Effect of Chilled Irrigation on Caliceal Fluid Temperature and Time to Thermal Injury Threshold During Laser Lithotripsy: In Vitro Model

Getting hot in here! Comparison of Holmium vs. thulium laser in an anatomic hydrogel kidney model

As laser technology has advanced, high-power lasers have become increasingly common. The Holmium: yttrium-aluminum-garnet (Ho:YAG) laser has long been accepted as the standard for laser lithotripsy. The thulium fiber laser (TFL) has recently been established as a viable option. The aim of this study is to evaluate thermal dose and temperature for the Ho:YAG laser to the TFL at four different laser settings while varying energy, frequency, operator duty cycle (ODC). Utilizing high-fidelity, 3D-printed hydrogel models of a pelvicalyceal collecting system (PCS) with a synthetic BegoStone implanted in the renal pelvis, laser lithotripsy was performed with the Ho:YAG laser or TFL. At a standard power (40W) and irrigation (17.9 ml/min), we evaluated four different laser settings with ODC variations with different time-on intervals. Temperature was measured at two separate locations. In general, the TFL yielded greater cumulative thermal doses than the Ho:YAG laser. Thermal dose and temperature were typically greater at the stone when compared away from the stone. Regarding the TFL, there was no general trend if fragmentation or dusting settings yielded greater thermal doses or temperatures. The TFL generated greater temperatures and thermal doses in general than the Ho:YAG laser with Moses technology. Temperatures and thermal doses were greater closer to the laser fiber tip. It is inconclusive as to whether fragmentation or dusting settings elicit greater thermal loads for the TFL. Energy, frequency, ODC, and laser-on time significantly impact thermal loads during ureteroscopic laser lithotripsy, independent of power.

WATTS happening? Evaluation of thermal dose during holmium laser lithotripsy in a high-fidelity anatomic model

PURPOSE

To evaluate the thermal profiles of the holmium laser at different laser parameters at different locations in an in vitro anatomic pelvicalyceal collecting system (PCS) model. Laser lithotripsy is the cornerstone of treatment for urolithiasis. With the prevalence of high-powered lasers, stone ablation efficiency has become more pronounced. Patient safety remains paramount during surgery. It is well recognized that the heat generated from laser lithotripsy has the potential to cause thermal tissue damage.

METHODS

Utilizing high-fidelity, 3D printed hydrogel models of a PCS with a synthetic BegoStone implanted in the renal pelvis, laser lithotripsy was performed with the Moses 2.0 holmium laser. At a standard power (40 W) and irrigation pressure (100 cm H2O), we evaluated operator duty cycle (ODC) variations with different time-on intervals at four different laser settings. Temperature was measured at two separate locations-at the stone and away from the stone.

RESULTS

Temperatures were highest closest to the laser tip with a decrease away from the laser. Fluid temperatures increased with longer laser-on times and higher ODCs. Thermal doses were greater with increased ODCs and the threshold for thermal injury was reached for ODCs of 75% and 100%.

CONCLUSION

Temperature generation and thermal dose delivered are greatest closer to the tip of the laser fiber and are not dependent on power alone. Significant temperature differences were noted between four laser settings at a standardized power (40 W). Temperatures can be influenced by a variety of factors, such as laser-on time, operator duty cycle, and location in the PCS.

Evaluation of a novel circulation system for ureteroscopic laser lithotripsy in vitro

PURPOSE

To evaluate the cooling effect and other advantages of a novel circulation system for ureteroscopic holmium laser lithotripsy (URSL) in a standardized in vitro model.

MATERIALS AND METHODS

The novel circulation system was assembled by connecting a 4Fr ureteral catheter and a filter. Trails were divided into a new URSL group and a conventional URSL group. First, different power settings (18-30 W) of the holmium laser and irrigation flow rates (20-50 mL/min) were used to evaluate the thermal effect on the lithotripsy site of all groups. Then, renal pelvic temperature and pressure were assessed during URSL at a power of 1.5 J/20 Hz and irrigation flow rates of (20-50 mL/min). Finally, the whole process of lithotripsy was performed at 1.5 J/20 Hz (operator duty cycle ODC: 50%) with an irrigation flow rate of 30 mL/min. The time required for lithotripsy, visual field clarity, and stone migration were observed.

RESULTS

Temperature of the lithotripsy point was significantly lower in the new URSL group than in the conventional group (P < 0.05) with irrigation rates (20, 30 mL/min). The renal pelvic pressure of the new group was significantly lower than that of the conventional group in which intrarenal hypertension developed at an irrigation rate of 50 ml/min. The new group had better visual clarity and lesser stone upward migration when lithotripsy was performed at 1.5 J/20 Hz and 30 ml/min.

