Holmium: YAG lithotripsy: photothermal mechanism

Application of Catheter-Assisted Circulation System in Ureteroscopic Holmium Laser Lithotripsy

Objective: Ureteroscopic lithotripsy (URSL) is the main method for treating ureteral calculi. The scholars used ureteroscopes with dual channels and access sheath to reduce the local temperature and flushing fluid pressure. This study compares the efficacy and safety of ureteral catheter-assisted URSL (UCA-URSL) and traditional URSL in treating ureteral calculi. Patients and Methods: A cross-regional retrospective case-control study in China, including 217 intention-to-treat patients from the First Affiliated Hospital of Kunming Medical University and Tongji Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology, from August 2023 to July 2024. The primary outcome was the temperature of the lithotripsy point. The secondary outcomes included stone-free rate (SFR), operation time, hospital stay, and postoperative complications. Results: Compared with the traditional URSL group, the catheter-assisted URSL group had a significantly lower lithotripsy point temperature (max, 37.9 ± 2.60°C vs 49.98 ± 5.04°C, p < 0.0001; mean, 32.3 ± 3.25°C vs 38.56 ± 2.70°C, p < 0.0001). In addition, the UCA-URSL group showed higher absolute SFR (immediately, 89.81% vs 53.21%, p < 0.0001; 3 months, 99.07% vs 72.48%, p < 0.0001), and reduced operation time (22.74 ± 7.08 minutes vs 26.40 ± 6.72 minutes, p = 0.0001), postoperative fever rate (1.85% vs 15.60%, p = 0.0003), and ureteral stricture rate (0% vs 3.67%, p = 0.04). Conclusions: In treating ureteral calculi, UCA lithotripsy shows better safety than traditional URSL. Catheter-assisted URSL can be used to improve traditional URSL.

Trilogy vs 100 W Ho:YAG Laser for Lithotripsy in Mini-Percutaneous Nephrolithotomy: Superior Stone-Free Rates in a Randomized Controlled Trial

OBJECTIVE

To compare the clinical outcomes of lithotripsy using the 100 W Ho:YAG laser and the Trilogy lithotripter in Mini-percutaneous nephrolithotomy (PCNL), and to determine the most effective method for stone clearance through a miniaturized percutaneous tract.

METHODS

This double-blind, randomized, single-center controlled trial (Clinicaltrials.gov ID: NCT04559321) enrolled patients with GUY's grade 1-2 kidney stones. Participants were randomly assigned to undergo Mini-PCNL using either the 100 W Ho:YAG laser (Lumenis Pulsed 100H) or the 1.5 mm Trilogy lithotripter (EMS-Nyon). Primary endpoints were stone lithotripsy time (SLT), lithotripsy rate (SLR), and stone-free rate (SFR). SLT was defined as the time from first activation of the lithotripter/laser until no further activations were needed. The study was terminated early in August 2023 following DSMB recommendations due to evidence of efficacy in one arm.

RESULTS

Eighty-three patients were analyzed (Laser, n=40; Trilogy, n=43), with comparable demographic and stone characteristics. Mean SLT was 8.02 minutes (Laser) vs 5.7 minutes (Trilogy, P=.199). SLR was 179 vs 212 mm³/min (P=.218), and operative time was 75.1±26.6 vs 85.9±28.1 minutes (P=.077). Trilogy achieved a significantly higher SFR (88.4% vs 70%, P=.038). Complication rates were low (2.3% Trilogy vs 10% laser, P=.142). Residual stone volume did not differ significantly between groups.

CONCLUSION

Trilogy lithotripsy resulted in higher SFR without increasing operative time or complications, supporting its use as an effective alternative to high-power laser lithotripsy in Mini-PCNL, especially where active suction is unavailable.

Warm irrigation fluid effect on Thulium fiber laser (TFL) ablation of uroliths

Prior laser studies have demonstrated that as the temperature of a medium increases, the amount of energy delivered to the target increases. We sought to investigate the role of irrigation fluid temperature on Thulium fiber laser (TFL) urolith ablation. 360 calculi were divided in vitro according to chemical composition: calcium oxalate monohydrate (COM), cystine (CYS), struvite (STR), calcium phosphate (CAP), uric acid (UA), and calcium oxalate dihydrate (COD). A 200 μm TFL was placed directly on each stone, while immersed in 0.9% NaCl at four different temperatures (25 C, 37 C, 44 C, 60 C) and a single laser pulse administered at distinct energy settings (0.1 J, 0.5 J, 1.5 J). Optical coherence tomography assessed the resulting ablation cone volume. Mean stone volume and porosity were evaluated through ANOVA and Tukey post-hoc analysis. A multivariate generalized model for each composition accounted for the impact of fluid temperature and laser energy on stone ablation. Warmer fluid temperatures yielded greater ablation cone volumes for most energy settings, excluding UA stones. When accounting for chemical composition, higher tensile strength stones (COM, CYS) benefited most from warmer fluid in comparison to frangible stones (CAP, STR). The effects of increasing fluid temperature are modest relative to laser pulse energy as a large temperature increase (i.e. 7ºC) is equivalent to a minor energy increase (i.e. 0.1 J). For non-UA stones, TFL ablation efficiency increases with warmer irrigation fluid. The effect, albeit modest compared to laser pulse energy, was most notable for COM and CYS stones.

Investigation of gaseous end products produced by thulium fiber laser lithotripsy of cystine, uric acid, and calcium oxalate monohydrate stones: A gas chromatographic and electron microscopic analysis

Laser lithotripsy mechanisms can cause the chemical decomposition of stone components and the emergence of different end products. However, the potentially toxic end products formed during thulium fiber laser (TFL) lithotripsy of cystine stones have not been sufficiently investigated. The aim of our in vitro study is to analyze the chemical content of the gas products formed during the fragmentation of cystine stone with TFL. Human renal calculi consisting of 100% pure cystine, calcium oxalate monohydrate, or uric acid were fragmented separately with TFL in experimental setups and observed for gas release. After the lithotripsy, only the cystine stones showed gas formation. Gas chromatography-mass spectrometry was used to analyze the gas qualitatively, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction was used to examine the dried cystine stone fragments. Fragmentation of the cystine stones released free cystine, sulfur, hydrogen sulfide, and carbon disulfide gas. The SEM-EDX and X-ray diffraction analyses revealed that the free cystine in the dried fragments contained 43.1% oxygen, 28.7% sulfur, 16.1% nitrogen, and 12.1% carbon atoms according to atomic weight. The detection of potentially toxic gases after lithotripsy of cystine stones with TFL indicates a risk of in vivo production. Awareness needs to be increased among healthcare professionals to prevent potential inhalation and systemic toxicity for patients and operating room personnel during TFL lithotripsy of cystine stones.

Morphological Characterization of Tissue Destruction According to the Distance Between Holmium:YAG Laser Tip and Tissue Surface

PURPOSE

Little is known about the soft tissue destruction by holmium laser clinically used for holmium laser enucleation of the prostate (HoLEP), subject to the distance between the laser fiber tip and the tissue surface. We aimed to investigate the impact of the distance between the laser fiber tip and the phantom surface (DLP) on a soft tissue phantom (STP) in relation to the surgical modes of HoLEP.

