Intrarenal pressure gradient in an ex-vivo porcine kidney model.

Introduction: Intrarenal pressure (IRP) is challenging to measure during retrograde intrarenal surgery (RIRS). Distal end-mounted pressure sensors in flexible ureteroscope (fURS) or ureteral access sheath (UAS) offer real-time pressure measurement, which may address this issue. Pyelorenal reflux occurs in the renal calyces, particularly at the fornices. No study has yet investigated whether there is a pressure differential between the renal pelvis and the calyces. This research aims to examine this topic using the porcine kidney model developed at our institution.

Materials and methods: Twelve adult porcine kidneys were used. Three pressure measuring catheters were inserted into upper, middle, and lower calyces. IRPs were studied using either conventional UAS (cUAS) or vacuum-assisted UAS (vaUAS) with a fourth measure monitor catheter inside and level with the tip of UAS and a 7.5F fURS. Incremental rate of irrigation was delivered through the fURS and IRPs were measured and recorded.

Result: In cUAS, there were statistically significant reductions in pressure, ranging from small to moderate, observed in both the upper and lower calyces compared to the renal pelvis. These pressure differences disappeared when irrigation reached >90 c.c./minute. In vaUAS with vent closed: The IRP remained negligible even with irrigation up to 140 c.c./minute. Interestingly, there were very small but significantly less pressures in all three calyces as compared to the real pelvises when irrigation rate was ≧90 c.c./minute. There were no differences in pressure with irrigation below 90 c.c./minute.

Conclusion: Real-time IRP measurement during RIRS with cUAS can provide valuable clinical insights. Porcine kidney studies show slightly less pressure in the calyces than the renal pelvis. vaUAS reduces high IRP and pressure gradients, potentially making real-time IRP measurement unnecessary.