Temperature Measurements During Flexible Ureteroscopic Laser Lithotripsy: A Prospective Clinical Trial.

Objective: The primary aim of the study was to explore intrarenal temperatures (IRTs) during flexible ureteroscopic laser lithotripsy (FURSL). The secondary aim was to investigate the correlation between temperatures and renal pelvis anteroposterior diameter (APD). Materials and Methods: From February 2023 to June 2023, 10 patients with an indwelling nephrostomy tube (NT) undergoing FURSL were enrolled in the study. Sheathless FURSL was performed using gravitational irrigation (23°C) at 60 cm. A sterile K-type thermocouple was inserted through the NT. Temperatures were recorded for 120 seconds with continuous laser activation and for another 60 seconds after deactivation. Thulium fiber laser delivered energy using a 150 μm fiber and incremental power settings of 5, 10, 20, and 30 W. The laser was deactivated whenever the IRT reached 43°C. Results: IRT correlated directly to power settings. Each time the power settings were increased, the temperature rose significantly. The increase in average peak temperature was 2.6°C between 5 and 10 W ( p  < 0.001), 3.4°C between 10 and 20 W ( p  < 0.001), and 2.5°C between 20 and 30 W ( p  < 0.001). Temperatures reached 43°C in three patients applying 20 W and in eight patients applying 30 W. The shortest activation-time until threshold was 12 and 28 seconds with 30 and 20 W settings, respectively. When reaching 43°C, temperatures remained above this threshold for an additional 29 seconds on average. There was a significant correlation between IRT and renal APD. For example, when 10 W was applied in the setting of APD ≤20 mm, the recorded temperature was on average 2.3°C higher compared with APD >20 mm, with the same power settings applied, p  < 0.001. Conclusion: During FURSL, IRT correlates directly with power settings and is inversely correlated with renal pelvic APD. Using a sheathless approach, power settings ≥20 W should arguably be avoided, especially in the context of a nondilated renal pelvis. ClinicalTrials: The study was registered on ClinicalTrials.gov (NCT05677425).