METHODS

STP responses to the laser pulses produced by a commercial holmium:yttrium aluminum garnet (Holmium:YAG) laser at an output setting 2 J were observed at different values of the DLP (0, 1, 2, 3, and 4 mm) to look at (1) the single laser pulse-induced cavitation bubble and its penetration into the STP, (2) the STP destruction by a single pulse, (3) the STP destruction by 60 pulses repeated at 12 Hz, and (4) the thermal effect by the multiple pulses visualized on a thermosensitive bovine serum albumin (BSA) STP.

RESULTS

We observed that the laser pulse produced a heated gas bubble in water centered at the laser fiber tip. The bubble shape depended on the DLP. The bubble completely penetrated into the STP at the DLP of 0 mm and the penetration decreased with the DLP. The size of the destruction of the STP by the laser pulses was shown to decrease as the DLP increased. Test with the BSA STP showed that, at the DLP of 3 mm, the destruction became insignificant while the thermal effects were still effective.

CONCLUSION

We illustrated that soft tissue destruction by the Holmium:YAG laser is associated with cavitation effects. We provide for the first time experimental evidence for various surgical modes in HoLEP such as incision and hemostasis in relation to the DLP.

Endoscopic interventions in pancreatic strictures and stones-A structured approach

Chronic pancreatitis (CP) is an irreversible disease of varied etiology characterized by destruction of pancreatic tissue and loss of both exocrine and endocrine function. Pain is the dominant and most common presenting symptom. The common cause for pain in CP is ductal hypertension due to obstruction of the flow of pancreatic juice in the main pancreatic duct either due to stones or stricture or a combination of both. With advances in technology and techniques, endoscopic retrograde cholangiography (ERCP) and stenting should be the first line of therapy for strictures of the main pancreatic duct (MPD). Small calculi in the MPD can be extracted by ERCP and balloon trawl. Extracorporeal shockwave lithotripsy (ESWL) remains the standard of care for large pancreatic calculi and aims to fragment the stones 3 mm or less that can easily be extracted by a subsequent ERCP. Single operator pancreatoscopy with intraductal lithotripsy is a technique in evolution and can be tried when ESWL is not available or is unsuccessful in producing stone fragmentation.

Endoscopic Retrograde Cholangiopancreatography for Management of Chronic Pancreatitis

Management of symptomatic chronic pancreatitis (CP) has shifted its approach from surgical procedures to minimally invasive endoscopic procedures. Increased experience and advanced technology have led to the use of endoscopic retrograde cholangiopancreatography (ERCP) as a therapeutic tool to provide pain relief and treat CP complications including pancreatic stones, strictures, and distal biliary strictures, pseudocysts, and pancreatic duct fistulas. In this article the authors will discuss the use of ERCP for the management of CP, its complications, recent advancements, and techniques from the most up to date literature available.

Effect of Self-Training Using Virtual Reality Head-Mounted Display Simulator on the Acquisition of Holmium Laser Enucleation of the Prostate Surgical Skills

PURPOSE

We aimed to evaluate the effect of self-training using a virtual reality head-mounted display simulator on the acquisition of surgical skills for holmium laser enucleation surgery.

METHODS

Thirteen medical students without surgical skills for holmium laser enucleation of the prostate were trained using multimedia to learn the technique via simulator manipulation. Thereafter, participants performed the technique on a virtual benign prostatic hyperplasia model A (test A). After a 1-week wash-out period, they underwent self-training using a simulator and performed the technique on model B (test B). Subsequently, participants were asked to respond to Training Satisfaction Questions. Video footage of hand movements and endoscope view were recorded during tests A and B for later review by 2 expert surgeons. A 20-step Assessment Checklist, 6-domain Global Rating Scale, and a Pass Rating were used to compare performance on tests A and B.

RESULTS

Thirteen participants completed both tests A and B. The 20-step Assessment Checklist and 6-domain Global Rating Scale evaluation results showed significantly improved scores in test B than in test A (P<0.05). No evaluator rated participants as passed after test A, but 11 participants (84.6%) passed after test B. Ten participants (76.9%) indicated that the simulator was helpful in acquiring surgical skills for holmium laser enucleation of the prostate.

CONCLUSION

The virtual reality head-mounted display holmium laser enucleation of the prostate simulator was effective for surgical skill training. This simulator may help to shorten the learning curve of this technique in real clinical practice in the future.

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.

Observation and comparison of gas formation during holmium:YAG laser lithotripsy of cystine, uric acid, and calcium oxalate stones: a chromatographic and electron microscopic analysis

The primary aim of the present in vitro study is to analyze the chemical content of the bubbles occurring during the fragmentation of cystine stones with both the high-power and low-power holmium:YAG (Ho:YAG) lasers. The secondary aim is to discuss their clinical importance. Three types of human renal calculi calcium oxalate monohydrate (COM), cystine, and uric acid were fragmented with both low-power and high-power Ho:YAG lasers in separate experimental setups at room temperature, during which time it was observed whether gas was produced. After laser lithotripsy, a cloudy white gas was obtained, after the fragmentation of cystine stones only. A qualitative gas content analysis was performed with a gas chromatography-mass spectrometry (GC-MS) device. The fragments in the aqueous cystine calculi setup were dried and taken to the laboratory to be examined by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray diffraction analysis. No gas production was observed after fragmentation in the COM and uric acid stones. Free cystine, sulfur, thiophene, and hydrogen sulfide gas were produced by both low-power and high-power Ho:YAG laser lithotripsy of the cystine stones. In the SEM-EDX mapping analysis, a free cystine molecule containing 42.8% sulfur (S), 21% oxygen (O), 14.9% carbon (C), and 21% nitrogen (N) atoms was detected in the cystine stone experimental setup. The evidence obtained, which shows that hydrogen sulfide emerges in the gaseous environment during Ho:YAG laser fragmentation of cystine stones, indicates that caution is required to prevent the risk of in vivo production and toxicity.

Performance of brushite plaster as kidney stone phantoms for laser lithotripsy

Artificial phantoms used in photothermal near-infrared laser lithotripsy research generally fail to mimic both the chemical and the physical properties of human stones. Though high-energy, 1 J pulses are capable of fracturing hard human stones into several large fragments along natural boundaries, similar behavior has not been observed in commonly used gypsum plasters like BegoStone. We developed a new brushite-based plaster formulation composed of ≈90% brushite that undergoes rapid fracture in the manner of human stones under fragmentation pulse regimes. Single-pulse (1 J) ablation crater volumes for phantoms were not significantly different from those of pure brushite stones. Control over crater volumes was demonstrated by varying phosphorous acid concentration in the plaster formulation. Fragmentation of cylindrical brushite phantoms was filmed using a high-speed camera which demonstrated rapid fragmentation in < 100 µs during the bubble expansion phase of a short pulse from a high-powered Ho:YAG laser (Lumenis Pulse 120 H). The rapid nature of observed fracture suggests increasing laser pulse energy by increasing laser pulse duration will not improve fragmentation performance of laser lithotripters. Brushite plaster phantoms are a superior alternative to gypsum plasters for laser lithotripsy research due to their better mimicry of stone composition, controllable single-pulse crater volumes, and fragmentation behavior.

