The key to microsurgery, such as replantation of severed fingers and free flaps, which are common in hand surgery, is blood flow. Only if the patient’s vascular condition after injury is good and the quality of the anastomosed vessels is high can the success of the surgery be ensured. For example, if a severed finger is severely crushed at the time of injury, even if it is severed from the proximal segment, there is no way to replant it. On the contrary, if it is a knife cut injury with good vascular condition, even if it is severed from the finger tip, there is a chance to replant it. Since the anastomosed blood vessel, stimulated by various reasons, will spasm and embolism after the operation, it is possible that surgical exploration or even necrosis will be required after the operation and the operation will fail. Therefore, all the doctor can do is to try to anastomize the blood vessel and anastomize more blood vessels to ensure the success of the operation.