Clinical experience with holmium:YAG laser lithotripsy of ureteral calculi

Assessing the Role of Light Absorption in Laser Lithotripsy by Isotopic Substitution of Kidney Stone Materials

Understanding the chemical characteristics of kidney stones and how the stone composition affects their fragmentation is key to improving clinical laser lithotripsy. During laser lithotripsy, two mechanisms may be responsible for stone fragmentation: a photothermal mechanism and/or microexplosion mechanism. Herein, we carry out an isotopic substitution of crystal H₂O with D₂O in calcium oxalate monohydrate and struvite stones to alter their optical properties to study the relationship between the absorption of the stones, at the wavelength of the Ho:YAG (2.12 μm) laser, and the fragmentation behavior. Changing the absorption of the stones at 2.12 μm changes the extent of fragmentation, whereas changing the absorption of the bulk medium has a negligible effect on fragmentation, leading to the conclusion that kidney stone ablation is dominated by a photothermal mechanism.

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.

Numerical Response Surfaces of Volume of Ablation and Retropulsion Amplitude by Settings of Ho:YAG Laser Lithotripter

Objectives

Although laser lithotripsy is now the preferred treatment option for urolithiasis due to shorter operation time and a better stone-free rate, the optimal laser settings for URS (ureteroscopic lithotripsy) for less operation time remain unclear. The aim of this study was to look for quantitative responses of calculus ablation and retropulsion by performing operator-independent experiments to determine the best fit versus the pulse energy, pulse width, and the number of pulses.

Methods

A lab-built Ho:YAG laser was used as the laser pulse source, with a pulse energy from 0.2 J up to 3.0 J and a pulse width of 150 μs up to 1000 μs. The retropulsion was monitored using a high-speed camera, and the laser-induced craters were evaluated with a 3-D digital microscope. The best fit to the experimental data is done by a design of experiment software.

Results

The numerical formulas for the response surfaces of ablation speed and retropulsion amplitude are generated.

Conclusions

The longer the pulse, the less the ablation or retropulsion, while the longer pulse makes the ablation decrease faster than the retropulsion. The best quadratic fit of the response surface for the volume of ablation varied nonlinearly with pulse duration and pulse number.

A Usability Comparison of Laser Suction Handpieces for Percutaneous Nephrolithotomy

INTRODUCTION

The holmium laser has revolutionized the practice of minimally invasive endoscopy for kidney stones. Recently, a novel, rigid handpiece for use in percutaneous nephrolithotomy (PCNL) that couples the holmium laser with suction has been developed. To date, limited data exist regarding the usability and ergonomics of such treatment systems. We thus sought to compare surgeon-rated usability with three different suction laser handpieces in a porcine model.

MATERIALS AND METHODS

We performed bilateral reverse PCNL on four female domestic farm pigs. After induction of general anesthesia, percutaneous access was obtained into each kidney by using biplanar fluoroscopy and 8 mm stones (plaster of Paris) were inserted into the calix or renal pelvis for treatment. Four surgeons tested the LASER Suction Tube (Karl Storz^®, Germany), LithAssist™ (Cook^® Medical), and Suction Handpiece (HP) (Lumenis^®, Israel) by using a combination of fragmentation (5 Joules/20 Hertz) and dusting (0.8 Joules/80 Hertz) settings on the Lumenis pulse 120 H laser. The primary outcome assessed was the ease of use of the three devices as measured by a surgeon questionnaire.

RESULTS

A total of 15 stones were treated in 8 renal units. The mean time required for stone fragmentation was 8 min. The mean handling and suction efficiency scores were similar between devices. The Suction HP offered the best laser fiber visibility during lithotripsy.

CONCLUSION

Suction laser handpieces offer an option to treat renal stones via PCNL, with limited differences noted in most surgeon ratings between devices.

A comparison of efficacies of holmium YAG laser, and pneumatic lithotripsy in the endoscopic treatment of ureteral stones

OBJECTIVE

We aimed to compare the effectiveness of holmium YAG laser and pneumatic lithotripsy in the treatment of ureteral stones.

MATERIAL AND METHODS

A total of 216 patients who had established indications of ureteroscopy between November 2011 and June 2012 were included in this study. Patients' files were retrospectively reviewed by dividing cases as groups that underwent pneumatic (PL) or laser lithotripsy (LL) procedures. Age, sex, stone burden and localization, duration of follow-up, operative times were evaluated. Stone-free rates were evaluated by ureteroscopical examination, postoperative scout films and ultrasonography.

RESULTS

Group PL consisted of 109 and group LL of 107 patients. Median age was 43.93±15.94 years in Group PL and 46.15±14.54 years in Group LL. Male to female ratio, stone burden and localization were similar for both groups. Overall success rate was 89.9% in Group PL and 87.9% in Group LL, respectively (p<0.791). With the aid of additional procedures, success rate was 100% for both groups at the end of the first month. Groups were not different as for operative time, rate of insertion of an ureteral catheter and its removal time. Hospitalization period was apparently somewhat shorter in Group LL (p=0.00).

CONCLUSION

Pneumatic lithotripsy can be as efficacious as laser lithotripsy and be used safely in the endoscopic management of ureteral stone. In comparison of both methods, we detected no differences as to operative time, success of operation and the time to removal of the catheter, however, hospitalization period was shorter in Group LL.

Minimally invasive management with holmium laser in total urinary tract calculi

OBJECTIVE

The purpose of this article was to study the management of total urinary tract calculi using holmium laser minimally invasive techniques.

BACKGROUND DATA

It is rare for patients to present kidney stones, ureteral stones, and bladder stones simultaneously, and their treatment is considered to be complicated and difficult, specifically by minimally invasive techniques.