CONCLUSION

The novel circulation system is more effective in reducing the thermal effects of URSL, pelvic pressure, stone upward migration, and improving the visual clarity of the operative field.

The heat is on: the impact of excessive temperature increments on complications of laser treatment for ureteral and renal stones

OBJECTIVE

Technological advancements in the field of urology have led to a paradigm shift in the management of urolithiasis towards minimally invasive endourological interventions, namely ureteroscopy and percutaneous nephrolithotomy. However, concerns regarding the potential for thermal injury during laser lithotripsy have arisen, as studies have indicated that the threshold for cellular thermal injury (43 °C) can be exceeded, even with conventional low-power laser settings. This review aims to identify the factors that contribute to temperature increments during laser treatment using current laser systems and evaluate their impact on patient outcomes.

MATERIALS AND METHODS

To select studies for inclusion, a search was performed on online databases including PubMed and Google Scholar. Keywords such as 'temperature' or 'heat' were combined with 'lithotripsy', 'nephrolithotomy', 'ureteroscopy', or 'retrograde intrarenal surgery', both individually and in various combinations.

RESULTS

Various strategies have been proposed to mitigate temperature rise, such as reducing laser energy or frequency, shortening the duration of laser activation, increasing the irrigation fluid flow rate, and using room temperature or chilled water for irrigation. It is important to note that higher irrigation fluid flow rates should be approached cautiously due to potential increases in intrarenal pressure and associated infectious complications. The utilization of a ureteral access sheath (UAS) may offer benefits by facilitating irrigation fluid outflow, thereby reducing intrapelvic pressure and intrarenal fluid temperature.

CONCLUSION

Achieving a balance between laser power, duration of laser activation, and irrigation fluid rate and temperature appears to be crucial for urologists to minimize excessive temperature rise.

Temperature changes of renal calyx during high-power flexible ureteroscopic Moses holmium laser lithotripsy: a case analysis study

PURPOSE

The risk of thermal damage increases with the introduction of high-power lasers during holmium laser lithotripsy. This study aimed to quantitatively evaluate the temperature change of renal calyx in the human body and the 3D printed model during high-power flexible ureteroscopic holmium laser lithotripsy and map out the temperature curve.

METHODS

The temperature was continuously measured by a medical temperature sensor secured to a flexible ureteroscope. Between December 2021 and December 2022, willing patients with kidney stones undergoing flexible ureteroscopic holmium laser lithotripsy were enrolled. High frequency and high-power settings (24 W, 80 Hz/0.3 J and 32 W, 80 Hz/0.4 J) were performed for each patient with room temperature (25 °C) irrigation. In the 3D printed model, we studied more holmium laser settings (24 W, 80 Hz/0.3 J, 32 W, 80 Hz/0.4 J and 40 W, 80 Hz/0.4 J) with warmed (37 °C) and room temperature (25 °C) irrigation.

RESULTS

Twenty-two patients were enrolled in our study. With 30 ml/min or 60 ml/min irrigation, the local temperature of the renal calyx did not reach 43 °C in any patient under 25 °C irrigation after 60 s laser activation. There were similar temperature changes in the 3D printed model with the human body under the irrigation of 25 °C. Under the irrigation of 37 °C, the temperature rise slowed down, but the temperature in the renal calyces was close to or even exceeded the 43 °C at the setting of 32 W, 30 ml/min and 40 W, 30 ml/min after continuing laser activation.

CONCLUSION

In the irrigation of 60 ml/min, the temperature in the renal calyces can still be maintained within a safe range after continuous activation of a holmium laser up to 40 W. However, continuous activation of 32 W or higher power holmium laser in the renal calyces for more than 60 s in the limited irrigation of 30 ml/min can cause excessive local temperature, in such situation room temperature perfusion at 25 ℃ may be a relatively safer option.

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.

Tissue thermal effect during lithotripsy and tissue ablation in endourology: a systematic review of experimental studies comparing Holmium and Thulium lasers

PURPOSE

We looked into the Thulium: yttrium-aluminum-garnet (TM:YAG), Thulium Fibre laser (TFL) and Holmium: yttrium-aluminum-garnet (Ho:YAG) thermal laser tissue effect during lithotripsy and tissue ablation.

METHODS

We performed a PubMed, Scopus, EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL) search.

