Malignant Hyperthermia

· Hypermetabolic state of skeletal muscle secondary to idiopathic block of calcium re-entry into the sarcoplasmic reticulum

· Epidemiology

1. Carries a multifactorial genetic predisposition

2. Incidence is 1/15,000 pediatric anesthetic administrations; 1/40,000 adult anesthetic administrations

3. 50% of cases are seen in patients who had undergone previous anesthesia without malignant hyperthermia

4. Having any relative with a history places patient at risk

5. Related traits include heavy musculature, Duchenne muscular dystrophy, and scoliosis

6. Mortality is up to 30%

· Dx (early):  increasing end tital pCO₂, tachycardia, arrhythmias

1. Progresses to coagulopathy (DIC), increasing metabolic acidosis, decreasing pO₂, pulmonary edema, increasing body temperature (at a rate of 1° C/5 minutes, up to 44° C), limb muscle rigidity, and rhabdomyolysis

2. Terminal events are hypotension, bradycardia, and cardiac arrest

· Prevention:

1. Identify patients at risk

2. Use non-halogenated anesthetics and non-depolarizing blockers

3. Prophylactic dantrolene 4-8 mg/kg/day for 1-2 days prior to planned anesthetic

· Intraoperative episode

1. Discontinue causative agent and change ventilator tubing

2. Give dantrolene 2.5 mg/kg IV.  Additional doses up to total of 10 mg/kg may be used

3. Hyperventilate patient with 100% O₂

4. Begin surface and cavity cooling

5. Give bicarb as needed for acidosis (1-2 meq/kg)

6. Administer IV insulin and glucose to lower potassium released by damaged muscle

7. Treat arrhythmias (procainamide)

8. Volume load and give osmotic diuretics to prevent renal damage from CPK