Femtosecond laser lithotripsy: a novel alternative for kidney stone treatment? Evaluating the safety and effectiveness in an ex vivo study

The Holmium (Ho:YAG) laser is presently the most extensively employed in laser lithotripsy for the management of kidney stones. Despite its adoption as the gold standard for laser lithotripsy, Ho:YAG laser lithotripsy poses three significant challenges, namely thermal effect, insufficient stone fragmentation, and stone displacement, which have garnered increased attention from urologic surgeons. Nowadays, the femtosecond laser is regarded as a potential alternative to the Ho:YAG laser due to its capacity to ablate diverse materials with minimal thermal effect. In our ex vivo investigation, we assessed the dimensions of ablation pits, the efficacy of ablation, the degree of stone fragmentation, the alterations in water temperature surrounding stones, and the degree of tissue damage associated with Femtosecond laser lithotripsy utilizing adjustable power settings (1-50 W). Our findings indicate that the ablation pits generated by the Femtosecond laser exhibited uniform geometries, and the effectiveness of ablation and fragmentation for Femtosecond laser lithotripsy were significantly and positively correlated with laser power. When the laser power remained constant, the Femtosecond laser with higher pulse energy demonstrated superior efficiency in stone ablation, but inferior performance in stone fragmentation. Conversely, the Femtosecond laser with higher pulse frequency exhibited the opposite behavior. Furthermore, the thermal effect increased proportionally with laser power, leading to a tentative recommendation of 10W laser power for future investigations. Our in vitro findings suggest that the Femtosecond laser holds promise as a safe and effective alternative to holmium lasers.

Management of Pancreatic Duct Stones: Nonextracorporeal Approach

Chronic pancreatitis (CP) is an ongoing inflammatory disease with most patients developing pancreatic calculi during their course of disease. Extracorporeal shock wave lithotripsy (ESWL) is a first-line treatment option in patients with large lumen obstructing pancreatic duct (PD) stones. In patients with CP and PD dilatation, digital single-operator pancreatoscopy (DSOP)-guided lithotripsy seems to be an appealing option to ESWL and surgery. DSOP-guided lithotripsy for the treatment of large symptomatic PD-stones has been demonstrated to be safe, technically, and clinically effective, and should be regarded as an alternative endoscopic treatment of certain patients.

Photonic Lithotripsy: Near-Infrared Laser Activated Nanomaterials for Kidney Stone Comminution

Near-infrared activated nanomaterials have been reported for biomedical applications ranging from photothermal tumor destruction to biofilm eradication and energy-gated drug delivery. However, the focus so far has been on soft tissues, and little is known about energy delivery to hard tissues, which have thousand-fold higher mechanical strength. We present photonic lithotripsy with carbon and gold nanomaterials for fragmenting human kidney stones. The efficacy of stone comminution is dependent on the size and photonic properties of the nanomaterials. Surface restructuring and decomposition of calcium oxalate to calcium carbonate support the contribution of photothermal energy to stone failure. Photonic lithotripsy has several advantages over current laser lithotripsy, including low operating power, noncontact laser operation (distances of at least 10 mm), and ability to break all common stones. Our observations can inspire the development of rapid, minimally invasive techniques for kidney stone treatment and extrapolate to other hard tissues such as enamel and bone.

Understanding the ablation rate of Holmium:YAG and thulium fiber lasers. Perspectives from an in vitro study

This study sought to analyze the ablation rates of Holmium:YAG (Ho:YAG) and thulium fiber laser (TFL) under different settings combinations. Lasering was carried out by a computed spiral pattern through a stepper motor bearing a laser fiber. BegoStones were placed inside a water container and lasered therein and the ablation rate was calculated. Different combinations were tested for ~12 Watts (W) for Ho:YAG and TFL lasers. Further 25 W combination for TFL were conducted testing higher frequencies. One-hundred-one experiments were conducted. Under ~12 W, the highest ablation rate for Ho:YAG was obtained with 40 Hz/0.3 J, and Virtual Basket™ (VB) emission mode [114.35 (88.30 - 126.40) mg/min] whereas for TFL, using 40 Hz/0.3 J, and long pulse [143.40 (137.40 - 146) mg/min]. A matched-comparison for 12 Hz/1 J settings showed that TFL outperformed Ho:YAG using medium pulse [63.30 (55.30 - 81.30) vs 132.00 (115.70 - 228.60) mg/min, p=0.016] and long pulse [62.90 (51.60 - 78.90) vs 134.70 (110.60 - 149.30) mg/min, p=0.016]. In the 40 Hz/0.3 J settings, TFL outperformed Ho:YAG (p=0.034). Nonetheless, Ho:YAG with VB's ablation rate increased [114.35 (88.30 - 126.40)], being comparable to that of TFL with medium pulse [127.5 (88.90 - 141.70)] (p=0.400). In TFL 25 W experiments, the ablation rate of 500 Hz / 0.05 J, was higher than those of 1000 Hz / 0.025 J (p=0.049). TFL ablation rate is higher than that of Ho:YAG. Moreover, the Virtual Basket™ emission mode, increased Ho:YAG ablation rates, resulting reaching similar to that of TFL in certain modalities.

Stone ablation efficacy: a comparison of a thulium fibre laser and two pulse-modulated holmium:YAG lasers

We present preliminary stone ablation rate results from an automated bench model using two pulse-modulated Ho:YAG lasers and a thulium fibre laser (TFL) in contact and non-contact modes. Ablation rate was assessed using automated apparatus that moved the laser fibre across flat BegoStone phantoms at a constant stone-to-fibre working distance (WD). Pre-soaked and unsoaked stones were used. A range of powers (20-60 W) was tested at WD of up to 3 mm. In pseudocontact, the prototype Ho:YAG laser produced higher ablation than the reference Ho:YAG laser at all powers tested (p < 0.002), and higher ablation than TFL at 20 W and 40 W (p < 0.001). At distance, ablation rates for the prototype were higher than the reference Ho:YAG laser using pre-soaked stones at WD up to 3 mm (p < 0.001). TFL required the laser fibre to be moved faster (5-12 mm/s) for optimal ablation, compared to 1-3 mm/s for the Ho:YAG lasers. TFL was unable to demonstrate ablation with unsoaked BegoStone. At any given power, similar ablation rates were achievable with all three lasers under optimised conditions. Novel pulse-modulation modes demonstrated higher ablation rates than the reference Ho:YAG laser's pulse-modulation at a range of powers and WDs. Ablation rate of Ho:YAG lasers decreased linearly with WD whereas the ablation rate of TFL decreased rapidly beyond 2 mm WD. TFL was more affected by scan speed and pre-soaking of stone than Ho:YAG lasers. Ho:YAG lasers may be more practical in clinical settings because they are less dependent on ablation technique.

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.

