What is the treatment for myoglobinuria?

Treatment of Myoglobinuria

The treatment of myoglobinuria should focus on aggressive intravenous hydration with mannitol-sodium bicarbonate infusion to prevent acute kidney injury, with a target urine output of >2 ml/kg/hr and urine alkalinization. 1

Pathophysiology and Diagnosis

• Myoglobinuria occurs when myoglobin, a heme-containing protein stored in muscle, leaks into plasma due to muscle damage (rhabdomyolysis) and is subsequently filtered by the kidneys, giving urine a dark, cola-like appearance 2, 3
• Common causes include trauma, crush injuries, excessive exercise, medications, toxins, malignant hyperthermia, and inherited metabolic disorders 4
• Symptoms typically include muscle weakness, myalgia, and dark urine; laboratory confirmation is essential to differentiate from hemoglobinuria 5

Treatment Algorithm

Immediate Management

• Insert a urinary catheter to monitor urine output, pH, and presence of myoglobinuria 6
• Initiate aggressive intravenous hydration to maintain urine output >2 ml/kg/hr 6, 1
• Administer sodium bicarbonate to alkalinize the urine, which prevents myoglobin precipitation in renal tubules 6, 1
• Consider mannitol infusion in combination with sodium bicarbonate, as this combination has been shown to improve outcomes in responsive patients 1

Monitoring and Supportive Care

• Monitor serum creatine kinase (CPK) levels, as higher initial values correlate with more severe muscle injury and poorer response to treatment 1
• Check electrolytes regularly, particularly potassium, as rhabdomyolysis can lead to life-threatening hyperkalemia 6
• Monitor renal function through BUN, creatinine, and urine output 1
• Assess for development of compartment syndrome through clinical examination of limbs for swelling, muscle softness, and peripheral pulses 6

Special Considerations

• Patients with higher initial CPK, serum phosphate levels, and hematocrit may have more severe muscle injury and may be less responsive to fluid therapy, potentially requiring dialysis 1
• If compartment syndrome develops, measure compartmental pressures and consider fasciotomies 6
• For patients with malignant hyperthermia-associated myoglobinuria, administer dantrolene (initial dose 2-3 mg/kg, followed by 1 mg/kg as needed) 6

Complications and Their Management

• Acute Kidney Injury: The most serious complication of myoglobinuria 2

  • Continue aggressive hydration and urine alkalinization 6
  • Consider hemodialysis if renal function deteriorates despite conservative management 1

• Electrolyte Abnormalities: Particularly hyperkalemia

  • Treat with sodium bicarbonate and/or glucose (50 ml 50%) with insulin (10 units) 6
  • Avoid calcium administration except in extreme cases, particularly in malignant hyperthermia 6

• Compartment Syndrome:

  • Regular assessment of limbs for swelling, muscle softness, and peripheral pulses 6
  • Perform fasciotomies if compartment syndrome develops 6

Prognosis

• Patients who respond to mannitol-sodium bicarbonate infusion with increased urine output typically have better outcomes and avoid the need for dialysis 1
• With prompt, aggressive treatment, recovery of muscle and renal function is usually complete in patients who survive the acute phase 2

Pitfalls to Avoid

• Delaying treatment while awaiting laboratory confirmation; initiate treatment based on clinical suspicion 5
• Inadequate fluid resuscitation; aggressive hydration is critical to prevent renal failure 1
• Failure to monitor for compartment syndrome, which may develop up to 24 hours after the initial event 6
• Overlooking the need for urine alkalinization, which is essential to prevent myoglobin precipitation 6, 1