METHODS

We collected seven cases of total urinary tract calculi from May 2007 to September 2012. Three cases were unilateral, and the others were bilateral. All of the cases presented calculus in the bladder, ureter, and kidney, which were secondary to the long-term indwelling double J stent or lower urinary obstruction.

RESULTS

Extracorporeal shock-wave lithotripsy (SWL) was administered first, followed by the operation. For patients with bilateral calculi, at one stage, ureteroscopic lithotripsy (URL) with holmium laser was performed in all four cases to remove the bladder and bilateral ureter stones. Then, all patients underwent percutaneous nephrolithotomy (PCNL) with holmium procedures to address the bilateral kidney and upper ureter stones at the second stage. The indwelling double J stents were removed at the same time. For the patients with unilateral calculi, we performed a single operation, but it was conducted using the same treatment sequence as the bilateral procedure. The related symptoms in all cases disappeared after the operation. Re-examination showed that the stones were nearly dissolved and that renal function was recovered.

CONCLUSIONS

URL with holmium laser for the bladder and ureters combined with PCNL to dissolve kidney and upper ureteral stones could be the ideal choice for the treatment of total urinary tract calculi.

Treatment of ureteral calculus obstruction with laser lithotripsy in an Atlantic bottlenose dolphin (Tursiops truncatus)

An adult female bottlenose dolphin (Tursiops truncatus) presented with acute anorexia secondary to progressive azotemia (blood urea nitrogen = 213 mg/dl, creatinine [Cr] = 9.5 mg/dl) and electrolyte abnormalities (K = 7.4 mEq/L). It was later diagnosed with postrenal obstruction secondary to bilaterally obstructing ureteral calculi seen on ultrasound. Treatment of the obstruction required two endoscopic procedures, cystoscopy for ureteral stent placement and ureteroscopy to perform intracorporeal lithotripsy on the obstructing calculi. Before the first procedure, the dolphin's azotemia was stabilized with aggressive fluid therapy, peritoneal dialysis, and treatment for acidosis. Diuresis subsequent to the fluid therapy enabled passage of the right obstructing urolith. For both endoscopic procedures, the dolphin was placed in left lateral recumbency due to the peritoneal dialysis catheter in the right retroperitoneal region. For the first procedure, a 12-French (Fr) flexible cystoscope was inserted retrograde into the bladder via the urethra, whereupon a calculus was seen obstructing the left ureteral orifice. A 4.8-Fr, 26-cm double-pigtail ureteral stent was placed up the left ureter to relieve the postrenal obstruction. Inadvertent proximal migration of the left ureteral stent occurred during the procedure. However, renal parameters (serum Cr = 5.8, K = 5.4) improved significantly by the next day. For the second procedure, 28 hr later, ureteroscopy was performed to treat the calculus and replace the existing stent with a longer stent. The left ureteral calculus was pulverized into tiny fragments by using a holmium:yttrium-aluminum-garnet laser inserted through a 6.9-Fr semirigid ureteroscope. The migrated stent was visualized in the distal left ureter and replaced with a 90-cm single-pigtail ureteral stent that was sutured exterior to the urogenital slit and removed 3 days later. Renal function normalized over the next several days, and the dolphin recovered over the next 2 mo.

Treatment of ureteral stones: A prospective randomized controlled trial on comparison of Ho:YAG laser and pneumatic lithotripsy

OBJECTIVES

To study the treatment of ureteric stones by HO:YAG laser lithotripsy and pneumatic lithotripsy and to evaluate the results of the two treatment modalities to assess effectiveness and complications.

MATERIALS AND METHODS

Over 1-year period, a total of 79 patients with 82 ureteral stones were randomized into two groups. In group 1 (39 cases with 41 ureteral stones) ureteroscopic HO:YAG laser lithotripsy was performed using a rigid 8 Fr-ureteroscope (LL group). In group 2 (40 cases with 41 ureteral stones) pneumatic lithotripsy was performed in like manner. Efficacy safety and complications in both groups were analyzed.

RESULTS

A total of 79 patients with 82 calculi were treated. Two cases in LL group and one in PL group had bilateral ureteral stones. Mean stone size was 12.07 mm in LL group and 10.2 mm in PL group. Stones located in lower ureter in 30 cases on LL group and 29 cases in PL group. Proximal migration of stone occurred in 1 case on LL group and in 3 cases on PL group. Successful fragmentation occurred in 37 cases on LL group and in 30 cases on PL group. Stone-free rate after 1 month in the base of Kidney Ureter Bladder (KUB) and sonography was 95% in LL group and 80.5% in PL group. Ureteral perforation, urinoma, and urosepsis were not seen in both groups.

CONCLUSION

HO:YAG laser has advantages over PL in high efficacy of stone fragmentation and a low-retrograde migration of ureteral stone treatment. Other complication of ureteral stone treatment with LL and PL are the same and very rare.

Comparison of percutaneous nephrolithotomy using pneumatic lithotripsy (lithoclast®) alone or in combination with ultrasonic lithotripsy

PURPOSE

Percutaneous nephrolithotomy (PCNL) is the procedure of choice for treating large renal stones. Pneumatic lithotripsy (Lithoclast®) is effective regardless of the stones' composition, and ultrasonic lithotripsy allows the aspiration of small debris during lithotripsy. We investigated the efficacy and safety of PCNL via Lithoclast® alone or combined with ultrasonic lithotripsy.

MATERIALS AND METHODS

Thirty-five (group A) and 39 (group B) patients underwent Lithoclast® PCNL and combination therapy, respectively, from May 2001 to March 2010, and the two groups were compared in terms of stone size, location, and composition; operative time; average number of treatments; hospital days; hemoglobin loss; ancillary procedures; rate of device failure; and initial and total stone-free rates.

