Laser Heating of Fluid With and Without Stone Ablation: In Vitro Assessment

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

Objective: The primary aim of the study was to explore intrarenal temperatures (IRTs) during flexible ureteroscopic laser lithotripsy (FURSL). The secondary aim was to investigate the correlation between temperatures and renal pelvis anteroposterior diameter (APD). Materials and Methods: From February 2023 to June 2023, 10 patients with an indwelling nephrostomy tube (NT) undergoing FURSL were enrolled in the study. Sheathless FURSL was performed using gravitational irrigation (23°C) at 60 cm. A sterile K-type thermocouple was inserted through the NT. Temperatures were recorded for 120 seconds with continuous laser activation and for another 60 seconds after deactivation. Thulium fiber laser delivered energy using a 150 μm fiber and incremental power settings of 5, 10, 20, and 30 W. The laser was deactivated whenever the IRT reached 43°C. Results: IRT correlated directly to power settings. Each time the power settings were increased, the temperature rose significantly. The increase in average peak temperature was 2.6°C between 5 and 10 W (p < 0.001), 3.4°C between 10 and 20 W (p < 0.001), and 2.5°C between 20 and 30 W (p < 0.001). Temperatures reached 43°C in three patients applying 20 W and in eight patients applying 30 W. The shortest activation-time until threshold was 12 and 28 seconds with 30 and 20 W settings, respectively. When reaching 43°C, temperatures remained above this threshold for an additional 29 seconds on average. There was a significant correlation between IRT and renal APD. For example, when 10 W was applied in the setting of APD ≤20 mm, the recorded temperature was on average 2.3°C higher compared with APD >20 mm, with the same power settings applied, p < 0.001. Conclusion: During FURSL, IRT correlates directly with power settings and is inversely correlated with renal pelvic APD. Using a sheathless approach, power settings ≥20 W should arguably be avoided, especially in the context of a nondilated renal pelvis. ClinicalTrials: The study was registered on ClinicalTrials.gov (NCT05677425).

Shock waves generated by toroidal bubble collapse are imperative for kidney stone dusting during Holmium:YAG laser lithotripsy

Holmium:yttrium-aluminum-garnet (Ho:YAG) laser lithotripsy (LL) has been the treatment of choice for kidney stone disease for more than two decades, yet the mechanisms of action are not completely clear. Besides photothermal ablation, recent evidence suggests that cavitation bubble collapse is pivotal in kidney stone dusting when the Ho:YAG laser operates at low pulse energy (Ep) and high frequency (F). In this work, we perform a comprehensive series of experiments and model-based simulations to dissect the complex physical processes in LL. Under clinically relevant dusting settings (Ep = 0.2 J, F = 20 Hz), our results suggest that majority of the irradiated laser energy (>90 %) is dissipated by heat generation in the fluid surrounding the fiber tip and the irradiated stone surface, while only about 1 % may be consumed for photothermal ablation, and less than 0.7 % is converted into the potential energy at the maximum bubble expansion. We reveal that photothermal ablation is confined locally to the laser irradiation spot, whereas cavitation erosion is most pronounced at a fiber tip-stone surface distance about 0.5 mm where multi foci ring-like damage outside the thermal ablation zone is observed. The cavitation erosion is caused by the progressively intensified collapse of jet-induced toroidal bubble near the stone surface (<100 μm), as a result of Raleigh-Taylor and Richtmyer-Meshkov instabilities. The ensuing shock wave-stone interaction and resultant leaky Rayleigh waves on the stone surface may lead to dynamic fatigue and superficial material removal under repeated bombardments of toroidal bubble collapses during dusting procedures in LL.

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.

Comparison of Low-Power vs High-Power Holmium lasers in pediatric RIRS outcomes

OBJECTIVES

to compare the outcomes of using low-power (up to 30W) vs high-power (up to 120W) holmium lasers in retrograde intrarenal surgery (RIRS) in children and to analyse if lasering techniques and the use of access sheath have any influence on the outcomes.

METHODS

We retrospectively reviewed data from 9 centres of children who underwent RIRS with holmium laser for the treatment of kidney stones between January 2015 and December 2020. Patients were divided into two groups: high-power and low-power holmium laser. Clinical, perioperative variables and complications were analysed. Outcomes were compared between groups using Student's T-test for continuous variables, and Chi-square and Fisher's exact test for categorical variables. A multivariable logistic regression analysis model was also performed.

RESULTS

314 patients were included. A high-power and low-power holmium laser was used in 97 and 217 patients, respectively. Clinical and demographic variables were comparable between both groups, except for stone size where the low-power group treated larger stones (mean 11.11 mm vs 9.70 mm; p 0.018). In the high-power laser group, a reduction in surgical time was found (mean 64.29 min vs 75.27 min; p 0.018) with a significantly higher stone-free rate (SFR) (mean 81.4% vs 59%; p <0.001). We found no statistical differences in complication rates. The multivariate logistic regression model showed lower SFR in the low-power holmium group, especially with larger (p = 0.011) and multiple stones (p < 0.001).

CONCLUSION

Our real-world pediatric multicenter study favours high-power holmium laser and establishes its safety and efficacy in children.  .