Malignant hyperthermia

Background

• Inherited disorder of skeletal muscles triggered most often by anesthesia inhalation agents and/or succinylcholine
• 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

Work-Up

1. Core temperature
2. CBC
3. Chem 7
4. Total CK
5. PT/PTT
6. ABG

Diagnosis

1. Muscle contraction
2. Fever

1. First signs
   1. Hypercarbia
   2. Sinus tachycardia
   3. Masseter spasm
   4. Temperature abnormalities (may be early)
2. Most common pattern
   1. Respiratory acidosis and muscular abnormalities

Presentations

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

Watch for it with succinylcholine use.

Types

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

DDx

See Acute Fever (DDX)

Treatment

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

Prognosis

Stable to Transfer Criteria

1. ETCO2 is declining or normal
2. HR is stable or decreasing
3. No ominous dysrhythmias
4. Temperature is declining
5. Generalized muscular rigidity is resolving (if present)
6. IV dantrolene administration has begun

Complications

1. Consciousness Level Change/Coma
2. Cardiac Dysfunction
3. Pulmonary Edema
4. Renal Dysfunction
5. Disseminated Intravascular Coagulation
6. Hepatic Dysfunction
7. Relapse
8. Death

See Also

• Succinylcholine
• Acute Fever (DDX)