RESULTS

The two groups did not differ significantly in preoperative stone size, location, or composition; the average number of treatments; or the initial and overall stone-free rates. However, combination therapy was associated with a significantly lower operative time (181±50 vs. 221±65 min, respectively, p=0.004), number of hospital days (11.6±3.8 vs. 14.2±4.4 days, respectively, p=0.009), and average hemoglobin loss (1.12±0.61 vs. 1.39±1.02 g/dl, respectively, p=0.013). Transfusions were required in 6 patients (4 and 2 in each group, respectively), but there were no significant complications related to percutaneous access. There were 2 (5.7%) mechanical failures (Lithoclast® probe fracture) in the group A and 5 (12.8%) in the group B (2 cases of suction tube obstruction, 3 cases of overheating).

CONCLUSIONS

The combination of ultrasonic lithotripter and Lithoclast® is more effective than Lithoclast® alone because it significantly decreases operative time, hemoglobin loss, and the hospital stay. This may reflect the superior power of Lithoclast® and the ability to aspirate the debris during ultrasonic lithotripsy.

Synchronous radiation with Er:YAG and Ho:YAG lasers for efficient ablation of hard tissues

Er:YAG and Ho:YAG laser beams were combined to irradiate hard tissues to achieve highly efficient ablation with low laser power. The delay time between pulses of the two lasers was controlled to irradiate alumina ceramic balls used as hard tissue models. With optimized delay time, the combined laser beam perforated the sample 40% deeper than independent radiation by either an Er:YAG or Ho:YAG laser. An ultra-high-speed camera and an infrared thermography camera were used to observe and investigate the ablation mechanisms.

A Review of Studies Reporting on Complications of Upper Urinary Tract Stone Ablation Using the Holmium:YAG Laser

Purpose:

A review of the literature of studies reporting complications of ureteroscopic urinary tract stone ablation using the holmium:YAG laser was performed.

Patients and methods:

Electronic databases were searched using specific keywords to identify relevant studies. Reference lists of identified articles were scrutinised for other studies and searches were conducted using the names of authors known to have published widely in this field. Two reviewers assessed retrieved articles for inclusion criteria. Patients <16 years old were excluded.

Results:

Overall, 48 studies published between 1994 and 2007 were included. Half were published since 2000. In total, 4454 patients were identified. Around half of studies were performed in North America (25). The number of patients per study varied from 8 to 598. The study populations were very heterogeneous in terms of stone position and size, and ureteroscope size and rigidity. Overall, 303 (6.8%) complications were identified. Post-operative ureteric stricture and perforation rates were both 1.0%. There were only six major complications identified (0.1%). The post-operative sepsis rate was 2% and one death was reported.

Conclusions:

Upper urinary tract stone ablation using the holmium:YAG laser is both safe and reliable. Follow-up imaging to detect procedure-specific complications would not appear to be routinely indicated given this low complication rate.

Lasers in percutaneous renal procedures

INTRODUCTION

Since the invention of lasers in 1960, they have been increasingly used in medicine. In this review paper, the types of lasers used in urology, in addition to their applications to percutaneous renal surgery will be reviewed. Specifically, use of lasers in the percutaneous management of renal stones, upper tract transitional cell carcinoma and stricture will be reviewed.

MATERIALS AND METHODS

Pubmed was searched for citations since 1966. The following terms were used: "lasers", "calculi", "endopyelotomy", and "transitional cell carcinoma".

RESULTS

Due to its minimal depth of penetration, holmium laser has proven to be safe and efficacious. It is currently the primary energy source for flexible instrumentation, and also has demonstrated efficacy in percutaneous lithotripsy (faster than ultrasonic lithotripsy and safer than electrohydraulic lithotripsy). Holmium laser been used for antegrade endopyelotomy and percutaneous resection of upper tract transitional cell carcinoma.

CONCLUSIONS

Holmium laser is safer than other lasers and has become the gold standard for laser lithotripsy for flexible instrumentation. It has been used successfully in the percutaneous management of renal stones, ureteropelvic junction obstruction, and upper tract transitional cell carcinoma. Holmium laser is an alternative energy source to conventional lithotripters and electrocautery for endopyelotomy and resection of upper tract transitional cell carcinoma.

Ureteric guidewire damage by Holmium:YAG laser: preliminary results

Typically, guidewires are regularly used to provide access or act as a guide during laser lithotripsy. This may result in the tip of the fibre being in close proximity to the guidewire during the firing period and consequently, this could result in accidental damage to the guidewires during the procedure. To replicate this scenario, an experimental model was designed enabling accurate and reproducible positioning of the laser fibre relative to the guidewire. The guidewire was exposed to the laser energy for a range of typical settings used in the clinic. The results demonstrate that the guidewire is susceptible to laser energy damage, especially in close proximity to the fibre.

New endourologic technology for simultaneous holmium:YAG laser lithotripsy and fragment evacuation for PCNL: ex-vivo comparison to standard ultrasonic lithotripsy

Percutaneous nephrolithotomy (PCNL) is a well established procedure and accepted as the standard of care for the treatment of large renal calculi. Since the introduction of the holmium:yttrium-aluminum-garnet (Ho:YAG) laser into clinical practice in 1990, it has been used successfully to treat various urologic conditions. Today it is the modality of choice for retrograde intracorporeal stone disintegration ureteroscopically, and has also been used successfully for PCNL. One disadvantage when using the Ho:YAG laser for disintegration of renal calculi is the need for graspers to extract fragments and the mobilization of fragments due to the lack of simultaneous suction. We present our experience with a Ho:YAG laser in combination with simultaneous suction in an in-vitro model using a new endourologic technique in comparison to conventional ultrasonic lithotripsy.

Dependence of calculus retropulsion on pulse duration during Ho: YAG laser lithotripsy

BACKGROUND AND OBJECTIVES

The purpose of this study was to investigate the effect of optical pulse duration on stone retropulsion during Ho:YAG (lambda = 2.12 microm) laser lithotripsy.

