Evaluation of Contemporary Holmium Laser Fibers for Performance Characteristics

Comparative Results of Vocal Fold Injury According to the Fiber-Based Laser in a Rabbit Vocal Fold Model

OBJECTIVES

We assessed the safety of flexible fiber-based lasers including the potassium-titanyl-phosphate (KTP), CO2, and Holmium lasers using a rabbit vocal fold model and provided the safety evidence of laser before human clinical trial.

METHODS

In all, 120 male New Zealand white rabbits were used. Each laser was used to induce acute and chronic vocal fold injuries in 40 rabbits. The same laser energy with the same intensity and frequency were used in all cases, and we evaluated outcomes via surface scanning electron microscopy (SEM) and histological examination 1 day after injury. Histological and high-speed vocal fold vibration examinations were evaluated 1 month after injury. Surface injury roughness grading was done via SEM, and the Acute injury ratio and lamina propria (LP) ratio were also calculated. The dynamic glottal gap was measured through functional analyses based on recordings from a high-speed digital camera.

RESULTS

The Holmium laser caused significantly more vocal fold damage than did the KTP and CO2 lasers as revealed by SEM and evaluation of acute and chronic injuries. Functional analysis with high-speed digital camera indicated that the holmium laser reduced dynamic glottal gap compared with the normal vocal fold, where the other lasers did not.

CONCLUSIONS

The histological and functional analyses of rabbit vocal fold experiments indicated that fiber-based laryngeal laser surgery for vocal fold lesions could be performed relatively safely using a KTP or CO2 laser.

Preliminary experience in endoscopic section of posterior urethral valves using the Holmium: YAG laser

INTRODUCTION

Refinements in endoscopic instrumentation, the widespread popularization of endourology and the minimal invasiveness of endoscopic approaches have led to evolving interest in expanding applications for their use and now include incision of posterior urethral valves (PUV). We aimed to report our paediatric experience of PUV incision with Holmium:YAG laser updating of the endoscopic technique, how we set parameters for the laser energy and provide some tips and tricks to increase the likelihood of completing treatment.

METHODS

A monocentric, prospective, continuous series of boys with PUV were treated endoscopically using a Holmium: YAG laser (1.2 J, 20 Hz, 800 μs). Feasibility was evaluated using operative time in minutes, spontaneous normal micturition after bladder catheter removal, and the duration of bladder catheterization in days in the absence of satisfactory micturition. Peri-operative complications were recorded. A VCUG was performed at 6 weeks postoperatively to exclude residual valves.

RESULTS

Since September 2018, 18 children with PUV were included. The median age at the time of endoscopic laser incision was 12 days (1 day-5 years). The median operative duration was 28 min (17-35). The urinary catheter was systematically removed on the first postoperative day. There were no intraoperative or anaesthesia-related complications. More specifically, no urethral injuries and no bleeding were recorded. No incomplete VUP incision was found on follow-up VCUG, and no endoscopic revision was necessary thus far, with a median follow-up of 44 months (6 months-60 months).

DISCUSSION

The use of the Holmium: YAG laser introduces new perspectives in the treatment of PUV. Its mechanism of action is considered a photothermic effect with a vapourization effect. The laser energy released by the Holmium: YAG source has a short tissue penetration distance and is strongly absorbed in an aqueous environment and therefore limits thermal tissue damage and favours early tissue re-epithelialization, reducing the risk of urethral stricture and decreasing postoperative oedema. The use of the laser in "incision" mode is the setting that most solicits the capacities of the laser (high energy, high frequency, and long pulse). The use of laser energy has the advantage of allowing tissue vapourization while ensuring maximal haemostasis and the possibility of introducing the laser fibre through the working channels of small, 6-Fr paediatric endoscopes.

CONCLUSION

In our experience, endoscopic PUV incision using the Holmium: YAG laser appears to be a safe and efficient technique.

Laser accessories: surgical fibers, strippers, cleavers, and protective glasses

PURPOSE OF REVIEW

This review provides most recent findings and developments relating to surgical laser fibers, strippers, cleavers, and protective glasses.

