Malignant Hyperthermia:
Prepared by MHAUS August 1999

° Can you pretreat malignant hyperthermia susceptible (MHS) patients with dantrolene?
Dantrolene pretreatment is not necessary, provided that a nontriggering anesthetic and appropriate monitoring are used and an adequate supply of dantrolene is available. Some experts have recommended dantrolene pretreatment of 2 mg/kg IV in a patient who has sustained a significant MH episode. Dantrolene may cause mild weakness in normal patients and significant weakness in patients with muscle disorders.

° Are MHS patients candidates for outpatient surgery?
MHS patients can safely undergo outpatient surgery using nontriggering anesthetics. After an uneventful anesthetic, an observation period of 3 to 5 hours is recommended. Following discharge, they should be provided with an emergency telephone number to contact if problems arise.

° Should surgery be done without a biopsy?
If there is a question of MH susceptibility and a biopsy has not been done, the patient should be considered susceptible and a nontriggering anesthetic technique used.

° What are the safe drugs?
Safe: Local or regional anesthesia and monitored anesthesia care are safe. Intravenous drugs, including propofol, barbiturates, benzodiazepines, and etomidate, are safe.
Unsafe: Succinylcholine and the potent inhalational agents, halothane, enflurane, isoflurane, and sevoflurane, and even agents such as ether, cyclopropane, and methoxyflurane, are triggers and are unsafe.

° How do you proceed with a patient if there is a family history of MH?
A patient with a family history of MH should be managed as susceptible-with a nontriggering anesthetic technique.

° How long should you monitor MHS patients after uneventful anesthesia?
An MH patient should be observed and monitored for 3 to 5 hours postoperatively.

° Where should an MHS patient be biopsied?
A biopsy for MH should be performed at one of the 8 US Muscle Biopsy Centers complying with a standard protocol for the caffeine-halothane contracture test.
(Current list; also be obtained from the MHAUS office by calling 1-800-986-4287 or 607-674-7901.)

° When should you discharge patients from ambulatory facilities after episodes of masseter spasm?
Masseter spasm has a spectrum of severity, ranging from a mild increase in jaw tension to "jaws of steel." A patient who exhibits marked rigidity of the jaw muscles should not be discharged. Overnight observation is required for temperature rise, myoglobinuria, elevated CK levels, or progression to an MH episode. Patients who experience milder increases in jaw tension should be observed for signs and symptoms of MH for at least 12 hours. If there is evidence of myoglobinuria, dark cola-colored urine, increase in temperature, pulse rate, or abnormality of acid-base balance, the patient should be admitted and observed overnight.

° What equipment preparation should be done before surgery on an MHS patient?
Machine: change absorbent, breathing circuit, drain and inactivate vaporizers, flush machine with 10 liters of air or oxygen for 10 minutes.
Monitors: Electrocardiography, blood pressure monitoring, oximeter, capnometer. Core temperature (nasopharyngeal, esophageal, axillary, tym panic, rectal) should also be monitored unless general anesthesia is very brief (<10-15 minutes).
Hypothermia blanket
Refrigerated saline
Drugs and supplies, including dantrolene

° What's recommended to be stocked on an MH cart?
Drugs: dantrolene, 36 vials; sterile water; dextrose 50%; antiarrhythmics; mannitol; calcium chloride; sodium bicarbonate; furosemide. Calcium channel blockers should not be used.
Ice bags and bucket; dispensing pin; urine specimen container/dipstick; temperature probes; nasogastric tube, Foley catheter; syringes; needles; MH treatment protocol; blood collection tubes for arterial blood gases, electrolytes, platelets, and coagulation studies; catheters for monitoring arterial, central venous pressures.

What should I do if I manage an acute MH case or suspicious MH case?
MH cases should be reported to the North American MH Registry, a division of MHAUS. Forms for data collection can he obtained from the MHAUS Office, 1-800-98MHAUS or via e mail at mhaus@norwich.net.
Advice regarding acute emergencies can be obtained through the MHAUS Hotline ( 1-800-MH-HYPER). Patients and their families should be put in contact with the Malignant Hyperthermia Association Office to obtain more detailed information regarding malignant hyperthermia and risks for family members.

DIRECTORY: NORTH AMERICAN MALIGNANT HYPERTHERMIA MUSCLE BIOPSY CENTERS

The following centers are complying with the standardization protocol for the caffeine halothane contracture test that resulted from six conferences held 11/87, 11/89, 6/90, 11/91, and 9/94 and 9/98:

Wake Forest University
School of Medicine
Winston-Salem, NC
Thomas E. Nelson, PhD
336-716-7194

Thomas Jefferson University
Philadelphia, PA
Henry Rosenberg, MD
215-955-5844

Mayo Clinic
Rochester, MN
Denise Wedel, MD
507-255-4236

Northwestern University
Chicago, IL
Silas Glisson, PhD
312-908-2541

Uniformed Services
University of the Health Sciences
Bethesda, MD
Sheila Muldoon, MD
301-295-3140

University of California
Davis, CA
Joseph Antognini, MD
530-752-7809

University of California
Los Angeles, CA
Jordan D. Miller, MD
310-825-7850

University of Minnesota
Minneapolis, MN
Paul A. laizzo, PhD
612-624-9990

Canadian Centers:
Toronto General Hospital
Toronto, Ontario
Jane Heggie, MD,FRCPC
416-340-3128

Ottawa Civic Hospital
Ottawa, Ontario
Gordon Reid, MD,FRCPC
613-761-4169

University of Manitoba
Winnipeg, Manitoba
Leena Patel, MD,FRCPC
204-787-2560