biopsy and a caffeine halothane contracture test (CHCT). In many cases, the consultant determines that the patient does not actually have MH. Some of the reactions reverse after discontinuance of the triggering agent and do not necessitate the use of dantrolene.

Clinical conditions associated with susceptibility to MH include King-Denborough syndrome, central core disease, and minicore myopathy. ^{[9, 10]} Individuals with these disorders have RYR1 mutations and should be considered at risk for MH.

King-Denborough syndrome is characterized by short stature, musculoskeletal abnormalities, and mental retardation. Some individuals with this syndrome also have central core disease. Central core disease is characterized by hypotonia, muscle weakness, and central cores on muscle biopsy. Minicore myopathy is a group of disorders characterized by severe hypotonia and generalized weakness.

It was long thought that muscular dystrophy was associated with susceptibility to MH, but that association is being questioned. There have been numerous reports of pediatric patients with Duchenne muscular dystrophy or Becker muscular dystrophy who experienced hyperkalemic cardiac arrest after induction with inhalation agents and succinylcholine but did not experience hypermetabolism. In addition, anesthesia-induced rhabdomyolysis (AIR) is seen in patients with muscular dystrophy with no signs of MH.

Although muscular dystrophy is not associated with MH, it is nonetheless wise to refrain from administering inhalational agents and succinylcholine to patients with muscular dystrophy so as to avoid AIR and hyperkalemic cardiac arrest. ^[11]

Masseter muscle rigidity (MMR) after succinylcholine administration may be associated with susceptibility to MH. Brief rigidity (< 20-30 s) is a normal response to succinylcholine. Rigidity lasting longer than 1 minute is seen as abnormal, and 20% of these patients will develop clinical MH within the next hour. Some patients have “jaws of steel,” which make airway management difficult.

Elective cases should be canceled, and the patient should be observed in the hospital for 24 hours for signs of MH. In the case of an emergency operation, safe techniques should be used, and MH should be watched for. Administration of dantrolene should be considered. All patients with MMR experience rhabdomyolysis and may have very high creatine kinase levels and myoglobinuria.