Malignant hyperthermia

Background

• Inherited disorder of skeletal muscles triggered most often by anesthesia inhalation agents, succinylcholine, heat or exercise
• Results in hypermetabolism, skeletal muscle damage, hyperthermia, and death if not treated quickly
• GENERALIZED rigidity NOT always present; if it occurs, MH is almost certain

Likelihood of Complications

• Increased time from 1st sign to 1st dantrolene
  • For every 30 minute increase in the interval, complication likelihood increases x 1.6
• Increased maximal temperature
  • For every 2°C increase in max temp, complication likelihood increases x 2.9

Clinical Features

• Muscle contraction
• Fever

• First signs
  • Hypercarbia
  • Sinus tachycardia
  • Masseter spasm
  • Temperature abnormalities (may be early)
• Most common pattern
  • Respiratory acidosis and muscular abnormalities

Presentations

• 99% Respiratory Acidosis
• 26% Metabolic Acidosis
• 80% Muscular Abnormalities

Watch for it with succinylcholine use.

Types

• Fulminant MH
  • muscle rigidity, high fever, increased HR shortly after induction of anesthesia
• Masseter muscle rigidity
  • jaw muscle rigidity after succinylchoine
  • More common in children
  • Presages MH in 20-30% cases
  • All patients demonstrate elevated CK and often gross myoglobinuria
  • CK >20,000IU = high likelihood of MH
• Late onset MH
  • Uncommon, may begin shortly after anesthesia termination (usually within first hour)

Differential Diagnosis

Altered mental status and fever

• Infectious
  • Sepsis
  • Meningitis
  • Encephalitis
  • Cerebral malaria
• Other
  • Neuroleptic malignant syndrome
  • Serotonin syndrome
  • Malignant hyperthermia
  • Sympathomimetic toxicity (cocaine, amphetamine, ketamine)
  • Anticholinergic toxicity
  • Heat stroke
  • Delirium tremens
  • Hypothalamic stroke
  • Pheochromocytoma
  • Thyroid storm

Evaluation

• Core temperature
• CBC
• Chem 7
• Total CK
• PT/PTT
• ABG

Management

• Initial
  • Declare MH Emergency: (call OR for anesthesia to bring MH cart)
  • Discontinue Triggering Agents
  • 100% Oxygen at High Flow
  • Give Dantrolene
    • Designate 2 or 3 people to mix sterile water into Dantrolene \
      • 60ml sterile water into each vial of dantrolene; may need up to 36 vials
      • If using Dantrium® (20mg/vial), each vial contains 3 g of mannitol (renal vasodilation); newer nanocrystalline dantrolene (250mg/vial) has 250mg mannitol per vial and requires mannitol supplementation
    • 2.5mg/kg IV push
    • Titrate to effect; may need more than 10mg/kg
  • Bicarb for metabolic acidosis
    • 1-2 mEQ/kg if blood gas values not yet available
  • Cool the patient if core temperature >39 deg C (102.2 deg F)
    • Stop cooling when temperature reaches 100.4
  • Dysrhythmias usually respond to treatment of acidosis and hyperkalemia
    • Standard therapy EXCEPT NO CA CHANNEL BLOCKERS:
      • may cause hyperkalemia or cardiac arrest in presence of dantrolene
  • Treat hyperkalemia: standard treatment, remember to check glucose levels q1h after treatment with insulin/glucose
  • Call MHAUS Hotline if needed: 1-800-644-0737
• Continued Care
  • Dantrolene 1mg/kg every 4-6 hours for 24–48 hours
  • Monitor for recrudescence (rate is 25%)
  • Follow electrolytes, blood gases, CK, core temperature, urine output and color, coagulation studies

Prognosis

Stable to Transfer Criteria

• ETCO2 is declining or normal
• HR is stable or decreasing
• No ominous dysrhythmias
• Temperature is declining
• Generalized muscular rigidity is resolving (if present)
• IV dantrolene administration has begun

Complications

• Consciousness Level Change/Coma
• Cardiac Dysfunction
• Pulmonary Edema
• Renal Dysfunction
• Disseminated Intravascular Coagulation
• Hepatic Dysfunction
• Relapse
• Death

See Also

• Succinylcholine
• Acute Fever (DDX)
• Toxidromes

Authors

Ross Donaldson