Malignant Hyperthermia (MH)

This category focuses on the inherited condition of Malignant Hyperthermia, its triggers, signs, and critical management.

Malignant Hyperthermia (MH)

Determining MH Risk

• The primary indicator is family history, as MH is an autosomal dominant inherited syndrome.

Individuals Most at Risk for MH

• Family history of MH.
• Scandinavian descent.
• Native American descent.
• Older children/young adults.
• Males (80% of cases).
• Geographic “Hot Spots”: Bay Area California, Wisconsin, North Carolina coast.

Pathophysiology of MH Crisis

• Calcium Release: Calcium is uncontrollably released into the muscle cells (the “door is stuck open”), leading to severe muscle rigidity.
• Mitochondrial Overdrive: Mitochondria are excessively signaled to produce energy, rapidly consuming oxygen and generating massive amounts of heat and CO2 as waste products.

Triggers for MH Episode

Two conditions must be met for an MH episode:

1. A genetically susceptible patient.
2. Exposure to a triggering agent (Succinylcholine/depolarizing agents, or volatile liquid inhalants).

Earliest Consistent Indicator of MH Crisis

• The rapid and sustained rise in end-tidal CO2 is the earliest and most consistent indicator. (Reflects the intense metabolic activity of mitochondria producing energy, consuming O2, and releasing CO2).

Early vs. Late Indicators of MH Crisis

• Early:
  • Rapid rise in CO2 (reflecting metabolic acidosis).
  • Jaw tightening (trismus).
  • Generalized muscle rigidity (due to calcium release).
  • Increased heart rate (tachycardia) (body trying to increase oxygen delivery).
  • Increased blood pressure (hypertension) (body trying to increase oxygen delivery).
• Late (Critical Signs):
  • Rapid increase in body temperature (a hallmark, but often a late sign).
  • Rapid color change in soda lime (due to increased CO2 absorption).
  • Decreased SpO2 (hypoxia) (the primary cause of mortality).
  • Hyperkalemia (another major cause of mortality from cellular breakdown).
  • Myoglobinuria (muscle breakdown, leading to lactic acid production and potential kidney damage).
  • Cardiac arrest (resulting from acidosis, hypoxia, and hyperkalemia).

Focus During an MH Episode

• The primary goal is to prevent cardiac arrest by:
  • Optimizing oxygenation.
  • Correcting acidosis and hyperkalemia (using bicarbonate, calcium, insulin, glucose).
  • Managing myoglobinuria (with diuretics and fluids to protect kidneys).

Steps for MH Crisis Management (Comprehensive Protocol)

1. Eliminate the Trigger: Immediately stop the triggering agent. Turn off all volatile gases. Flush the anesthesia machine system and change the breathing circuit. Nitrous oxide may be safely used.
2. Hyperventilate with Oxygen: Provide 100% oxygen and hyperventilate as rapidly and as much as physiologically possible.
3. Call for Expert Consultation: Contact MHAUS (Malignant Hyperthermia Association of the United States) at 1-800-MH-HYPER.
4. Administer Dantrolene:
   • Dose: 2.5 mg/kg (range 2-3 mg/kg) mixed ONLY with preservative-free sterile water.
   • Preparation: Withdraw 60 mL of sterile water, add to the Dantrolene vial, reconstitute, then withdraw and administer.
   • Ryanodex: A newer, more concentrated powdered Dantrolene; only requires 1 vial and is more expensive.
5. Treat Metabolic Acidosis: Administer intravenous sodium bicarbonate to counteract lactic acidosis and help the liver process it.
6. Manage Hyperkalemia: Treat with insulin, glucose/D50 (to prevent hypoglycemia), and calcium (to stabilize cardiac membranes and mitigate cardiac effects of hyperkalemia, such as arrhythmias and QT prolongation).
7. Address Myoglobinuria: Administer diuretics and fluids to prevent kidney damage.
8. Cool the Patient: Apply ice packs and a cooling blanket. Use iced normal saline IV fluids (avoid LR as it contains potassium and lactate).
9. Monitor Labs and ECG: Regularly check electrolytes and perform ECGs for arrhythmias.
10. Post-Crisis Care: Transfer the patient to the ICU for prolonged monitoring (longer than 24 hours) as MH can recur.

Dantrolene Dose and Preparation

• Dose: 2.5 mg/kg (2-3 mg/kg).
• Preparation: ONLY mix with preservative-free sterile water. Add 60 mL of sterile water per vial, reconstitute, then draw up and administer.

Average Dantrolene Dose for Adults

• An average adult typically requires 9 vials of Dantrolene, with each vial containing 60 mL.

Hyperkalemia Treatment in MH Crisis

• Insulin
• Glucose/D50 (to prevent hypoglycemia caused by insulin).
• Calcium (to stabilize the heart and prevent arrhythmias).

Medications to AVOID During MH Crisis

• Calcium Channel Blockers: These are contraindicated because the calcium gates are already “stuck open” and leaking calcium. Calcium channel blockers would only trap more calcium within the cells, worsening the crisis.

Most Effective Ways to Warm a Patient

• Bair Hugger.
• Hot line (fluid warmer).