Device measures force during UAS insertion


A novel investigational ureteral access sheath force sensor served as an effective tool for the safe deployment of a ureteral access sheath in initial clinical experience, researchers reported at the 2018 World Congress of Endourology and SWL in Paris.

A novel investigational ureteral access sheath force sensor (UAS-FS) served as an effective tool for the safe deployment of a ureteral access sheath in initial clinical experience, researchers reported at the 2018 World Congress of Endourology and SWL in Paris.

The UAS-FS was developed at the University of California, Irvine. Used in conjunction with fluoroscopy, it continuously measures force during UAS insertion, displays the data in a digital readout, and gives auditory and visual alerts when a preset maximum force is reached.

“I am a strong proponent for the use of a ureteral access sheath because I know it reduces intrarenal pressure and significantly reduces risk of sepsis. I also believe it might improve stone-free rates and therefore the number of procedures patients undergo. Concern over causing ureteral injury during UAS passage, however, has limited its uptake among urologists,” said Kamaljot Kaler, MD, clinical assistant professor at the University of Calgary, Southern Alberta Institute of Urology in Calgary.

“Our experience indicates that the UAS-FS is a useful adjunctive safety tool that could afford urologists greater comfort and confidence with UAS insertion.”

As a fellow in endourology, image-guided therapy, and robotic surgery at the University of California, Irvine, Dr. Kaler and his mentor, Ralph Clayman, MD, had the vision for developing a device that could provide live feedback on UAS deployment force in order to prevent clinically significant ureteral injury. They collaborated on the design with colleagues in the department of engineering at the University of California, Irvine. The team’s goal is to bring the UAS-FS onto the market as a disposable or reusable device.

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The protocol for clinical investigation of the UAS-FS considered findings from initial testing in a porcine model that showed ureteral injury occurred during UAS insertion when the peak force reached 8 Newtons (N). In the clinical trial, UAS insertion was initiated using a 14/16F device. If the level of applied force reached 7-8 N, a fluoroscopic image was obtained, and the UAS was removed and downsized to a 12/14F sheath. If the force during its insertion reached the upper limit, the sheath was withdrawn and replaced with a 9.5/11F sheath.

Four urologists are participating in the clinical trial. Data were analyzed from 56 patients undergoing routine ureteroscopy. There were 64 UAS deployments in the series; 39 (61%) were completed at a force <8 N using a 16F UAS, 18 (28%) were done with a 14F UAS, and seven (11%) used an 11F device.

The post-ureteroscopic lesion scale (PULS) grade averaged 0.76 and was 0-2 in all patients except one. The latter case involved a PULS 3 injury in a patient who underwent serial insertion of three sheaths; peak forces reached 8.1 N initially with a 16F UAS, 8.9 N with a 14F UAS, and 5.0 N using an 11F UAS. The patient had no symptomatic or radiographic evidence of stricture when followed at 2 months.

“Based on this study and further porcine studies, Dr. Clayman has decreased the force threshold to 5-6 N in an attempt to entirely eliminate the risk of injury. In our study, no patients had a PULS score >1 when we limited the insertion force to <5 N,” Dr. Kaler said.

Next: No difference with tamsulosinNo difference with tamsulosin

Thirty-seven (66%) of the patients in the study received oral tamsulosin (Flomax) for up to 1 week prior to ureteroscopy. There was no significant difference in the mean initial peak pressure reached comparing patients treated with tamsulosin with the group that did not.

“Tamsulosin can help induce a state of ureteral relaxation, and we found previously in a retrospective study that the 16F UAS deployment rate was significantly higher among patients receiving preoperative tamsulosin than in those who did not,” Dr. Kaler said.

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“Considering that previous endoscopic intervention could result in ureteral dilation and facilitate UAS insertion, we are now analyzing the data from our UAS-FS study to see if such a history could be a confounding factor explaining the observed lack of effect of tamsulosin pretreatment on peak pressure.”

“Anecdotally,” he added, “I have been starting all patients undergoing percutaneous nephrolithotomy or ureteroscopy on tamsulosin 1 week prior to their procedure and have not yet had a single case where I was unable to insert a UAS.”


The University of California Irvine, Dr. Clayman, and Dr. Kaler hold patents on the UAS-FS.

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