Characterization of Fluid Dynamics and Temperature Profiles During Ureteroscopy with Laser Activation in a Model Ureter

Ureteral Tissue Temperature During Ureteroscopy With Ho:YAG Laser Activation in an In Vivo Porcine Model

OBJECTIVE

To measure temperature of the outer ureteral wall and calculate thermal dose with different irrigation and laser power settings during ureteroscopy in a porcine in vivo model.

METHODS

The ureters of two porcine subjects were exposed through laparotomy incisions. A length of PFA tubing, with equally spaced windows, was inserted into the ureter through a ureterotomy. An array of thermocouples was positioned on the outside of the ureter, colocated with the windows. A LithoVue Elite (Boston Scientific) ureteroscope with a wire thermocouple attached was inserted into the tube adjacent to the ureteral windows. Trials of 60 seconds laser activation were performed at different power and irrigation rates. Thermal dose was calculated at each thermocouple with the threshold of thermal injury considered to be 120 equivalent minutes.

RESULTS

All trials conducted with 8 mL/min irrigation: 20 W laser power produced elevated ureteral temperatures. Thermal doses exceeded the thermal injury threshold along a 3 cm length of ureter in some cases. 67% of trials using 15 mL/min irrigation: 30 W laser power also produced suprathreshold thermal doses within ureteral tissue. Employing a 50% operator duty cycle at these same settings decreased thermal dose below threshold. Thermal dose did not reach the threshold of thermal injury in any trials with 40 mL/min irrigation.

CONCLUSION

Ureteroscopy in a porcine model with commonly used irrigation rates and laser settings can elevate ureteral temperatures and produce thermal doses above the threshold of thermal injury.

Factors affecting the thermal effects of lasers in lithotripsy: A literature review

Objective

The use of lasers has been an important part of urology in the treatment of stone and prostate disease. The thermal effects of lasers in lithotripsy have been a subject of debate over the years. The objective of this review was to assess the current state of knowledge available on the thermal effects of lasers in lithotripsy, as well as explore any new areas where studies are needed.

Methods

In August 2022, a keyword search on Google Scholar, PubMed, and Scopus for all papers containing the phrases "thermal effects" AND "laser" AND "lithotripsy" AND "urology" was done followed by citation jumping to other studies pertaining to the topic and 35 relevant papers were included in our study. The data from relevant papers were segregated into five groups according to the factor studied and type of study, and tables were created for a comparison of data.

Results

Temperature above the threshold of 43 °C was reached only when the power was >40 W and when there was adequate irrigation (at least 15-30 mL/min). Shorter lasing time divided by lithotripsy time or operator duty cycles less than 70% also resulted in a smaller temperature rise.

Conclusion

At least eight factors modify the thermal effects of lasers, and most importantly, the use of chilled irrigation at higher perfusion rates, lower power settings of <40 W, and with a shorter operator duty cycle will help to prevent thermal injuries from occurring. Stones impacted in the ureter or pelvi-ureteric junction further increase the probability of thermal injuries during laser firing.

Exploring optimal settings for safe and effective thulium fibre laser lithotripsy in a kidney model

OBJECTIVES

To explore the optimal laser settings and treatment strategies for thulium fibre laser (TFL) lithotripsy, namely, those with the highest treatment efficiency, lowest thermal injury risk, and shortest procedure time.

MATERIALS AND METHODS

An in vitro kidney model was used to assess the efficacy of TFL lithotripsy in the upper calyx. Stone ablation experiments were performed on BegoStone phantoms at different combinations of pulse energy (EP ) and frequency (F) to determine the optimal settings. Temperature changes and thermal injury risks were monitored using embedded thermocouples. Experiments were also performed on calcium oxalate monohydrate (COM) stones to validate the optimal settings.

RESULTS

High EP /low F settings demonstrated superior treatment efficiency compared to low EP /high F settings using the same power. Specifically, 0.8 J/12 Hz was the optimal setting, resulting in a twofold increase in treatment efficiency, a 39% reduction in energy expenditure per unit of ablated stone mass, a 35% reduction in residual fragments, and a 36% reduction in total procedure time compared to the 0.2 J/50 Hz setting for COM stones. Thermal injury risk assessment indicated that 10 W power settings with high EP /low F combinations remained below the threshold for tissue injury, while higher power settings (>10 W) consistently exceeded the safety threshold.

CONCLUSIONS

Our findings suggest that high EP /low F settings, such as 0.8 J/12 Hz, are optimal for TFL lithotripsy in the treatment of COM stones. These settings demonstrated significantly improved treatment efficiency with reduced residual fragments compared to conventional settings while keeping the thermal dose below the injury threshold. This study highlights the importance of using the high EP /low F combination with low power settings, which maximizes treatment efficiency and minimizes potential thermal injury. Further studies are warranted to determine the optimal settings for TFL for treating kidney stones with different compositions.

Thermal Safety Boundaries for Laser Power and Irrigation Rate During Ureteroscopy: In Vivo Porcine Assessment With a Ho:YAG Laser

OBJECTIVE

To map thermal safety boundaries during ureteroscopy (URS) with laser activation in two in vivo porcine subjects to better understand the interplay between laser power, irrigation rate, and fluid temperature in the collecting system.

METHODS

URS was performed in two in vivo porcine subjects with a prototype ureteroscope containing a thermocouple at its tip. Up to 6 trials of 60 seconds laser activation were carried out at each selected power setting and irrigation rate. Thermal dose was calculated for each trial, and laser power-irrigation rate parameter pairs were categorized based on number of trials that exceeded a thermal dose of 120 equivalent minutes.

RESULTS

The collecting fluid temperature was increased with greater laser power and slower irrigation rate. In the first porcine subject, 25 W of laser power could safely be applied if irrigation was at least 15 mL/min, and 48 W with at least 30 mL/min. Intermediate values followed a linear curve between these bounds. For the second subject, where the calyx appeared larger, 15 W laser power required 9 mL/min irrigation, 48 W required 24 mL/min, and intermediate points also followed a near-linear curve.

CONCLUSION

This study validates previous bench research and provides a conceptual framework for selection of safe laser lithotripsy settings and irrigation rates during URS with laser lithotripsy. Additionally, it provides insight and guidance for future development of thermal mitigation strategies and devices.

Retrograde intra renal surgery and safety: pressure and temperature. A systematic review

PURPOSE OF REVIEW

Retrograde intra renal surgery (RIRS) with laser lithotripsy represents the gold-standard to treat renal stones up to 20 mm. Controlling intraoperative parameters such as intrarenal pressure (IRP) and temperature (IRT) is mandatory to avoid complications. This article reviews advances in IRP and IRT over the last 2 years.

RECENT FINDINGS

We conducted a PubMed/Embase search and reviewed publications that include temperature and pressure during RIRS. Thirty-four articles have been published which met the inclusion criteria. Regarding IRP, a consensus has emerged to control IRP during RIRS, in order to avoid (barotraumatic and septic) complications. Several monitoring devices are under evaluation but none of them are clinically approved for RIRS. Ureteral access sheath, low irrigation pressure and occupied working channel help to maintain a low IRP. Robotic systems and suction devices would improve IRP intraoperative management and monitoring. IRT determinants are the irrigation flow and laser settings. Low power settings(<20 W) with minimal irrigation flow (5-10 ml/min) are sufficient to maintain low IRT and allows continuous laser activation.

SUMMARY

Recent evidence suggests that IRP and IRT are closely related. IRP depends on inflow and outflow rates. Continuous monitoring would help to avoid surgical and infectious complications. IRT depends on the laser settings and the irrigation flow.