What are the laboratory findings and management strategies for rhabdomyolysis (muscle breakdown), including the underlying reasons?

From the Guidelines

Rhabdomyolysis should be diagnosed and managed through a combination of laboratory findings, including plasma myoglobin, plasma creatine phosphokinase (CPK), and kalaemia measurements, along with aggressive intravenous fluid resuscitation and monitoring of urine output and pH, as recommended by recent guidelines 1. The diagnosis of rhabdomyolysis is primarily based on elevated serum creatine kinase (CK) levels, typically greater than 5 times the upper limit of normal, along with myoglobinuria causing dark or tea-colored urine. Management focuses on aggressive intravenous fluid resuscitation with normal saline at 1-2 L/hour initially, then adjusted to maintain urine output of 200-300 mL/hour, as well as monitoring and correcting electrolyte abnormalities, particularly hyperkalemia, hypocalcemia, hyperphosphatemia, and hyperuricemia. Some studies suggest that the measurement of plasma myoglobin may be more sensitive and specific than CPKs in identifying the risk of acute kidney injury, which is correlated with increased mortality 1. Key aspects of management include:

• Aggressive intravenous fluid resuscitation to prevent acute kidney injury
• Monitoring of urine output and pH, with a goal of maintaining urine pH at 6.5 or higher
• Correction of electrolyte abnormalities, particularly hyperkalemia
• Identification and treatment of the underlying cause of rhabdomyolysis
• Serial CK measurements to monitor treatment response. Urinary alkalinization with sodium bicarbonate may be considered to reduce myoglobin toxicity, though its benefit remains controversial, and renal replacement therapy is indicated for severe cases with refractory hyperkalemia, acidosis, or volume overload 1.

From the Research

Lab Findings in Rhabdomyolysis

• Elevated creatine kinase levels are used to confirm the diagnosis of rhabdomyolysis 2
• Electrolyte abnormalities, such as hyperkalemia, hyperphosphatemia, and hypo/hypercalcemia, are common in rhabdomyolysis 3
• Myoglobinuria is a key feature of rhabdomyolysis, and myoglobin has been identified as the primary muscle constituent contributing to renal damage 2

Management of Rhabdomyolysis

• Early and aggressive fluid resuscitation is the main intervention for preventing and treating acute kidney injury (AKI) in rhabdomyolysis 4, 2, 5
• Aggressive intravenous fluid resuscitation (IVFR) has been shown to decrease the incidence of acute renal failure (ARF) and need for dialysis in patients with rhabdomyolysis 4
• The use of bicarbonate and mannitol is not recommended, as they have not been shown to improve outcomes in patients with rhabdomyolysis 4, 2
• Hyperkalemia and compartment syndrome are additional complications of rhabdomyolysis that must be treated effectively 2

Complications of Rhabdomyolysis

• Acute kidney injury (AKI) is a common complication of rhabdomyolysis, and early recognition and treatment are crucial to prevent long-term renal damage 2, 5
• Hypercalcemia can occur during the recovery phase of rhabdomyolysis-induced AKI, and can be severe and life-threatening 3
• Mobilization of calcium from calcium phosphate deposits in the injured muscles is thought to be the main reason for hypercalcemia and hypercalciuria in rhabdomyolysis-induced AKI 3