Rhabdomyolysis Associated Acute Kidney Injury

Rhabdomyolysis is skeletal muscle necrosis with release of intracellular contents (myoglobin, potassium, phosphate, CK), and AKI complicates 15 to 50% of cases.

• Causes: trauma and crush injury, prolonged immobilisation, exertion (marathon, military training, sickle trait), seizures, heat stroke, drugs (statins, especially with fibrates or interacting agents; cocaine, amphetamines, alcohol, antipsychotics), toxins (snake venom), infections (influenza, COVID-19, Legionella), metabolic (hypokalaemia, hypophosphataemia, hypothyroidism), inherited (McArdle, CPT2, mitochondrial), compartment syndrome.
• AKI mechanisms: renal vasoconstriction, myoglobin cast obstruction, direct tubular toxicity from ferrihaem, volume depletion by sequestration of fluid into muscle.
• CK over 5000 U/L carries increased AKI risk; peak at 24 to 72 hours.
• Complications: hyperkalaemia, hypocalcaemia early then hypercalcaemia, hyperphosphataemia, hyperuricaemia, metabolic acidosis, DIC, compartment syndrome.

• Muscle pain, swelling, weakness, tenderness (classic triad with dark urine), though many have no muscle symptoms.
• Dark tea- or cola-coloured urine, oliguria.
• Features of the cause: coma, trauma, seizures, heat, alcohol, drug history.
• Compartment syndrome: tense swollen limb, severe pain on passive stretch.
• Arrhythmias from hyperkalaemia.

CK over 5 times the upper limit of normal (usually over 10,000 U/L); also raised AST, ALT, LDH, aldolase.

Urine dipstick positive for blood with no red cells on microscopy (myoglobinuria).

Electrolytes (hyperkalaemia, hypocalcaemia, hyperphosphataemia), urate, creatinine (disproportionate rise relative to urea), bicarbonate, coagulation (DIC).

ECG for hyperkalaemia.

Investigate cause: TSH, toxicology screen, viral PCR, drug review; metabolic myopathy testing (lactate forearm test, genetics) for recurrent exertional episodes.

Compartment pressure measurement when suspected.

• Early aggressive IV fluids: isotonic saline or balanced crystalloid 1 to 1.5 L/h initially (10 to 15 mL/kg/h), titrated to urine output 200 to 300 mL/h (about 3 mL/kg/h) until CK falls below 1000 to 5000 U/L and myoglobinuria clears; monitor for overload. Start within 6 hours of injury, including in the field in crush syndrome.
• Hyperkalaemia: calcium gluconate 10% 10 to 20 mL IV for ECG changes (give cautiously, hypocalcaemia is not otherwise treated unless symptomatic), insulin 10 units with 25 g glucose, salbutamol 10 to 20 mg nebulised, potassium binders, early dialysis.
• Bicarbonate and mannitol are not routinely recommended; consider bicarbonate if urine pH can be kept above 6.5 and serum pH remains under 7.5 with calcium monitoring.
• Treat the cause: stop statins and offending drugs, cool for heat stroke, control seizures, correct electrolytes (phosphate, potassium).
• Fasciotomy for compartment syndrome (pressure over 30 mmHg or delta pressure under 30 mmHg).
• Renal replacement therapy for refractory hyperkalaemia, acidosis, overload, oliguric AKI; high-flux or cut-off membranes do not clearly benefit myoglobin clearance.
• Monitor CK every 12 hours, electrolytes, urine output, and creatinine until stable.
• Recurrent exertional rhabdomyolysis: evaluate for metabolic myopathy; advise gradual training and hydration.