Extracorporeal circulation is mostly associated with CLS disease. Capillary leak syndrome (CLS) refers to a group of clinical syndromes such as tissue interstitial edema, hypoproteinemia, hypovolemic shock, and acute renal ischemia due to capillary endothelial cell injury caused by various pathogenic factors and increased vascular permeability resulting in massive plasma protein and water infiltration into the tissue interstitium. CLS is a sudden, reversible capillary hyperosmolarity in which plasma rapidly infiltrates from the vasculature into the tissue interstitium, causing rapid onset of progressive systemic edema, hypoproteinemia, a dramatic decrease in effective blood volume, a decrease in both blood pressure and central venous pressure, weight gain, hemoconcentration, and in severe cases, multi-organ failure. The risk of CLS is from local inflammatory changes to large scale inflammatory lesions that cannot be effectively controlled, and in severe cases, MODS and even multi-organ failure can occur. the mechanism of CLS is related to the following factors. 1. increased capillary hydrostatic pressure; 2. increased capillary permeability; 3. decreased plasma colloid osmotic pressure; 4. obstructed lymphatic return.