Effect of Conventional Versus Flexible and Navigable Suction Ureteral Access Sheaths on Ureteral Temperature Modulation During High-power Ho:YAG Laser Lithotripsy: An In Vitro Evaluation.

Background and objective: Ureteral thermal injury during high-power laser lithotripsy with holmium:yttrium-aluminum-garnet (Ho:YAG) laser has become a clinical concern. We evaluated the influence of irrigation flow rates on ureteral temperature profiles during high-power Ho:YAG lithotripsy in an in vitro model. Methods: A customized silicone model of the urinary tract was used to simulate retrograde intrarenal surgery. A 6-mm stone was fixed 3 cm below the model ureteropelvic junction and treated with Ho:YAG laser at 6 W (0.6 J/10 Hz), 12 W (0.6 J/20 Hz), or 24 W (0.6 J/30 Hz) for 40 s. Steady irrigation at 30-60 ml/min was maintained via an automated irrigation system. We evaluated conventional ureteral access sheath (C-UAS) and flexible and navigable suction UAS (FANS) options in four sizes (10/12 Fr, 11/13 Fr, 12/14 Fr, 13/15 Fr). Temperature data were captured via four thermometer probes. Statistical analyses were performed using two-way analysis of variance (device × flow interaction test), with multiplicity controlled using Tukey's honestly significant difference test. Key findings and limitations: A higher flow rate and use of suction via FANS significantly reduced the elevation in ureteral temperature during laser application. At <12 W and 30-35 ml/min, the temperature with a C-UAS remained safe (<43°C) when the ratio of the endoscope to sheath diameter (RESD) was ≤0.75. At 24 W, maintenance of a safe temperature depended on the flow rate and RESD. With a C-UAS, the temperature exceeded 43°C at flows ≤40 ml/min; RESD of 0.77 (Fr 8.5/Fr 11-13) required a flow rate of 50 ml/min to remain below 43°C. When suction was applied via FANS, an endoscope size of 7.5 Fr kept the temperature at <43°C, even at flow rates of ≤40 ml/min; an endoscope size of 8.5 Fr and sheath size of 10-12 Fr (RESD 0.85) required a flow rate of ≥45 ml/min. Limitations of our in vitro model include the absence of physiological factors such as renal blood flow, and the varied stone compositions encountered in clinical practice. Conclusion and clinical implications: FANS demonstrated superior thermal safety over C-UAS, particularly at high laser power. FANS use with optimized irrigation can effectively prevent ureteral thermal injury during laser lithotripsy. Patient summary: We looked at how the sheath design and the flow rate of the irrigation fluid affect the temperature during laser surgery for urinary stones. Our results suggest that an optimum flow rate and a special type of flexible sheath with suction can help in avoiding thermal damage to tissue, even at high laser power.