Catheterization is a common operation in clinical practice, mainly for patients with lower urinary tract obstruction, such as elderly men with significantly enlarged prostate gland, resulting in difficulty in cerebral urination, or after coma resulting in inability to urinate on their own, and patients who need catheterization before general anesthesia. The first release of urine from catheterization should not exceed 1000 ml, and in patients with severe bladder filling, the first release of urine should be less than 500 ml. This is because if too much urine is released, it can lead to a sudden reduction in bladder pressure and can cause bleeding from a full bladder. In addition, because if too much urine is catheterized, it will cause the pressure in the abdominal cavity to decrease and blood will tend to converge in the abdominal cavity, thus inducing hypotension in the patient. Therefore, it is safer not to release too much urine by catheterization and to release urine intermittently by repeatedly clamping the catheter shut.