STUDY DESIGN/MATERIALS AND METHODS

A clinical Ho:YAG laser with pulse durations was employed to fragment calculus phantoms and to evaluate stone phantom retropulsion. At a given pulse energy, optical pulse durations were divided into two discrete conditions: short pulse (tau(p): 120 to approximately 190 microseconds at FWHM) and long pulse (tau(p): 210 to approximately 350 microseconds at FWHM). Plaster of Paris calculus phantoms were ablated at different energy levels using optical fibers of varying diameters (273, 365, and 550 microm in core size). The dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera; the laser-induced craters were evaluated with optical coherent tomography (OCT). Bubble formation and collapse were recorded with a fast flash photography setup, and acoustic transients were measured with a hydrophone.

RESULTS

Shorter pulse durations produced more stone retropulsion than longer pulses at any given pulse energy. Regardless of pulse duration, higher pulse energy and larger fibers resulted in larger ablation volume and retropulsion (P<0.05). For shorter pulse durations, more rapid bubble expansion was observed and higher amplitudes of the collapse pressure wave were measured (P<0.05).

CONCLUSION

Less retropulsion and equivalent fragmentation occurred when Ho:YAG pulse duration increased.

Holmium:YAG laser treatment of ureteral calculi: a 5-year experience

The purpose of this study was to provide an account of the 5-year experience we have gained using holmium:yttrium-aluminium-garnet (Ho:YAG) lasertripsy in the treatment of ureteral stones. One-hundred thirty-seven transurethral ureterolithotripsies were performed in 131 patients. A Ho:YAG laser device, fibres with diameters of 360 and 550 mum, a video camera as well as semi-rigid and flexible ureterorenoscopes were used. Results showed that the direct success rates-which meant stone-free ureters on the first post-operative day-in the upper, middle and lower ureters were 84.6, 88.7 and 94.8%, respectively. The final success rates--which meant stone-free ureters 4 weeks after the operation without a second intervention--were 84.6, 96.7 and 96.7%, respectively. The pulsatile Ho:YAG laser beam fragmented all kinds of stones easily. No ureteral stricture or reflux was identified during the follow-up period. The advantages of Ho lasertripsy outweighed its disadvantages. Based on our experience, the Ho:YAG laser is one of the most effective and safest energy sources in the treatment of ureteral calculi.

Urinary calculus fragmentation during Ho: YAG and Er:YAG lithotripsy

BACKGROUND AND OBJECTIVES

We tested Ho:YAG and Er:YAG laser ablation of human urinary calculi to determine if Er:YAG is a more efficient lithotripsy device.

STUDY DESIGN/MATERIALS AND METHODS

Ablation efficiency of Ho:YAG and Er:YAG lasers was tested at varying energy settings, ranging from the damage threshold to clinical energy setting associated with Ho:YAG laser. Stones of known composition (calcium oxalate monohydrate (COM), cystine, and uric acid (UA)) were irradiated. Crater width, depth, and ablation volumes were determined using an optical coherence tomography (OCT).

RESULTS

For all stones and energy settings, the Er:YAG laser produced deeper craters and larger ablation volumes than Ho:YAG laser. The Ho:YAG laser created wider craters during the multiple pulse process and the shape of craters was irregular.

CONCLUSIONS

The Er:YAG laser is more efficient than the Ho:YAG laser for lithotripsy. The deeper craters produced by the Er:YAG laser is attributed to the high absorption of energy at its wavelength.

Complications of pneumatic ureterolithotripsy in the early postoperative period

PURPOSE

To document the perioperative and early postoperative complications of pneumatic ureterolithotripsy.

PATIENTS AND METHODS

Between January 1997 and December 2003, pneumatic ureterolithotripsy was performed in 665 male and 314 female patients for stones >0.5 cm. The age range was 9 months to 72 years (mean 41 years). Preoperatively, intravenous urography, urinalysis, and urine culture were done. Cefepime 1 g was given as prophylactic antimicrobial therapy 1 hour prior to surgery. A plain film of the urinary tract was taken immediately before the procedure. The operations were carried out with the patient under general anesthesia. Rigid ureteroscopes (6.9F ACMI "micro-6" or 8F-10F Storz) and the Vibrolith (Elmed, Ankara, Turkey) pneumatic lithotripter were used. The fragments were extracted with forceps or baskets. Urinalysis and culture as a routine postoperative evaluation and a plain film or ultrasonogram of the urinary tract when needed were done 1 week after the procedure.

RESULTS

The stones were completely removed in 847 patients (86.5%); 783 (80%) of them went home on the day of surgery. A ureteral stent was needed in 401 patients (41.0%). Perioperative complications were migration of the stone into the kidney in 70 patients (7.2%), mucosal damage in 34 (3.5%), ureteral perforation in 17 (1.7%), ureteral avulsion in 4 (0.4%), and conversion to open surgery in 3 (0.2%). During the early postoperative period, flank pain (18.4%), pelvic discomfort (5.5%), macroscopic hematuria (7.3%), and urinary tract infection (5%) were recorded.

CONCLUSION

Ureterolithotripsy by a pneumatic lithotripter is a minimally invasive, highly tolerable procedure with a low complication rate and short hospital stay when performed meticulously with appropriate instruments.

Laparoscopic Ureterolithotomy: The Method of Choice in Selected Cases

OBJECTIVE

To evaluate retrospectively the results and complication, efficacy, and safety rates of laparoscopic ureterolithotomy in the treatment of large, impacted ureteric stones.

