AUA 2019: Assessing the Threshold for Injury When Passing An Ureteral Access Sheath: How Much Force is Too Much?

Chicago, IL ( The use of a ureteral access sheath during ureteroscopy remains controversial. On the one hand, ureteral access sheaths facilitate repeated access to the kidney, and are associated with shorter operative times and lower intrarenal pressure. However, on the other hand, ureteral injury is a potential complication of access sheath deployment. Currently, there is no standardized approach for safe access sheath deployment and the force applied is dependent on the subjective haptic feedback experienced by the surgeon.

In an effort to determine the threshold for safe passage of the ureteral access sheath, researchers at the University of California, Irvine, developed a novel device that continuously transmits the real-time deployment force to a tablet via a Bluetooth connection. The device has a strain gauge mechanism that engages with the butt end of the access sheath and provides visual and auditory signals as to the amount of force being applied during deployment.

The objective of this study was to use the ureteral access sheath force sensor in a clinical setting during routine ureteroscopy, in order to determine the range of safe deployment forces for passage of a ureteral access sheath. A 16 Fr access sheath was used in each initial attempt. If the force reached 8 N, a smaller sheath was used instead (14 Fr or 11 Fr sheath). At the end of the procedure, upon removal of the access sheath, the ureter was inspected and a post-ureteroscopic lesion scale (PULS) was determined. The PULS grading system ranges from 0 to 5, where 0 indicates no ureteral lesion and 5 indicates complete transection of the ureter. Complicated ureteroscopy is defined as splitting of the ureter, that is PULS 3 or higher. The deployment force of the access sheath was measured in 72 ureters in 65 patients, with stones in either the proximal ureter or in the kidney. Half of the patients underwent prone PCNL and an access sheath was deployed to facilitate endoscopic guided percutaneous access. A quarter of the ureters were pre-stinted and two-thirds of the patients received one week of preoperative tamsulosin in an attempt to induce ureteral relaxation. 

A 16 Fr access sheath was successfully deployed in 71% of cases with a mean force of 5.4 N. Accordingly, in the remaining 29% of cases, a smaller sheath was used instead. In two-thirds of cases, at the end of the procedure, the PULS score was 0 or 1. A single PULS 3 injury was noted following the deployment of a 14 Fr sheath; in this case, peak pressure of 9 N was recorded. Limiting the deployment force below 5 N consistently resulted in a PULS score of 0-1. On multivariate analysis, successful deployment of 16 Fr access sheath was significantly associated with pre-stinted ureters. One week of preoperative treatment with tamsulosin was not associated with lower PULS score, lower peak force applied, or successful deployment if the 16 Fr access sheath.

In conclusion, the UCI-developed force sensor proved to be a reliable means for measuring deployment force during the passage of a ureteral access sheath in the clinical setting. Using an upper limit of 8 N, there was a single PULS 3 injury and no PULS 4 or 5 injuries. Limiting the deployment force to less than 5 N consistently resulted in no significant ureteral injury. Presenting, but not tamsulosin was associated with securing a larger access sheath and a low PULS score.

Presented by: Shlomi Tapiero, MD, Department of Urology, University of California, Irvine, USA
Co-authors: Kamaljot S. Kaler2, Linda M. Huynh1, Mitchell O’Leary1, Vinay Cooper1, Zachary A. Valley1, Renai Yoon1, Roshan M. Patel1, Michael Klopher3, Jaime Landman1, and Ralph V. Clayman1
1Department of Urology, University of California, Irvine, USA,  
2Department of Surgery, Section of Urology, University of Calgary
3California Institute for Telecommunications and Information Technology (Calit2) University of California, Irvine

Written by:  at the American Urological Association's 2019 Annual Meeting (AUA 2019), May 3 – 6, 2019 in Chicago, Illinois