This brochure addresses malignant hyperthermia (MH) as a serious concern in the practice of oral and maxillofacial surgery, as well as in the practices of dentistry in which general anesthesia is used.

Exactly what is MH?  MH is a syndrome, a distinctive set of signs and symptoms that may occur in susceptible individuals on exposure to certain drugs used to produce general anesthesia or relaxation of the muscle during anesthesia.  MH susceptibility (MHS) is due to an underlying inherited muscle disorder (genetic defect) that puts one at risk for developing the MH syndrome.

It is important to note that for MHS patients, surgery with general anesthesia using the potent triggering agents does not always cause an MH episode.  An MHS individual may undergo anesthesia involving triggering drugs on several occasions with no problem, only to react with an MH episode during the next exposure to these agents.  Therefore, MH is a concern for any practice that utilizes general anesthesia.

How can the clinician prevent a condition that shows no sign or symptom until after anesthesia has been administered?  The honest answer is that it probably can't be prevented altogether. 

But, if certain procedures are employed preoperatively, including preventive techniques with at risk patients, and if an MH episode is recognized early and treated promptly, the tragic consequences of MH can be greatly reduced or avoided.  The MHAUS pamphlets What is Malignant Hyperthermia? and Preventing Malignant Hyperthermia - An Anesthesia Protocol are recommended for their detailed description of MH, its signs and symptoms, and treatment.

All patients should be questioned as to previous personal or family experience with general anesthesia, particularly sudden death during or after anesthesia.  Patients with muscular dystrophy and certain myopathies are at risk for MH or an MH-like syndrome when given succinylcholine or gas anesthesia (except nitrous oxide). 

SPECIFIC SIGNS OF MH INCLUDE:

• Sudden increase in end-tidal CO(2-3 x normal)
• Generalized muscle rigidity
• Masseter muscle rigidity
• Hyperthermia (often a late sign)

BE SUSPICIOUS OF MH WHEN THERE IS:

• Unexplained tachycardia, tachypnea
• Rhabdomyolysis - pigmenturia
• Unanticipated acidosis
• Patients who experience brown or cola colored urine within 24 hours of anesthesia should be evaluated for MH.

• 36 vials of dantrolene sodium
• bacteriostatic sterile water (3,000 ml) for solubilizing dantrolene
• a means to continuously monitor body temperature, end-tidal CO2 and oxygen saturation
• a machine to manufacture ice and a refrigerator to store at least 3,000 ml of cold IV normal saline

Succinylcholine is a potent trigger of MH. The FDA recommends that succinylcholine should be used only on indication (e.g. rapid sequence induction) rather than routinely, especially in children. Fortunately, the short-acting nondepolarizing relaxants are not triggers and provide a relatively brief period of muscle relaxation.

ANESTHETIZING MHS PATIENTS

Intravenous conscious sedation with local anesthesia may be safely administered to the MHS patient in the office setting for such procedures as the surgical removal of impacted third molars. Deep sedation or general anesthesia may also be used (obviously so long as no triggering agents are administered). Because laryngospasm may occur in the unconscious patient, and succinylcholine is contraindicated in MHS patients, a nondepolarizing muscle relaxant must be available.

More rigorous standards are recommended if intubation anesthesia or a prolonged procedure under general anesthesia is anticipated.

• avoid the use of MH-triggering drugs
• continuously monitor the patient's exhaled CO2 concentration
• use a continuous temperature monitor (e.g. in the nasopharynx, axilla,
  esophagus or rectum)
• have an MH cart in the OR, stocked with adequate supplies of dantrolene sodium

TRIGGERING AGENTS:

Volatile inhalation anesthetics (including halothane, enflurane, isoflurane, desflurane, sevoflurane) and succinylcholine.

SAFE AGENTS:

• Barbiturates
• Benzodiazepines
• Etomidate
• Ketamine
• Narcotics
• Nitrous Oxide
• Opioids
• Propofol
• Local Anesthetics (amides and esters) with or without vasoconstrictors

SAFE MUSCLE RELAXANTS:

• Atracurium
• Doxacurium
• Mivacurium
• Pancuronium
• Pipecuronium
• Rocuronium
• Vecuronium

Pretreatment with dantrolene is not generally recommended.

IF MH OCCURS

When MH is diagnosed, the clinician should discontinue all anesthetic agents immediately and terminate the surgery as soon as possible. The emergency squad should be called for transportation to the nearest hospital; the hospital emergency room should be notified of the specific disorder in order to be prepared to continue treatment on arrival. Immediate consultation may be obtained by calling the MH Hotline: 1-800-MH-HYPER or 1-800-644-9737.

TREATMENT SEQUENCE:

• Discontinue triggering agents
• Hyperventilate with 100% O2 at 3-4 x normal minute ventilation
• Give dantrolene sodium IV 2.5 mg/kg, repeated as necessary based
  on ongoing signs of MH
• Give bicarbonate 1-2 mEq/kg in absence of blood gas analysis
• In case of hyperthermia:

­ Cold IV fluids (normal saline)
­ External ice packs to groin and axilla
­ Lavage of stomach with cold solutions

Arrhythmias usually respond to correction of acidosis and hyperkalemia; antiarrhythmic agents, excluding calcium-channel blockers, may be used for refractory or dangerous arrhythmias

Following a fulminant MH episode, the patient should be placed in an intensive care unit for at least 24 hours after all signs have returned to normal. Dantrolene treatment should be continued during this period. The usual dose is 1 mg/kg every 4 to 6 hours IV.

PREPARATION OF DANTROLENE SODIUM:

• 36 vials should be on hand (20 mg/vial)
• Add 60 ml of sterile water without bacteriostatic agent to each vial of dantrolene to reconstitute the drug 
• Shake vigorously to reconstitute (until clear)
• Use IV spike transfer pins to reconstitute
• Once mixed, protect from direct light
• 2.5 mg/kg body weight given initially, repeated every 5 to 10 minutes
• Continue administration until signs of MH abate
• Use reconstituted drug within 6 hours

Additional resources available through MHAUS:  a wall poster outlining emergency treatment and a protocol for being prepared for MH episodes.

INFORMATION RESOURCES

In the U.S., MHAUS serves as your best source of information and educational materials for health care professionals and MH-susceptible individuals.  Since 1981, MHAUS has been dedicated to reducing morbidity and mortality of MH through support information, as well as improving medical care, scientific understanding and research related to MH and other kinds of heat-related syndromes.  Contact MHAUS at 607-674-7901 or e-mail to info@mhaus.org.  Information is available via the Internet at www.mhaus.org.

REPORTING MH EPISODES TO NORTH AMERICAN MH REGISTRY OF MHAUS:

Report MH and MH-like episodes to the North American MH Registry of MHAUS, which serves as your best source of patient-specific MH information.  Reporting forms and information are available by contacting the:

North American MH Registry of MHAUS
Barbara Brandom, MD, Director
U of Pittsburgh Children's Hospital
Anesthesiology Dept, Room 7499
3705 Fifth Ave at DeSoto St
Pittsburgh PA 15213-2583
1-888-274-7899(toll free) or 412-692-5464

Updated Jan 02
MHDD-3

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