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

Evaluating safe irrigation rates for Tm fiber laser lithotripsy to prevent thermal injury: an in vitro and numerical simulation

PURPOSE

To evaluate temperature changes and thermal injury during thulium fiber laser (TFL) lithotripsy in the urinary tract and identify the safe irrigation rate, providing a reference for optimal parameter settings in clinical practice.

METHODS

An in vitro thermal injury experiment was conducted using a home-made TFL operating at 40 W. The experiment utilized a glass tube simulating the urinary tract. A peristaltic pump circulated 25 °C saline at irrigation rates ranging from 10 to 40 mL/min. Real-time temperature measurements were recorded using thermocouples, and thermal injury was assessed by calculating the thermal dose threshold. Additionally, a validated numerical simulation model was developed to analyze temperature distributions and predict safe irrigation rates at 20 and 30 W.

RESULTS

In the in vitro experiment, at 40 W, severe thermal injury occurred in the urinary tract when the irrigation rate was below 30 mL/min, particularly in the ureter and renal calyx. The numerical simulation model demonstrated a high degree of consistency with the experimental results. According to the simulation, at 30 W, thermal injury occurred in the renal calyx when the irrigation rate was below 20 mL/min. At 20 W, thermal injury was observed in the renal calyx when the irrigation rate was below 10 mL/min.

CONCLUSIONS

The increase in temperature and the extent of thermal injury were strongly dependent on laser power and irrigation rate, with a lesser dependence on anatomical location. The accuracy of the numerical simulation was validated through experiments, demonstrating its capability to reliably predict temperature variations and thermal injury under different laser power settings and irrigation rates.

Initial experience of thulium fiber laser in retrograde intrarenal surgery for ureteral and renal stones in Japan: surgical outcomes and safety assessment compared with holmium: yttrium-aluminum-garnet with MOSES technology

BACKGROUND

Thulium fiber laser (TFL) has been used for the treatment of ureteral and renal stones in Japan since October 2023. However, there are no reports on the initial results of TFL in Japan. This study aimed to assess the initial results of TFL in retrograde intrarenal surgery (RIRS) and to compare them with those of holmium: yttrium-aluminum-garnet (Ho: YAG) laser with MOSES technology.

METHODS

This retrospective single-center study compared perioperative results, complications, and the "stone-free" rate (defined as ≤ 2 mm fragments on computed tomography 1 month after RIRS) between the TFL (60 W) (group A, n = 48) and Ho: YAG laser with MOSES technology (120 W) (group B, n = 48) laser. The inclusion criteria were renal or ureteral stones ≤ 20 mm in diameter and those scheduled for single-stage RIRS.

RESULTS

The two groups had similar baseline patient characteristics. No significant differences were found in operative time (45 vs. 54 min, P = 0.10), laser time (15 vs. 10 min, P = 0.12), stone-free rate (97.9% vs. 95.8%, P = 1.00), ureteral injury (2.1% vs. 8.3%, P = 0.36), or postoperative fever (0% vs. 4.2%, P = 0.49) between groups A and B. However, significant differences were found in basketing time (7 vs. 21 min, P < 0.01) between groups A and B.

CONCLUSIONS

Our study showed that RIRS with TFL had similar results and no difference in complications compared to RIRS with Ho: YAG laser with MOSES technology. The TFL had a significantly shorter basketing time than the Ho: YAG laser with MOSES technology. Furthermore, future research is needed to determine suitable laser settings for the TFL.

Rise in intraluminal temperature during ureteroscopy: Is this a concern?

The global increase in urolithiasis prevalence has led to a shift towards minimally invasive procedures, such as retrograde intrarenal surgery, supported by advancements in laser technologies for lithotripsy. Pulsed lasers, particularly the holmium YAG and the newer thulium fiber laser, have significantly transformed the management of upper urinary tract stones. However, the use of high-power lasers in these procedures introduces risks of heat-related injury. Laser lithotripsy works through photothermal and photomechanical effects to fragment stones, but up to 96% of the laser energy is converted into heat, increasing the risk of thermal damage to the surrounding urothelial mucosa. Studies show that even at low-power settings, intrarenal temperatures can exceed the threshold for cellular injury, particularly in confined spaces like the ureter. This narrative review explores strategies to mitigate thermal injury, including optimizing laser settings, improving irrigation flow rates, and incorporating novel methods such as cold irrigation, controlling outflow resistance, and using suction. Understanding these approaches is crucial to enhancing patient safety during high-power laser lithotripsy procedures.

