If you cannot pass urine after a urinary catheter is inserted, you should first determine whether urine is being produced. An ultrasound should be done first to clarify the urine inside the bladder and whether there is any discomfort such as bulging and fullness in the abdomen. If urinary retention is present, a urinary catheter change should be performed, most of which is caused by an obstructed urinary catheter. This can occur in post-operative patients, such as those who have undergone surgery for stones as well as urological procedures, where tiny stones, blood clots or detached mucous membranes can enter the lumen of the catheter, thus blocking the passage for urine discharge. It can also be seen in patients with bladder spasm after surgery, in which case it is possible to inject saline into the urethra, but no urine is discharged. Patients are advised to have their doctor apply antispasmodic medication in a timely manner, which can relieve bladder spasm and thus allow urine to pass on its own. If there is never any urine elimination, it is still recommended to replace the urinary catheter with a new one.