What is MH?

Malignant hyperthermia (MH) is a pharmacogenetic disease that causes a fast rise in body temperature and severe muscle contractions when an affected person receives general anesthesia using volatile anesthetics or succinylcholine.4

The disorder is due to an acceleration of the metabolism in skeletal muscle. The signs of MH include hypercarbia, muscle rigidity, fast-rising body temperature, tachycardia, myolysis, increased ETCO2, hyperkalemia, and acidosis. Immediate treatment with the drug dantrolene sodium usually reverses the signs of MH. The underlying defect is abnormally increased levels of cell calcium in the skeletal muscle.

Featured Video: MH Insights

Time to treatment is critical
Watch as Henry Rosenberg, MD, and President of the Malignant Hyperthermia Association of the United States (MHAUS), provides insight into the importance of timely treatment during an MH crisis.

How prevalent is MH?

MH is relatively uncommon, with approximately 1 in 2,000 patients having a genetic mutation that makes them susceptible.5 MH occurs in approximately 1 in 100,000 adult surgeries and 1 in 30,000 pediatric surgeries,5 or approximately 500 to 800 cases annually.6

Early signs of MH

There are multiple signs that may trigger a diagnosis of MH by anesthesia practitioners.

Most anesthesiologists and CRNAs report that hypercarbia is the first clinical symptom that makes them suspect MH.2 While clinical manifestations of MH can vary, additional symptoms mentioned include muscle rigidity and tachycardia.

The administration of RYANODEX® (dantrolene sodium) for injectable suspension to conscious human volunteers is associated with loss of grip strength and weakness in the legs, as well as drowsiness and dizziness.1

Complications associated with MH treatment

Time delays and high fluid volumes associated with traditional MH treatment contribute to further complications during an MH crisis.7


  • Stopping the triggering agents and getting dantrolene sodium administered to the patient as quickly as possible are the greatest priorities in an MH crisis
  • Every delay in treatment increases the risk of further complication during an MH crisis8
  • The risk of complications increases by over 30% for every 20-minute delay in treating MH from its first symptom8

High fluid volumes

With traditional MH treatment, the 2.5 mg/kg loading dose of dantrolene sodium requires significant volumes of sterile water for injection for the majority of patients (eg, 750 mL for a 100 kg patient).9,10

Complications from high fluid volume7

  • Pulmonary edema
  • Acute respiratory distress syndrome (ARDS)
  • Increased alveolar to arterial oxygen gradient
  • Hyponatremia
  • Phlebitis
  • Cellulitis