If you do urological surgery, you need to flush the bladder before removing the urinary catheter. If you do other parts of the surgery, such as breast surgery, thyroid surgery, etc., if you need to put a urinary catheter, you generally do not need to flush the bladder when removing the urinary catheter. If you do urinary system surgery, such as bladder surgery, etc., you need to flush the bladder before removing it, which can make the bladder full and stimulate the bladder wall to promote the establishment of the urinary reflex, prevent urinary retention after removing the tube, and avoid increasing the pain of the patient by leaving the urinary catheter in place again. Before removing the urinary catheter, the bladder is usually rinsed continuously with 250 ml of sterile saline at 37~38℃, and there is no obvious bleeding and the drainage is smooth before the urinary catheter can be removed. If you do other parts of the surgery, such as breast surgery, thyroid surgery, etc., because of anesthesia, surgery time needs to be placed on the urinary catheter, remove the urinary catheter does not need to be flushed before the bladder.