In collaboration with the UC California Institute of Telecommunications and Information Technology, the UC Irvine Department of Urology has developed a novel UAS force sensor that can accurately measure real time force in 1/100ths of a Newtons (N).
As such, with the usage of this sensor, Minh-Chau et al. explored the largest physiological diameter to which the human ureter could be dilated below 6 N, a maximum threshold of force that was previously shown to allow the safe deployment of an ureteral access sheath.
This was a prospective study of nephrolithiasis patients who underwent a ureteroscopic or percutaneous stone removal procedure involving the usage of a ureteral access sheath. Forty-four ureters (15 males and 29 females) were sequentially sized with 35 cm cook urethral dilators, starting with the 10 F dilator followed by the passage of dilators in 2F increments (12F, 14F, 16F, 18F, 20F, 22F, and 24F) until a force measurement of 6N was recorded. An ureteral access sheath (max 16 F) similar in size to the largest dilator successfully inserted under 6 N was then placed.
The mean size of the dilator safely accepted by the ureters was 14 F. Of 44 ureters, 30% accepted a dilator < 12F, 25% accepted a 14F, 27% accepted a 16F, and 18% accepted a >18F dilator (18-24F) under 6 N. A pre-stented ureter, two on preoperative Tamsulosin, and one with no preoperative treatment only accepted the smallest size dilator of 10 F. Despite adhering to the safety threshold of 6 N, a Post-Ureteroscopic Lesion Scale (PULS) score of 3 was individually identified in three ureters at the proximal, mid, and distal ureter, respectively. The maximum force of insertion in these ureters were 5.87 N, 5.08 N, and 7.4 N, respectively. Two ureters were pre-stented, with one also receiving preoperative Tamsulosin. The passage of a larger urethral dilator was associated with a pre-existing ureteral stent alone (p = 0.023) or in combination with preoperative Tamsulosin (p = 0.049). Average dilator sizes were increased to 16 F and 17 F, respectively. Pre-stented ureters safely accepted a urethral dilator ≥ 16 in 82% and ≥ 18F 36% of ureters under 6 N versus 33% and 12%, respectively, in unstented ureters.
Through this study assessing the maximum luminal diameter that the human ureter could be safely dilated for surgical stone removal procedures, Minh-Chau and colleagues presented the following conclusions:
- On average, the human ureter can safely accept a 14 F urethral dilator.
- Pre-stenting alone and in combination with preoperative Tamsulosin increased the average dilator size to 16 F and 17 F, respectively.
- A ≥ 18F urethral dilator could safely pass in over one third of presented ureters.
Presented by: Minh-Chau Vu, B.S., Department of Urology, University of California, Irvine
Co-Authors: Andrew S. Afyouni, Sohrab N. Ali, Pengbo Jiang, Roshan M. Patel, Michael Klopfer, Jaime Landman, Ralph V. Clayman
Written by: Minh-Chau Vu, B.S., Department of Urology, University of California, Irvine during the 2022 American Urological Association (AUA) Annual Meeting, New Orleans, LA, Fri, May 13 – Mon, May 16, 2022.