MATERIALS AND METHODS

Between September 1994 and December 2003, 73 patients underwent 75 laparoscopic ureterolithotomies (LUL). Mid- and upper-ureteric stones were removed retroperitoneally in 69 cases (92%). Lower ureteric stones were removed transperitoneally in 6 cases (8%). There were 2 (3%) bilateral LULs in one session, 7 (10%) ipsilateral percutaneous nephrolithotomy, and 6 (8%) ipsilateral ureteroscopy in the same session. The mean age of the patients was 39 years (range, 15-70 years). Mean stone size was 25 mm (range, 12-55 mm).

RESULTS

The success rate was 98.7%, with 1 patient (1.3%) requiring conversion to an open procedure. There were no major complications. Mean operative time was 45 minutes (range, 15-100 minutes). Postoperative analgesic medication was required for 1 day in 39 patients (52%). The postoperative hospital stay ranged from 2 to 5 days (mean, 3 days).

CONCLUSION

On the basis of our experience, laparoscopic ureterolithotomy is a safe and effective method for the treatment of large, dense, and impacted ureteric stones. In selected cases it can be the first choice of treatment.

Percutaneous nephrolithotomy with holmium: Yttrium-aluminum-garnet laser and fiber guider—report of 349 cases

OBJECTIVES

To assess the efficacy and safety of holmium:yttrium-aluminum-garnet (YAG) laser lithotripsy for percutaneous nephrolithotomy in a cohort of 349 consecutive procedures.

METHODS

We retrospectively reviewed the charts of 334 patients who had undergone 349 percutaneous nephrolithotomy (PCNL) procedures conducted at our hospital from January 2001 to March 2004 in which the holmium:YAG laser with a self-made fiber guider was used for lithotripsy.

RESULTS

The average patient age was 54.1 years, and the average stone size was 3.3 +/- 1.8 cm. The average operative time was 99 +/- 38 minutes, and the average postoperative hospital stay was 4.0 +/- 2.3 days. The overall stone-free rate was 83.7%. The postoperative urinary tract infection rate was 7.2%. The postoperative transfusion rate was 2.0%. The holmium:YAG laser was effective against all kinds of stones, but sometimes it was time consuming to use the holmium:YAG laser to disintegrate a very large stone. Thirteen PCNLs (3.7%) to treat large complete staghorn stones were performed in combination with a pneumatic lithotriptor. Of the 349 procedures, 152 (43.6%) had bloodless tracts afterward, and all 152 procedures had been performed with the nephrostomy tube-free modification.

CONCLUSIONS

The holmium:YAG laser is an effective and safe lithotriptor for most percutaneous stone surgery. However, in patients with a very large stone burden, the combination of this technology with another, more powerful, intracorporeal lithotriptor may be necessary.

Porcine skin ED50 damage thresholds for 2,000 nm laser irradiation

BACKGROUND AND OBJECTIVES

To gain refinement in safe-exposure limits, indicated by the maximum permissible exposure (MPE) limits, the minimum visible lesion thresholds for three spot sizes (5-15 mm) and four exposure durations (0.25-2.5 seconds) were determined for the skin at 2,000 nm continuous wave laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

A series of experiments were conducted in vivo on female Yucatan mini-pigs to determine the ED50 damage thresholds for 2,000 nm continuous wave laser irradiation. The study employed Gaussian laser beam exposures with spot diameters (1/e2) of 4.83, 9.65, and 14.65 mm and exposure durations of 0.25, 0.5, 1.0, and 2.5 seconds as a function of laser power. The effect of each irradiation was evaluated within 1 minute after irradiation and the final determination was made at 48 hours post-exposure. Probit analysis was conducted to estimate the dose for 50% probability of laser-induced damage (ED50), defined as persistent redness at the site of irradiation for the mini-pig skin after 48 hours.

RESULTS

The MPE spot size and exposure duration trends for 2,000 nm laser exposure is consistent for exposure diameters less than 3.5 mm. However, for larger exposure diameters of 4.83, 9.65, and 14.65 mm and exposure duration longer than 0.25 second, the current MPEs are bigger than one tenth of our damage thresholds. For Gaussian laser profile, which is common for many laser output irradiance distributions, lower energy is required to generate a lesion on skin for smaller spot sizes and shorter exposure duration. On the other hand, for spot sizes greater than 4.83 mm and exposure duration over 0.25 second, the average radiant exposure at threshold is inversely proportional to spot size. The irradiance-time and temperature-time power law at the threshold were investigated as well and showed that the irradiance-time power law was a close approximation to estimate laser irradiance at ED50 damage threshold.

CONCLUSIONS

The thresholds study shows that consideration for lowering the MPE standards should be explored as the laser beam diameter becomes larger than 3.5 mm. Based on the limited experimental data, the duration and size dependences of the ED50 damage thresholds could be described by an empirical equation: Irradiance at the threshold = (5.669-1.81xspot diameter)xexposure duration -0.794.

A perspective on laser lithotripsy: the fragmentation processes

This paper describes in simple terms the physics of laser-calculus interactions and introduces a method with which physicians can understand or evaluate the application of any new laser technique for use in lithotripsy or other medical fields. Tissue optical properties and laser parameters govern the mechanism(s) of fragmentation of urinary or biliary calculi. Laser pulse energies for clinical lithotripsy range from Q0 = 20 mJ to 2 J for short-pulsed lasers to long-pulsed lasers, respectively. Lasers with short pulse durations (i.e., less than a few microseconds) fragment calculi by means of shockwaves following optical breakdown and plasma expansion of ionized water or calculus compositions or by cavitation collapse, thus manifesting a photoacoustical effect. Laser-tissue interactions involving dominant photomechanical or photoacoustical effects are usually stress confined. Long-pulsed lasers (i.e., >100 microsec), on the other hand, generate minimal acoustic waves, and calculi are fragmented by temperatures beyond the thresholds for vaporization of calculus constituents, melting, or chemical decomposition.

