What are the key characteristics and management strategies for malignant hyperthermia?

Malignant Hyperthermia: Characteristics and Management

Malignant hyperthermia is an autosomal dominant disorder that causes a hypermetabolic crisis requiring immediate treatment with dantrolene, not calcium gluconate, and typically presents with metabolic acidosis rather than respiratory alkalosis. 1, 2

Key Characteristics of Malignant Hyperthermia

Genetic and Epidemiological Features

• MH is an autosomal dominant genetic disorder affecting skeletal muscle calcium regulation 2
• It is not rare in children - pediatric patients can develop MH during anesthesia, as demonstrated in case reports of children with conditions like cerebral palsy 3
• Prevalence varies from 1:16,000 to 1:100,000 anesthetics 4
• Genetic mutations in RYR1 (50-86% of cases) and CACNA1S (1% of cases) have been identified 4

Pathophysiology

• Characterized by excessive calcium release from the sarcoplasmic reticulum leading to:
  • Uncontrolled skeletal muscle hypermetabolism
  • Rapid increase in metabolism
  • Hyperthermia
  • Muscle rigidity 4, 2

Clinical Presentation

• Triggered by:
  • Volatile anesthetic agents (halothane, sevoflurane, desflurane, isoflurane)
  • Depolarizing muscle relaxants (succinylcholine) 1
• Classic signs include:
  • Increased end-tidal CO₂ (early sign)
  • Tachycardia
  • Tachypnea
  • Hyperthermia (can exceed 41°C)
  • Muscle rigidity (including masseter spasm)
  • Metabolic acidosis (not respiratory alkalosis) 1, 5
  • Hyperkalemia
  • Myoglobinuria
  • Rhabdomyolysis 2

Management of Malignant Hyperthermia Crisis

Immediate Actions

1. Stop all triggering agents immediately 1
2. Hyperventilate with 100% oxygen at high flow (2-3 times normal minute volume) 1
3. Call for help and declare an emergency 1
4. Switch to non-triggering anesthesia (TIVA) 1
5. Inform surgeon and request termination/postponement of surgery 1

Pharmacological Management

1. Dantrolene administration (first-line treatment):

   • Initial dose: 2 mg/kg IV
   • Repeat until stabilization of cardiac and respiratory systems
   • Maximum dose may exceed 10 mg/kg if needed 1, 6
   • Note: Calcium gluconate is NOT used to prevent MH - it is actually used to treat hyperkalemia during an MH crisis 1

2. Management of complications:

   • Hyperkalemia: 50% dextrose (50 ml) with 50 IU insulin; CaCl₂ 0.1 mmol/kg IV 1, 6
   • Acidosis: Hyperventilate to normocapnea; sodium bicarbonate if pH < 7.2 1
   • Arrhythmias: Amiodarone 300 mg for adults; β-blockers for persistent tachycardia 1

Cooling Measures

• IV administration of 2000-3000 ml chilled (4°C) 0.9% saline 1
• Surface cooling: wet cold sheets, fans, ice packs in axillae and groin 1
• Stop cooling once temperature < 38.5°C 1

Monitoring and Supportive Care

• Continue routine anesthetic monitoring (SaO₂, ECG, NIAP, E'CO₂) 1
• Measure core temperature continuously 1
• Establish good IV access with wide-bore cannulas 1
• Monitor for compartment syndrome, myoglobinuria, and organ dysfunction 1
• Maintain urinary output > 2 ml/kg/h using:
  • Furosemide 0.5-1 mg/kg
  • Mannitol 1 g/kg
  • IV crystalloids 1, 6

Post-Crisis Management

• Monitor patient for minimum 24 hours in ICU/HDU 1
• Watch for recrudescence of symptoms 7
• Refer patient and family members to specialized MH center for further testing 1, 7
• Diagnostic testing includes:
  • In vitro contracture testing (gold standard)
  • Genetic testing for RYR1 and CACNA1S mutations 4, 2

Common Pitfalls to Avoid

• Delaying dantrolene administration while confirming diagnosis - early treatment is critical 5
• Mistaking early signs (like increased EtCO₂) for other conditions 7
• Failing to recognize MH in patients without prior history - it can occur even in patients with previous uneventful anesthesia 1
• Using calcium gluconate as prevention - it is not effective for preventing MH 1
• Failing to monitor for recrudescence after initial treatment 7