Comparison of Fragmentation and Dusting Modality Using Holmium YAG Laser during Ureteroscopy for the Treatment of Ureteral Stone: A Single-Center's Experience

Laser ureteroscopic lithotripsy (URSL) is an efficacious treatment for ureteral stones. There have been few previous studies comparing the different energy and frequency settings for URSL in a single center. We compared these two laser modalities, which were simultaneously used in our medical center for the treatment of ureteral stones. Patients who underwent fragmentation or dusting laser URSL between September 2018 and June 2020 were retrospectively reviewed. We compared patients who underwent fragmentation and dusting laser and assessed the enhancing factors for stone free rate. There were a total of 421 patients with ureteral stones who met the study criteria. There was no significant difference between the characteristics of both groups. The fragmentation group had a better stone free rate and a lower retropulsion rate compared with the dusting group. Multivariate analysis revealed that stone basket use, no upper ureteral stone or pyuria significantly improved the stone free rate. Both laser modes were effective and safe for ureteral lithotripsy although the fragmentation system showed slightly higher effectiveness and lower complication rate.

Risk Factors for Transurethral Coagulation for Hemostasis During Holmium Laser Enucleation of the Prostate

PURPOSE

We aimed to identify risk factors for transurethral coagulation (TUC) using bipolar electrocautery for hemostasis during holmium laser enucleation of the prostate (HoLEP) surgery for benign prostatic hyperplasia (BPH).

METHODS

We analyzed the clinical outcomes of HoLEP surgery performed by a single surgeon between January 2010 and April 2020 at the Seoul National University Hospital. Patient characteristics and perioperative parameters were used to identify the risk factors for TUC. The TUC group was defined as a case of conversion to hemostasis using electrocautery during the hemostasis step after enucleation.

RESULTS

Of 1,563 patients, 357 underwent TUC (TUC group; 22.8%) as an adjuvant (n=299, 19.1%) or salvage (n=58, 3.7%) therapy. Patients in the TUC group were older (mean±standard deviation, 70.6±7.3 years vs. 69.3±7.0 years; P=0.002), had more 5-alpha reductase inhibitor (5-ARI) use (35.6% vs. 25.9%, P<0.001), higher serum prostate-specific antigen (PSA) (5.4 ±4.8 ng/mL vs. 3.8 ±4.5 ng/mL, P <0.001), larger total prostate volume (TPV) (89.5 ±44.7 mL vs. 66.0 ±32.6 mL, P<0.001), and larger transitional zone volume (TZV) (57.3±34.9 mL vs. 37.7±24.2 mL, P<0.001) than those who did not undergo TUC (non-TUC group). In univariate logistic regression analysis, age, 5-ARI use, PSA, TPV, and TZV correlated with TUC, whereas in multivariate logistic regression analysis, only TZV was associated with TUC. The odds ratios (ORs) of TUC were analyzed per TZV quartile. Compared to TZV<22.3 mL, the OR was 2.42 in 34.1 mL≤TZV<53.5 mL (95% confidence interval [CI], 1.58-3.72; P<0.001), 5.17 in ≥53.5 mL (95% CI, 3.44-7.77; P<0.001).

CONCLUSION

The risk of TUC during HoLEP surgery increases in patients with TZV >35 mL. Therefore, TUC may be potentially necessary in patients with a large transition zone volume in patients with BPH.

Laser lithotripsy using dusting technique (low energy, high frequency) for symptomatic upper urinary tract stones

Background

A prospective study to assess the feasibility of stone dusting technique (low energy and high frequency) during laser lithotripsy in symptomatic upper urinary tract |(UUT) stones.

Methods

Sixty patients with symptomatic single or multiple UUT stones less than 3 cm in diameter were included. Patients with coagulation disorders and active UTIs were excluded. All patients were clinically evaluated and underwent non-contrast spiral CT (NCSCT) to detect stone site, size, number, Hounsfield unit. A rigid or flexible ureteroscope was used with stone dusting using the Ho: YAG laser at low-energy and high-frequency (0.5 J & 20 Hz) set. Operative and fluoroscopy time, total energy delivered, type of stent, hospitalization time, complications and its grade, and stone-free rate using NCSCT after 4 weeks were recorded.

Results

The mean stone size ± SD (range) was 1.55 ± 0.55 (0.5–3) cm; out of sixty patients (50 with single stone and 10 with multiple stones), fifty-five patients were stone-free at 4 weeks. Complications had occurred in 11 patients (eight with grade I, one with grade II, and two with grade IIIa) according to Clavien–Dindo grading of surgical complications. Stone size was the only parameter which correlated significantly with stone-free rate. No significant correlation was found between incidence of complications and other parameters (stone size, site, BMI, age and operative time).

Conclusions

Stone dusting technique is feasible, safe and effective in management of UUT stones.

New Lasers for Stone Treatment

Laser technology has been a breakthrough in urology. The new era in endocorporeal laser lithotripsy has recently begun in mid-2020, where promising technologies tested in vitro have reached their approval for clinical use and, in that way, have made it possible to confirm their safety and advantages in the real world, for the patient and for the urologist.

Prediction models of low-power holmium laser effectiveness in renal stone lithotripsy during retrograde intrarenal surgery

The objectives of this study are to develop prediction models for total laser energy (TLE) in order to infer surgical time and assist operative planning of intrarenal low-power Ho:YAG laser lithotripsy, and to predict the fragmented volume as well as the stone-free status (SFS). A retrospective review was performed, comprising all single surgeon standardized retrograde intrarenal surgery and low-power Ho:YAG laser lithotripsy at a tertiary care centre between October 2014 and September 2019. Automated measurement of stone volume and stone density (MSD), measured in Hounsfield units (HU), was employed in both pre- and post-operative non-contrast-enhanced computed tomography (NCCT), using a standardized technique on Osirix Lite® software. SFS was defined as complete absence of stone fragments, or fragments < 0.1 cm on meticulous inspection at the end of the procedure, and residual stone burden < 0.0005 cm³ on postoperative NCCT at 3 months. Statistical analysis was performed using the STATA® version 13.1 software for regression models. A p value < .05 was considered statistically significant. A total of 100 patients met the inclusion criteria, requiring a median of 22.3 kJ/cm³ (13.4-36.0) and resulting in a SFS of 41% at 3 months. In a multivariate analysis, according to stone composition, predicted TLE is equal: for uric acid (UA), 11.17 × volume(cm³) + 0.17 × MSD(HU) + 7.48 kJ; for mixed stones, 11.17 × volume(cm³) + 0.17 × MSD(HU) + 6.26 kJ; for calcium oxalate monohydrate (CaOM) stones, 11.17 × volume(cm³) + 0.17 × MSD(HU) + 1.14 kJ; and for calcium phosphate (CaPh) stones 11.17 × volume(cm³) + 0.17 × MSD(HU) - 1.94 kJ. Predicted fragmented volume is equal to 0.93 × volume(cm³) cm³. The significant predictors for SFS were UA stones, the presence of multiple stones, and lower TLE. In clinical practice, our models for intrarenal low-power Ho:YAG laser lithotripsy indicate that larger, denser, and UA stones are associated to higher TLE, and that single and UA stones are more commonly associated to SFS. Since higher TLE means longer operative time, when adjusting for laser parameters, our prediction models may help urologists plan surgeries more precisely based on stone characteristics, ultimately optimizing patients' treatment.

