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The American Society of Anesthesiologists is an educational, research and scientific association of physicians organized to raise and maintain the standards of the medical practice of anesthesiology and improve the care of the patient.


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August 1, 2013 Volume 77, Number 8
Malignant Hyperthermia in the ASC and Office-Based Setting: Recent Developments in Preparation and Management Andrew Herlich, D.M.D., M.D., FAAP, Committee on Ambulatory Surgical CareMHAUS Consultant

The unexpected triggering of malignant hyperthermia (MH) in an ambulatory surgery center (ASC) or office-based setting is unnerving. Despite routine MH mock drills in these settings, an MH episode is one of the least expected and most feared crises. Fortunately, a recent cooperative effort from the Malignant Hyperthermia Association of the United States (MHAUS), Society for Ambulatory Anesthesia (SAMBA), the Ambulatory Surgery Foundation, the Society for Academic Emergency Medicine, and the National Association of Emergency Medical Technicians has created an orderly guideline/algorithm for treatment and transfer to an acute care facility.1 The guideline was created to address the variability of ambulatory facilities, receiving hospitals and available personnel. What was clearly drawn from other experiences was the fact that the grab-and-go approach without stabilization of the MH patient would have unfavorable outcomes.1 The grab-and-go approach is most frequently used in the pre-hospital care environment. In contrast, inter-facility transfer required greater control of the MH crisis. Administration of an initial dose of dantrolene and greater efforts of overall stabilization were deemed to be highly important. Complete stabilization may not be practical and should not delay the transfer of the MH patient to the acute care facility. A similar approach was created for MH in the office-based environment. Posters and forms are available from MHAUS to assist the ASC and office practice in the management of MH and appropriate transfer to an acute care facility. There are specific forms and posters for both the ASC and office-based environment. In all instances, after initiation of treatment, early calls to the MHAUS Hotline (1-800-MH-HYPER or 1-800-644-9737) and 911 will help with the orderly transfer. MH Hotline consultants will help guide treatment and answers questions during the crisis. Early calls to EMS will expedite emergent transfer to the receiving facility with most appropriate personnel to continue treatment.

In the last several years, dantrolene has become easier to reconstitute. The manufacturers only produce dantrolene that takes no longer than 20 seconds to reconstitute and thoroughly mix. Rapid administration of dantrolene is now more realistic in any environment. Additional changes have occurred with anesthesia machines. Modern anesthesia machines are far more complex than their predecessors. The once tried-and- true universal approach of flushing the machine with a 10 liter flow of 100 percent oxygen for 20 minutes has likely become insufficient. Each machine and manufacturer has a different preparation time and approach. Preparation of the newer anesthesia machines may take as long as 70 minutes.2 A one-hour preparation time of the anesthesia machine in the ASC or office-based environment would likely create poor throughput for patients and not be economically viable for any practice. Having a second, clean anesthesia machine is exceedingly expensive and not economically viable. To facilitate a rapid process and make the necessity of a “clean machine” more available, activated charcoal filters are attached to both limbs of the breathing circuit. Within two minutes, the volatile agents are less than five parts per million.3 This approach works during the unexpected MH crisis as well as the preparation of a “clean” machine. Either the triggering anesthetic is discontinued or the vaporizers have been removed. Several sets of charcoal filters may be necessary depending upon the severity and stabilization time of the crisis.

The suitability of MH-susceptible patients for ambulatory surgical procedures may be controversial. It is highly unlikely that MH-susceptible patients will trigger if vaporizers are removed from the anesthesia machine, the soda lime is changed to fresh soda lime, and from administration of a stress free, non-triggering anesthetic. Despite the non-triggering anesthetic, MH-susceptible patients should be ready for discharge from the facility provided they have an uneventful anesthetic and two-hour stay in the PACU.4

Many MH-susceptible patients undergo routine dental treatment, endoscopies or other superficial procedures in the office-based setting. Most of these patients have received topical anesthesia, local anesthesia or intravenous sedation with non-triggering agents. In contrast, a number of publications recommend that the more invasive procedures should take place in the ASC or hospital setting.5,6 As more procedures are shifted from the hospital to the ASC or office-based setting, more MH episodes are possible. Appropriate patient selection and practicing MH crisis management using available guidelines should make the transfer to the acute care facility less complicated for the anesthesiologist and safer for the patient. Finally, if a patient experiences an MH crisis in the ambulatory environment, both the patient and the anesthesiologist will benefit by contacting the North American Malignant Hyperthermia Registry and completing an Adverse Metabolic or Muscular Reaction to Anesthesia, or AMRA, report. These reports, along with other helpful information, are available at the MHAUS website ( with easy links to the report form. Patients should be encouraged to contact the Medic Alert Foundation ( and receive a special bracelet or necklace. Future MH events may be prevented.

Andrew Herlich, D.M.D., M.D., FAAP is Professor and Vice-Chair for Faculty Development, Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania. He is an MHAUS Hotline consultant.


  1. Larach MG, Dirksen SJ, Belani KG, et al. Creation of a guide for the transfer of care of the malignant hyperthermia patient from ambulatory surgery centers to receiving hospital facilities. Anesth Analg. 2012;114(1):94-100.
  2. Kim TW, Nemergut ME. Preparation of modern anesthesia workstations for malignant hyperthermia-susceptible patients. Anesthesiology. 2011;114(1):205-212.
  3. Birgenheier N, Stoker R, Westenskow D, Orr J. Activated charcoal effectively removes inhaled anesthetics from modern anesthesia machines. Anesth Analg. 2011;112(6):1363-1370.
  4. Brandom BW. Ambulatory surgery and malignant hyperthermia. Curr Opin Anesthesiol. 2009; 22(6):744-747.
  5. Ahmad S. Office based--is my anesthetic care any different? Assessment and management. Anesthesiol Clin. 2010;28(2):369-384.
  6. Gurunluoglu R, Swanson JA, Haeck PC; ASPS Patient Safety Committee. Evidence-based patient safety advisory: malignant hyperthermia. Plast Reconstr Surg. 2009;124(suppl 4):68S-81S.

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