CUA 2018: Initial Clinical Testing of Ureteral Access Sheath Force Sensor to Prevent Ureteral Injuries

Halifax, Nova Scotia ( Ureteral injury during ureteroscopy is one major concern during stone ablative surgery. In order to better protect the ureter from damage due to the ureteroscope, a ureteral access sheath (UAS) is typically inserted into the ureter. Though this insertion of this device is meant to prevent injury, the insertion of the UAS, if done incorrectly, can, in fact, damage the ureter due to insertion forces alone. In modern clinical practice, the amount of force that results in patient injury has yet to be defined. Ergo, Dr. Kam Kaler presented his findings on UAS insertion forces using a novel force sensor, shown below. 
UAS deployments were measured in 35 patients undergoing ureteroscopy at the University of California, Irvine Medical Center. Tamsulosin was given up to one week prior to surgery in two-thirds of the patients. The UAS force sensor was used to record insertion forces exerted by a 14/16F UAS from the tip of the meatus until the ureteropelvic junction. Dr. Kaler then explained that in a previous study conducted by his team, the upper limit of force that caused ureteral damage in a porcine ureter was 8 Newtons (N). Therefore, if the sensor determined that a force of 8N was reached, the UAS was removed and replaced by a smaller one (either 12/14F or 9.5/11F). Following the conclusion of the procedure, an exploratory ureteroscopy was performed to determine ureteral injury using the Post Ureteroscopic Lesion Scale (PULS). 

Among 35 patients, there were a total of 41 ureters that were measured for UAS insertion forced. The 16F UAS could be inserted successfully (< 8N) in 63% of deployments. The remaining ureters successfully passed a 14F or 11.5F sheath 32% and 5% of deployments, respectively. Maximum peak pressure was most commonly recorded at the mid-ureter, however, this occurred only 17% of the time. A solitary PULS grade 3 injury occurred in a patient who had the 16F and 14F sheaths fail before successfully having the 11.5F sheath inserted last. The peak forces experienced in each of these attempts were 8.1N, 8.9N, and 5.0N, respectively. Interestingly, though this negates Dr. Kaler’s stance, there was no significant difference between initial peak pressures in the tamsulosin vs. non-tamsulosin groups. Dr. Kaler believes that this disparity occurred only because of particular prestenting, but this was not investigated fully. 

In his conclusion, Dr. Kaler explained that the novel force device was invaluable in measuring insertion forces in a clinical setting. The main takeaway that this study showed, however, was that limiting the insertion force to < 5N resulted in a PULS score of less than 1. This may prove to be a new method for improving patient care in the clinical setting. 

Presented by Kam Kaler, MD

Written by Zachary Valley, Department of Urology, University of California-Irvine, Twitter: @ZacharyAValley, at the 73rd Canadian Urological Association Annual Meeting - June 23 - 26, 2018 - Halifax, Nova Scotia