Three major factors of deep vein thrombosis: stagnant venous blood flow, venous wall damage and blood hypercoagulability stagnant venous blood flow is caused by spinal anesthesia or general anesthesia during surgery, resulting in dilatation of peripheral veins and slowing down of venous flow; complete paralysis of lower limb muscles during surgery due to anesthesia and loss of contractile function, and bed rest after surgery due to incision pain and other reasons, resulting in a relaxed state of lower limb muscles, resulting in stagnant blood flow. This can lead to deep vein thrombosis in the lower limbs. Injury to the venous wall Chemical injury Intravenous injection of various irritant solutions and hypertonic solutions, such as various antibiotics, organic iodine solution, hypertonic glucose solution, etc. can stimulate the venous lining to varying degrees, leading to phlebitis and venous thrombosis.