FY26 MH 2025 1124

Malignant Hyperthermia

• Discuss a malignant hyperthermia (MH) crisis
• Understand who is at risk for a MH crisis
• Recognize signs / symptoms of malignant hyperthermia crisis
• Discuss drug dosage / administration during a malignant hyperthermia crisis
• Understand your role during a malignant hyperthermia crisis

Objectives

• A rare but lethal syndrome that occurs in certain patients when they are exposed to specific agents used to induce general anesthesia

• Malignant hyperthermia (MH) crisis is characterized by:
• Sustained muscle contractions
• Hypermetabolism
• Hyperthermia

Malignant Hyperthermia

• In some patients, MH-triggering agents (commonly used to induce general anesthesia) cause cellular reactions leading to sustained muscle contraction without relaxation

• Calcium ion levels in the skeletal muscle increase until the acute cellular catabolic processes occur that lead to MH

• Sustained muscle contractions cause hypermetabolism, which leads to an increased use of adenosine triphosphate (ATP) and an increased production of lactic acid, carbon dioxide, and heat

• Hypermetabolism causes the patient to experience hypercapnia and respiratory acidosis

MH Crisis Explained

• Depletion of ATP stores in the body (due to hypermetabolism) disrupts skeletal muscle cell membranes allowing electrolytes, enzymes, and myoglobin to leak into the bloodstream

• Hyperkalemia results in cardiac arrhythmias

• Increased creatine kinase allows for prolonged muscle contractions

• Myoglobin obstructs renal tubules, resulting in renal damage and possible renal failure

• Sustained hypermetabolism causes a quick and dramatic rise in the patient's core body temperature

MH Crisis Explained

• MH susceptibility is an autosomal dominant trait
• Children and siblings of an MH patient have a 50 percent chance of inheriting the gene defect and are considered susceptible

• However, not everyone who has the gene defect develops MH when exposed to triggering anesthetics

• For example, individuals with the gene defect may tolerate one surgery well then develop MH during a subsequent procedure

Who is at Risk?

• 1:30,000 for children and adolescents

• 1:100,000 for adults

• More common in men

• Has been reported in pregnant women without adverse fetal effects

• Family history and previous exposure to anesthetics are not reliable predictors of potential MH occurrence

Incidence

• Neuroleptic malignant syndrome

• Iatrogenic overheating

• Pheochromocytoma

• Heat illness

• Sepsis

• Hypoxic encephalopathy

• Cocaine / ecstasy overdose

• Thyroid storm

• Faulty equipment for monitoring temperature and/or carbon dioxide

• Intrathecal injection of inappropriate radiological contrast agent

• Sudden cardiac arrest in patients with an occult myopathy

Conditions that Mimic MH

Cyclopropane

Enflurane

Sevoflurane

Methoxyflurane

Ether

Desflurane

Succinylcholine (a depolarizing muscle relaxant)

Halothane

Isoflurane

MH-Triggering Agents

• Local anesthetics do not trigger MH

• Spinal, regional, epidural or local are preferred when anesthetizing an MH-susceptible patient

Safe Anesthetic Agents

Intraop Processes

The following precautions are taken prior to surgeryfor patients with a personal or familial history of MH Volatile anesthetic agents are removed from the anesthesia machine and the system is flushed according to manufacturer recommendations. This may require flowing 10 L/min of medical air.

1. Preparing the anesthesia machine
2. Removing triggering agents

- or -

The anesthesia machine is flushed with high fresh gas flows (at least 10 L/min) and activated charcoal filters are placed on the proximal ends of both the inspiratory and expiratory ports.

The anesthesia team removes any available succinylcholine from the patient’s assigned operating room/procedural area for the duration of the case

• Increased end tidal carbon dioxide (ETCO2) with a corresponding decrease in O2 – usually the first sign!

• Muscle rigidity (masseter muscle spasm that may spread to chest and extremities)

• Unexplained, marked sinus tachycardia within 30 minutes of induction (or medication

administration)

• Cardiac dysrhythmias

• Tachypnea

• Unstable blood pressure

• Myoglobinuria

• Skin mottling and cyanosis

• Rapidly rising core body temperature (one degree Fahrenheit per minute)

Signs and Symptoms

Rise in core body temperature is a LATE sign!

EARLY RECOGNITION is the first step in managing an MH crisis!

Call for Help

The second step in managing an MH crisis is to call for help!

