Thermal effect of holmium laser lithotripsy under ureteroscopy

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.

Arterial pseudoaneurysm: a rare complication following laser lithotripsy-case series and literature review

OBJECTIVE

To perform a comprehensive narrative review that will examine the risk factors and treatment outcomes of arterial pseudoaneurysm following laser flexible ureteroscopy (F-URS).

METHODS

A retrospective case series and a review of literature was performed. Clinical records from three patients treated for postoperative arterial pseudoaneurysm from January of 2021 to November 2023 were identified. A comprehensive literature review was also performed. The MEDLINE and Scopus databases were searched. The analysis was made by a narrative synthesis.

RESULTS

Three cases of postoperative arterial pseudoaneurysm were included, one from our center, one from Dubai, UAE, and one from Barcelona. The literature review identified six case reports, two after endocorporeal laser lithotripsy with thulium fiber laser (TFL) and four with Ho:YAG laser. All cases, from our series and literature review, presented with macroscopic hematuria and used high-power laser settings. All cases were treated by selective embolization.

CONCLUSION

Ho:YAG or TFL lasers are both capable of causing arterial pseudoaneurysms following F-URS if high-power settings are used. Selective artery embolization continues to be the treatment of choice with good outcomes.

Assessing renal tissue temperature changes and perfusion effects during laser activation in an in vivo porcine model

INTRODUCTION

High fluid temperatures have been seen in both in vitro and in vivo studies with laser lithotripsy, yet the thermal distribution within the renal parenchyma has not been well characterized. Additionally, the heat-sink effect of vascular perfusion remains uncertain. Our objectives were twofold: first, to measure renal tissue temperatures in response to laser activation in a calyx, and second, to assess the effect of vascular perfusion on renal tissue temperatures.

METHODS

Ureteroscopy was performed in three porcine subjects with a prototype ureteroscope containing a temperature sensor at its tip. A needle with four thermocouples was introduced percutaneously into a kidney with ultrasound guidance to allow temperature measurement in the renal medulla and cortex. Three trials of laser activation (40W) for 60 s were conducted with an irrigation rate of 8 ml/min at room temperature in each subject. After euthanasia, three trials were repeated without vascular perfusion in each subject.

RESULTS

Substantial temperature elevation was observed in the renal medulla with thermal dose in two of nine trials exceeding threshold for tissue injury. The temperature decay time (t½) of the non-perfused trials was longer than in the perfused trials. The ratio of t½ between them was greater in the cortex than the medulla.

CONCLUSION

High-power laser settings (40W) can induce potentially injurious temperatures in the in vivo porcine kidney, particularly in the medullary region adjacent to the collecting system. Additionally, the influence of vascular perfusion in mitigating thermal risk in this susceptible area appears to be limited.

Laser safety, warnings, and limits in retrograde intrarenal surgery

OBJECTIVE

To analyze the current information about laser safety in retrograde intrarenal surgery (RIRS), focusing on the two main laser technologies that we use in urology, the holmium:yttrium-aluminum-garnet (Ho:YAG) laser, and the thulium fiber laser (TFL).

METHODS

Narrative overview of the most relevant articles published in MEDLINE and Scopus databases about this subject.

RESULTS

TFL and Ho:YAG laser at similar settings (0.2 J/40 Hz) have similar volume-averaged temperature increase and the average heating rate increase proportionally to laser power, especially when high frequencies are used. Recent preclinical data, comparing both laser technologies at different laser settings, agreed that when the delivered energy increases in expenses of higher frequencies, the thermal damage increases too. Higher frequencies, despite of the rise of temperature in the irrigation medium, can cause accidental thermal lasering lesions.

CONCLUSION

The use of low frequency settings and a proper irrigation is critical to avoid thermal injury in endoscopic laser lithotripsy. In addition, the use of laser safety eyeglasses is recommended in Ho:YAG and TFL ELL.

Temperature effect of Moses™ 2.0 during flexible ureteroscopy: an in vitro assessment

Introduction

One of the main issues related to the use of high-power lasers is the associated rise in temperature. The aim of this study was to characterize temperature variations with activation of the Moses™ 2.0 laser.

Material and methods

An in vitro experimental study was designed using a high-fidelity uretero-nephroscope simulation model to assess changes in temperature during intracorporeal laser lithotripsy. Renal and ureteral temperature records were obtained from the treatment of BegoStones positioned in the renal pelvis. Different laser settings over three time periods and two possible irrigation flow speeds were evaluated. We considered 43°C as the threshold since it is associated with denaturation of proteins. The Wilcoxon-Mann-Whitney test was used to assess quantitative variables and the Kruskal-Wallis test for categorical variables.

