A catheter is a rubber-like catheter that is mainly used for patients who are unable to urinate, usually for acute urinary retention or chronic urinary retention, who need to be catheterized and who are unable to urinate on their own after surgery, and who need to be catheterized to discharge urine to avoid overfilling of the bladder and causing hydronephrosis and renal insufficiency. The catheter is mainly a rubber or silicone tube, which is divided into double-lumen and triple-lumen. The double-lumen catheter has two ventilation holes from the urethral opening to the outlet: one is used to discharge urine; the other is used to form an air sac. The three-chamber catheter is usually two hollow tubes: one is for drainage; the other tube is for flushing, while the middle one is for the airbag.