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Malignant Hyperthermia (MH)

 

 

Signs (early)

 

  • ↑ EtCO2

  • Tachycardia

  • Tachypnea

  • Mixed acidosis

  • Masseter spasm/trismus

  • Sudden cardiac arrest due to hyperkalemia

 

Signs (may be later)

 

  • Hyperthermia

  • Muscle rigidity

  • Myoglobinuria

  • Arrhythmias

  • Cardiac arrest

 

 

Differential Diagnosis

 

  • Neuroleptic malignant syndrome: similar presentation to MH but associated with use of antipsychotic neuroleptic medications (also treated with dantrolene)

  • Thyroid storm: fever, tachycardia, altered mental status

  • Anaphylaxis: cardiovascular collapse without hypermetabolic features

  • Pheochromocytoma: significant hypertension

  • Drug toxicity: consider clinical context, screen urine/plasma

 

 

Management

 

  • Alert surgeon & call for help

  • Stop anesthetic triggers (volatiles & succinylcholine), ↑ fresh gas flow to 10L/min; do not change machine or circuit

  • If available, insert activated charcoal filters into the inspiratory & expiratory limbs of the breathing circuit

  • ↑ to 100% FiO2 & ↑ minute ventilation

  • Halt surgery; if emergent, continue with non-triggering anesthetic

  • Call MH hotline: 

    • MHAUS (Malignant Hyperthermia Association of the United States) 

      • 1 800 644 9737 (within USA); 00 1 209 417 3722 (outside USA)

  • Assign several people to prepare dantrolene 2.5 mg/kg IV bolus:

    • Dilute each 20 mg dantrolene vial in 60 mL preservative-free sterile water

    • For 70 kg person, give 175 mg (prepare 9 vials of 20 mg dantrolene) 

    • Rapidly administer dantrolene & continue giving until patient stable

    • May need > 10 mg/kg

  • Cool patient: IV fluids, ice packs, gastric / peritoneal lavage

  • Treat arrhythmias:

    • Usually secondary to hyperkalemia

    • Treat in standard fashion, however avoid calcium channel blockers

  • Treat metabolic acidosis:

    • Sodium bicarbonate 1 to 2mEq/kg PRN for base excess greater than -8 

  • Treat hyperkalemia:

    • Hyperventilation

    • Calcium chloride 10mg/kg (max dose 2g) or calcium gluconate 30mg/kg (max 3g) 

    • D50 1 amp IV (25g dextrose) + regular insulin 10 units IV → monitor glucose 

    • Sodium bicarbonate 1 amp

    • Furosemide 0.5-1mg/kg once 

    • For refractory hyperkalemia, consider beta-agonist, kayexalate, dialysis, or ECMO if in cardiac arrest

  • Monitor temperature, electrolytes, arterial/venous blood gases, creatine kinase, urine output, coagulation studies, lactic acid

  • Place foley catheter, monitor urine output

  • When stable, transfer to post anesthesia care unit or intensive care unit for at least 24 hours

  • Monitor for recurrence & continue dantrolene 1 mg/kg q 4-6 hours x 24 to 48 hours

  • Refer for genetic counseling/in-vitro muscle contracture testing

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