Enumerate the causes and the drugs useful in the treatment of Malignant hyperthermia
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"malignant hyperthermia" AND treatment
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Malignant Hyperthermia (MH) - Causes and Treatment
Definition and Pathophysiology
Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle in which triggering agents cause uncontrolled release of calcium (Ca²+) from the sarcoplasmic reticulum via the ryanodine receptor (RyR1). The sustained rise in myoplasmic Ca²+ drives skeletal muscle into a hypermetabolic state, producing the fulminant syndrome.
The molecular basis is most commonly a mutation in the RYR1 gene (sarcoplasmic reticulum Ca²+ release channel), identified in 50-80% of genotyped susceptible patients. Three mutations in CACNA1S (encoding the alpha-1 subunit of the sarcolemmal L-type Ca²+ channel / DHPR) also account for a smaller proportion.
Causes (Triggering Agents)
A. Primary Pharmacological Triggers
| Category | Agents |
|---|---|
| Volatile halogenated anesthetics | Halothane, Isoflurane, Sevoflurane, Desflurane, Enflurane |
| Depolarizing neuromuscular blocker | Succinylcholine (suxamethonium) |
B. Non-Anesthetic / Predisposing Causes
- Vigorous exercise in a hot environment - can precipitate an episode in genetically susceptible individuals even without anesthetic exposure
- Neuroleptic agents - trigger via raising myoplasmic Ca²+ levels (produces the related "Neuroleptic Malignant Syndrome," occurring in ~0.2% of patients on neuroleptics, typically within the first 30 days of therapy)
C. Predisposing Myopathies / Genetic Conditions
- Evans myopathy (King-Denborough syndrome) - most common predisposing myopathy; autosomal dominant
- Central core disease
- Multiminicore disease
- Nemaline myopathy
- Mutations in RYR1 gene (>230 identified mutations) - autosomal dominant with incomplete penetrance
- Mutations in CACNA1S gene (3 mutations) encoding the DHPR/Cav1.1
Note: Males are more susceptible than females; the pediatric population accounts for 52.1% of all MH reactions.
Clinical Features (to recognize MH early)
| System | Features |
|---|---|
| Earliest sign | Rising end-tidal CO₂ despite increased minute ventilation |
| Cardiovascular | Sinus tachycardia, ventricular arrhythmias, hypotension |
| Respiratory | Tachypnea, cyanosis, pulmonary edema |
| Musculoskeletal | Generalized rigidity, masseter muscle spasm |
| Metabolic | Hyperthermia (late sign - can rise 1°C every 5 min), metabolic + respiratory acidosis, hyperkalemia, hypercalcemia |
| Hematologic/Renal | Rhabdomyolysis (CK peaks day 2-3), DIC, myoglobinuria, acute tubular necrosis, renal failure |
Treatment (Drugs + Supportive Measures)
Step 1 - Immediate Measures
- Discontinue all triggering agents (volatile anesthetics + succinylcholine)
- Hyperventilate with 100% oxygen at 10 L/min (flush the anesthetic circuit)
- Establish airway and initiate controlled ventilation
Step 2 - Specific Pharmacological Treatment
1. Dantrolene Sodium (First-line, most important drug)
- Class: Hydantoin derivative; direct-acting skeletal muscle relaxant
- Mechanism: Antagonizes the ryanodine receptor (RyR1), directly inhibiting Ca²+ release from the sarcoplasmic reticulum, thereby reversing the hypermetabolic state
- Dose:
- Initial IV bolus: 2.5 mg/kg (some sources cite 2-3 mg/kg)
- Repeat every 5-10 minutes as necessary
- Maximum total dose: 10 mg/kg (some protocols continue beyond this if signs persist)
- Maintenance: ~1 mg/kg IV every 4-6 hours for up to 48 hours to prevent recrudescence
- Formulations: Standard lyophilized powder (requires reconstitution) and a newer nanocrystalline suspension (Ryanodex) with improved solubility that speeds administration
- Effect: Has reduced MH mortality from ~60-80% to less than 1.4-5%
- Note: Prophylactic dantrolene is NOT recommended for known MH-susceptible patients receiving nontriggering anesthetics
2. Sodium Bicarbonate
- Dose: 1-2 mEq/kg IV
- Indication: Correction of metabolic acidosis
- Also used for hyperkalemia management (drives K+ into cells)
3. Glucose + Insulin
- Indication: Treatment of life-threatening hyperkalemia
- Used together with sodium bicarbonate and hyperventilation
Step 3 - Active Cooling Measures
| Method | Details |
|---|---|
| IV iced (cold) saline | 15 mL/kg every 15 minutes (up to 3 doses) |
| Gastric, rectal, bladder lavage | Cold saline irrigation |
| Surface cooling | Ice packs to groin, axillae, neck; cooling blankets |
| Target temperature | Maintain below 39°C; stop cooling before hypothermia sets in |
Step 4 - Cardiovascular Support
- Vasopressors (e.g., norepinephrine) for persistent hypotension
- Antiarrhythmic agents for persistent ventricular arrhythmias
- Procainamide has been used successfully when dantrolene is unavailable
- Avoid calcium channel blockers if dantrolene is being used (risk of hyperkalemia and cardiovascular collapse)
Step 5 - Renal Protection (from Rhabdomyolysis)
- Maintain urine output >2 mL/kg/hour
- Aggressive IV fluid resuscitation (normal saline ~400 mL/hr)
- Diuretics (mannitol, furosemide) to maintain urinary flow and prevent myoglobin precipitation in renal tubules
- Urine alkalinization with bicarbonate (if urine pH <6.5) to prevent myoglobin precipitation
Step 6 - Monitoring and Follow-up
- Monitor temperature, vital signs, urine output, CK, glucose, coagulation, acid-base, and electrolytes
- Observe for at least 48-72 hours to ensure no recrudescence (late recurrence can occur)
- Refer to the Malignant Hyperthermia Association of the United States (MHAUS) hotline for real-time expert guidance
Summary Table of Drugs
| Drug | Role | Dose / Notes |
|---|---|---|
| Dantrolene sodium | First-line specific antidote | 2.5 mg/kg IV bolus, repeat up to 10 mg/kg total; then 1 mg/kg q4-6h x 48h |
| Sodium bicarbonate | Correct metabolic acidosis; treat hyperkalemia | 1-2 mEq/kg IV |
| Glucose + Insulin (IV) | Treat hyperkalemia | Standard hyperkalemia protocol |
| Vasopressors (norepinephrine, etc.) | Hemodynamic support | Titrated to MAP |
| Antiarrhythmics (procainamide) | Refractory ventricular arrhythmias | Standard dosing |
| Mannitol / Furosemide | Renal protection (force diuresis) | Target UO >2 mL/kg/h |
Sources:
- Miller's Anesthesia, 10th Edition, pp. 4525-4526
- The Essentials of Forensic Medicine and Toxicology, 36th Edition (2026), pp. 555-556
- Goldman-Cecil Medicine, Chapter 99 & Chapter 400
- Sabiston Textbook of Surgery, p. 322
- Katzung's Basic and Clinical Pharmacology, 16th Edition, Chapter 16
- Recent PubMed Review (Pinyavat et al., 2024, Crit Care Med) - current review confirming the above management framework
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