Malignant Hyperthermia:  Diagnosis & Management

(updated 12/2009)

Spectrum Policies re: MH patients at free-standing Surgi-Centers: Click Here

 increased pCO2 ,tachypnea
 cardiac dysrhythmias
 increased Temperature
 masseter muscle spasm
 increased plasma CK + myoglobin concentration

-Dantrolene  2-3 mg/kg IV
  repeat q 5-10'  up to 10 mg/kg
  then 1 mg/kg q 6' x 72 hr
-conclude surgery ASAP
-stop inhaled anesthetic and vent w/ 100% O2
-active cooling: iced saline gavage & surface cooling
-correct metabolic acidosis: NaHCO3 1-2 meq/kg
-maintain Urine Output: fluids, mannitol 0.25 g/kg, lasix 1 mg/kg
-Rx cardiac dysrhythmias:
  procainamide  15 mg/kg
-transfer to ICU

Answers to 10 Common Questions
Prepared by MHAUS updated 2007

  1. Pretreatment of MH Susceptible Patients
  2. MH Susceptible Patients & Outpatient Surgery
  3. Surgery Without Muscle Bx Confirmation
  4. Safe Drugs
  5. Patients w/ Family Hx of MH
  6. Post-op Monitoring of MH Susceptible Patients
  7. Arranging Muscle Biopsy
  8. Monitoring Patients after Masseter Spasm
  9. Preparing to Anesthetize MH Susceptible Patients UPDATED
  10. Stocking an MH Cart

° Should Malignant Myperthermia Susceptible (MHS) patients be pretreated with dantrolene?
Dantrolene prophylaxis is not recommended for most MH-susceptible patients. Dantrolene can worsen muscle weakness in patients with muscle disease and should be used with caution. For most procedures, even those requiring general anesthesia, dantrolene prophylaxis may be omitted.

° Are MHS patients candidates for outpatient surgery?
MHS patients can safely undergo outpatient surgery using non-triggering anesthetics and may be discharged on the day of surgery if the anesthetic has been uneventful. A minimum period of 1 hour in PACU monitoring vital signs at least every 15 minutes and 1.5  hours in phase 2 PACU/step down is recommended.

° 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 are safe, including propofol, barbiturates, benzodiazapines, etomidate..
Unsafe: Succinylcholine and the potent inhalational agents, halothane, enflurane, isoflurane, desflurane, sevoflurane and even agents such as ether, cyclopropane and methoxyflurane 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?
The patient susceptible to MH undergoing outpatient surgery may be discharged on the day of surgery if the anesthetic has been uneventful. A minimum period of 1.0 hour in PACU monitoring vital signs at least every 15 minutes and 1.5 hours in phase 2 PACU/step down is recommended.

° Where should an MHS patient be biopsied?
A biopsy for MH should be performed at one of the U.S. Muscle Biopsy Centers complying with a standard protocol for the caffeine-halothane contracture test. (A listing can be obtained from the MHAUS office by calling 1-800-986-4287 or 607-674-7901or going to this link.)

° 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? UPDATED
Machine: change absorbent (soda lime), breathing circuit, drain and inactivate vaporizers, flush machine with 10 liters of air or oxygen for 10 minutes minimum.
(DRAGER PRIMUS machines must be flushed at least 70 minutes with a 10L oxygen flow.)
Monitors: Electrocardiography, blood pressure monitoring, oximeter, capnometer. Core temperature (nasopharyngeal, esophageal, axillary, tympanic, rectal) should also be monitored unless general anesthesia is very brief (<10-15 minutes).
Hypothermia blanket
Refrigerated saline
Drugs and supplies, including dantrolene immediately available

° What's recommended to be stocked on an MH cart?

(At Maine Medical Center, dantrolene is stocked in the Red Malignant Hyperthermia Kit tackle box in the Anesthesia Workroom above the sink; instructions for mixing Dantrolene with 60cc sterile water per vial are included)

Drugs: dantrolene, 36 vials; sterile water; dextrose 50%; antiarrhythmics; 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
Advice regarding acute emergencies can be obtained through the MHAUS Hotline (1-800-644-9737). 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.