Rhabdomyolysis

Aka: Rhabdomyolysis

1. Definition
   1. Skeletal muscle breakdown
2. Pathophysiology
   1. Muscle injury allows calcium influx
   2. Increased intracellular calcium destroys muscle fibers
   3. Release of muscle fiber contents into circulation
      1. Myoglobin
      2. Potassium
      3. Phosphate
      4. Creatine Phosphokinase
      5. Uric Acid
   4. Myoglobin overloads Haptoglobin binding capacity
   5. Myoglobin blocks renal tubules
   6. Results in Renal Failure
3. Causes
   1. See Rhabdomyolysis Causes
4. Signs
   1. Muscle pain (myalgias)
   2. Muscle Weakness
   3. Localized swelling or bruising
   4. Constitutional symptoms
      1. Fever
      2. Malaise
      3. Nausea or Vomiting
      4. Confusion, agitation, or Delirium
   5. Urinary tract symptoms
      1. Tea-colored urine
      2. Anuria
5. Labs
   1. Urinalysis: Findings suggestive of Myoglobinuria
      1. Dipstick orthotoluidine positive for blood
      2. No Red Blood Cells seen in freshly spun sediment
   2. Creatine Phosphokinase increased
      1. CPK over 16,000 associated with Renal Failure
   3. Myoglobin level increased in urine or serum
      1. Results not available for days after sending sample
      2. Not helpful in acute diagnosis
6. Complications
   1. Electrolyte disturbance
      1. Hyperkalemia
      2. Hypocalcemia
   2. Acute Renal Failure (Acute Tubular Necrosis)
      1. Accounts for 5 to 15% of Acute Renal Failure cases
      2. Mechanism: Myoglobin overload, hypovolemia, acidosis
      3. Associated with Creatinine kinase over 16,000 units/L
   3. Miscellaneous complications
      1. Liver inflammation
      2. Cardiac arrhythmia or Cardiac Arrest
      3. Disseminated Intravascular Coagulation
      4. Compartment Syndrome
7. Management: Intravenous fluids
   1. Initial: Forced diuresis
      1. Start immediately (especially in first 6 hours)
      2. Protocol
         1. Normal Saline 1.5 Liters per hour
         2. Urine output should approach 300 ml/hour
      3. End-points
         1. No Myoglobinuria
         2. Creatine Phosphokinase (CPK) less than 1000
   2. Maintenance: Alkalinize Urine pH > 6.5
      1. Protocol
         1. Saline 0.45% with
         2. Sodium Bicarbonate 40 meq (1 to 2 ampules) and
         3. Mannitol 10 grams per liter
      2. Contraindications
         1. Persistent oliguria despite hydration listed above
         2. Hypocalcemia (provoked by Sodium Bicarbonate)
   3. Monitoring of elderly with comorbid conditions
      1. Intensive care unit admission
      2. Hourly vital signs including input and output
      3. Consider invasive monitoring
8. Management: Acute Renal Failure
   1. Results from Acute Tubular Necrosis
   2. Daily Hemodialysis may be indicated
   3. Many patients show partial or complete renal recovery
9. Precautions
   1. Aggressive hydration is critical
   2. Avoid Diuretics (may provoke Renal Failure)
   3. Do not correct Hypocalcemia unless symptomatic
      1. Anticipate Serum Calcium increase in recovery phase
      2. Calcium re-mobilized from injured muscles
10. References
    1. Marx in Rosen (2002) Emergency Medicine 1762-70
    2. Sauret (2002) Am Fam Physician 65(5):907-12