Percutaneous ureterolithotomy: direct method for removal of impacted ureteral stones

PURPOSE

We report 52 percutaneous urterolithotomies in 51 patients having large, impacted middle ureteral stones. Direct percutaneous stone removal can be performed as successfully as in cases of renal stones treated with percutaneous nephrolithotomy.

METHODS

The operation is performed under local anesthesia; therefore, the procedure is quicker and simpler than the laparoscopic or retroperitoneoscopic intervention. All patients became stone free. In two patients (4%), ultrasound disintegration was necessary; in the remaining cases, there was no need for any fragmentation: the stone was removed intact. A retroperitoneal drain was always left at the end of the procedure. With the exception of two cases, the ureter was always stented without closure of the ureteral incision.

RESULTS

Fever (> or = 38 degrees C) was observed in 15 patients (29%) for 2 days. Retroperitoneal hematoma 5 cm in diameter was seen in one patient. One patient had urine leakage through the retroperitoneal drain in the postoperative period for 18 days. Also, one patient came back 3 days after discharge with urine leakage through the percutaneous retroperitoneal tract.

CONCLUSION

Direct percutaneous ureterolithotomy is an effective way to remove impacted middle ureteral stones but is advisable only for endourologists with considerable experience.

Outpatient ureteroscopic lithotripsy: selective internal stenting and factors enhancing success

PURPOSE

To evaluate a policy of selective, short-duration internal stenting after outpatient ureteroscopic laser lithotripsy.

PATIENTS AND METHODS

From January 1997 to April 1998, 62 patients (34 male, 28 female) with a mean age of 50 (range 21-80) years underwent outpatient ureteroscopic lithotripsy using a holmium laser (365 microm; 0.5-1.4J/5-10 Hz) and 6F/7.5F semirigid ureteroscope. Internal stents were inserted selectively in patients with severe preoperative obstruction (intravenous urogram finding), tight stone impaction (endoscopic finding), or significant residual obstruction (on-table retrograde pyelogram finding) despite stone clearance. Patient demographics, stone measures, stone clearance rates, complications, postoperative pain scores, analgesic requirement, and follow-up imaging were compared for the stented and unstented patients.

RESULTS

With the present criteria of selective internal stenting, stents were inserted in 56% of the patients for a mean duration of 3.6 weeks. Excluding those patients with residual stones requiring further interventions, the stenting rate was 39% with a mean duration of 1.9 weeks. There was no difference in patient characteristics, stone burden, and stone levels between the stented and unstented group. The mean operating time for the unstented group was shorter than for the stented group (45.6 minutes v 56.6 minutes; P = 0.03). The stone clearance rates were similar for the two groups (96% v 97%), but the complication rate of the stented group was higher (8.6% v 3.7%). The mean postoperative pain score and analgesic requirement were similar in the two groups on postoperative day 1 but significantly less in the unstented group on day 3.

CONCLUSIONS

The criteria for selective internal stenting are useful in determining when a stent should be used. By omitting the stent insertion in the absence of these criteria, operating time, postoperative pain, and analgesic requirement were reduced without increasing the complication rate. Ureteral stricturing was absent despite the low stenting rate.

Experience with the holmium laser as an endoscopic lithotrite

INTRODUCTION

Holmium laser lithotripsy represents an additional option in the management of urinary tract calculi. We report the results of a cohort of patients with ureteric and bladder calculi treated with this modality.

METHODS

Twenty-three patients underwent holmium laser lithotripsy to treat ureteric or bladder calculi. Power settings of 0.5 J to deliver 2.5-4.0 watts were used for the ureteric calculi, and up to 30 watts for the bladder calculi.

RESULTS

The mean ureteric stone size was 7.3 mm (range 4-10 mm). One stone was upper ureteric, seven were mid-ureter and nine were lower-ureter. Eighteen of the 19 patients with ureteric calculi were free of stones 28 days postoperatively. The remaining patient was clear by 12 weeks. All patients with bladder calculi were completely cleared of stones. There were no intraoperative complications.

DISCUSSION

Ureteric stone position can limit the use of extracorporeal shock wave lithotripsy due to imaging difficulties. Ureteric lithotripsy overcomes this problem. The holmium laser has proven to be safe and effective in clearing urinary stone burdens of a variety of sizes, sites and compositions in this cohort of patients.

Free electron laser lithotripsy: threshold radiant exposures

PURPOSE

To determine the threshold radiant exposures (J/cm2) needed for ablation or fragmentation as a function of infrared wavelengths on various urinary calculi and to determine if there is a relation between these thresholds and lithotripsy efficiencies with respect to optical absorption coefficients.

MATERIALS AND METHODS

Human calculi composed of uric acid, calcium oxalate monohydrate (COM), cystine, or magnesium ammonium phosphate hexahydrate (MAPH) were used. The calculi were irradiated in air with the free electron laser (FEL) at six wavelengths: 2.12, 2.5, 2.94, 3.13, 5, and 6.45 microm.

RESULTS

Threshold radiant exposures increased as optical absorption decreased. At the near-infrared wave-lengths with low optical absorption, the thresholds were >1.5 J/cm2. The thresholds decreased below 0.5 J/cm2 for regions of high absorption for all the calculus types. Thresholds within the high-absorption regions were statistically different from those in the low-absorption regions, with P values much less than 0.05.

CONCLUSIONS

Optical absorption coefficients or threshold radiant exposures can be used to predict lithotripsy efficiencies. For low ablation thresholds, smaller radiant exposures were required to achieve breakdown temperatures or to exceed the dynamic tensile strength of the material. Therefore, more energy is available for fragmentation, resulting in higher lithotripsy efficiencies.