RECENT FINDINGS

The smallest core diameter that can be used with Holmium:YAG lasers is 200 μm. Smaller core diameter fibers can be used with the Thulium fiber laser and offer better flexibility and lower risk of fracture, at the risk of greater burnback effect. Misleading discrepancies between the true diameter of laser fibers and their packaging labels must be considered. Fiber tip degradation from the burnback occurs within few minutes, thus questioning the need for time-consuming fiber tip reprocessing with fiber strippers and special cleaving tools. This shortcoming also applies to instrument-protecting ball-tip fibers. Cleavage of fiber tips through their protective jackets ('coated tips') is a cheaper alternative for instrument protection, additionally offering better visual control of the fiber tip. Third-generation side-firing greenlight laser fibers are still prone to rapid deterioration. Laser eyewear does not seem necessary for Holmium:YAG applications, whereas laser-specific protective glasses should be worn for greenlight laser applications.

SUMMARY

With better understanding of laser accessories, practicing urologists may tailor their practice to reach optimal efficacy and safety for Holmium:YAG, Thulium fiber laser and Greenlight laser applications.

Comparison of Holmium:YAG and Thulium Fiber Lasers on the Risk of Laser Fiber Fracture

Objectives: To compare the risk of laser fiber fracture between Ho:YAG laser and Thulium Fiber Laser (TFL) with different laser fiber diameters, laser settings, and fiber bending radii. METHODS: Lengths of 200, 272, and 365 μm single use fibers were used with a 30 W Ho:YAG laser and a 50 W Super Pulsed TFL. Laser fibers of 150 µm length were also tested with the TFL only. Five different increasingly smaller bend radii were tested: 1, 0.9, 0.75, 0.6, and 0.45 cm. A total of 13 different laser settings were tested for the Ho:YAG laser: six fragmentation settings with a short pulse duration, and seven dusting settings with a long pulse duration. A total of 33 different laser settings were tested for the TFL. Three laser settings were common two both lasers: 0.5 J × 12 Hz, 0.8 J × 8 Hz, 2 J × 3 Hz. The laser was activated for 5 min or until fiber fracture. Each measurement was performed ten times. Results: While fiber failures occurred with all fiber diameters with Ho:YAG laser, none were reported with TFL. Identified risk factors of fiber fracture with the Ho:YAG laser were short pulse and high energy for the 365 µm fibers (p = 0.041), but not for the 200 and 272 µm fibers (p = 1 and p = 0.43, respectively). High frequency was not a risk factor of fiber fracture. Fiber diameter also seemed to be a risk factor of fracture. The 200 µm fibers broke more frequently than the 272 and 365 µm ones (p = 0.039). There was a trend for a higher number of fractures with the 365 µm fibers compared to the 272 µm ones, these occurring at a larger bend radius, but this difference was not significant. Conclusion: TFL appears to be a safer laser regarding the risk of fiber fracture than Ho:YAG when used with fibers in a deflected position.

Basic and advanced technological evolution of laser lithotripsy over the past decade: An educational review by the European Society of Urotechnology Section of the European Association of Urology

Laser disintegration of urinary stones is a cornerstone of urolithiasis treatment in the modern era. Despite the wide clinical use of stone lasers, basic and advanced technological achievements and developments are difficult to comprehend and interpret by the average urologist. A descriptive analysis of laser production and stone disintegration mechanisms was performed. We focused on physics of modern types of lithotripters, the construction of laser fibers, laser parameters, new modes, settings, and lithotripsy techniques. The main principle of laser emission remains the same since the first emitting laser was produced. Peak power density and short interaction time lead to photothermal effects responsible for stone disintegration. Modern lithotripters such as Holmium: YAG (low/high power, Moses technology) and thulium fiber laser show basic construction differences with the physical properties of the latter being superior, at least in in vitro studies. By adjusting lasing parameters, a wide spectrum of stone ablation from fragmentation to dusting can be achieved. New technology allows for the production of real dust. Knowledge of laser fiber construction and physical properties are useful in marketing and clinical use. Urologists should understand the physical and physiological background of the lasers used in their everyday practice for stone fragmentation.

