Prior to UAS deployment, two wires are placed into the upper tract under fluoroscopic guidance, one functioning as a safety wire and the other a working wire which is generally a stiff wire with a stainless steel core. The UAS is then moistened to ensure lubrication and advanced over the stiff wire under direct fluoroscopic guidance. It is important to ensure that the inner dilating cannula is securely engaged with the outer sheath during advancement to prevent ureteral injury from the exposed edge of the outer sheath. Once placed in satisfactory position, the inner dilating cannula and working wire are removed and the procedure performed.

While a UAS may be inserted without adjunctive maneuvers in the majority of endoscopic cases, it is not uncommon to encounter difficulty in passing the UAS. Harper et al. identified the following groups as at risk for conventional UAS insertion failure: young males with tight ureteral orifices, duplicated collecting systems, and small caliber ureters [9]. If UAS placement is difficult the following manipulations may be attempted. Ensure the stiff working wire is correctly positioned with adequate coil in the intrarenal collecting system. Then eliminate slack in the guidewire by appropriately tensioning the wire while making sure it is not withdrawn. These two manipulations assist in straightening the ureter thereby facilitating UAS acceptance. If the aforementioned manipulations do not permit UAS passage, gentle coaxial dilation with the internal obturator of the UAS or specially designed ureteral dilators may prove useful, but care should be taken to avoid applying excess sheer force that could lead to ureteral injury or avulsion [10]. Should the preceding measures fail, balloon dilation of the ureter may be performed. However, this may increase the risk of ureteral perforation. Finally, placement of an indwelling ureteral stent allows for passive ureteral dilation and successful UAS or ureteroscope insertion in 10–14 days.

In vitro and clinical studies can be used to predict how specific UASs may perform with regard to kinking and buckling. In a randomized trial comparing the 12/15 F Applied Access Forte XE (Applied Medical, Rancho Santa Margarita, California) to the 12/14 F Cook Flexor (Cook Urological, Spencer, Indiana) access sheath, Monga et al. analyzed the ease of placement and rate of device failure [3]. While there were no statistical differences between the two groups with regard to preoperative stenting or use of rigid ureteroscopy before UAS placement, the device failure rates were 44% and 0% for the Applied Medical and Cook UASs, respectively (p  <  0.001). The device failures identified included buckling (25%), kinking (25%), and difficulty passing instruments (13%). The Cook sheath was also found to be superior with regard to ease of placement [3]. In a study evaluating the physical properties of next-generation UASs, Pedro and colleagues used an ex vivo model to better predict possible clinical failures [11]. Specifically, they evaluated the pressures at which buckling and kinking occurred, measured the coefficient of friction for each sheath during placement, and correlated that measurement to overall ease of placement. Testing included the Cook Flexor (Cook, 12/14 F  ×  35 cm), Gyrus-ACMI UroPass (ACMI, 12/14 F  ×  38 cm), Bard Aquaguide (Bard, 11/13 F  ×  35 cm), and Boston Scientific Navigator (BSCI-11, 11/13 F  ×  36 cm and BSCI-13, 13/15 F  ×  36 cm) UASs. The authors found that the Cook UAS performed best with regard to buckling. The Bard catheter was the most likely to kink, while the ACMI was superior with regard to kinking. There was no significant difference between the tested sheaths with regard to the coefficient of friction upon placement [11].