Novel pressure- and temperature-controlled flexible ureteroscope system with a suction ureteral access sheath: a multicenter retrospective feasibility study

PURPOSE

The purpose of this study was to assess the feasibility of a pressure-controlled and temperature-controlled flexible ureteroscope system (PT Scope™) during flexible ureteroscopy.

MATERIALS AND METHODS

We developed the PT Scope™, a novel ureteroscope system with capabilities for monitoring and controlling intrarenal pressure and temperature to maintain them within set parameters. Data were retrospectively collected from 48 consecutive patients diagnosed with upper urinary tract stones who underwent flexible ureteroscopic lithotripsy using the PT Scope™ across five centers in China. Analyses focused on 24-h postoperative stone-free rates, intrarenal pressure and temperature measurements, and other procedural data.

RESULTS

Among the 48 patients treated with the PT Scope™ system, a significant stone-free rate of 89.6% was achieved within 24 h postoperation, without any instances of intraoperative complications such as perforation or mucosal hemorrhage. Only two patients reported mild postoperative pain and were managed with NSAIDs, and there were no cases of postoperative fever or sepsis. The average maximum intrarenal pressure and temperature were recorded at 30.2 ± 4.20 mmHg and 36.6 ± 4.27 °C, respectively. Notably, during lithotripsy, both the pressure and temperature were maintained below 30 mmHg and 43 °C for 99% of the procedure duration, respectively.

CONCLUSION

This preliminary investigation indicates that the PT Scope™ is a safe and effective tool for the treatment of upper urinary tract stones, offering the benefit of regulating intrarenal pressure and temperature within predetermined limits. These findings support the feasibility of the system for clinical application.

Temperature profile during endourological laser activation: introducing the thermal safety distance concept

PURPOSE

To examine temporal-spatial distribution of heat generated upon laser activation in a bench model of renal calyx. To establish reference values for a safety distance between the laser fiber and healthy tissue during laser lithotripsy.

METHODS

We developed an in-vitro experimental setup employing a glass pipette and laser activation under various intra-operative parameters, such as power and presence of irrigation. A thermal camera was used to monitor both temporal and spatial temperature changes during uninterrupted 60-second laser activation. We computed the thermal dose according to Sapareto and Dewey's formula at different distances from the laser fiber tip, in order to determine a safety distance.

RESULTS

A positive correlation was observed between average power and the highest recorded temperature (Spearman's coefficient 0.94, p < 0.001). Irrigation was found to reduce the highest recorded temperature, with a maximum average reduction of 9.4 °C at 40 W (p = 0.002). A positive correlation existed between average power and safety distance values (Spearman's coefficient 0.86, p = 0.001). A thermal dose indicative of tissue damage was observed at 20 W without irrigation (safety distance 0.93±0.11 mm). While at 40 W, irrigation led to slight reduction in mean safety distance (4.47±0.85 vs. 5.22±0.09 mm, p = 0.08).

CONCLUSIONS

Laser settings with an average power greater than 10 W deliver a thermal dose indicative of tissue damage, which increases with higher average power values. According to safety distance values from this study, a maximum of 10 W should be used in the ureter, and a maximum of 20 W should be used in kidney in presence of irrigation.

Japanese survey of perioperative complications and ureteral stricture after ureteroscopy with laser lithotripsy for upper urinary tract stones in multicenter collaborative study

OBJECTIVES

This study aimed to investigate perioperative complications and the details of postoperative ureteral stricture after ureteroscopy with laser lithotripsy (URS-L) for upper urinary tract stones in Japan.

METHODS

Patient data on intra- and postoperative complications after ureteroscopy using URS-L were retrospectively collected from multiple centers in Japan between April 2017 and March 2020 with the cooperation of the Japanese Society of Endourology and Robotics. Data included the number of patients undergoing URS-L, number and type of intra- and postoperative complications, and detailed characteristics of postoperative ureteral stricture.

RESULTS

In total, 14 125 patients underwent URS-L over 3 years at 82 institutions. Annual URS-L numbers gradually increased from 4419 in 2017, to 4760 in 2018, and 4946 in 2019. The total complication rate was 10.5%, which was divided into intra-operative complications in 1.40% and postoperative complications in 9.18%. The annual incidences of intra- and postoperative complications were not significantly different from year to year (p = 0.314 and p = 0.112). Ureteral perforation, ureteral avulsion, and the intra-operative conversion rate were 1.35%, 0.03%, and 0.02%, respectively. Fever >38°C, septic shock, blood transfusion, and postoperative mortality were 7.44%, 0.81%, 0.07%, and 0.04%, respectively. Ureteral stricture occurred in 0.8% of cases. The median length of stricture site was 10.0 mm and the success rate of stricture treatment was 54.6%.

