Objectives. To evaluate the impact of the ureteral access sheath on intrarenal pressures during flexible ureteroscopy in light of the recent resurgence in their use. As such, using human cadaveric kidneys, we studied changes in intrarenal pressure in response to continuous irrigation at different pressures with and without access sheaths of various sizes and lengths. Methods. This study was performed using seven cadaveric kidneys. In three kidneys the study was done in situ with a 7.5F flexible ureteroscope (URS) passed by itself and then passed through a 10/12F sheath (35 and 55 cm in length), whereas, in four kidneys, due to narrowing of the intramural ureter, the study was done ex vivo using the unsheathed URS and then passing the 7.5F flexible URS via the 10/12F, 12/14F, and 14/16F sheaths (all 35 cm in length). A 10F Cope loop pyelostomy was placed to measure intrapelvic renal pressure. Three sets of 3-minute readings (ie, flow and intrarenal pressure) were taken with the tip of the URS at the distal ureter, middle ureter, and renal pelvis (just above the ureteropelvic junction); the entire process was done at three different irrigant pressure settings: 50, 100, and 200 cm H2O. Irrigant flow and intrarenal pressures were measured at all three settings using the URS passed without a sheath and then with the URS passed through the various sheaths positioned at the distal ureter, middle ureter, and renal pelvis. Results With all of the sheaths, intrapelvic pressure remained low (less than 30 cm H2O), and there was a 35% to 80% increase in irrigant flow versus the control unsheathed URS. With the sheath in place, the majority of the irrigant drained alongside the URS and out the sheath. Flow and pressure with the 12/14F sheath were equivalent to the 14/16F sheath. Conclusions. The 12/14F access sheath provides for maximum flow of irrigant while maintaining a low intrarenal pelvic pressure. Even with an irrigation pressure of 200 cm H2O, renal pelvic pressure remained below 20 cm H2O.
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