Endoscopic lithotripsy with the holmium:YAG laser

BACKGROUND AND OBJECTIVE

The holmium:YAG (Ho:YAG) laser can be used not only for soft tissue but also for hard tissue such as urinary calculi. The objective of this study was to assess the usefulness of the Ho:YAG laser for endoscopic lithotripsy in patients with urinary tract stone. STUDY DESIGN/MATERIASL AND METHODS: Of 102 procedures performed among 96 patients, 88 were transurethral ureterolithotripsy (TUL), seven were percutaneous nephrolithotripsy, and seven were transurethral cystolithotripsy. Six patients had bilateral stones. The fragments were reduced as much as possible with the Ho:YAG laser.

RESULTS

The efficacy rate of the 102 lithotripsy procedures was 93%. With respect to the effect of TUL, the efficacy rates of 40 procedures for the proximal ureter, 18 procedures for the midureter, and 30 procedures for the distal ureter were 85%, 94%, and 100%, respectively.

CONCLUSION

The Ho:YAG laser produced a sufficiently strong lithotripsy force on all stones. The results of this study indicate that lithotripsy of urinary tract stones with the Ho:YAG laser can achieve a clinical outcome equivalent to or exceeding that of pulsed dye laser lithotripsy. The Ho:YAG laser is a multipurpose laser and thus is a cost effective and very useful means for endoscopic lithotripsy of urinary tract stones.

Identifying stone composition using infrared analysis of filtered urine after ureteroscopic lithotripsy

BACKGROUND AND PURPOSE

With the development of small-caliber ureteroscopes and lithotripsy devices, it is now possible to perform intracorporeal stone fragmentation without dilatation of the ureteral orifice. Ureteral stones are typically fragmented into small particles that can be difficult to retrieve for stone analysis. Infrared spectroscopy (IRS) of the precipitate from urine after intracorporeal lithotripsy represents a method for obtaining stone analysis.

PATIENTS AND METHODS

A total of 69 patients underwent ureteroscopic lithotripsy with the holmium laser or the electrohydraulic probe for stones in the ureter (N = 65) or kidney (N = 4). Each patient's bladder was then drained and the urine filtered. The resulting precipitate was analyzed using IRS.

RESULTS

The amount of material for analysis was < or =1 mg in 56 patients (82%). Stone composition was positively identified in 44 patients (64%). Material suitable for analysis was recovered from 73% of patients when the bladder was drained with a cystoscope sheath compared with 43% when a urethral catheter was used (P = 0.03). There was no significant difference in pretreatment stone size in the patients who had a positive v a negative result (11.7 mm v 10.9 mm; P = 0.06). Similarly, the stone location was not significantly related to the likelihood of positive analysis (P = 0.29).

CONCLUSION

Straining the urine after ureteroscopic intracorporeal lithotripsy and analyzing the precipitate with IRS is able to identify stone composition in the majority of patients. This method is especially useful in the setting of holmium laser lithotripsy, in which the majority of the stone is converted to spontaneously passable particles.

Holmium:YAG laser lithotripsy: A dominant photothermal ablative mechanism with chemical decomposition of urinary calculi

BACKGROUND AND OBJECTIVE

Evidence is presented that the fragmentation process of long-pulse Holmium:YAG (Ho:YAG) lithotripsy is governed by photothermal decomposition of the calculi rather than photomechanical or photoacoustical mechanisms as is widely thought. The clinical Ho:YAG laser lithotriptor (2.12 microm, 250 micros) operates in the free-running mode, producing pulse durations much longer than the time required for a sound wave to propagate beyond the optical penetration depth of this wavelength in water. Hence, it is unlikely that shock waves are produced during bubble formation. In addition, the vapor bubble induced by this laser is not spherical. Thus the magnitude of the pressure wave produced at cavitation collapse does not contribute significantly to lithotripsy.

STUDY DESIGN/MATERIALS AND METHODS

A fast-flash photography setup was used to capture the dynamics of urinary calculus fragmentation at various delay times following the onset of the Ho:YAG laser pulse. These images were concurrently correlated with pressure measurements obtained with a piezoelectric polyvinylidene-fluoride needle-hydrophone. Stone mass-loss measurements for ablation of urinary calculi (1) in air (dehydrated and hydrated) and in water, and (2) at pre-cooled and at room temperatures were compared. Chemical and composition analyses were performed on the ablation products of several types of Ho:YAG laser irradiated urinary calculi, including calcium oxalate monohydrate (COM), calcium hydrogen phosphate dihydrate (CHPD), magnesium ammonium phosphate hexahydrate (MAPH), cystine, and uric acid calculi.

RESULTS

When the optical fiber was placed perpendicularly in contact with the surface of the target, fast-flash photography provided visual evidence that ablation occurred approximately 50 micros after the initiation of the Ho:YAG laser pulse (250-350 micros duration; 375-400 mJ per pulse), long before the collapse of the cavitation bubble. The measured peak acoustical pressure upon cavitation collapse was negligible (< 2 bars), indicating that photomechanical forces were not responsible for the observed fragmentation process. When the fiber was placed in parallel to the calculus surface, the pressure peaks occurring at the collapse of the cavitation were on the order of 20 bars, but no fragmentation occurred. Regardless of fiber orientation, no shock waves were recorded at the beginning of bubble formation. Ablation of COM calculi (a total of 150 J; 0.5 J per pulse at an 8-Hz repetition rate) revealed different Ho:YAG efficiencies for dehydrated calculus, hydrated calculus, and submerged calculus. COM and cystine calculi, pre-cooled at -80 degrees C and then placed in water, yielded lower mass-loss during ablation (20 J, 1.0 J per pulse) compared to the mass-loss of calculi at room temperature. Chemical analyses of the ablated calculi revealed products resulting from thermal decomposition. Calcium carbonate was found in samples composed of COM calculi; calcium pyrophosphate was found in CHPD samples; free sulfur and cysteine were discovered in samples composed of cystine samples; and cyanide was found in samples of uric acid calculi.

