## 4 Discussion
Taking into account the results of the analysis of variance in our experiment, both analyzed parameters, UAS size and the laser setting, are statistically significant factors affecting the temperature profile during the RIRS procedure. However, treating the examined parameters as independent variables, it has been demonstrated that the laser setting, as an independent variable, has a comparatively greater impact on the temperature than the UAS size. Thermal damage is measured in experimental studies by crossing a thermal dose threshold. [PERSON] and [PERSON] developed an equation to assess the thermal dose calculated as an exposure time at a reference temperature of 43 \({}^{\circ}\)C. This equation is also known as cumulative equivalent minutes at 43 \({}^{\circ}\)C (CEM\({}_{43}\)). CEM\({}_{43}\) above 70 min resulted in acute and significant damage (up to and including coagulative necrosis), while acute and minor damage was also observed at CEM\({}_{43}\) below 20 min [13]. The temperature generated in the pelvicalyceal system during lithotripsy is the result of several factors, among which the laser power and the irrigation flow play a pivotal role. Increases in intrarenal temperature may potentially result in irreversible cellular damage. Additionally, such temperature increments may adversely affect the genetic expression and composition of cells, ultimately progressing to urothelial cellular death [14]. Hyperthermia induces numerous cellular changes and disrupts cellular homeostasis. An overriding event in this process is the denaturation and aggregation of proteins, resulting in cell-cycle arrest, protein-synthesis inhibition, and impeding DNA-repair mechanisms [15]. Up to now, published results of experimental studies on animals and in vitro models have focused on the impact of various laser powers settings and the type of irrigation system used on changes in IPT. The use of a ureteral access sheath may offer benefits by facilitating irrigation fluid outflow, thus lowering intrapelvic pressure and decreasing intrarenal fluid temperature [16]. But the issue of how the size of the UAS affects temperature remains a considerably less explored topic. [PERSON] et al. evaluated the effect of laser settings and irrigation flow on temperature in an in vitro setting. Based on an experimental study in the absence of continuous saline irrigation, all settings ranging up to 20 W total power exceeded the upper thermal damage threshold, reaching a maximum temperature over 100 \({}^{\circ}\)C when a power of 20 W was applied. A safe temperature profile was observed when a 100 mL/min irrigation flow rate was employed. However, when reduced to 50 mL/min, a temperature measurement of 40 \({}^{\circ}\)C was only detected at a 20 W total power setting [17]. In another study, [PERSON] et al. assessed the change in IPT using a bench model by employing various Holmium-YAG laser settings and two sizes of laser fibers (200 and 272 \(\upmu\)m). When irrigation was shut off, the model exceeded 45 \({}^{\circ}\)C (the maximum temperature limit of the study), irrespective of tank temperature and laser settings, for both fibers. With the 272 \(\upmu\)m laser fiber, this limit was reached as early as the 30 th second. Conversely, when irrigation was open, the authors did not surpass the maximum temperature limit, regardless of tank temperature and laser setting [18]. Both quoted studies were conducted under in vitro conditions; however, the temperature assessment was carried out after laser activation, without an actual lithotripsy of the stone. A similar ex vivo experiment (using a glass test tube) was conducted by [PERSON] et al. The authors investigated changes in fluid temperature during holmium laser activation, employing settings with a power output up to 40 watts and various irrigation flow rates. Temperature showed an upward trend with the rise in laser power output and the decline in irrigation flow rate.