‘It’s Getting Hot in Here’: A Discussion on Malignant Hyperthermia

What is malignant hyperthermia?

Malignant hyperthermia (MH) is a rare but life-threatening condition triggered by certain medications. Although it is estimated to occur in 1:30,000 pediatric and 1:100,000 adult general anesthetic cases, these estimates are subject to error mostly due to underreporting or failure to recognize. MH was first described in 1960, and mortality was estimated to be 70%-80% over the following 10 years. Mortality began to decline during the 1970s as IV dantrolene was introduced. Despite the availability of dantrolene, deaths from MH still occur with a mortality rate of approximately 4%.

MH is a disorder due to an acceleration of the metabolism in the skeletal muscle. MH is hereditary and only diagnosed via a muscle biopsy, so we often have to rely on subjective patient information about family history. Because of this situation, you may hear anesthesiologists asking your patients if they had any issues with anesthesia in the past.

How is MH triggered?

MH is triggered by many common anesthetic gases that typically end in “-flurane.” MH is also triggered by succinylcholine, a common paralytic used for intubation. An MH crisis usually occurs within one hour of administration of one of these medications. Sometimes a crisis will start within minutes. In extremely rare cases, an MH crisis can occur up to 24 hours after administration.

What are the signs and symptoms of MH?

Identifying MH early is a crucial component of MH management and prevention of complications. Hence, nurses need to be knowledgeable about the signs and symptoms of MH, which include:

• Initial: Unexplained tachycardia, tachypnea, muscle rigidity, masseter muscle rigidity, a sudden increase in end-tidal carbon dioxide (ETCO2) and metabolic acidosis
• Late: Fever, rhabdomyolysis, mottled skin and myoglobinuria

What is the treatment for patients with MH?

During an MH crisis, the anesthesia or other healthcare provider treats the patient, and the nursing staff assists.

1. Call MH hotline: 800-MH-HYPER
   When MH is suspected, someone must call for help at 800-MH-HYPER (800-644-9737). The MH hotline should be available in the departments where an MH crisis is most likely to occur (usually on all phones in pre-op, PACU, operating room (OR) suites, OR front desk, ICU, labor and delivery OR suites).
2. Stop the triggering agents
   Discontinue volatile agents and succinylcholine. If surgery must be continued, maintain general anesthesia with IV non-triggering agents (e.g., IV sedatives, narcotics, amnestic, non-depolarizing neuromuscular blockers and nitrous oxide).
3. Hyperventilate the patient to lower the ETC02.
4. Medications
   Prepare dantrolene sodium as ordered and administer it to the patient. Immediate treatment with this medication usually reverses the signs of MH. Follow the manufacturer’s guidelines on medication preparation and administration.
   • a. Treatment Goals
   • i. ETCO2<6kPa
   • ii. Normal minute ventilation
   • iii. Core temperature <38.5 °C
5. Cool the patient with ice packs, lavages, IV fluids
   • a. Stop cooling when temperature reaches <38 °C or 100.5 °F.
6. Insert lines
   • a. Insert a urinary catheter, nasogastric or orogastric tube, peripheral IVs and an arterial line.
7. Manage metabolic acidosis
8. Transfer to ICU

What do we monitor post-crisis in the ICU?

After the patient experiences an MH crisis, they are transferred to the ICU for close monitoring for at least 24 hours. Post-crisis, the ICU RN will continue administering the MH medication as ordered, according to the manufacturer’s guidelines. The patient’s heart rate, respiratory rate, temperature, ETCO2, oxygen saturation, muscle tone and urine output should be monitored at least hourly for 24 hours. The Association of Surgical Technologists (AST) recommends that labs should be drawn at a minimum of q 8 hours x 4 and should include arterial blood gases (ABGs), lactic acid, potassium and creatine kinase (CK).

Additional items to monitor and manage:

• Acidosis
  The primary way to manage acidosis with an MH crisis is through hyperventilation. Use caution with hyperventilation and administration of sodium bicarbonate as this medication can cause a low pH level. Low pH values are associated with poor outcomes in MH.
• Hyperkalemia
  Treatment of the patient should be with sodium bicarbonate and/or glucose with insulin. Although calcium is usually a first-line treatment for hyperkalemia, it is not the case with MH, as there is some evidence that an influx of extracellular calcium contributes to calcium overload of the myoplasm and can lead to muscle rigidity.
• Arrhythmias
  The most frequent kind of arrhythmia associated with an MH crisis is tachyarrhythmia. It is recommended to use an antiarrhythmic agent, a short-acting beta-blocker or magnesium. (National Institutes of Health, 2023)
• Myoglobinuria
  Urine output needs to be monitored closely (q 1 hour) because dantrolene is filtered through the kidneys, and acute kidney failure can occur. Urine output should be maintained at >0.5 mL/kg/hr. More research is needed; however, it is thought that administering sodium bicarbonate to alkalinize the urine may prevent acute kidney injury from myoglobinuria.
• Disseminated intravascular coagulation
  The occurrence of disseminated intravascular coagulopathy during an MH reaction is associated with poor outcomes. It is recommended to use platelets, fresh frozen plasma and cryoprecipitate. (Hopkins, et al., 2021)
• Compartment syndrome
  Any patient who develops myoglobinuria should be monitored for the development of compartment syndrome. CK levels may not peak for up to 24 hours after an MH event. Regular assessment of the limbs for swelling, muscle softness and peripheral pulses or peripheral oxygen saturation should be made. If there is any suspicion that compartment syndrome has developed, the compartmental pressures should be measured.

Patient and Family Education

When an MH crisis occurs, patient and family education is vital. Before the patient’s discharge from the hospital, the patient and their family should be informed about the suspected diagnosis of MH. They should be provided with written information about the suspected diagnosis and its implications for future anesthetic management for their whole family.

Other Important Considerations

Because MH is a crisis, hospitals and nursing staff should be adequately prepared. AST recommends having an MH cart readily available for staff to use if a crisis occurs. Refrigerated supplies that may be needed to decrease body temperature should be accessible. Staff must know the location of the MH cart, chilled fluids, ice machines and other equipment/medications for an MH crisis.

The Malignant Hyperthermia Association of the United States (MHAUS) recommends dantrolene be accessible within 10 minutes once the decision is made to treat the patient. Furthermore, MHAUS recommends that the MH crisis cart should have the following supplies:

• Medications/supplies shall include but not be limited to:
  • Dantrolene
  • Sterile water for injection
  • Sodium bicarbonate
  • 2% lidocaine
  • Calcium chloride
  • Dextrose 50%
  • Regular insulin
• Equipment:
  • Syringes
  • Needles
  • Foley catheter kit with urometer
  • Nasogastric/orogastric tubes
  • Supplies to insert invasive lines
  • Blood tubes and labels
  • Other general and monitoring equipment, nursing or lab supplies deemed appropriate
• Minimum of 3 liters of refrigerated saline solution

Recommendations

To increase awareness of MH, AST recommends that staff participate in mock MH crisis drills. These drills are performed with staff in all areas that directly recover patients. These drills should cover:

• Pathophysiology
• Agents capable of triggering MH
• Clinical signs of MH
• Treatment of patients with MH
• Medications of choice to treat patients with MH
• Location of the MH cart
  • How to use the supplies in the MH cart
  • Hands-on demonstration of how to prepare dantrolene

Special Acknowledgement

I acknowledge and thank my co-author, Jennifer Bielat (she/her), MBA-HA, BSN, RN, CNOR, a nursing professional development specialist for surgical services at HCA Mountainview Hospital, for contributing to the development of this blog.

Is your unit ready to manage an MH crisis?