CONCLUSION

Although URS-L utilization has increased in Japan, the annual complication rate has remained steady. Although URS-L is a useful and less invasive procedure, devastating complications can still occur.

Monitoring Intrarenal temperature changes during Ho: YAG laser lithotripsy in patients undergoing retrograde intrarenal surgery: a novel pilot study

Ho: YAG laser lithotripsy is widely used for urinary stone treatment, but concerns persist regarding its thermal effects on renal tissues. This study aimed to monitor intrarenal temperature changes during kidney stone treatment using retrograde intrarenal surgery with Ho: YAG laser. Fifteen patients were enrolled. Various laser power settings (0.8 J/10 Hz, 1.2 J/12 Hz) and irrigation modes (10 cc/min, 15 cc/min, 20 cc/min, gravity irrigation, and manual pump irrigation) were used. A sterile thermal probe was attached to a flexible ureterorenoscope and delivered into the calyceal system via the ureteral access sheath. Temperature changes were recorded with a T-type thermal probe with ± 0.1 °C accuracy. Laser power significantly influenced mean temperature, with a 4.981 °C difference between 14 W and 8 W laser power (p < 0.001). The mean temperature was 2.075 °C higher with gravity irrigation and 2.828 °C lower with manual pump irrigation (p = 0.038 and p = 0.005, respectively). Body mass index, laser power, irrigation model, and operator duty cycle explained 49.5% of mean temperature variability (Adj. R2 = 0.495). Laser power and operator duty cycle positively impacted mean temperature, while body mass index and specific irrigation models affected it negatively. Laser power and irrigation rate are critical for intrarenal temperature during Ho: YAG laser lithotripsy. Optimal settings and irrigation strategies are vital for minimizing thermal injury risk. This study underscores the need for ongoing research to understand and mitigate thermal effects during laser lithotripsy.

Optimal parameter settings of thulium fiber laser for ureteral stone lithotripsy: a comparative study in two different testing environments

This study aims to identify optimal parameters for using Thulium fiber lasers (TFL) in ureteral stone lithotripsy to ensure laser safety and maximize efficacy. Our goal is to improve the outcomes of single-use semi-rigid ureteroscopy for treating stones located in the proximal ureter. A clinically relevant thermal testing device was designed to investigate heating effects during TFL stone fragmentation. The device was utilized to identify safe power thresholds for TFL at various irrigation rates. Three other devices were used to assess varying pulse energy effects on stone fragmentation efficiency, dusting, retropulsion, and depth of tissue vaporization. Comparative experiments in fresh porcine renal units were performed to validate the efficacy and safety of optimal TFL parameters for semi-rigid ureteroscopy in proximal ureteral stone procedures. Our study found that the improved device generated a higher thermal effect. Furthermore, the safe power threshold for laser lithotripsy increased as the irrigation rate was raised. At an irrigation rate of 40 ml/min, it is safe to use an average power of less than 30 watts. Although increasing pulse energy has a progressively lower effect on fragmentation and dust removal efficiency, it did lead to a linear increase in stone displacement and tissue vaporization depth. Thermal testing showed 20 W (53.87 ± 2.67 °C) indicating potential urothelial damage. In our study of laser lithotripsy for proximal ureteral stones, the group treated with 0.3 J pulses had several advantages compared to the 0.8 J group: Fewer large fragments (> 4 mm): 0 vs. 1.67 fragments (1-2.25), p = 0.002, a lower number of collateral tissue injuries: 0.50 (0-1.25) vs. 2.67 (2-4), p = 0.011, and lower stone retropulsion grading: 0.83 (0.75-1) vs. 1.67 (1-2), p = 0.046. There was no significant difference in operating time between the groups (443.33 ± 78.30 s vs. 463.17 ± 75.15 s, p = 0.664). These findings suggest that TFL irradiation generates a greater thermal effect compared to non-irradiated stones. Furthermore, the thermal effect during laser lithotripsy is influenced by both power and irrigation flow rate. Our study suggests that using a power below 15 W with an irrigation flow rate of 20 ml/min is safe. Moreover, a pulse energy of 0.3 J appears to be optimal for achieving the best overall stone fragmentation effect.