Monitoring intrarenal temperature changes in the treatment of kidney stones with retrograde intrarenal surgery using Holmium YAG laser

Aim: Laser systems release heat energy in their interactions with the environment due to their physicochemical properties. Thermal damage can occur when living tissues are exposed to this released heat energy for a specific dose and duration. With today's knowledge, Holmium: Yttrium-Aluminum-Garnet laser is an effective and reliable treatment modality for kidney stones in appropriate indications. This study aimed to monitor intrarenal temperature changes when treating kidney stones using retrograde intrarenal surgery with Holmium: Yttrium-Aluminum-Garnet laser. Material and Method: Between March 2023 and August 2023, fifteen patients with kidney stones of a size and nature that could be treated with the retrograde intrarenal surgery method in locations allowing flexion/deflection of the instrument where a thermal probe was attached externally and who agreed to participate were included in the study. The laser system was activated at different power settings (0.8 J/10 Hz, 1.2 J/12 Hz, 1.5 J/20 Hz, and 1.4 J/ 15 Hz), and irrigation models (10 cc/min, 15 cc/min, 20 cc/min, gravity irrigation, and manual pump irrigation). We used A T-type thermal probe with a measurement accuracy of ± 0.1°C to measure temperature changes. We recorded temperature and time variables. The threshold temperature value, which protein denaturation begins in the porcine urinary system, was accepted as 43°C. Results: Fifteen patients were included in the study. It was observed that intrarenal temperature began to rise with laser activation and plateaued after a certain period. Dramatic decreases in temperature were observed when laser activation was stopped during transitions between study models. At 8 watts of laser power, the threshold temperature was not reached in any study model, while in the 14 watts laser model, the threshold temperature was not reached in the 15 cc/min and 20 cc/min irrigation models. In the 8 watts laser power, the average temperature was higher in the 10 cc/min irrigation model compared to the 20 cc/min irrigation model (33.7 °C compared to 30.2 °C; p=0.011). At 14 Watts laser power, the average temperature was found to be the lowest in the manual irrigation model, compared to gravity irrigation, 20 cc/min, 15 cc/min, and 10 cc/min irrigation models (31.1 °C compared to 36.1 °C, 33.5 °C, 35.7 °C, 37.1 °C, respectively; p<0.001). Univariate and multivariate regression models showed that laser power and irrigation rate significantly affected average temperature (p<0.001), with laser power having a higher adjusted effect than irrigation rate. The laser power and irrigation rate variables could explain approximately 50.1% of the average temperature. No perioperative or postoperative complications occurred in the cases, and no significant difference was observed in the follow-up creatinin tests between the preoperative period, the first day postoperatively and the first month postoperatively. (0.82 mg/dL compared to 0.80 mg/dL, 0.80 mg/dL, respectively; p=0.570). Conclusion: During Holmium: Yttrium-Aluminum-Garnet laser lithotripsy, there can be an increase in temperature in the calyceal fluid. Lower laser power, continuous and higher irrigation rates can maintain intrarenal temperatures within a safe thermal range. Considering the threshold value of 43 °C, the temperature remainig above this threshold for a certain period does not adversely affect postoperative kidney functions. However, since the reliablethermal dose and duration are not yet known, mainly when high laser power and low irrigation are used during surgery, the issue of temperature increase should always be in the operator's mind. Keywords: Retrograde intrarenal surgery, Holmium: Yttrium-Aluminum-Garnet laser, Intrarenal temperature, Laser lithotripsy