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Background/Objectives: Intrarenal pressure (IRP) plays a critical role in ensuring the safety of retrograde intrarenal surgery (RIRS), as elevated IRP is associated with complications such as pyelovenous backflow, infection, and renal injury. LithoVue™ Elite (LVE) is the first commercially available ureteroscope (URS) capable of providing real-time IRP measurements. Conventionally, IRP has been measured via a percutaneous nephrostomy catheter (PNC), which may not accurately reflect dynamic changes during endoscopic procedures. Recently, small ureteral access sheaths (UASs) have been increasingly used to minimize ureteral injury risk. This study aimed (1) to assess the accuracy of LVE compared with that of IRP measured by a PNC and (2) to evaluate appropriate irrigation settings suitable for small UASs using porcine kidney models and LVE. Methods: An 11/13-Fr UAS and a 10/12-Fr UAS were inserted into each model, and an automatic irrigation pump (AIP) and hand pumping (HP) with a 20-cc syringe were used. IRP was measured at various LVE tip positions (renal pelvis and upper, middle, and lower calyces) with different irrigation settings, repeated four times in each. Simultaneously, the IRP via the PNC located in the upper calyx and renal pelvis was measured. Results: LVE showed high concordance with the PNC across the upper, middle, and lower calyces (p > 0.05). However, at the renal pelvis, LVE measured IRP values that were significantly higher than the PNC by a mean of 1.93 ± 0.93 mmHg (p < 0.001). For the 11/13-Fr UAS, the IRP remained below 30 mmHg across all irrigation settings with an AIP and HP. In contrast, the 10/12-Fr UAS maintained 30 mmHg only with limited AIP settings, while HP resulted in high IRP, exceeding 100 mmHg at any location. Intergroup comparisons demonstrated that the IRP with the 10/12-Fr UAS was significantly higher than that with the 11/13-Fr UAS at any irrigation pressure setting across all URS tip positions (p < 0.05). Intragroup comparisons indicated a significant pressure difference between the upper, middle, and lower calyces and the renal pelvis in both models at all irrigation settings (p < 0.05). Conclusions: LVE provided accurate IRP measurements compared to the PNC. The IRP was significantly influenced by UAS size, irrigation setting, and URS tip position. When using small UASs, selecting appropriate irrigation settings is essential to maintain the safe threshold. Full article