• Adult Hospital
• In non-OR areas, call 1-1111 “Activate Malignant Hyperthermia Protocol”
• In OR areas, call the OR board
• Children’s Hospital
• Call 1-1111 and "Activate Malignant Hyperthermia,” and
• Call the Airway Phone to give additional information
• Off-campus locations (VSCF, VHBM, FEL, etc.)
• Call 911, and
• Prepare patient for transport to Vanderbilt emergency department, and
• Treat patient until emergency medical services arrives

MH Cart Locations

The third step is to obtain closest MH cart to your area**

Malignant Hyperthermia (MH) Cart Locations - Main Campus

** appropriate for non-licensed staff to perform

MH Cart Locations

The third step is to obtain closest MH cart to your area**

Malignant Hyperthermia (MH) Cart Locations - Ambulatory

** appropriate for non-licensed staff to perform

MH Cart Locations

The third step is to obtain closest MH cart to your area**

Malignant Hyperthermia (MH) Cart Locations - Regional

** appropriate for non-licensed staff to perform

• Discontinue potent inhaled anesthetics

• Ventilate patient with 100 percent oxygen

• Intubate patient (if not already)

• Remove vaporizers from anesthesia machine

MH Treatment

• Attach vapor-clean to anesthesia machine and change out anesthesia tubing

• Reconstitute and administer Ryanodex

Ryanodex…

• Is reconstituted with 5mL of sterile water (without a bacteriostatic agent) per vial

• Shake vial until thoroughly mixed (it should be a uniform orange color)

• Mixing should take no more than 10 seconds

• Must be used within 6 hours after reconstituted

• Must be stored at a controlled temperature of 68 to 77 degrees Fahrenheit

• Contains 250mg of dantrolene per vial (50mg/mL)

• Each vial contains 125mg of

mannitol (which is subtherapeutic for diuresis)

MH Treatment

2.5mg/kg up to a maximum dose of 10mg/kg

• Initiate cooling procedures

• Iced normal saline 1000mL intravenously every 10 minutes for 30 minutes

• Surface ice packs to cool the patient (around axillae, groin, neck, and head where vessels are close to the skin surface) and/or a hypothermia blanket**

• Iced lavage of stomach (possible rectal or nasogastric tube lavage) – this requires a provider order

MH Treatment

Stop cooling measures when temperature falls to 38°C – beware of unintentional hypothermia!

• Terminate surgery as soon as possible

• Obtain labs: arterial blood gases (ABGs), electrolytes, serum enzymes, CBC with platelets, CK, PT, PTT

** appropriate for non-licensed staff to perform

• Insert temperature probe (if not previously done)

• Insert urinary catheter with Urimeter

• Insert arterial line and central line (if not previously done)

• Provider/RN to administer drugs as ordered:

MH Treatment

• Sodium bicarbonate
• Furosemide
• Mannitol
• Regular insulin in D50W
• Calcium chloride

Resources

• Ryanodex Dosing Guide

• MH Response Algorithm

• Response plans by location:

• VUH OR/Procedural Response Plan

• VCH OR/Procedural Response Plan

• VUMC Non-Procedural Areas Response Plan

• VPH Response Plan

• FEL OR Response Plan

• VSC Franklin (formerly VBJ) OR Response Plan

The anesthesia provider is in charge

The circulator:

•Notifies the OR board and PACU •Ensures MH cart is brought into the OR •Assumes the role of recorder/timekeeper •Inserts the urinary catheter

OR Roles & Responsibilities

The OR scrub person:

•Maintains sterility of surgical supplies/instruments •Can get and apply ice packs •Can get MH cart

• Admit to the intensive care unit (ICU) for 24 to 48 hours

• Monitor vital signs, electrocardiogram readings, pulse oximetry levels, ETCO2 levels, urinary output, myoglobinuria levels, skin appearance, and level of consciousness

• Continue monitoring labs: ABGs, serum myoglobin, CPK, electrolyte levels, clotting studies

• Recrudescence (recurrence) occurs in 25 percent of patients

• A certified registered nurse anesthetist or anesthesiologist accompanies MH patients during transport to the ICU for post-MH-event care

Post-acute Treatment

• Ali, S. Z., Taguchi, A., & Rosenberg, H. (2003). Malignant hyperthermia. Best Practice & Research Clinical Anesthesiology, 17(4), 519-533.

• Dunn, D. (1997). Malignant hyperthermia. AORN Journal, 65(4), 728-754.

References

• Malignant Hyperthermia Association of the United States - www.mhaus.org

• VUMC SOP - Malignant Hyperthermia Management. https://powerdms.com/link/VanderbiltUMC/document/?id=2355258