Objectives: To assess the effect of irrigation settings and the size of ureteral access sheath (UAS) on the maximal intra-pelvic pressure (IPPmax) during ureteroscopy (URS) in pigs. Materials and Methods: In supine position, three anesthetized female pigs underwent cystoscopy to insert a 6F ureteral catheter in each ureter. Pigs were then turned to prone position to establish a percutaneous access, insert a 10F nephrostomy tube in the kidney, and connect it to a urodynamic device. An 8F semi-rigid ureteroscope or the Flex-X2 Flexible Ureteroscope was used with two irrigation settings: gravity flow and manual pumping using a commercial pump. URS was performed without UAS and with the UAS 9.5/11, 12/14, 14/16 at the ureteropelvic junction and the IPPmax was recorded. Results: Under gravity irrigation, the recorded IPPmax during semi-rigid URS in the distal ureter and the renal pelvis was 0 and 30 cmH₂O, respectively. Further, the IPPmax during flexible URS in the renal pelvis without UAS, with UAS 9.5/11.5, with UAS 12/14, and with UAS 14/16 was 23, 6, 2, and 1 cmH₂O, respectively. Under manual pumping, the IPPmax during semi-rigid URS in the distal ureter and the renal pelvis was 84 and 105 cmH₂O, respectively. Further, the IPPmax during flexible URS in the renal pelvis without UAS, with UAS 9.5/11.5, with UAS 12/14, and with UAS 14/16 was 45, 46, 18, and 1 cmH₂O, respectively. Conclusion: Manual pumping can significantly increase the IPPmax to unsafe levels during URS. The UAS can significantly decrease the IPPmax, even under manual pumping. The larger the UAS, the lower the IPPmax. The use of UAS can render URS safer by acting as a safeguard against the consequences of increased IPP, even under forced irrigation.

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