Results

The highest increase in intrarenal temperature was reached with 30 seconds of laser activation at a laser setting of 0.5 J/100 Hz (50 W) and a flow of 10 mL/min. Only 15 seconds of activation was sufficient for most settings to exceed 43°C. The ureteral temperature did not increase significantly, regardless of the combination of laser setting, time, or irrigation flow, except when 30 W was used for a 30 second period. Multivariate analysis showed that an irrigation flow of 20 mL/min produced an intrarenal temperature decrease of 4.7-9.2°C (p <0.001).

Conclusions

Use of high-power lasers, both for the ureter and kidney, should involve consideration of temperature increases evidenced in this study, due to the potential biological risk entailed.

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.

Renal pseudoaneurysm after holmium laser lithotripsy with flexible ureteroscopy: an unusual case report and literature review

Pseudoaneurysms of the renal arteries are caused by focal rupture or perforation of the arterial wall, resulting in local bleeding. Such pseudoaneurysms can be observed in conditions such as nodular polyarteritis, penetrating or closed renal injury, and medically induced injuries (such as renal puncture biopsy, percutaneous nephrostomy, or partial nephrectomy). Flexible ureteroscopy (FURS) is performed entirely through the urethra to prevent potentially severe kidney damage. Because of this, almost no renal parenchymal hemorrhage occurs after FURS laser lithotripsy. Only four cases had been documented in the literature as of December 2022. In this report, we describe a 53-year-old man with a history of recurrent kidney stones who underwent FURS laser lithotripsy for bilateral kidney stones. The procedure was smoothly performed, and no active bleeding occurred. However, the patient developed recurrent macroscopic hematuria after discharge from the hospital, and renal angiography revealed a pseudoaneurysm in the distal right kidney. The pseudoaneurysm was treated with selective arterial embolization. Serious complications of FURS surgery are rare, particularly the formation of pseudoaneurysms. We report the present case to bring this potential complication to the attention of urologists.

Temperature change during laser upper-tract endourological procedures: current evidence and future perspective

PURPOSE OF REVIEW

To examine the most recent data on temperatures produced during laser lithotripsy and to provide several strategies for maintaining lower values and reducing the risk of complications during endourological treatment.

RECENT FINDINGS

Endourologists have access to a wide range of alternatives with the help of the holmium: yttrium-aluminum-garnet (Ho:YAG), thulium: yttrium-aluminum-garnet (TM:YAG), and thulium fiber laser (TFL) that compose a robust and adaptable laser lithotripsy armamentarium. Nevertheless, the threat of thermal damage increases as the local temperature rises with high total power. Most endourologists are not familiar with normal and pathological temperature ranges, how elevated temperatures affect perioperative problems, or how to avoid them.

SUMMARY

Increased temperatures experienced during laser lithotripsy may affect the course of the healing process. All lasers display a safe temperature profile at energies below 40 W. At equal power settings, Ho:YAG, Tm:YAG, and TFL lasers change the temperature comparably. Shorter on/off laser activation intervals, chilled irrigation, open irrigation systems, and UASs all aid in maintaining acceptable temperatures.

Endourologic Procedures of the Upper Urinary Tract and the Effects on Intrarenal Pressure and Temperature

Introduction: Endourologic procedures, including ureteroscopy (URS) and percutaneous nephrolithotomy (PCNL), are associated with an elevation in intrarenal pressures (IRPs) and irrigation temperatures. Recent research has focused on methods to reduce IRP and irrigation temperatures, with the ultimate goal to limit the consequences associated with these deviations. The purpose of our study is to provide a narrative review on the effects of endourologic procedures on pressure and temperature and provide recommendations to minimize these changes. Methods: A literature review was performed using PubMed. The search was limited to English human and nonhuman studies. Abstracts were reviewed for inclusion in our narrative review. Results: Human and animal models suggest that URS and PCNL are associated with peak IRPs above a "safe" threshold. Strategies to minimize pressures focus on minimizing irrigation flow into the upper tract and maximizing flow out of the system. High IRP has been associated with postoperative pain and infectious complications. Elevated irrigation temperatures are associated with high-power lasers during URS. Strategies to minimize irrigation temperatures focus on maximizing irrigation flow during laser activation and minimizing thermal energies associated with lithotripsy. Conclusions: Rises in pressure and irrigation temperatures associated with endourologic procedures are becoming increasingly recognized in the urologic community. Human studies examining "safe" thresholds for IRP and irrigation temperatures are limited. Temperature- and pressure-sensing technologies will aid in identifying the clinical consequences of elevated IRPs and irrigation temperatures, resulting in strategies to minimize them.

