Is a Ureteral Access Sheath Necessary for Maintaining Safe Intrarenal Pressures During Retrograde Lithotripsy Using a Flexible 7.5 Fr Scope and a High-Power TFL? In Vivo Experimental Study

<i>Background and Objectives</i>: To evaluate the effect of a ureteral access sheath (UAS) on the maximal intra-pelvic pressure (IPP max) during retrograde lithotripsy of hard and soft stones in a porcine model. <i>Materials and Methods</i>: A 22 Fr percutaneous tract was established in the upper calyces of the kidneys in three female pigs. A custom-made Foley catheter with a urodynamic catheter was inserted into the pelvicalyceal system and connected to a urodynamic device for real-time IPP measurement. A Pusen Uscope 7.5 Fr single-use ureteroscope (Zhuhai Pusen Medical Technology, Jinhua, China) with manual pump irrigation was used. BegoStone™ powder (Bego, Lincoln, RI, USA) was prepared in two powder-to-water ratios (15:3 and 15:6) to create hard and soft stones, respectively. Stones were positioned in the pelvicalyceal system through the percutaneous tract, and retrograde intrarenal lithotripsy was performed in three settings: without UAS and with a 9.5/11 Fr UAS, with lasing in the center of the pelvis, and during lithotripsy of soft and hard stones. <i>Results</i>: With manual pump irrigation and without a UAS, the IPP max reached 55 cmH₂O during lasing in the pelvis center. During lithotripsy of soft and hard stones, the IPP max increased to 62 and 65 cmH₂O, respectively. Using a UAS, the IPP max was significantly lower: 18 cmH₂O in the center of the pelvis, and 25 and 29 cmH₂O during lithotripsy of soft and hard stones, respectively. <i>Conclusions</i>: Manual pump irrigation without a UAS can elevate IPP max to potentially unsafe levels during retrograde correct flexible lithotripsy, even when using a 7.5 Fr flexible scope. The addition of a UAS helps maintain the IPP max within safer limits.