Ex vivo study: is it possible to overcome the blurriness caused by holmium laser fragmentation of kidney stones?

Better endoscopic vision is mandatory for successful ureteroscopic stone operations to achieve shorter operating time. However, an important impairing factor for a good endoscopic view is the cloudiness of vision which was formed during laser fragmentation. Holmium laser fragmentation of calcium oxalate stones produces calcium carbonate solubility of which is dependent on pH, citrate, and phosphate. In this ex vivo research, the solubility of calcium carbonate has been investigated in solutions composed of various concentrations of citrate and phosphate buffered at different pH levels after laser fragmentation of calcium oxalate stones. Calcium oxalate stones were placed into the laboratory tubes filled with various concentrations of citrate-phosphate buffers with different pH values. Laser energy in dusting mode was applied to the stones and spectrophotometric measurement for optical density (OD) was calculated for each buffered solution for clarity comparison. In the first phase, solutions composed of four different molar concentrations of citrate-phosphate buffer (0.2, 0.3, 0.4 and 0.5 molars) at various pH levels were used. Then, the next phase of the study was designed to compare solutions demonstrating the lowest OD values with an isotonic saline solution. The results were most convenient at 0.5 molarity (pH = 6) followed by 0.4 molarity (pH = 7) in the first phase (OD values of 0.054 and 0.065, respectively). In the next phase, OD values of both buffered solutions were significantly lower than those of isotonic saline solution (p = 0). Two specific buffers have provided better optic visibility values after laser fragmentation supporting their use as an irrigation solution for the favor of less cloudiness.

The Role of Cavitation in Energy Delivery and Stone Damage During Laser Lithotripsy

Purpose: Although cavitation during laser lithotripsy (LL) contributes to the Moses effect, the impact of cavitation on stone damage is less clear. Using different laser settings, we investigate the role of cavitation bubbles in energy delivery and stone damage. Materials and Methods: The role of cavitation in laser energy delivery was characterized by using photodetector measurements synced with high-speed imaging for laser pulses of varying durations. BegoStone samples were treated with the laser fiber oriented perpendicularly in contact with the stone in water or in air to assess the impact of cavitation on crater formation. Crater volume and geometry were quantified by using optical coherence tomography. Further, the role of cavitation in stone damage was elucidated by treatment in water with the fiber oriented parallel to the stone surface and by photoelastic imaging. Results: Longer pulse durations resulted in higher energy delivery but smaller craters. Stones treated in water resulted in greater volume, wider yet shallower craters compared with those treated in air. Stones treated with the parallel fiber showed crater formation after 15 pulses, confirmed by high-speed imaging of the bubble collapse with the resultant stress field captured by photoelastic imaging. Conclusions: Despite improved energy delivery, the longer pulse mode produced smaller crater volume, suggesting additional processes secondary to photothermal ablation are involved in stone damage. Our critical observations of the difference in stone damage treated in water vs in air, combined with the crater formation by parallel fiber, suggest that cavitation is a contributor to stone damage during LL.

Gas Bubble Anatomy During Laser Lithotripsy: An Experimental In Vitro Study of a Pulsed Solid-State Tm:YAG and Ho:YAG Device

Purpose: To examine gas bubbles generated by two laser lithotripsy devices, a pulsed thulium solid-state laser and a holmium:yttrium-aluminum-garnet (Ho:YAG) device, and their possible effects in lithotripsy. Materials and Methods: We investigated two Dornier laser devices, a Medilas H Solvo 35 and a pulsed solid-state thulium laser evaluation model (Dornier MedTech Laser GmbH, Wessling, Germany). Our setup consisted of a water-filled glass tank heated to 37/60/70°C. Different laser power/frequency settings and short/long pulses were examined for both laser devices. We analyzed the impact of degraded, cut, and broken fibers on gas bubble anatomy. Furthermore, high-speed recordings of BegoStone ablation were analyzed. For all recordings, we used a Photron Nova S12 camera. Results: These two devices produced differently shaped gas bubbles under different fiber conditions, temperatures, power settings, and short and long pulse settings, which explain the differing repulsive force and pressure values. Inside the gas bubble, a cone was visible whose angle correlates with the protruding jet. We observed turbulences and swirls moving back and forth the fiber tip. During fragmentation, sparks are generated that demonstrate the photothermal effect, and we recorded stone fragments being pulled toward the fiber. Both devices showed comparable results with differences mainly due to pulse lengths. Conclusion: The shapes of the vapor bubbles formed during laser lithotripsy depend on several factors. Excessive transoperative fiber cleavage seems to be unnecessary. Due to the large gas bubbles observed and because of the amount of potential pressure generated, only low energies should be applied in the ureter.

[Innovative laser technologies in the treatment of urolithiasis : A change to more gentle methods with increased patient safety]

Management of urolithiasis has undergone fundamental changes with the introduction of extracorporeal shock wave lithotripsy (ESWL) and percutaneous and ureterorenoscopic techniques in the 1980s. Since then, these minimally invasive techniques have been continuously optimized and specific laser techniques for stone disintegration have emerged. Besides the established holmium laser, other types of lasers are also emerging. Especially the thulium fiber laser is the subject of promising research due to its variable adjustment options. In terms of patient safety, both holmium and thulium techniques seem to be similar . While serious direct physical lesions are rare, there is increasing evidence of clinically relevant secondary thermal injury due to increased temperatures in the upper urinary tract during treatment. Our research group has recently demonstrated in both in vitro and in vivo (porcine animal model) experiments that monitoring the fluorescence spectra of calculi allows precise target differentiation between stone, tissue, and endoscope components. Consequently, pulse emissions were only emitted when stone material was detected. We believe that target monitoring will minimize the risk of laser-induced urothelial damage and decrease energy release into the upper urinary tract allowing adequate temperature management.

Temperature Assessment of a Novel Pulsed Thulium Solid-State Laser Compared with a Holmium:Yttrium-Aluminum-Garnet Laser

Purpose: To compare a novel Thulium laser device with the commonly used Holmium:Yttrium-Aluminum-Garnet (Ho:YAG) laser in terms of the in vitro temperatures generated. Methods: Our study investigated and compared an evaluation model of a solid-state Thulium laser with a Medilas H Solvo 35 Holmium laser device, both by Dornier (Dornier MedTech Laser GmbH, Wessling, Germany). Our in vitro model consisted of a 20 mL test tube placed in a 37°C water bath. Constant irrigation was set at 50 mL/minute with a Reglo Z Digital pump (Cole Parmer, Chicago, IL). Four hundred micrometers of Dornier laser fibers were used. The temperature was measured with a type K thermocouple and a real-time data logger from Pico (PICO Technology, Cambridgeshire, United Kingdom). Power settings between 2 and 30 W were investigated. Each measurement lasted 120 seconds and was repeated five times. The data were evaluated by MATLAB^® (The Mathworks, Inc., Natick, MA). Results: The resulting temperatures were directly proportional to the power supplied. When comparing Holmium with Thulium, we observed maximum deviations of ≤0.82 K in temperatures at 120 seconds. The highest investigated laser power of 30 W yielded maximum temperatures differing by 6.7 K from the initial value. Out of the five comparisons, Thulium showed marginally yet significantly lower end temperatures in four cases and slightly lower cumulative equivalent minutes at 43°C (CEM₄₃) values in three cases. Conclusion: The Thulium laser resembles the Holmium device in the temperatures generated during in vitro application. An increase in laser power, thus, leads to equivalent increases in temperature that are largely independent of frequency, pulse duration, and single pulse energy. Pulsed Thulium:Yttrium-Aluminum-Garnet (Tm:YAG), Ho:YAG, and Thulium fiber laser seem to share a similar risk profile for patients in terms of temperature development. Intrarenal power outputs exceeding 10 W during clinical application should be compensated by ensuring sufficient irrigation.

