Ureteral access sheath insertion forces: implications for design and training

Ureteral access sheaths (UAS) vary in their ability to resist buckling forces. We evaluated the forces utilized during simulated placement of a UAS. A model UAS (21F OD, 9F ID) was made of polyolefin material. Mounted to the distal tip of the catheter was a spring (7/32″ × 1″ × 0.28″ wire thickness). When simulating catheter insertion, the spring was placed in contact with an Extech^™ 475040 Digital Force Gauge to measure the peak compression force (Newton). Three repetitions of the task were performed by practicing urologists (n = 8) and urology residents (n = 5). Participants were instructed to “Push until you feel a level of resistance that would make you stop if you were putting in a real ureteral access sheath”. Urologists applied a maximum force of 6.55 ± 0.45 N while urology residents applied a maximum force of 4.84 ± 0.64 N. There was a significant difference in the forces applied between the two groups (P = 0.035). No significant difference in the variance (ranges or spread) of forces applied by the urologists and residents were identified (P = 0.11). One-way analysis of variance demonstrated no differences in the force applied between the first, second and third attempt (P = 0.80). Quantifying the insertion forces used during placement of a UAS will facilitate the design of UAS and provides information critical to the design of ureteroscopic simulators. Understanding the range of forces used by experienced urologists will help establish competency parameters for professionals in training.