CONCLUSION

These experimental results provide convincing evidence that long-pulse Ho:YAG laser lithotripsy causes chemical decomposition of urinary calculi as a consequence of a dominant photothermal mechanism.

Impact of holmium laser settings and fiber diameter on stone fragmentation and endoscope deflection

We compared the impact of various energy settings, frequency, and fiber diameters on the stone fragmentation capabilities of the holmium laser. Stone phantoms, made from plaster of Paris and uniform in weight, were treated with one of two laser fiber sizes: small (200 and 365 microm) and large (550 and 1000 microm). Stones were immersed in water and fragmented for 3 minutes at 0.5, 1.0, or 2.0 J and 5, 10, or 15 Hz. The mean percentage decrease in weight in the two groups was compared using one-way ANOVA. The effect on flexible ureterorenoscope deflection of the small fibers was tested in two different ureterorenoscopes. Raising the energy level when using the small fibers resulted in more weight loss (P < 0.05). Increasing the frequency up to 10 Hz also resulted in a significant increase in weight loss (P < 0.05), yet above 10 Hz, there was no significant additional weight loss noted for either small fiber. There was no significant difference in the weight loss produced by the two fibers unless the energy setting was >1.0 J. Studies with the large fibers demonstrated similar results, with significant increments of weight loss occurring with increased energy (P < 0.05), while nonsignificant differences were seen for the two fiber diameters. Increasing laser frequency up to 15 Hz resulted in a significant increase in weight loss for the large fibers. Loss of ureterorenoscope deflection ranged from 7% to 16% and 18% to 37% for the 200-microm and 365-microm fibers, respectively. Small-diameter fibers, in combination with semirigid or flexible ureteroscopes, should be used to treat upper urinary tract stones. The 365-microm fiber should be utilized for the management of ureteral stones, as minimal endoscopic deflection is required to access these calculi. Because the 200-microm fibers are considerably more expensive, their use should be reserved for fragmentation of intrarenal calculi, where maximum deflection is required during flexible ureterorenoscopy. The ideal energy and frequency settings for the small fibers are <1.0 J and 5 to 10 Hz. Larger fibers can be used for managing bladder or renal calculi, as there is no need for significant fiber deflection. The 550-microm fiber is preferred, as it is comparable in efficacy to the 1000-microm fiber and is less expensive. Energy and frequency can be maximized to 2.0 J and 15 Hz without damage to the fiber, but visibility can be affected by high frequencies. Appropriate fiber selection and energy/frequency settings will allow access to most stones throughout the urinary tract, maximize fiber life, and minimize fiber expense.

The holmium laser in urology

OBJECTIVE

To review the physics related to the holmium laser, its laser-tissue interactions, and its application to the treatment of urological diseases.

SUMMARY AND BACKGROUND DATA

The holmium: YAG laser is a solid-state, pulsed laser that emits light at 2100 nm. It combines the qualities of the carbon dioxide and neodymium:YAG lasers providing both tissue cutting and coagulation in a single device. Since the holmium wavelength can be transmitted down optical fibers, it is especially suited for endoscopic surgery.

METHODS

The authors provide a review of the literature as it relates to the holmium laser and its application to urology.

RESULTS

The holmium wavelength is strongly absorbed by water. Tissue ablation occurs superficially, providing for precise incision with a thermal injury zone ranging from 0.5 to 1.0 mm. This level of coagulation is sufficient for adequate hemostasis. The most common urologic applications of the holmium laser that have been reported include incision of urethral and ureteral strictures; ablation of superficial transitional cell carcinoma; bladder neck incision and prostate resection; and lithotripsy of urinary calculi.

CONCLUSIONS

The holmium: YAG laser is a multi-purpose, multi-specialty surgical laser. It has been shown to be safe and effective for multiple soft tissue applications and stone fragmentation. Its utilization in urology is anticipated to increase with time as a result of these features.

Application of the holmium:YAG laser for prostatectomy

OBJECTIVE

The authors review the current knowledge regarding the application of the Holmium: YAG laser for prostatectomy.

SUMMARY BACKGROUND DATA

Conventional surgical therapies for benign prostatic hyperplasia (BPH) are effective but associated with relatively high morbidity. Laser prostatectomy, using either Neodymium:YAG or potassium-titanyl-phosphate lasers, has emerged as a new and much safer operative approach to relieve symptoms of benign prostatic hyperplasia. However, these laser wavelengths possess key disadvantages that have limited their acceptability and dissemination in everyday urologic practice.

METHODS

THE authors review their own extensive experience in the development of clinical application of Holmium: YAG laser technology for prostatectomy, as well as the published reports in the current medical literature now dealing with this subject.

RESULTS

In multiple clinical trials, Holmium:YAG laser resection of the prostate has proven efficacious in relieving symptomatic BPH. Both objective urodynamic measures of voiding outcomes and symptomatic improvement have been shown to be equivalent to standard electrocautery resection of the prostate. At the same time, these studies have demonstrated the superior safety and hemostasis of Holmium:YAG laser prostatectomy compared to electrocautery resection, similar to prior laser prostatectomy procedure. Unlike prior forms of laser prostatectomy, Holmium:YAG laser resection of the prostate acutely removes all obstructing prostate tissue, so that the postoperative catheterization requirement is typically only overnight and improvement in voiding is immediate. Current operative techniques and the latest technological developments to facilitate Holmium:YAG laser prostatectomy are described.

CONCLUSIONS

Holmium: YAG laser prostatectomy combines the best features of prior laser prostatectomy technologies, including minimal complications and morbidity, with the efficacy and immediacy of voiding outcomes associated with conventional electrocautery resection of the prostate.