Introduction: Prior clinical studies, using a novel UCI ureteral access sheath (UAS) force sensor have indicated that passage of a ureteral access sheath at < 6 Newtons (N) results in no harm to the ureter. Armed with this information, we sought to define, for the first time, the natural distensibility of the human ureter using sequential urethral dilators in combination with the UCI force sensor while limiting the applied force to 6 N. Methods: Seventy-five patients (46 females and 29 males) undergoing either ureteroscopy and/or percutaneous stone removal underwent ureteral sizing by passing a series of 35 cm long, urethral dilators in 2 Fr increments within the pre-defined force threshold limit of < 6 N. After 6 N was attained, the size of the urethral dilator was recorded and then ureteroscopy was performed and a post-ureteroscopic lesion scale (PULS) was determined. Next, a similar sized UAS, up to 16 Fr was inserted as part of the planned procedure. A multivariable logistic regression analysis was performed assessing the impact of age, gender, tamsulosin, stents, and the combination of tamsulosin and stents on the ability to pass dilators > 16 Fr. Results: Among 75 patients, urethral dilators were successfully passed at the 6 N threshold in 37.3% at = 12 Fr, 24% at 14 Fr, 24% at 16 Fr, and 14.6% at > 18 Fr (18-24 Fr). The mean maximum dilator diameter was 14 Fr. Logistic regression revealed that preprocedural ureteral stenting favored passage of > 16 Fr dilators (OR 15.47, 95% CI 1.44 – 166.86; p = 0.024). Neither gender nor age were significant differentiators. The effect of tamsulosin alone was not statistically significant (OR 0.60, 95% CI 0.15 – 2.32; p = 0.454). The interaction effect was not significant suggesting that the effect of stent plus tamsulosin did not differ from stent alone (OR for interaction = 1.85, range 0.089 – 38.63; p = 0.690). Conclusions: The unstented human ureter can be safely sized to an average circumference of 14Fr; this increases to 16 Fr in the prestented ureter. SOURCE OF Funding: None.
