Introduction

Excessive ureteral access sheath insertion force (UASIF) during retrograde intrarenal surgery (RIRS) poses risk of ureteral mucosal injury. However, the optimal UASIF has not yet been defined. Our aim was to develop a homemade UASIF measurement gauge and to validate its feasibility before application to clinical practice.

Methods

Our homemade UASIF measurement gauge consisted of four parts: (A) a V-block jig to secure the UAS, (B) a linear jig to offset torque at sheath exertion, (C) a commercial digital force gauge (IMADA ZTA-50N, IMADA instruments, Korea) capable of 1 g readability ranging from 1.0 to 5,000 g at a millisecond frequency, and (D) an aluminum linear shaft to install and secure all jigs (Fig.1). A 12/14Fr diameter UAS (Navigator^TM HD, Boston Scientific, USA) and biologic material were used to measure the UASIF at various experimental settings.

Results

To evaluate measurement deviations that may arise from coaxial forces induced by buckling and kinking of the UAS, serial weights (1 g - 170 g) were applied and measured at two locations on the V-block jig: at the UAS fixation groove and at parallel to the linear shaft (Fig.2). Linear measurements at both locations showed excellent concordance (r=0.989, p<0.001). To analyze the reproducibility of UASIF measurement, a vice grip was applied to a biologic material at four different friction settings. UASIF was measured at each friction setting by four operators (Fig.3). UASIF increased linearly to friction increment, and showed excellent reproducibility for maximal UASIF values with a mean standard deviation of 4.24 g (Fig.3). At a fixed friction, higher insertion velocity resulted with greater maximal UASIF (Fig.4).

Conclusions

Our homemade UASIF measurement gauge would be applicable to clinical practice. It can be utilized to help better elucidate which parameters, or combinations of parameters, will predict successful UAS deployment.

Funding

none