RESULTS

During lithotripsy, the Ho:YAG generated temperatures from 24 to 68.7 °C at powers < 20 W, the Tm:YAG from 43.7 °C at 30 W to 68 °C at powers < 20 W, and the TFL from 33 to 40.46 °C. During ablation, the Ho:YAG and continuous wave (cw) Tm:YAG tissue incision depths ranged from 0.08 to 2.26 mm, and from 0.28 to 3.22 mm. The Ho:YAG and Tm:YAG vaporization areas ranged from 0.044 to 0.078 mm² and from 0.050 to 0.078 mm³ and their coagulation zones were 0.075 mm² and 0.125 mm³ respectively. Ho:YAG and Tm:YAG laser damage zones ranged from 0.093 to 2.6 mm³ and from 0.207 to 0.98 mm³ respectively. The TFL incision depth ranged from 0.04 to 5.7 mm. The cw and SuperPulsed (SP) vaporization volumes ranged from 8 to 28.2 mm³/s and from 4 to 11 mm³/s. TFL coagulation depth and coagulation zone ranged from zero to 1.1 mm, 2.2 to 5.1 mm³ in SP mode and from 7.7 to 18.1 mm³ in cw mode.

CONCLUSION

During lithotripsy all lasers caused similar temperature changes and had a safe temperature profile at < 40 W. During tissue ablation, Ho:YAG has a deeper incision depth, while cwTm:YAG and cwTFL have broader coagulation and total laser areas.

Thulium Fiber Laser Behavior on Tissue During Upper- and Lower-Tract Endourology

PURPOSE OF REVIEW

To present the latest evidence on thulium fiber laser (TFL) effects on tissue, during lithotripsy and ablation, emphasizing on generated temperatures, thermal damage thresholds, incision depths, areas of coagulation, and laser damage.

RECENT FINDINGS

Lasers are frequently utilized during endoscopic treatment of different urological conditions. The holmium:yttrium-aluminum-garnet (Ho:YAG) is most frequently used for various types of stones and soft tissue. The TFL has been recently introduced, offering several advantages. However, its activity on tissue during upper and lower tract endourology is poorly understood. At equivalent power settings, TFL and Ho:YAG generate similar temperature changes during lithotripsy. TFL has a shallow incision depth during tissue ablation. Compared to SP TFL, (cw) TFL results in a broader coagulation zone, whereas SP TFL gives of Ho:YAG-similar incision, and (cw) TFL offers a quick, precise cut with more carbonization.

A Practical Guide for Intra-Renal Temperature and Pressure Management during Rirs: What Is the Evidence Telling Us

INTRODUCTION

One of the main limitations of Ho:YAG lithotripsy is represented by its advancement speed. The need for faster lithotripsy has led to the introduction of high-power laser equipment. This general trend in increasing Ho:YAG lithotripsy power has certain points that deserve to be considered and analyzed. The objective is to carry out a narrative review on intrarenal temperature and pressure during ureteroscopy.

METHODS

A literature search using PUBMED database from inception to December 2021 was performed. The analysis involved a narrative synthesis.

RESULTS

Using more power in the laser correlates with an increase in temperature that can be harmful to the kidney. This potential risk can be overcome by increasing either the irrigation inflow or outflow. Increasing irrigant flow can lead to high intrarenal temperature (IRP). The factors that allow the reduction of intrarenal pressure are a low irrigation flow, the use of a ureteral access sheath of adequate diameter according to the equipment used, and the occupation of the working channel by the laser or basket.

CONCLUSION

To maintain a safe temperature profile, it has been proposed to use chilled irrigation fluid, intermittent laser activation or to increase irrigation flow. This last recommendation can lead to increased IRP, which can be overcome by using a UAS. Another option is to use low power laser configurations in order to avoid temperature increases and not require high irrigation flows.

The effect of prolonged laser activation on irrigation fluid temperature: an in vitro experimental study

PURPOSE

To investigate the effect of prolonged laser activation on irrigation fluid temperature by varying the power settings flow rate (10-30 ml/min).

MATERIALS AND METHODS

An experimental study using a 20 ml syringe, 12/14 ureteral access sheath, a dual-lumen catheter and a thermocouple was performed. The laser was fired with 12 W (0.3 J × 40 Hz), 40 W (1 J × 40 Hz), 60 W (1.5 J × 40 Hz) using Quanta Ho 150 W (Quanta System, Samarate, Italy). All trials were performed with fluid outflow rate of 10, 20 and 30 ml/min with the fixed fluid volume at 10 ml.

