Malignant Hyperthermia Anesthesia 2024

Malignant Hyperthermia Overview

  • Definition: Malignant hyperthermia (MH) is a hypermetabolic response to certain anesthetic agents leading to serious complications.

    • Symptoms: Increased CO2 production, muscle rigidity, fever, tachycardia, tachypnea, acidosis, hyperkalemia, myoglobinuria (rhabdomyolysis), cyanosis, and potential death.

    • Incidence: Approximately 1 in 100,000 anesthetics; about 600 cases reported annually in the US.

Triggering Agents of MH

  • MH Trigger Agents:

    • Potent volatile anesthetics: Sevoflurane, Isoflurane, Desflurane.

    • Succinylcholine.

  • Non-MH Trigger Agents:

    • Opioids, Non-depolarizing neuromuscular blocking agents (NMBA), Ketamine, Propofol, Etomidate, Thiopental, Benzodiazepines, Nitrous Oxide.

Clinical Signs of MH

  • Specific Signs:

    • Muscle rigidity (especially masseter), Increased CO2 production (sharp rise in end-tidal CO2), Myoglobinuria (rhabdomyolysis).

    • Marked temperature elevation.

  • Non-specific Signs:

    • Tachycardia, Tachypnea, Acidosis (respiratory/metabolic), Hyperkalemia.

Signs of an MH Crisis

  • Early Signs:

    • Skeletal muscle rigidity, Increased end-tidal CO2, Muscle spasms, Tachycardia, Acidosis (both metabolic and respiratory).

  • Late Signs:

    • Elevated temperature, Myoglobinuria, Elevated Creatine levels, Hypocalcemia, Hyperkalemia, Cardiac arrest.

Genetics of MH

  • Modes of Inheritance:

    • Autosomal dominant, Autosomal recessive, Unclassified modes.

  • Genetic Location:

    • Gene associated with MH is on Chromosome 19 (RYR1 mainly in skeletal muscle and RYR2 in myocardium).

Ryanodine Receptor and Calcium Dynamics

  • Function of Ryanodine Receptors:

    • Regulate calcium release from the sarcoplasmic reticulum into muscle cells.

    • Elevated intracellular calcium levels lead to muscle contraction and hypermetabolism.

Pathophysiology of MH

  • Mechanism:

    • Genetic abnormalities in skeletal muscle receptors cause excess calcium accumulation.

    • Ineffective control of calcium levels results in heat production and muscle contraction due to enhanced glycolysis and actin-myosin filament activation.

Epidemiology of MH

  • Mortality Rate:

    • From a study of 291 MH events, 2.7% resulted in cardiac arrest; 1.4% resulted in death, with a median age of 20 years.

Complications of MH

  • Common Complications:

    • Disseminated intravascular coagulation (DIC), Pulmonary edema, Acute renal failure due to rhabdomyolysis, CNS damage (hypoxia/acidosis), Cardiovascular issues (arrhythmias).

Management of an MH Crisis

  • Immediate Therapy:

    • Stop inhalational agents and succinylcholine, hyperventilate with 100% oxygen.

    • Administer bicarbonate (1-2 mg/kg as required), call for assistance.

    • Dantrolene (2.5 mg/kg IV push, repeat PRN) to counteract calcium release.

    • Cooling measures: gastric lavage, surface cooling, wound irrigation. Avoid calcium channel blockers.

  • Follow-up Care:

    • Monitor arterial, venous blood gases, electrolytes, and coagulation studies.

Dantrolene Administration

  • Dosage:

    • Initial dose: 2.5 mg/kg mixed with sterile water; median usage during crisis often reaches 17 vials.

Preventing MH

  • Best Treatment:

    • Avoidance through education and diagnostic testing (Muscle Contracture Testing, Caffeine Halothane Contracture Test).

    • Sensitivity approaching 100% for detecting MH susceptibility.

Diagnostic Testing for MH

  • Genetic Testing:

    • RYR1 gene sequencing to identify causative mutations.

    • Currently, 29 known mutations linked to MH susceptibility.

Preparing for MH Susceptible Patients

  • Preparatory Steps:

    • Use dedicated anesthesia machines, flush systems with oxygen, eliminate triggering agents, monitor temperature, have dantrolene available in the room.

MHAUS and Resources

  • Malignant Hyperthermia Association of the United States (MHAUS):

    • Non-profit organization focused on education and emergency support.

    • Resources: Medical professionals hotline (1-800-MH-HYPER), general information lines, and community support.

Example MH Policy in Anesthesia

  • Purpose:

    • Outline preparations for potential MH cases during anesthesia.

  • Procedure Summary:

    • Prepare MH cart and equipment, flush anesthesia machines with oxygen, and ensure proper measures are in place for immediate response.

  • Special Considerations:

    • Communicate patient management strategies to postoperative care teams.