This study aimed to assess the impact of irrigation flow rates on intrarenal temperature dynamics during laser lithotripsy under varying laser power settings, using a controlled ex vivo experimental setup. The findings may help define safe parameters for endourological stone treatment and minimize thermal injury risk.

A prospective experimental study was conducted using an anatomically accurate, 3D-printed kidney model developed for ex vivo simulation of retrograde intrarenal surgery. Laser lithotripsy was carried out with a thulium fiber laser at two power settings: 25W and 40W. The procedures were performed under three different irrigation conditions: no irrigation, low flow (15 ml/min), and high flow (40 ml/min). All experimental conditions were evaluated both in the presence and absence of artificial stone fragments.
Intrarenal temperature was continuously recorded throughout each trial. Key parameters assessed included average and peak temperatures, the time required to reach critical thermal thresholds (43°C, indicative of tissue damage, and 56°C, associated with protein denaturation), total duration of laser activation, and the cumulative energy delivered.

In the absence of irrigation, intrarenal temperatures rapidly reached critical levels. At 25W, 43°C was reached within 9 seconds and 56°C after 64 seconds; at 40W, these thresholds were exceeded at 3 seconds and 16 seconds, respectively. With 15 ml/min irrigation and no stone, 25W reached 43°C in 10 seconds, while 40W reached 43°C in 6 seconds and 56°C in 43 seconds. Increasing irrigation to 40 ml/min delayed or prevented temperature elevation: 25W did not exceed safety thresholds, and 40W reached 43°C only after 112 seconds.
When artificial stones were present, thermal dynamics showed similar trends. Without irrigation, 25W reached 43°C in 6 seconds and 56°C in 91 seconds; 40W exceeded these thresholds in 7 and 51 seconds, respectively. At 15 ml/min, 25W reached 43°C in 76 seconds, while 40W reached 43°C in 11 seconds and 56°C in 110 seconds. At 40 ml/min irrigation, neither setting reached critical temperature limits.

Irrigation flow rate was a decisive factor in thermal regulation during laser lithotripsy. Higher flow rates significantly delayed or prevented the rise in intrarenal temperatures to potentially harmful levels, even under high-power settings. The presence of stone material slightly modified thermal behavior but did not alter overall trends.

Irrigation at 40 ml/min provided optimal thermal safety during laser lithotripsy, preventing critical temperature elevations at both 25W and 40W power settings. Moderate irrigation (15 ml/min) may be acceptable for short activation periods at lower power. These findings underscore the importance of intraoperative irrigation control and support further investigation in vivo to balance thermal safety with intrarenal pressure risks.