Only rapid, specific treatment can save a patient with MH from death. Before investigators discovered that dantrolene sodium is an effective treatment for MH, >70% of patients who developed the disease died.12 Mortality has since dropped to ≤15%.14 With a presumptive diagnosis of MH, dantrolene should be prepared and given immediately. The drug inhibits the release of calcium from the sarcoplasmic reticulum of skeletal muscle by limiting the activation of RYR1.
Successful resuscitation of patients with MH hinges on the following:
Making a prompt diagnosis. While most episodes of MH occur shortly after induction of anesthesia or during the intraoperative course, nearly 2% of MH cases occur postoperatively15—some as long as 12 hours after exposure to the presumed trigger.
Immediately discontinuing triggering anesthetics and starting dantrolene. The patient should be kept anesthetized using nontriggering agents (TABLE 1), and surgery should be concluded as quickly as possible.
Preparation of dantrolene is a tedious process because of its poor water solubility. One to 2 minutes are needed for the preparation to solubilize. Initial treatment with dantrolene is 2.5 mg/kg administered intravenously (via peripheral or central line). This dose (or up to 10 mg/kg) can be repeated every 5 to 10 minutes until major symptoms such as hypercarbia, arrhythmias, hyperpyrexia, and metabolic acidosis abate. Thereafter, dantrolene is continued at 2.5 mg/kg every 4 hours for 24 hours.
Cooling the patient. A patient should be cooled using ice packs, gastric lavage with ice water, cold intravenous fluid, or ice water lavage at the surgical site. Active cooling should stop when the patient’s temperature reaches 100°F (so as not to cause hypothermia). Cooling should not, however, prevent or slow the administration of dantrolene.
Treating acidosis, arrhythmias, electrolyte disturbances, coagulopathy, excess myoglobin, and acute renal failure. Arrhythmias should not be treated with calcium channel blockers.
Monitoring patients in the ICU for potential adverse effects of dantrolene that can include sedation and muscle weakness. Mechanical ventilation may be needed. (The malignant hyperthermia hotline [800-644-9737] at MHAUS is available 24 hours a day to assist clinicians with questions regarding diagnosis and treatment.)
Keeping patients safe by properly testing them
The CHCT is 97% sensitive and 78% specific for MH.16 It is an invasive procedure, requiring the patient to undergo anesthesia. The test costs more than $5,000, which most insurance companies will cover.17
The CHCT is performed only on fresh muscle, and only 5 centers in North America perform the test. The number of centers is kept to a minimum to maintain high procedural quality. The biopsy specimen is taken from the vastus lateralis. Because of the size of the specimen required to perform the test, a child weighing <20 kg or <5 years of age is usually not tested but simply presumed to be MH susceptible.18
Incidence of MH is increasing
The number of reported cases of malignant hyperthermia (MH) has increased over the last 20 years, but the exact incidence is unknown. It varies not only by country, but, within the United States, from state to state, and even within states, presumably due to variations in the genetic pool. Michigan, Nebraska, West Virginia, and Wisconsin report especially high incidences.19
MH is more common in men than women (58% vs 42%, respectively, of affected patients ). The last major survey of MH incidence was published in 2009.20 In the survey years (2000-2005), MH incidence increased from 10.2 to 13.3 patients per million hospital discharges. Mortality in the same period decreased from 16.1% to 6.5%.
Counseling patients and their families
Make sure affected individuals and family members know the life-threatening implications of this condition; that it is familial and that its onset does not always occur with a first exposure to anesthesia, but sometimes with a subsequent exposure. Explain that MH is not an “allergy to anesthesia” or an “allergy to succinylcholine.” Patients can undergo anesthesia safely in the future if performed with a nontriggering agent and associated technique. Anesthesiologists today are well trained to manage these patients with minimum risk.
Counsel first-degree relatives of MH patients about undergoing the CHCT. Molecular genetic testing, which requires a blood draw but is less sensitive than the CHCT, may be another option. If an MH patient was diagnosed using this blood test, relatives may opt to be tested this way, as well. If genetic test results for relatives are positive, these individuals are presumed to have MH and should be treated as such, saving them the expense and risk of undergoing muscle biopsy. If genetic test results are negative, the CHCT should be considered or patients should be presumed to be MH susceptible.