MH: Presentation

Malignant hyperthermia (MH) is a rare complication of anesthesia that typically presents with the sudden onset of hypermetabolism after general anesthesia has been induced, usually as a result of exposure to inhaled, halogenated anesthetics and/or succinylcholine. Nearly 50% of patients with MH have had a prior uneventful anesthetic where they were exposed to a triggering agent. The underlying mechanism may be related to an abnormal ryanodine receptor that causes release of calcium from the sarcoplasmic reticulum resulting in uncontrolled muscle contractions and increased aerobic and anaerobic metabolism and resulting lactic acidosis. As muscle membranes break down potassium is released from muscle cells leading to hyperkalemia.

The early signs include masseter muscle rigidity (often as trismus: forceful contraction of the jaw), tachycardia and hypercarbia. Tachypnea may also be observed when muscle relaxation is not present. Hyperthermia is a late sign with core temperature rising as much as 1⁰ C every 5 minutes. General muscle rigidity is not always present.

Signs:

Hypermetabolism

• ↑CO₂ production

• ↑ O₂ consumption

• Metabolic acidosis

• Cyanosis

Increased sympathetic activity

• ↑ HR

• ↑ BP

• Arrhythmias

Muscle damage

• Masseter muscle rigidity

• General rigidity

• ↑ serum CK

• ↑ K

• Myoglobinemia/myoglobinuria

Hyperthermia

• Fever

• Diaphoresis

Malignant Hyperthermia Protocol

1. Discontinue volatile anesthetic and succinylcholine. Call for help.

2. Hyperventilate patient with 100% oxygen at high flows

3. Sodium bicarbonate (1-2 mEq/kg IV)

4. Mix dantrolene with sterile distilled water and administer 2.5 mg/kg IV

5. Institute cooling measures (lavage, cooling blanket, cold IV solutions)

6. Inotropes and antiarrhythmics as needed

7. Additional doses of dantrolene

8. Change circuit and soda lime

9. Monitor urine output, K, Ca, blood gases, end-tidal CO₂, clotting studies

10. Treat hyperkalemia with dextrose (25-50 g IV) and insulin (10-20 U IV)

11. Invasive monitoring with arterial line and central line

12. Call MHAUS hotline: 1-800-MH-HYPER