Midurethral sling (MUS) surgery is used to treat women with SUI, but accepted protocols for voiding trials after midurethral sling placement do not exist. Primarily, many surgeons measure postvoid residual (PVR) urine volume. This is done by retrograde filling of the bladder with a predetermined amount of normal saline or water. The catheter is then removed and the patient is permitted to void into a collection basin. The amount in the basin is subtracted from the filled amount. The need for catheterization is generally based on arbitrarily determined ratios of voided urine to PVR or postoperative.