Clinical meaning
Crush syndrome is a systemic manifestation of muscle cell damage (rhabdomyolysis) resulting from prolonged compression of skeletal muscle (typically >1 hour). During compression, ischemia causes ATP depletion, disrupting Na+/K+-ATPase and Ca2+-ATPase pumps. Intracellular calcium rises, activating proteases and lipases that destroy the sarcolemma. Upon release of the compressive force (extrication), reperfusion delivers oxygen to damaged cells, generating reactive oxygen species that amplify cellular injury. Simultaneously, the contents of destroyed myocytes flood the systemic circulation: potassium (life-threatening hyperkalemia and cardiac arrest), myoglobin (precipitates in renal tubules causing AKI), phosphorus (hyperphosphatemia, binds calcium), uric acid, creatine kinase, and lactic acid. The triad of crush syndrome is: hyperkalemia (most immediately lethal), myoglobinuric AKI, and hypovolemic shock (third-spacing of fluid into damaged muscle -- up to 12 liters in bilateral lower extremity crush).
Diagnosis & workup
Diagnostics & workup: - Serum CK (creatine kinase): gold standard marker; CK >5,000 U/L significantly predicts AKI; CK >15,000-20,000 U/L nearly universal AKI risk; peak at 24-72 hours after injury; can exceed 100,000 U/L - BMP: hyperkalemia (may be rapidly lethal), hyperphosphatemia, hypocalcemia (calcium binds phosphorus), elevated BUN/creatinine (AKI), metabolic acidosis - Urine: dark tea/cola-colored urine (myoglobinuria); urine dipstick positive for 'blood' but microscopy shows NO red blood cells (myoglobin cross-reacts with hemoglobin reagent) - ECG: monitor for hyperkalemic changes (peaked T waves → widened QRS → sine wave → cardiac arrest) - Lactate: elevated from tissue ischemia and hypovolemic shock - Urine myoglobin: confirms myoglobinuria but may clear faster than CK; a negative urine myoglobin does NOT exclude rhabdomyolysis if CK is elevated - Compartment pressures: assess for compartment syndrome in affected extremities (crush injury and compartment syndrome frequently coexist)