Advanced application of holmium: YAG laser combined ALA-PDT for the treatment of refractory condylomata acuminata in anal canal

BACKGROUND

Anal canal condylomata acuminata is a disease caused by the human papilloma virus. Conventional cauterizing laser treatment cannot achieve a satisfactory result owing to a high recurrence rate, and the application of 5-aminolaevulinic acid-photodynamic therapy (ALA-PDT) also has limitations in the anal canal. Holmium yttrium aluminum garnet (Ho: YAG) laser with fiber is found to be effective at removing canal lesions, and may create suitable conditions for ALA-PDT. We aim to investigate the feasibility of Ho: YAG laser combined with ALA-PDT and to explore a more optimal therapy in refractory anal canal condylomata.

METHODS

Data of 37 patients with anal canal condylomata (number of warts≥ 10 lesions) from May 2017 to March 2019 were reviewed. In total 17 cases were treated with Ho: YAG laser plus ALA-PDT, and 20 patients treated with CO₂ laser plus ALA-PDT were selected as control. Wart clearance and recurrence rates were evaluated as well as laser complications.

RESULTS

Most warts (88.23 %) were removed after a session of Ho: YAG laser pretreatment. The average number of laser sessions required to clear all warts was 1.94 in the Ho: YAG laser plus ALA-PDT group. Meanwhile, no wound infections or defecation disfunctions were found. Ho: YAG laser with ALA-PDT could significantly reduce wart recurrence rates (17.6 %) in comparison with CO₂ laser with ALA-PDT (55 %).

CONCLUSIONS

Ho: YAG laser combined with ALA-PDT raised the cure rate of refractory anal canal condylomata and has important guidance implications for clinical application.

Advances in Lasers for the Treatment of Stones-a Systematic Review

PURPOSE OF REVIEW

Laser lithotripsy is increasingly used worldwide and is a continuously evolving field with new and extensive research being published every year.

RECENT FINDINGS

Variable pulse length Ho:YAG lithotripters allow new lithotripsy parameters to be manipulated, and there is an effort to integrate new technologies into lithotripters. Pulsed thulium lasers seem to be a viable alternative to holmium lasers. The performance of similar laser fibers varies from manufacturer to manufacturer. Special laser fibers and "cleaving only" fiber tip preparation can be beneficial for the lithotripsy procedure. Different laser settings and the surgical technique employed can have significant impact on the success of laser lithotripsy. When safely done, complications of laser lithotripsy are rare and concern the endoscopic nature of procedure, not the technology itself, making laser lithotripsy one of the safest tools in urology. Laser lithotripsy has had several new developments and more insight has been gained in recent years with many more advances expected in the future.

Impact of the Curve Diameter and Laser Settings on Laser Fiber Fracture

OBJECTIVE

To analyze the risk factors for laser fiber fractures when deflected to form a curve, including laser settings, size of the laser fiber, and the fiber bending diameter.

MATERIALS AND METHODS

Single-use 272 and 365 μm fibers (Rocamed^®, Monaco) were employed along with a holmium laser (Rocamed). Five different fiber curve diameters were tested: 9, 12, 15, 18, and 20 mm. Fragmentation and dusting settings were used at a theoretical power of 7.5 W. The laser was activated for 5 minutes and the principal judgment criterion was fiber fracture. Every test for each parameter, bending diameter, and fiber size combinations was repeated 10 times.

RESULTS

With dusting settings, fibers broke more frequently at a curved diameter of 9 mm for both 272 and 365 μm fibers (p = 0.037 and 0.006, respectively). Using fragmentation settings, fibers broke more frequently at 12 mm for 272 μm and 15 mm for 365 μm (p = 0.007 and 0.033, respectively). Short pulse and high energy were significant risk factors for fiber fracture using the 365 μm fibers (p = 0.02), but not for the 272 μm fibers (p = 0.35). Frequency was not a risk factor for fiber rupture. Fiber diameters also seemed to be involved in the failure with a higher number of broken fibers for the 365 μm fibers, but this was not statistically significant when compared with the 272 μm fibers (p > 0.05).

CONCLUSION

Small-core fibers are more resistant than large-core fibers as lower bending diameters (<9 mm) are required to break smaller fibers. In acute angles, the use of small-core fibers, at a low energy and long-pulse (dusting) setting, will reduce the risk of fiber rupture.