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.

Thulium fiber laser: ready to dust all urinary stone composition types?

PURPOSE

To evaluate whether stone dust can be obtained from all prevailing stone composition types using the thulium fiber laser (TFL) for lithotripsy. Where applicable, stone dust was further characterized by morpho-constitutional analysis.

METHODS

Human urinary stones were submitted to in vitro lithotripsy using a FiberLase U2 TFL generator with 150 µm silica core fibers (IPG Photonics^®, IPG Medical™, Marlborough, MA, USA). Laser settings were 0.05 J, 320 Hz and 200 μs. A total of 2400 J were delivered to each stone composition type. All evaluated stones had a > 90% degree of purity (calcium oxalate monohydrate, calcium oxalate dihydrate, uric acid, carbapatite, struvite, brushite and cystine). Spontaneously floating stone particles were considered as stone dust and collected for analysis by scanning electron microscopy and Fourier transform infrared spectroscopy.

RESULTS

Stone dust could be retrieved from all evaluated urinary stones after TFL lithotripsy. Most stone dust samples revealed changes in crystalline organization, except for calcium oxalate monohydrate and carbapatite, which conserved their initial characteristics. Mean maximal width of stone dust particles did not exceed 254 µm.

CONCLUSIONS

The TFL is capable to produce stone dust from all prevailing stone types. Morpho-constitutional changes found in stone dust suggest a photothermal interaction of laser energy with the stone matrix during TFL lithotripsy.

Ho: YaG laser lithotripsy: recent innovations

PURPOSE OF REVIEW

The aim of this study was to summarize the recent innovations of the holmium laser with special respect to lithotripsy. Therefore, we reviewed and discussed the most recent and pivotal publications on this topic.

RECENT FINDINGS

The current literature underlines Holmium:yttrium-aluminium-garnet (Ho:YAG) lithotripsy as a well tolerated and efficient method to treat urinary calculi. Because of modifiable adjustments of pulse energy, pulse frequency, and pulse length, especially with newer generations of holmium lasers, urologists can accurately choose between the 'fragmentation' and 'dusting' technique with its alterations. Recently, the 'Moses mode' as a new feature incorporated in the Lumenis Pulse P120H holmium laser showed less retropulsion with higher rates of stone ablation because of an improved energy transmission from the laser fiber towards the targeted calculus in in-vitro studies.

SUMMARY

Based on technological developments, Ho:YAG laser lithotripsy has become more efficient in reducing retropulsion and increasing stone ablation volume. However, despite its widespread use as a lithotripter, a newly developed thulium fiber laser, which has already shown promising results in experimental studies, could become an alternative in future practice.

Characteristics of Bubble Oscillations During Laser-Activated Irrigation of Root Canals and Method of Improvement

BACKGROUND AND OBJECTIVES

Laser-activated irrigation of dental root canals is being increasingly used as its efficacy has been shown to be superior compared with conventional techniques. The method is based on laser-initiated localized fluid evaporation and subsequent rapid bubble expansions and collapses, inducing microfluid flow throughout the entire volume of the cavity. The irrigation efficacy can be further improved if optimally delayed "SWEEPS" double laser pulses are delivered into the canal. This study aims to show that the irrigation efficacy, as measured by the induced pressure within the canal, is related to the double pulse delay, with the maximal pressure generated at an optimal delay. The second aim is to find a method of determining the optimal delay for different cavity dimensions and/or laser parameters.

STUDY DESIGN/MATERIALS AND METHODS

Experiments were made in transparent models of root canals where Er:YAG laser (λ = 2.94 μm, pulse duration t_p  = 25 or 50 microseconds, and pulse energies up to E_L  = 40 mJ) was used with a combination of cylindrical and conical fiber-tip geometries (diameters 400 and 600 µm). High-speed photography (60,000 fps) and average pressure measurements inside the canal were used for process characterization.

RESULTS

The results show that a pressure amplification of more than 1.5 times occurs if the laser pulse delay approximately coincides with the bubble oscillation time. Correlations between normalized oscillation time and canal diameter for a wide range of laser pulse energies (R²  = 0.96) and between the average pressure within the canal and the bubble oscillation periods (R²  = 0.90) were found. A relationship between the bubble oscillation time and the diameter of the treated cavity was found depending on the bubble oscillation time in an infinite fluid reservoir.

CONCLUSIONS

The bubble oscillation time within a constrained volume can be determined based on the known oscillation time in infinite space, which offers a fast and simple solution for optimization of the laser parameters. These findings enable determination of optimal conditions for shock wave generation, and improvement of root canal irrigation at the same dose of laser energy input, leading to improved treatment efficacy and safety. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals, Inc.

How Lasers Ablate Stones: In Vitro Study of Laser Lithotripsy (Ho:YAG and Tm-Fiber Lasers) in Different Environments

Introduction: There are two main mechanisms of stone ablation with long-pulsed infrared lasers: photothermal and photomechanical. Which of them is primary in stone destruction is still a matter of discussion. Water holds importance in both mechanisms but plays a major role in the latter. We sought to identify the prevailing mechanism of stone ablation by evaluating the stone mass loss after lithotripsy in different media. Materials and Methods: We tested a holmium:yttrium-aluminum-garnet (Ho:YAG) laser (100 W; Lumenis), a thulium-fiber laser U1 (TFL U1) (120 W; NTO IRE-Polus, Russia), and a SuperPulse thulium-fiber laser U2 (TFL U2) (500 W; NTO IRE-Polus). A single set of laser parameters (15 W = 0.5 J × 30 Hz) was used. Contact lithotripsy was performed in phantoms (BegoStones) in different settings: (a) hydrated phantoms in water, (b) hydrated phantoms in air, (c) dehydrated phantoms in water, and (d) dehydrated phantoms in air. Laser ablation was performed with total energy of 0.3 kJ. Phantom mass loss was defined as the difference between the initial phantom mass and the final phantom mass of the ablated phantoms. Results: All lasers demonstrated effective ablation in hydrated phantoms ablated in water; no visual differences between the lasers were detected. The ablation of dehydrated phantoms in air was also effective with visible vapor during ablation and condensation on the cuvette wall. Dehydrated phantoms in water and in air show minimal to no ablation accompanied with formation of white crust on phantom surface. Among laser types, TFL U2 had the highest phantom mass loss in all groups except for dehydrated phantoms ablated in air. Conclusions: Our results suggest that both photothermal and thermomechanical ablation mechanisms (explosive vaporization) occur in parallel during laser lithotripsy. In Ho:YAG and TFL U2 stone ablation explosive vaporization prevails, whereas in TFL U1 ablation photothermal mechanism appears to predominate.

