Blood leaving the veins is the clinical manifestation of crush syndrome. Crush syndrome is a series of pathological changes in the body caused after a person is crushed by a stone and earth, especially a muscular limb is crushed for more than one hour (e.g. thigh). Due to the damage to the skin and flesh, blood leaving the veins and channels, stagnation of blood and Qi, occlusion of meridians, localized pain, swelling of the limb, indentation and hardening of the skin, subcutaneous stasis of blood, and increased skin tension. What are the causes of blood leaving the vasculature? Extrusion syndrome occurs mostly in accidental injuries such as house collapse, engineering collapse, traffic accidents, etc. It can occur in batches during wartime or in severe natural disasters such as strong earthquakes. In addition, it is occasionally seen in patients in coma and surgery, where the limb is pressed for a long time by the self-pressure of a fixed body position. Pathophysiology of crush syndrome Muscles suffer heavy smash injuries, bleeding and swelling occur, muscle tissue undergoes necrosis and releases a large number of metabolites, myoglobin, potassium ions, creatine, creatinine, muscle ischemia and hypoxia, acidosis, etc. can prompt the escape of potassium ions from the cells to the outside, thus causing a rapid increase in blood potassium concentration. After limb crush injury, hypovolemic shock occurs so that the peripheral blood vessels are constricted, the kidneys show ischemia, renal blood flow and glomerular filtration are reduced, the renal tubules mainly rely on the glomerular outflow artery for blood supply, and the glomerular artery is constricted, which can aggravate the degree of tubular ischemia and even necrosis. The increase of pentoxifylline and renin in shock can aggravate the damage of renal tubules. A large amount of myoglobin released after muscle tissue necrosis requires renal tubular filtration, which can be deposited in the renal tubules under acidosis and acidic urine, forming myoglobin tubular pattern, aggravating the degree of renal damage, and eventually acute renal failure occurs. The diagnosis can be made based on the patient’s medical history or injury, clinical manifestations and laboratory tests. In addition, it should be noted that patients who die within a short time after crush injury are often caused by traumatic hemorrhagic shock or cardiac arrest due to hyperkalemia, while patients who die after several days are often caused by renal failure or multi-organ failure due to crush injury. Therefore, in forensic autopsy work, if the cause of death is highly suspected to be extrusion syndrome, the kidney must be taken for pathological examination and confirmed to prevent misdiagnosis.