For 7 days after flap surgery, the flap is in the change phase, which is the danger period, and if the flap is still alive after 7 days, it has passed the danger period. Flap surgery refers to the transplantation of tissue blocks consisting of skin and subcutaneous tissue from one part of the body to another. It can be used for tissue repair, organ reconstruction, enhancing local blood flow and improving nutritional status. The flap is usually in the change phase for 7 days after surgery, which is a dangerous period and may result in necrosis due to vasospasm or blockage of blood vessels; if the flap is still alive after 7 days, the flap is fully viable. However, the survival time of the flap is related to its type, for example, if good circulation is established after 3-5 days for a tipped graft or a local transposition graft, the flap is viable; for a free flap graft with anastomosis of blood vessels, the survival time is 7-10 days. After flap survival, the flap still needs to be protected to avoid infection and avoid wearing clothes and shoes that cause friction on the flap and lead to flap necrosis.