RESULTS

Continuous laser activation for 10 min with the outflow rate of 10 ml/min using only 12 W resulted to continuous temperature rise to as high as 83 °C. Similar rise of temperatures were observed for 40 W and 60 W with 10 ml/min outflow rate with intermittent laser activation. With 20 and 30 ml/min outflow rates the maximum temperatures for all power settings were below the threshold (< 43 °C). However, the time to reach the same total emitted energy was 60% and 40% shorter 60 W and 40 W, respectively.

CONCLUSION

Our study found that continuous laser activation with as less as 12 W using 10 ml/min outflow rate increased the irrigation fluid temperature above the threshold only after 1 min. In the current experimental setup, with the fluid outflow rate of 20 and 30 ml/min safe laser activation with 60 W and 40 W (temperature < 43 °C) can be achieved reaching the same total emitted energy as with 12 W in significantly shorter time period.

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.

Chilled irrigation for control of temperature elevation during ureteroscopic laser lithotripsy: in vivo porcine model

INTRODUCTION

Multiple studies have shown significant heating of fluid within the urinary collecting system with high-power laser settings. Elevated fluid temperatures may cause thermal injury and tissue damage unless appropriately mitigated. A previous in vitro study demonstrated that chilled (4 °C) irrigation slowed temperature rise, decreased plateau temperature, and lowered thermal dose during laser activation with high-power settings. We sought to evaluate the thermal effects of chilled, room temperature, and warmed irrigation during ureteroscopy with laser activation in an in vivo porcine model.

MATERIALS AND METHODS

Seven female Yorkshire cross pigs (45-55 kg) were anesthetized and positioned supine. Retrograde ureteroscopy was performed with a thermocouple affixed 5 mm from the distal end of the ureteroscope. In two pigs a holmium:YAG laser was activated for 60 seconds at irrigation rates of 8 ml/min, 12 ml/min, and 15 ml/min with chilled, room temperature, or warmed irrigation. In five pigs core body temperature was recorded for one hour with or without continuous chilled irrigation at 15 ml/min.

RESULTS

At irrigation rates ≥ 12 ml/min, temperature curves appeared uniformly offset, warmed > room temperature > chilled irrigation. The threshold of thermal tissue injury was reached during laser activation for all irrigation temperatures at 8 ml/min. The threshold was not reached with chilled irrigation at 12 ml/min or 15 ml/min, or with room temperature irrigation at 15 ml/min. The threshold was exceeded at all irrigation rates with warmed irrigation. There was no significant change in core body temperature after delivering chilled irrigation at 15 ml/min compared with no irrigation for 60 minutes.

CONCLUSION

Irrigation with chilled saline solution during ureteroscopic laser lithotripsy slows temperature rise, lowers peak temperature, and lengthens the time to thermal injury compared to irrigation with room temperature or warmed saline solutions. Core body temperature was not significantly impacted by chilled irrigation.

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.

Patterns of Laser Activation During Ureteroscopic Lithotripsy: Effects on Caliceal Fluid Temperature and Thermal Dose

Introduction: Characterizing patterns of laser activation is important for assessing thermal dose during laser lithotripsy. The objective of this study was twofold: first, to quantify the range of operator duty cycle (ODC) and pedal activation time during clinical laser lithotripsy procedures, and second, to determine thermal dose in an in vitro caliceal model when 1200 J of energy was applied with different patterns of 50% ODC for 60 seconds. Methods: Data from laser logs of ureteroscopy cases performed over a 3-month period were used to calculate ODC (lasing time/lithotripsy time). Temporal and rolling 1-minute average power tracings were generated for each case. In vitro experiments were conducted using a 21 mm diameter glass bulb in a 37°C water bath, simulating a renal calix. A LithoVue ureteroscope with attached thermocouple was inserted and 8 mL/min irrigation was delivered with a 242 μm laser fiber within the working channel. In total, 1200 J of laser energy was applied in five different patterns at 20 W average power for 60 seconds. Thermal dose was calculated using the Sapareto and Dewey t₄₃ method. Results: A total of 63 clinical cases were included in the analysis. Mean ODC was 32% overall and 63% during the 1-minute of greatest energy delivery. Mean time of pedal activation was 3.6 seconds. In vitro studies revealed longer pedal activation times produced higher peak temperature and thermal dose. Thermal injury threshold was reached in 9 seconds when 40 W was applied at 50% ODC with laser activation patterns of 30 seconds on/off and 15 seconds on/off. Conclusion: ODC was quantified from clinical laser lithotripsy cases: 32% overall and 63% during 1-minute of peak power. Time of pedal activation is an important factor contributing to fluid heating and thermal dose. Awareness of these concepts is necessary to reduce risk of thermal injury during laser lithotripsy procedures.