Malignant Hyperthermia

Last updated: March 18, 2021

Malignant hyperthermia (MH) was first described by Denborough in 1962 when deaths were occurring during and immediately (within 24 hours) following the administration of anesthesia medications. The common denominator in these patients was sudden and critical increases in body temperature. These occurrences were quick to reveal that MH is passed down through families (Denborough, Forster, Lovell, Maplestone, & Villiers, 1962).

Patients at risk for MH are very difficult to screen. Although the exact incidence of MH is unknown, the occurrence is estimated to range from 1:5,000–15,000 to 1:50,000–100,000 surgeries (Kim, 2012). Anesthesia agents trigger MH, and it is silent until it has already occurred.

Half of the patients who have an MH crisis have had prior exposure to anesthesia agents known to trigger a crisis without any such reaction. Males have a higher incidence than females, and patients less than the age of 50 are more likely to have MH. Pediatric patients are most frequently affected. Pediatric patients with a history of rheumatoid arthritis have the highest incidence of anesthesia-induced malignant hyperthermia (Butterworth, Mackey, & Wasnick, 2013). Although the most common patients are surgical patients, MH has also been reported after anesthesia medications are used for sedation in surgeon’s offices, intensive care units, dental offices, and emergency departments (National Institute of Arthritis and Musculoskeletal and Skin Diseases, 2018).

The most common medications administered prior to an MH event include succinylcholine, sevoflurane, desflurane, isoflurane, and halothane. Some non-triggering anesthetic agents that are recommended for patients with a previous diagnosis of MH include thiopental sodium and pancuronium, droperidol, benzodiazepines, and ester-type local anesthetics.

An uncontrolled increase in skeletal muscle metabolism is a characteristic of MH. The calcium stores in muscle cells are released, and the muscles contract and stiffen at the same time. The patient experiences a sudden and quite dramatic increase in body temperature that can be as dramatic as 1–2 degrees Celsius every five minutes.

If appropriately treated, the mortality rate is less than 10%. If not recognized and treated, the mortality rate can be expected to be as high as 80%. Most professionals believe that this could be much lower with proper preparedness for rapid recognition and treatment of malignant hyperthermia (McCarthy, 2004). One of the ways that the surgical team can better prepare is by maintaining an emergency cart dedicated to the treatment of malignant hyperthermia. The recommended contents of such a cart are found at the end of this article.

Signs and symptoms

  • Increase in C02 not explained by other causes
  • Rapid respirations
  • Tachycardia
  • One of the first muscles to stiffen is the masseter muscle (trismus). This may be noticed during intubation
  • Hypotension
  • Central cyanosis
  • Skin mottling and diaphoresis
  • Cardiac arrhythmias
  • The dramatic increase in body temperature

The increase in body temperature is not the first sign in MH. This is usually a late but confirming occurrence. Because of the increase in skeletal muscle metabolism and damage, a number of key changes in baseline lab results are common. Blood gases are helpful in diagnosis.

In malignant hyperthermia you would expect to see:

  • Hypercarbia, or hypercapnia
  • Respiratory and metabolic acidosis
  • pH <7.25
  • PCO2 >60 mmHg
  • Base excess <8 mEq/L

You would expect to see a result above normal in the following lab results:

  • PCO2
  • Potassium
  • Calcium
  • Magnesium
  • Lactate
  • Pyruvate
  • Creatine phosphokinase
  • Myoglobin
  • Glucose
  • Creatinine

You would expect to see a result below normal in the following lab results:

  • pH Level
  • P02
  • Sodium
  • Prothrombin time
  • Platelets

The following treatment protocol is published by the Malignant Hyperthermia Association of the United States (MHAUS) (Malignant Hyperthermia Association of the United States, n.d). Although written in a specific order, many of the following interventions should be done simultaneously. Early diagnosis and treatment are essential to limit mortality.

Treatment Dosage or action
Immediately discontinue anesthesia, including succinylcholine Continue a life-threatening surgery but with the use of a different anesthetic agent and machine to prevent residual inhalation from triggering a second episode.
Hyperventilate 100% oxygen at a high flow rate of 10 L/min to treat the effects of hypercapnia, metabolic acidosis, and increased oxygen consumption.
Dantrolene 2.5 mg/kg IV as soon as possible, given every 5 minutes until the symptoms subside.
Change ventilator tubing and soda-lime canister Some anesthesia providers may still perform this action, but research has shown that it is not necessary to change the circuit and anesthesia machine since the oxygen delivery rapidly clears the machine of any residual gases.
Sodium bicarbonate 1–2 mEq/kg IV to combat metabolic acidosis due to an increase of lactate in the circulatory system.
Ice packs Apply to the groin area, axillary regions, and sides of the neck—where major arteries are located. Also, apply to wrists and ankles/feet.
Iced lavage Lavage the stomach and rectum with cold fluids to lower temperature. It is recommended not to lavage the bladder since the fluids can alter the true amount of urine being excreted by the patient, which can alter the measurement of output.
Mannitol or furosemide Muscle cells are destroyed during an MH crisis and the myoglobin that is released accumulates in the kidneys, obstructing urinary flow, referred to as myoglobinuria. Diuretics are given IV to promote and maintain urinary flow in order to prevent renal damage. Mannitol 0.25 g/kg IV; furosemide 1 mg/kg IV up to four doses each. Urinary output of 2 ml/kg/hr or higher must be maintained to prevent renal failure.
Procainamide 200 mg IV to treat arrhythmias secondary to electrolyte imbalances.
Dextrose and insulin Treat hyperkalemia due to the release of potassium into the circulatory system as muscle cells are destroyed. Dextrose 25–50 g IV, regular insulin 10 units in 50 ml of 50% dextrose in water given IV.
Monitor urine output Insert Foley catheter if one is not in place.
Monitor electrolyte levels Blood samples were taken every 10 minutes to measure sodium, potassium, chlorides, calcium, phosphate, and magnesium levels.
Perform clotting studies PT, or prothrombin time; PTT, or partial thromboplastin time.
Arterial blood gasses (ABGs) Every 5–10 minutes. ABGs include partial pressures of oxygen (PaO2), carbon dioxide (PaCO2), and the pH of an arterial blood sample. Oxygen content (O2CT), oxygen saturation (SaO2), and bicarbonate (HCO3-) values are also measured.
Arterial blood pressure (AVP) Insert arterial line if one is not in place.
Central venous pressure (CVP) Insert central line if one is not in place.
Capnography Monitor carbon dioxide (CO2) levels in the respiratory gasses continuously.