Thulium fiber laser: the new player for kidney stone treatment? A comparison with Holmium:YAG laser

PURPOSE

To compare the operating modes of the Holmium:YAG laser and Thulium fiber laser. Additionally, currently available literature on Thulium fiber laser lithotripsy is reviewed.

MATERIALS AND METHODS

Medline, Scopus, Embase, and Web of Science databases were searched for articles relating to the operating modes of Holmium:YAG and Thulium fiber lasers, including systematic review of articles on Thulium fiber laser lithotripsy.

RESULTS

The laser beam emerging from the Holmium:YAG laser involves fundamental architectural design constraints compared to the Thulium fiber laser. These differences translate into multiple potential advantages in favor of the Thulium fiber laser: four-fold higher absorption coefficient in water, smaller operating laser fibers (50-150 µm core diameter), lower energy per pulse (as low as 0.025 J), and higher maximal pulse repetition rate (up to 2000 Hz). Multiple comparative in vitro studies suggest a 1.5-4 times faster stone ablation rate in favor of the Thulium fiber laser.

CONCLUSIONS

The Thulium fiber laser overcomes the main limitations reported with the Holmium:YAG laser relating to lithotripsy, based on preliminary in vitro studies. This innovative laser technology seems particularly advantageous for ureteroscopy and may become an important milestone for kidney stone treatment.

Management of Pancreatic Duct Stones

PURPOSE OF REVIEW

Pancreatic duct stones are sequela of chronic pancreatitis. They can cause pancreatic duct obstruction which is the most important cause of pain in chronic pancreatitis. Stone resolution has shown to improve pain. The goal of this review is to highlight recent endoscopic and surgical advancements in treatment of pancreatic duct stones.

RECENT FINDINGS

Stone fragmentation by extracorporeal shock wave lithotripsy has become first line and the mainstay of treatment for majority of patients with pancreatic duct stones. Introduction of digital video pancreatoscopy in the last few years with the capability of guided lithotripsy has provided a robust therapeutic option where extracorporeal shock wave lithotripsy is unsuccessful or unavailable. Historically, surgery has been considered a more reliable and durable option when feasible. However, it had not been compared with more effective endoscopic therapy. Lithotripsy (extracorporeal and pancreatoscopy guided) is evolving as a strong treatment modality for pancreatic stones.

Holmium:Yttrium-Aluminum-Garnet Laser Pulse Type Affects Irrigation Temperatures in a Benchtop Ureteral Model

Introduction: MOSES^™ technology is a holmium:yttrium-aluminum-garnet laser pulse mode shown to minimize stone retropulsion. This may facilitate lithotripsy at higher power settings. However, power and heat production are proportional, and temperatures capable of tissue injury may occur during ureteroscopic lithotripsy. Although previous in vitro studies demonstrate the importance of irrigation and activation time on heat production, the impact of pulse type has not been evaluated. Methods: A flexible ureteroscope with a 365 μm laser fiber was placed in an 11/13 F access sheath inserted into a 50 mL saline bag to simulate a ureter, renal pelvis, and antegrade irrigant flow. A thermocouple was placed adjacent to the laser tip, and the laser fired for 30 seconds at 0.6 J/6 Hz, 0.8 J/8 Hz, 1 J/10 Hz, 1 J/20 Hz, and 0.2 J/70 Hz at irrigation pressure of 100 mmHg. Four runs were tested per setting using short pulse, long pulse (LP), MOSES-contact (MC), and MOSES-distance (MD) modes. The mean temperature changes (dT) were compared and thermal dose was calculated in cumulative equivalent minutes at 43°C (CEM43) using an adjusted baseline of 37°C. CEM43 ≥ 120 minutes was considered the tissue injury threshold. Results: At 0.8 J/8 Hz, LP produced the greatest dT, significantly higher than MC (p = 0.041). CEM43 did not exceed the injury threshold. At 1 J/10 Hz, dT was significantly higher for LP versus MC and MD (p = 0.024 and 0.045, respectively). Thermal dose remained below the injury threshold. No differences in dT were seen between pulse types at 0.6 J/6 Hz, 0.2 J/70 Hz, or 1 J/20 Hz. At 1 J/20 Hz, thermal dose exceeded the injury threshold for all pulse types within 3 seconds. Conclusions: Laser pulse type and length seemed to impact heat production in our ureteral model. LP produced significantly greater temperatures at 0.8 J/8 Hz and 1 J/10 Hz relative to MOSES settings. Fortunately, thermal dose remained safe at these settings. Both LP and MOSES technology have been shown to reduce stone retropulsion. At power ≤10 W, the latter may confer this advantage with decreased heat production.

Polymer-Mineral Composites Mimic Human Kidney Stones in Laser Lithotripsy Experiments

Despite the widespread use of laser lithotripsy to fragment kidney stones in vivo, there is a lack of robust artificial stone models to replicate the behavior of human stones during lithotripsy procedures. This need for accurate stone models is particularly important as novel laser technologies are introduced in the field of lithotripsy. In this work, we present a method to prepare composite materials that replicate the properties of human kidney stones during laser lithotripsy. Their behavior is understood through the lens of near-IR spectroscopy and helps to elucidate the mechanism of laser lithotripsy in kidney stone materials.

The Rise and Fall of High Temperatures During Ureteroscopic Holmium Laser Lithotripsy

Introduction: Temperatures over 43°C-the threshold for cellular injury-may be achieved during ureteroscopic holmium laser lithotripsy. The time to reach and subsequently clear high temperatures at variable laser power settings and irrigation pressures has not been studied. Methods: A flexible or semirigid ureteroscope was placed within an 11/13 F ureteral access sheath inserted into a 250-mL saline bag simulating a normal-caliber ureter, renal pelvis reservoir, and antegrade irrigation flow. A thermocouple was placed adjacent to a 365 μm fiber fired for 45 seconds at 0.6 J/6 Hz, 0.8 J/8 Hz, 1 J/10 Hz, 1 J/20 Hz, and 0.2 J/80 Hz. Irrigation pressures of 200, 100, and 0 mm Hg were tested. Mean temperature changes were recorded with 6°C increase as a threshold for injury (as body temperature is 6°C below 43°C). Results: Semirigid scope: At 200 mm Hg no temperature changes >6°C were observed. At 100 mm Hg, changes >6°C occurred with 1 J/20 Hz within 1 second of activation and returned to ≤6°C within 1 second of cessation. At 0 mm Hg, changes >6°C occurred with all settings; within 1 second at power ≥10 W. Temperatures returned to ≤6°C within 5-10 seconds. Flexible scope: At 200 mm Hg, changes >6°C occurred at 1 J/10 Hz (15 seconds), 0.2 J/80 Hz (3 seconds), and 1 J/20 Hz (2 seconds). Temperatures returned within 6°C of baseline within 2 seconds. At 100 mm Hg, changes >6°C occurred in all but 0.6 J/6 Hz. Temperatures returned to ≤6°C in 5-10 seconds. At 0 mm Hg, all settings produced changes >6°C within 3 seconds, except 0.6 J/6 Hz (35 seconds). Temperatures returned to ≤6°C in under 10 seconds. Conclusions: High temperatures were achieved in our in vitro model in as little as 1 second at common irrigation pressures and laser settings, particularly with a flexible ureteroscope and power ≥10 W. However, with laser cessation, temperatures quickly returned to a safe level at each irrigation pressure.

