Malignant Hyperthermia

Malignant Hyperthermia (Definition)

Inherited disease that causes a rapid rise in body temp (fever) & severe muscle contractions when the affected person receives general anesthesia

MH critical statistic

• MH is a true medical emergency

• Approximately 5% of those who develop MH do not survive

What are indications of MH

• PO2 low & pCO2 high

• INC’ng temp

• Acidosis (metabolic/respiratory)

What can we do on pump if MH develops?

• Administer drugs quickly

• Turn up FiO2 & sweep

• Cool the blood w/ the HC & put ice bags on the neck

• Ultrafiltration to remove inflammatory markers and high levels of K

MH origin pathophysiology

• A mutation of the Ryanodine receptor located in the sarcoplasmic reticulum

• Results in a drastic INC in intracellular calcium and muscle contraction as a result of exposure to various general anesthetic agents

MH Hallmark

The process of reabsorbing this excessive calcium & muscle contraction consumes large amounts of ATP and generates excessive heat (hyperthermia)

Final result of the pathophysiology of MH

• The muscle cells are eventually depleted of ATP & die

• This releases large amounts of K in the bloodstream causing hyperkalemia, followed by cardiac arrhythmias & other complications

Volatile Anesthetic gases (triggers of MH)

• Isoflurane

• Sevoflurane

• Halothane

• Desflurane

• Enflurane

• Methoxyflurane

Depolarizing muscle relaxant (Triggers of MH)

Succinylcholine

Anesthetic gas alternatives

• Narcotics

• Propofol

• Ketamine

• Etomidate

• Nitrous oxide

Non-depolarizing muscle relaxant (alternatives)

• Pancuronium

• Vecuronium

• Rocuronium

Signs & Symptoms of MH

• INC temp (>37C)

• INC HR

• Tachypnea

• INC CO2 production (Hypercapnia)

• INC O2 consumption (VO2)

• Metabolic acidosis

• Muscle rigidity

• Hyperkalemia

• Arrhythmias

Timing of signs & symptoms

• S & S usually develop w/in 1 hr after exposure to the trigger substance

• May occur several hours later in rare cases

Complications of MH

• Myopathy (muscle weakness)

• Rhabdomyolysis (breakdown of muscle tissues)

• Acidosis

• Kidney failure

• DIC

• Brain injury

• Death

• Myoglobinuria (Red-brownish urine)

Treatment for MH

• Initial dose of 2.5 mg/kg Dantrolene (up to 10 mg/kg)

• Discontinuation of triggering agent

• Supportive therapy

  • Cool the patient

  • Correct acidosis

Treatment notes

• Treatment must be instituted rapidly

• Obtaining a good pre-op history is the best way to avoid MH

Calc for determining how much Dantrolene to give for a 70kg pt

• 2.5 mg x 70 kg = 175 mg Dantrolene needed

• Dantrolene comes in 20 mg vials

• 175/20 = 875, so 9 vials are needed

How much Dantrolene should be kept on hand? (Dantrium/Revonto)

• Stock a minimum of 36 - 20 mg vials

• Reconstitute w/ 60 mL sterile water

How much Dantrolene should be kept on hand? (Ryanodex)

• Stock a minimum of 3 - 250 mg vials

• Reconstitute w/ 5 mL Sterile water

Perfusion Considerations

• Unexplained hyperthermia

• Unexplained acidosis

• Unexplained decline in SvO2

• Blood gas analysis

• Priming solutions

• Thermal manipulation

• Rapid bypass initiation

• Portable life support