Introduction: The use of a ureteral access sheath (UAS) may provide significant advantages, particularly, in the treatment of a large renal stone burden. However, in some patients, the passage of a UAS up the ureter is impossible. We prospectively evaluated the ability to insert a 14F UAS and analyzed the possible predictors for an effective insertion. Patients and Methods: In a bicenter prospective study, 248 consecutive patients undergoing ureteroscopy and retrograde intrarenal surgery (RIRS) were recruited. In each case, we attempted initially to pass a 14F Flexor-Cook UAS. If passage was difficult, gradual dilation using semirigid ureteral dilators (Cook Medical) was performed. Patients were categorized into three groups: effective passage, with and without dilation, and failure to pass the UAS. Age, gender, body-mass index (BMI), an indwelling Double-J stent, and a history of previous ureteroscopy or Double-J stent were all analyzed, as possible predictors for an effective UAS insertion. Results: In 22% of the patients, we could not pass a 14F UAS. Of the preoperative parameters that were examined, we found three independent predictors for an effective 14F UAS insertion: age (odds ratio: 1.5 and 95% CI [1.3, 1.9]), previous same-side procedures (odds ratio: 9.7 and 95% CI [8.3, 14.5]), and an indwelling Double-J stent (odds ratio: 21.73 and 95% CI [20, 30]). The gender, BMI, and side of surgery did not predict the success rate. Conclusions: Insertion of a 14F UAS before RIRS may fail in approximately one-fifth of the patients. An indwelling Double-J stent, a history of previous ureteroscopy or Double-J stent, and older age are all significant predictors for an effective 14F UAS insertion.
