## 4 Discussion  
Procedures of retrograde intrarenal surgery using a flexible ureterorenoscope and laser fiber constitute one of the most frequently performed procedures in endourology. A contemporary technological challenge in the treatment of kidney stones is the intraoperative real-time monitoring of pressure and temperature in the pelvicalyceal system during RIRS. Of the two mentioned physical parameters that are essential factors determining patient safety, IPP (intrarenal pelvic pressure) is significantly better understood and studied. We have research results both in vivo and in vitro, unequivocally indicating the need for intrapelvic pressure monitoring during laser lithotripsy. A breakthrough in endourology \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Contrast** & **Estimate** & \(SE\) & \(df\) & \(t\) & \(p\) & \(d\) \\ \hline
10/12 Fr–12/14 Fr & 25.32 & 9.32 & 250 & 2.72 & **0.007** & 0.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Contrast analysis of the UAS factor for all lasers’ power. \(SE\)—the standard error; \(df\)—degrees of freedom; \(t\)—the t Student test statistic; \(d\)—the [PERSON]’s d effect size. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Contrast** & **Estimate** & \(SE\) & \(df\) & \(t\) & \(p\) & \(d\) \\ \hline
12 W–15 W & \(-\)3.48 & 13.04 & 250 & \(-\)0.27 & 0.999 & 0.05 \\
12 W–18 W & \(-\)42.15 & 13.04 & 250 & \(-\)3.23 & **0.012** & 0.63 \\
12 W–20 W & \(-\)74.77 & 13.04 & 250 & \(-\)5.74 & **<0.001** & 1.12 \\
12 W–25 W & \(-\)92.19 & 13.04 & 250 & \(-\)7.07 & **<0.001** & 1.39 \\
15 W–18 W & \(-\)38.67 & 13.04 & 250 & \(-\)2.97 & **0.027** & 0.58 \\
15 W–20 W & \(-\)71.29 & 13.04 & 250 & \(-\)5.47 & **<0.001** & 1.07 \\
15 W–25 W & \(-\)88.71 & 13.04 & 250 & \(-\)6.81 & **<0.001** & 1.33 \\
18 W–20 W & \(-\)32.62 & 13.04 & 250 & \(-\)2.50 & 0.093 & 0.49 \\
18 W–25 W & \(-\)50.04 & 13.04 & 250 & \(-\)3.84 & **0.001** & 0.75 \\
20 W–25 W & \(-\)17.42 & 13.04 & 250 & \(-\)1.34 & 0.669 & 0.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Contrast analysis of temperature differences within laser power factors for all UASs. \(SE\)—the standard error; \(df\)—degrees of freedom; \(t\)—the t Student test statistic; \(d\)—the Cohen’s d effect size. equipment comes in the form of the LithoVue Elite ureteroscope from Boston Scientific Corp. (Marlborough, MA, USA). This pioneering flexible ureterorenoscope is the first of its kind, equipped with the capability for the ongoing intraoperative monitoring of intrarenal pressure (IPP) during retrograde intrarenal surgery (RIRS) [12]. Monitoring intraoperative temperature still remains a terra incognita in everyday practice and constitutes a much less explored issue. Furthermore, understanding the changes in physical parameters occurring during laser lithotripsy in the kidney is a crucial element in ensuring the safety of this procedure for the patient. The thermal cytotoxic effect is influenced not only by the peak maximum temperature achieved during a procedure, but also by the duration of exposure. During laser activation in the system, energy is absorbed by water, leading to a temperature increase. In a theoretical model of a completely closed and isolated system, this would result in an unlimited temperature rise. However, in a partially open and non-isolated system like the kidney, the temperature increase due to laser-energy absorption is offset by the heat outflow with the irrigation fluid and by the energy transfer through the pelvicalyceal system wall. The higher the temperature in the system, the greater the heat outflow becomes (a larger amount of energy per unit volume flowing out of the system), leading to a point where the generated energy equals the outflowing energy, and the temperature level stabilizes. The equilibrium temperature reached in such a system depends both on the laser power used and the flow rate.