Anesthesia Considerations 

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