Dantrolene, a skeletal muscle relaxant specifically developed for the treatment of MH, is the backbone of the treatment regimen. The administration is every 6–8 hours for 24–72 hours after the initial episode. The dose is 1 mg/kg. The standard dose is based on an adult that weighs 70 kg; thirty-six 20 mg vials of dantrolene will be needed to stabilize the patient. Rarely does the total required dosage exceed 10 mg/kg? A common complication of dantrolene is phlebitis; therefore, it is recommended that it be given via a central line (Butterworth, 2013).

To reduce the time needed to implement a definitive treatment, it is recommended that each operating room, outpatient surgery center, and physician office where surgical procedures are performed have a cart dedicated to MH (MHAUS, n.d.).

The supplies, equipment, and medications for the cart are as follows:

General equipment and supplies

  • 60 mL syringes (5)
  • 16G, 18G, 20G IV catheters, 2 inches (4)
  • 22G IV catheter, 1 inch (4)
  • 24G IV catheter, 1 inch (4)
  • IV solutions
  • NG tubes, various sizes
  • 60 mL Toomey syringes (2) with adaptor (used with NG irrigation)
  • Foley catheter tray
  • Urine meter
  • Urine collection container to determine myoglobin level
  • Urinalysis test strips
  • Irrigation tray with 60 mL irrigation syringe
  • 10–12 bags of saline kept in a refrigerator for IV cooling
  • Small and large plastic bags for ice
  • Bucket for ice
  • 3 mL syringes or ABG kit (6) for blood gas analysis
  • Blood specimen tubes
  • Steri-drape or some type of adhesive drape to cover and protect the surgical site
  • Pulmonary artery, esophageal, nasopharyngeal, tympanic membrane, bladder, and rectal temperature probes
  • Blood administration sets and pumps
  • Central venous catheter kits of various sizes
  • Transducer kits for arterial and CVP cannulation
  • Gastric lavage set with a three-way indwelling catheter for insertion into the rectum

Pharmaceuticals

  • Dantrolene 20 mg each (36)
  • Sterile water 100 mL (36)
  • 50 mL sodium bicarbonate 8.4% (5)
  • 50 mL mannitol 20% (10)
  • 2 mL prefilled syringes of furosemide (4)
  • 100 U vial of regular insulin
  • 50 mL 50% dextrose in water (2)
  • 10 mL calcium chloride (2)
  • Heparin 1000 U vials (3)
  • Lidocaine 2% for injection (3 preloaded syringes)
  • Amiodarone 150 mg per vial (3)

Works cited

  • Butterworth, J. F., Mackey, D. C., & Wasnick, J.D. (2013). Morgan and Mikhail's Clinical Anesthesiology (5th ed.). New York City, NY: McGraw-Hill Companies, Inc.
  • Denborough M. A., Forster, J. F. A., Lovell, R. R. H., Maplestone, P. A., & Villiers, J. D. (1962). Anaesthetic deaths in a family. British Journal of Anaesthesia, 34, 395-396.
  • Kim, D. C. (2012). Malignant hyperthermia. Korean Journal of Anesthesiology, 63(5), 391–401. Retrieved from https://doi.org/10.4097/kjae.2012.63.5.391
  • Nagelhout, J. & Zaglaniczny, K. L. (2001). Nurse Anesthesia (2nd ed). Philadelphia: W.B. Saunders.
  • Malignant Hyperthermia Association of the United States. (n.d). Emergency treatment for an acute MH event. Retrieved from https://www.mhaus.org/healthcare-professionals/.
  • McCarthy, E. J. (2004). Malignant hyperthermia: Pathophysiology, clinical presentation, and treatment. AACN Clinical Issues, 15(2): 231-237. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/15461040
  • National Institute of Arthritis and Musculoskeletal and Skin Diseases. (2018, April 3). Retrieved from https://www.niams.nih.gov/
This page is written by on Apr 6, 2018.
This page is last reviewed and updated by on Jun 30, 2020.