Malignant Hyperthermia Treatment & Management

Indications for treatment of malignant hyperthermia (MH) with dantrolene include signs of hypermetabolism, a rapid rise in carbon dioxide in the face of an increase in the minute ventilation, tachycardia, muscle and or jaw rigidity (after succinylcholine), and fever (a late sign).

Not all of these indications are present in all patients. If an acute MH reaction appears likely, it is best to start giving dantrolene and other recommended treatment modalities promptly rather than wait too long and have a bad outcome. The longer the wait before initiation of therapy, the lower the likelihood of a complete recovery. If an MH reaction is suspected, referral to a MH muscle biopsy testing center is indicated.

A fulminant, rapidly progressive MH reaction requires early diagnosis and early rapid administration of dantrolene, discontinuance of triggering agents, and assistance from extra personnel. The surgeon should be notified immediately and should stop the procedure as soon as possible (see below). (For more information, see Malignant Hyperthermia in the Operating Room.) 

Cooling and early treatment of hyperkalemia are desirable. Calcium-channel blockers should be avoided if dantrolene is used, because they may cause hyperkalemia. An MH tote or cart containing dantrolene and the necessary supplies should be readily available to help reverse the process more quickly. The recommendation is that 36 dantrolene vials (containing 20 mg/vial) should be immediately available wherever general anesthesia is administered. Availability of a further 24 vials within 1 hour has also been recommended. ^[13] It is helpful to place an MH treatment poster in the operating room.

Dantrolene is a hydantoin derivative that directly interferes with muscle contraction by inhibiting calcium ion release from the sarcoplasmic reticulum, possibly by binding to ryanodine receptor type 1 (RYR-1). The initial dose is 2.5 mg/kg, repeated every 5 minutes until reversal of the reaction occurs or a total dose of 10 mg/kg (or 20 mg/kg, according to some practitioners) is reached. If there is no clinical response, another diagnosis should be considered.

Dantrolene will also lower an elevated temperature in disorders other than MH, such as thyroid storm, neuroleptic malignant syndrome (NMS), and sepsis. Each 20-mg vial of lyophilized powder contains sodium hydroxide for a pH of 9-10 and mannitol, which makes the solution isotonic. The half-life is 6-10 hours.

Once the initial reaction is controlled, continued monitoring in the intensive care unit (ICU) for 24-48 hours is recommended, along with administration of dantrolene (1 mg/kg every 4-6 hours, or an equivalent amount given as a continuous infusion). Myoglobinuria should be watched for and treated with fluids and diuretics if it occurs. The creatine kinase level will peak about 8-10 hours after the event and should be followed until it returns to near normal.

A newer version of dantrolene dissolves in 15 seconds and thereby improves the rapidity of treatment. Another improvement is the addition of charcoal filters that can be placed in the anesthesia machine circuit. These filters can remove the inhalation agent in 1-2 minutes and help quickly reverse the effects of the MH reaction.

The patient and the family members will need to be educated about MH and should be referred to a testing center for a caffeine halothane contracture test (CHCT). Relevant information is available from the Malignant Hyperthermia Association of the United States (MHAUS) at www.mhaus.org.

A diagnosis of trismus after giving succinylcholine with induction raises the question of whether the surgical procedure should be canceled; a clinical episode will follow the trismus 20% of the time. When the anesthesia provider first suspects that an MH reaction may be occurring, the surgeon should be notified promptly, and a decision should be made about whether the procedure is to be continued or canceled. If the procedure is canceled, the patient should be observed in the hospital for 24 hours for signs of MH.

If the procedure is to be performed, the following considerations should be kept in mind in planning anesthesia for an MH-susceptible patient:

• Avoid triggering agents (eg, major inhalational agents and succinylcholine)
• Use nontriggering general, regional, spinal, epidural, or local anesthesia or monitored anesthesia care (MAC)
• Watch for signs of MH
• Use a clean anesthesia machine; remove vaporizers or tape them in the off position, change soda lime and barium hydroxide lime, replace the circuits, replace the fresh gas tubing if possible, and run oxygen through the machine at 10 L/min for 20 minutes (10 minutes if the fresh gas tubing was replaced)
• The procedure can be done on an outpatient basis; if all goes well, the patient can safely be dismissed after 2-3 hours