Assessing critical temperature dose areas in the kidney by magnetic resonance imaging thermometry in an ex vivo Holmium:YAG laser lithotripsy model

PURPOSE

We aimed to assess critical temperature areas in the kidney parenchyma using magnetic resonance thermometry (MRT) in an ex vivo Holmium:YAG laser lithotripsy model.

METHODS

Thermal effects of Ho:YAG laser irradiation of 14 W and 30 W were investigated in the calyx and renal pelvis of an ex vivo kidney with different laser application times (t_L) followed by a delay time (t_D) of t_L/t_D = 5/5 s, 5/10 s, 10/5 s, 10/10 s, and 20/0 s, with irrigation rates of 10, 30, 50, 70, and 100 ml/min. Using MRT, the size of the area was determined in which the thermal dose as measured by the Cumulative Equivalent Minutes (CEM₄₃) method exceeded a value of 120 min.

RESULTS

In the calyx, CEM₄₃ never exceeded 120 min for flow rates ≥ 70 ml/min at 14 W, and longer t_L (10 s vs. 5 s) lead to exponentially lower thermal affection of tissue (3.6 vs. 21.9 mm²). Similarly at 30 W and ≥ 70 ml/min CEM₄₃ was below 120 min. Interestingly, at irrigation rates of 10 ml/min, t_L = 10 s and t_D = 10 s CEM₄₃ were observed > 120 min in an area of 84.4 mm² and 49.1 mm² at t_D = 5 s. Here, t_L = 5 s revealed relevant thermal affection of 29.1 mm² at 10 ml/min.

CONCLUSION

We demonstrate that critical temperature dose areas in the kidney parenchyma were associated with high laser power and application times, a low irrigation rate, and anatomical volume of the targeted calyx.

Generated temperatures and thermal laser damage during upper tract endourological procedures using the holmium: yttrium-aluminum-garnet (Ho:YAG) laser: a systematic review of experimental studies

PURPOSE

To perform a review on the latest evidence related to generated temperatures during Ho:YAG laser use, and present different tools to maintain decreased values, and minimize complication rates during endourological procedures.

METHODS

We performed a literature search using PubMed, Scopus, EMBASE, and Cochrane Central Register of Controlled Trials-CENTRAL, restricted to original English-written articles, including animal, artificial model, and human studies. Different keywords were URS, RIRS, ureteroscopy, percutaneous, PCNL, and laser.

RESULTS

Thermal dose (t43) is an acceptable tool to assess possible thermal damage using the generated temperature and the time of laser exposure. A t43 value of more than 120 min leads to a high risk of thermal tissue injury and at temperatures higher than 43 °C Ho:YAG laser use becomes hazardous due to an exponentially increased cytotoxic effect. Using open continuous flow, or chilled irrigation, temperatures remain lower than 45 °C. By utilizing high-power (> 40 W) or shorter laser pulse, temperatures rise above the accepted threshold, but adding a ureteral access sheath (UAS) helps to maintain acceptable values.

CONCLUSIONS

Open irrigation systems, chilled irrigation, UASs, laser power < 40 W, and shorter on/off laser activation intervals help to keep intrarenal temperatures at accepted values during URS and PCNL.

Pelvicalyceal Volume and Fluid Temperature Elevation During Laser Lithotripsy

BACKGROUND

While high-power laser systems facilitate successful ureteroscopic treatment of larger and more complex stones, they can substantially elevate collecting system fluid temperatures with potential thermal injury of adjacent tissue. The volume of fluid in which laser activation occurs is an important factor when assessing temperature elevation. The aim of this study was to measure fluid temperature elevation and calculate thermal dose from laser activation in fluid-filled glass bulbs simulating varying calyx/pelvis volumes.

MATERIALS AND METHODS

Glass bulbs of volumes 0.5, 2.8, 4.0, 7.0, 21.0, and 60.8 ml were submerged in a 16 L tank of 37˚C deionized water. A 230-µm laser fiber extending 5mm from the tip of a ureteroscope was positioned in the center of each glass bulb. Irrigation with 0, 8, 15, and 40 ml/min of room temperature DI water was applied. Once steady state temperature was achieved, a Ho:YAG laser was activated for 60 seconds at 40W (0.5J x 80Hz, SP). Temperature was measured from a thermocouple affixed to the external tip of the ureteroscope. Thermal dose was calculated using the Dewey and Sapareto t43 methodology.

