Crush Syndrome

Crush syndrome is the systemic response to traumatic rhabdomyolysis after prolonged compression of a large muscle mass, usually for over 1 hour and typically 4 to 6 hours, as in earthquakes, building collapse and mining accidents. Release of the compression reperfuses injured muscle, so fluid shifts into damaged muscle (up to 10 to 12 L), causing hypovolemic shock. Potassium, myoglobin, phosphate, urate and lactic acid flood the circulation.

Victims may look well while trapped, so hyperkalemia and cardiac arrest can follow sudden release (the "smiling death"). Of earthquake victims, 2 to 15% have crush injuries, and over half of crush syndrome patients develop acute kidney injury from myoglobin tubular injury, volume depletion and acidosis. Mortality is up to 20% without dialysis.

Hyperkalemia, hypocalcemia (calcium deposits in injured muscle), metabolic acidosis, hyperphosphatemia and hyperuricemia develop, and the severity of each depends on muscle mass and duration of compression. Complications: lethal hyperkalemia, hypovolemic shock, acute kidney injury, disseminated intravascular coagulation, compartment syndrome, sepsis and acute respiratory distress syndrome.

• Before release: the limb may be pain-free or numb, with limited symptoms
• After release: a swollen, tense, pale or blistered limb, motor and sensory loss, and weak pulses
• Dark tea-colored urine, oliguria and anuria
• Hypotension, tachycardia and cold peripheries
• Arrhythmia, muscle weakness and cardiac arrest from hyperkalemia
• Red flags: compression for over 4 hours, peaked T waves or a wide QRS on ECG, urine output under 20 mL/h, and tense compartments

1. Clinical diagnosis from history of compression and examination, with early recognition even when the patient appears well.
2. Potassium (point-of-care testing in the field if available) and ECG: peaked T waves, flattened P waves, wide QRS.
3. Creatine kinase: usually over 5000 units/L, and often over 100,000 units/L. Peak at 24 to 72 hours.
4. Other blood tests: creatinine, urea, calcium (low), phosphate (high), uric acid, blood gases, lactate, full blood count and coagulation studies.
5. Urinalysis: heme-positive dipstick with few or no red cells, and measurement of urine output with a catheter.
6. Compartment pressure when limbs are tense: a perfusion pressure (diastolic pressure minus compartment pressure) under 30 mmHg indicates compartment syndrome.
7. Ultrasound for volume status, and radiographs for fractures.

Differentials: hemorrhagic shock, compartment syndrome without systemic crush, nontraumatic rhabdomyolysis, spinal injury and other causes of acute kidney injury.

1. Before extrication (when access allows): insert an IV or intraosseous line, and start 0.9% saline 1000 to 1500 mL/h for 2 hours in adults (children 15 to 20 mL/kg/h), then 500 mL/h. Avoid fluids containing potassium (such as lactated Ringer solution). Target urine output of over 200 to 300 mL/h. Continue for at least 24 hours and until urine is clear and CK falls, stopping if overload develops.
2. Hyperkalemia prophylaxis and treatment:
   • Salbutamol 10 to 20 mg nebulized once.
   • Calcium gluconate 10% 10 to 20 mL IV over 5 to 10 minutes, repeated for ECG changes. Do not give calcium for asymptomatic hypocalcemia.
   • Regular insulin 10 units IV with 50 mL of 50% dextrose, with glucose checks hourly.
   • Sodium bicarbonate 50 mmol IV for acidosis with hyperkalemia.
3. Alkalinization and diuresis: when urine pH is under 6.5, add sodium bicarbonate 50 mmol to each litre of 0.45% saline alternating with 0.9% saline, to keep urine pH over 6.5 and blood pH under 7.5. Mannitol 1 g/kg IV (maximum 200 g a day) only when urine output is over 20 mL/h, and stop if osmolar gap exceeds 55 mOsm/kg.
4. Pain relief and care: ketamine 0.25 to 0.5 mg/kg IV or morphine 0.05 to 0.1 mg/kg IV titrated, wound care, tetanus toxoid 0.5 mL IM and cefazolin 2 g IV for open wounds.
5. Tourniquet or amputation in the field only when it is needed to save the life of an entrapped patient who cannot otherwise be released.
6. Fasciotomy: only for confirmed compartment syndrome (perfusion pressure under 30 mmHg) and a viable limb, since fasciotomy in crush syndrome without it raises infection and mortality.
7. Renal replacement therapy: for hyperkalemia over 6.5 mmol/L not responding to treatment, pH under 7.1, oliguria with fluid overload, or uremic symptoms. Intermittent haemodialysis is preferred, daily if needed, until recovery.
8. Coagulopathy: fresh frozen plasma 15 mL/kg and platelets for bleeding.
9. Amputation of a non-viable limb, or for uncontrollable sepsis or life-threatening hyperkalemia.

Follow-up: creatinine and electrolytes daily during admission, rehabilitation for muscle and nerve injury, and renal review at 3 months. Prevention is rapid rescue and early fluid access.