Malignant Hyperthermia Crisis - Dantrolene and Supportive Care

Key Points

• Rising end-tidal CO2 is often an earlier clue than high temperature.
• Stop volatile anesthetics and succinylcholine immediately.
• Dantrolene is the specific lifesaving therapy and should not be delayed.
• Initial dantrolene is 2.5 mg/kg IV, repeated until the crisis is controlled.
• Large cumulative doses may be required.
• Treat hyperkalemia and acidosis aggressively.
• Avoid calcium-channel blockers with dantrolene.
• Recrudescence can occur, so ICU monitoring and maintenance dantrolene are required.

Algorithm

1. Recognize unexplained hypercarbia, tachycardia, rigidity, acidosis, hyperkalemia, or rapidly rising temperature.
2. Stop trigger agents and call for the MH cart and help.
3. Hyperventilate with 100% oxygen and high fresh-gas flow.
4. Give dantrolene 2.5 mg/kg IV rapidly and repeat until hypermetabolism is controlled.
5. Cool significant hyperthermia and stop active cooling near 38 C.
6. Treat hyperkalemia, acidosis, arrhythmias, and DIC as indicated.
7. Transfer to ICU and continue maintenance dantrolene with serial laboratory monitoring.
8. Refer for definitive susceptibility evaluation and future trigger-free anesthesia planning.

Clinical Synopsis & Reasoning

Malignant hyperthermia results from abnormal skeletal-muscle calcium regulation, most commonly involving RYR1 susceptibility. It can occur during anesthesia or shortly afterward. Hyperthermia is an important feature but is often late; waiting for a very high temperature delays treatment. An unexpected rise in end-tidal CO2 despite adequate ventilation, tachycardia, masseter or generalized rigidity, mixed metabolic and respiratory acidosis, hyperkalemia, dark urine, and rapidly increasing temperature should trigger immediate concern.

Discontinue all volatile anesthetics and succinylcholine. Call for the malignant hyperthermia cart and additional personnel, inform the surgeon, and stop or abbreviate surgery when feasible. Increase minute ventilation with 100% oxygen at high fresh-gas flow. Remove or disable vaporizers and use activated charcoal filters according to institutional preparation if available; do not delay dantrolene while changing the machine.

Obtain blood gas, potassium, CK, glucose, coagulation studies, renal function, and urine assessment for myoglobin. Continuous core-temperature monitoring is required. Hyperkalemia and acidosis can cause ventricular dysrhythmia. Disseminated intravascular coagulation is a late severe feature. The diagnosis is clinical during the crisis; susceptibility testing with genetic evaluation or contracture testing is arranged after recovery.

Treatment Strategy & Disposition

MHAUS recommends an initial IV dantrolene dose of 2.5 mg/kg given rapidly. Repeat doses as often as needed until end-tidal CO2 falls, rigidity resolves, heart rate improves, and hypermetabolism is controlled. Doses above 10 mg/kg may be required; if the patient does not respond to substantial dosing, reconsider alternative diagnoses while continuing appropriate treatment. Reconstitute enough drug rapidly and assign team members specifically to preparation.

Cool actively when core temperature is markedly elevated, using chilled IV fluid and external cooling. Stop active cooling as temperature approaches approximately 38 C to avoid overshoot. Treat hyperkalemia with calcium, insulin/dextrose, and other standard measures. Sodium bicarbonate can be used for severe metabolic acidosis. Avoid calcium-channel blockers in the setting of dantrolene because dangerous hyperkalemia and cardiovascular collapse have been reported. Treat dysrhythmias with standard agents excluding that interaction.

After stabilization, monitor in an ICU. MHAUS recommends maintenance dantrolene 1 mg/kg every 4 to 6 hours or equivalent infusion while observing for recrudescence, generally for at least the early post-crisis period and until clinical stability criteria are met. Follow CK, potassium, renal function, urine output, coagulation, and temperature. Provide genetic/MH-center referral and counsel the patient and relatives about future trigger-free anesthesia.

Epidemiology / Risk Factors

• MH susceptibility is inherited, often in an autosomal-dominant pattern involving calcium-regulation genes.
• An uneventful previous anesthetic does not eliminate future MH risk.
• Volatile anesthetics and succinylcholine are classic triggers.
• Prompt dantrolene treatment has dramatically reduced mortality.

Investigations

Adjunctive Measures

Pharmacology

Prognosis / Complications

• Early recognition and dantrolene produce high survival rates.
• Delayed treatment increases risk of rhabdomyolysis, renal failure, DIC, cardiac arrest, and death.
• Recrudescence can occur after initial stabilization.
• Future anesthesia is safe when triggering drugs are avoided and an MH-prepared system is used.

Patient Education / Counseling

• Tell the patient that future anesthesiologists must know about the suspected or confirmed MH episode.
• Recommend medical-alert identification.
• Family members may also need evaluation because susceptibility can be inherited.
• Trigger-free anesthesia can be performed safely with appropriate preparation.
• Report dark urine, severe muscle pain, weakness, or fever during post-crisis recovery.

Notes

MHAUS emphasizes rapid dantrolene rather than an arbitrary cumulative-dose ceiling. A patient whose ETCO2 and rigidity remain uncontrolled may require more than 10 mg/kg, although lack of response should prompt reassessment for thyroid storm, sepsis, pheochromocytoma, equipment problems, or other mimics.

Temperature management is supportive. Antipyretics such as acetaminophen do not correct the skeletal-muscle hypermetabolism that drives MH and should never replace dantrolene and active cooling.

References

1. MHAUS Managing a Malignant Hyperthermia Crisis — Link
2. MHAUS Dantrolene Administration After an MH Event — Link