RESULTS

The extent of temperature elevation and thermal dose from laser activation were inversely related to the volume of fluid in each model and the irrigation rate. The time to threshold of thermal injury was only 3 seconds for the smallest model (0.5ml) without irrigation but was not reached in the largest model (60.8ml) regardless of irrigation rate. Irrigation delivered at 40 ml/min maintained safe temperatures below the threshold of tissue injury in all models with 1 minute of continuous laser activation.

CONCLUSIONS

The volume of fluid in which laser activation occurs is an important factor in determining the extent of temperature elevation. Smaller volumes receive greater thermal dose and reach threshold of tissue injury more rapidly than larger volumes.

Single-use flexible ureteroscopes: how to choose and what is around the corner?

PURPOSE OF REVIEW

The pace of technology development with single-use endoscopy has led to a range of disposable ureteroscopes. We review the development of single-use scopes, deconstruct the basic design and functional characteristics of available devices, and discuss future directions for next-generation platforms.

RECENT FINDINGS

Currently available devices are differentiated on the basis of several core features. The optical, deflection and irrigation characteristics are marginally different with no device clearly superior in every category. Studies comparing single-use ureteroscopes in patients linked to outcomes are limited. The incorporation of next-generation technologies into these platforms include sensors to monitor intrarenal pressure and temperature, suction of fluid and fragments, and computer vision for artificial intelligence.

SUMMARY

Each ureteroscope has specific features that may be advantageous in different circumstances. Single-use devices could transform the ureteroscope from a visual conduit to a transformative surgical instrument that improves outcomes and reduces complications.

Temperature profiles of calyceal irrigation fluids during flexible ureteroscopic Ho:YAG laser lithotripsy

PURPOSE

To evaluate calyceal irrigation fluid temperature changes during flexible ureteroscopic Ho:YAG laser lithotripsy.

METHODS

Between May 2019 and January 2020, patients with kidney stones undergoing flexible ureteroscopic Ho:YAG laser lithotripsy were enrolled. A K-type thermocouple was applied for intraoperative temperature measurement. Laser was activated at different power (1 J/20 Hz and 0.5 J/20 Hz) and irrigation (0 ml/min, 15 ml/min and 30 ml/min) settings, temperature-time curve was drawn and time needed to reach 43 °C without irrigation was documented.

RESULTS

Thirty-two patients were enrolled in our study. The temperature-time curve revealed a quick temperature increase followed by a plateau. With 15 ml/min or 30 ml/min irrigation, 43 °C was not reached after 60 s laser activation at both 1 J/20 Hz and 0.5 J/20 Hz. At the power setting of 1 J/20 Hz and irrigation flow rate of 15 ml/min, the temperature rise was significantly higher than other groups. Without irrigation, the time needed to reach 43 °C at 1 J/20 Hz was significantly shorter than that at 0.5 J/20 Hz (8.84 ± 1.41 s vs. 13.71 ± 1.53 s).

CONCLUSION

Ho:YAG laser lithotripsy can induce significant temperature rise in calyceal fluid. With sufficient irrigation, temperatures can be limited so that a toxic thermal dose is not reached, when irrigation is closed, the temperature increased sharply and reached 43 °C in a few seconds.

Thermal effect of holmium laser during ureteroscopic lithotripsy

Background

Holmium laser lithotripsy is the most common technique for the management of ureteral stone. Studies founded that holmium laser firing can produce heat which will cause thermal injury towards ureter. The aim of our current study is to explore factors affecting thermal effect of holmium laser during ureteroscopic lithotripsy.

Methods

An in vitro experimental model is design to simulate the ureteroscopic lithotripsy procedure. Different laser power settings (10w (0.5JX20Hz, 1.0 JX10Hz), 20w (1.0 JX20Hz, 2.0 JX10Hz), 30w (1.5JX20Hz, 3.0 JX10Hz)) with various firing time (3 s, 5 s, 10s) and irrigation flow rates(10 ml/min, 15 ml/min, 20 ml/min and 30 ml/min) were employed in the experiment. The temperature around the laser tip was recorded by thermometer.

Results

The temperature in the “ureter” rises significantly with the increasing laser power, prolonging firing time and reducing irrigation flow. The highest regional temperature is 78.0 °C at the experimental set-up, and the lowest temperature is 23.5 °C. Higher frequency setting produces more heat at the same power. Laser power < =10w, irrigation flow> = 30 ml/min and “high-energy with low-frequency” can permit a safe working temperature.

Conclusion

We clarify that the thermal effect of holmium laser is related with both laser working parameters and irrigation flow. The proper setting is the key factor to ensure the safety during ureteroscopic holmium laser lithotripsy.