Fragments and dust after Holmium laser lithotripsy with or without "Moses technology": How are they different?

Urinary stones can be readily disintegrated by Holmium:YAG laser (Holmium laser lithotripsy), resulting in a mixture of small stone dust particles, which will spontaneously evacuate with urine and larger residual fragments (RF) requiring mechanical retrieval. Differences between fragments and dust have not been well characterized. Also, it remains unknown how the recently introduced "Moses technology" may alter stone disintegration products. Three complementary analytical techniques have been used in this study to offer an in-depth characterization of disintegration products after in vitro Holmium laser lithotripsy: stereoscopic microscopy, scanning electron microscopy and Fourier-transform infrared spectroscopy. Dust was separated from fragments based on its floating ability in saline irrigation. Depending on initial crystalline constituents, stone dust either conserved attributes found in larger RFs or showed changes in crystalline organization. These included conversion of calcium oxalate dihydrate towards calcium oxalate monohydrate, changes in carbapatite spectra towards an amorphous phase, changes of magnesium ammonium phosphate towards a differing amorphous and crystalline phase and the appearance of hydroxyapatite on brushite fragments. Comparatively, "Moses technology" produced more pronounced changes. These findings provide new insights suggesting a photothermal effect occurring in Holmium laser lithotripsy. Figure: Appearance of hydroxyapatite hexagons on stone dust collected after Holmium laser lithotripsy of a brushite stone using "Moses technology."

Role of lasers in urology

Laser technology has long been a standard treatment for many diseases. In particular, laser treatment is considered the standard of care in various urological diseases. While originally primarily restricted to stone treatment, lasers have since evolved to play an important role even in the treatment of malignant diseases. In this review, we take a closer look at the history of lasers in urology and some implications for treatments today.

Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency

PURPOSE

To evaluate how variable working distances between the laser fiber and the stone influence ablation volume.

METHODS

A laser fiber was fixed on a robotic arm perpendicular to an artificial stone. A single laser pulse was triggered at different working distances (0-2.0 mm in 0.2 mm increments) between the distal fiber tip and the stone. To achieve a measurable impact, pulse energy was set to 2 and 3 J, with either short or long pulse duration. Ablation volume was calculated with an optical microscope. Experiments were repeated five times for each setting.

RESULTS

Highest ablation volume was observed with a long pulse of 3 J at a working distance of 0.4 mm between the laser fiber and the stone surface (p value < 0.05). At 2 J, the highest ablation volume was noticed with a short pulse in contact mode. However, ablation volume of the latter was not significantly greater than with a long pulse of 2 J at a working distance of 0.4 mm (p value > 0.05). Compared to lithotripsy in contact mode, triggering a single long pulse at 0.4 mm increased ablation volume by 81% (p value = 0.016) at 2 J and by 89% (p value = 0.034) at 3 J.

CONCLUSIONS

For Ho:YAG laser lithotripsy, ablation volume may be higher in non-contact mode using long pulses, rather than in direct contact to the stone. Findings of the current study support the need of further studies of lithotripsy in non-contact mode.

Pancreatoscopy in endoscopic treatment of pancreatic duct stones: a systematic review

INTRODUCTION

Treatment of chronic calcifying pancreatitis is challenging and requires an interdisciplinary approach including endoscopist, surgeon and radiologist. With advances in endoscopic technology therapeutic interventions in the pancreatic duct became available. Extracorporeal shock wave lithotripsy (ESWL) is still recommended to be first line treatment, hence peroral pancreatoscopy- (POP) -guided intracorporal lithotripsy is a promising supplement in endoscopic therapy especially if ESWL is unsuccessful or not available.

EVIDENCE AQUISITION

Evidence from published trials, abstracts and case reports on direct pancreatoscopic treatment of main pancreatic duct (MPD) stones was reviewed with focus on efficiency and safety of available technologies, endoscopes and lithotripsy devices. A systematic Medline and Cochrane Database search for relevant studies was performed.

EVIDENCE SYNTHESIS

Seventeen relevant publications meeting the inclusion criteria have been identified (two prospective series, seven retrospective trials, six case reports, two abstracts, for a total of 225 patients). Successful ductal clearance for POP-guided treatment was reported between 37.5% and 100%. Clinical success was reported between 74% and 100%. Adverse event (AE) rate for POP-guided therapy is reported with 0-30%. There is no reported mortality following POP treatment. Three ongoing trials found to be registered.

CONCLUSIONS

POP-guided lithotripsy seems to be a promising alternative in a very selected patient cohort. Good powered randomized controlled trials are needed to prove efficiency and safety of the new technique also for large numbers of patients before it can be recommended as general practice. The focus of future studies should not only be on technical success, but also clinical success and patient-reported outcomes (quality of life).

Holmium-YAG laser: impact of pulse energy and frequency on local fluid temperature in an in-vitro obstructed kidney calyx model

During laser lithotripsy, energy is transmitted to both the stone and the surrounding fluid. As the energy is delivered, the temperature will rise. Temperatures ≥60  °  C can cause protein denaturation. The objective of this study is to determine the time it takes from body temperature (37°C) to 60°C at various laser power settings. A Flexiva TracTip 200 optical fiber was submerged alongside a negative temperature coefficient-type thermistor in 4 mL of saline in a glass test tube. A Lumenis VersaPulse Powersuite 100-W holmium:yttrium aluminum garnet laser was activated at 0.2- to 1.5-J pulse energies, 6- to 50-Hz frequencies, and 2- to 22.5-W average power. Temperature readings were recorded every second from 37°C until 60°C. Time and heating rate were measured. The procedure was repeated three times for each setting. Average time from 37°C to 60°C for settings (1) 0.2 J/50 Hz, (2) 0.6 J/6 Hz, (3) 1 J/10 Hz, and (4) 1.5 J/10 Hz was 60.3, 172.7, 58, and 43.3 s, respectively. Time from 37°C to 60°C decreased as frequency increased for every given pulse energy. Average heating rate increased proportionally to power from 0.06°C/s at 2 W to 0.74°C/s at 22.5 W. During laser lithotripsy, there is a rapid increase in the temperature of its surrounding fluid and temperatures ≥60  °  C may be reached. This could have local tissue effects and some caution with higher power settings should be employed especially where irrigation is limited. Further studies incorporating irrigation and live tissue models may aid to further define the risks.