Risk assessment of holmium laser induced ureteral stricture:experiments using a pig model.

Abstract

PURPOSE: To systematically evaluate the safety boundaries of holmium laser application during ureteroscopy by quantifying thermal dose and to explore the detailed repair mechanisms of the ureter and kidneys following injury. METHODS: Twelve female piglets were selected. Key variables included holmium laser power, irrigation flow rates (0, 7.5, 15 mL&#xa0;min), and fluid temperatures. Thermal dose was calculated as Cumulative Equivalent Minutes at 43 &#xb0;C (CEM43). Trauma and repair processes were assessed via microscopic imaging, Masson staining, and immunohistochemistry for inflammatory and fibrosis markers. Statistical analyses were performed using two-way analysis of variance (ANOVA). RESULTS: At an irrigation flow rate of 15 mL&#xa0;min, the temperature rise was minimal with a negligible thermal dose (CEM43 <&#xa0;1), ensuring safety even at 30 W. In contrast, compromised irrigation (7.5 mL&#xa0;min) or no-flow conditions resulted in rapid heat accumulation, with CEM43 values reaching extreme levels (>10) at high powers. In the kidneys, the repair process involved a transition from inflammation to fibrosis over time, which was correlated with an M1-to-M2 macrophage polarization. Crucially, anatomical ureteral stricture was observed only when the laser-induced injury involved &#x2265;3/4 of the ureteral circumference. CONCLUSION: Sufficient irrigation is critical to maintain thermal safety. While thermal exposure induces fibrotic changes driven by macrophage polarization, mechanical injury extent (&#x2265;3/4 circumference) appears to be the dominant predictor for the formation of ureteral stricture. These findings emphasize the importance of maintaining high-flow irrigation and minimizing extensive circumferential damage during surgery.