Lasers for stone treatment: how safe are they?

PURPOSE OF REVIEW: To update laser lithotripsy advances in regard to new laser types and technologies as well as review contemporary laser safety concerns. RECENT FINDINGS: The high prevalence of urolithiasis and the continuing miniaturization of scopes has encouraged the growth of laser lithotripsy technology. The holmium:yttrium-aluminum-garnet (Ho:YAG) laser has been used for over 20 years in endourology and has been extensively studied. Holmium laser power output is affected by a number of factors, including pulse energy, pulse frequency, and pulse width. Several recent experimental studies suggest that the new dual-phase Moses 'pulse modulation' technology, introduced in high-power laser machines, carries a potential to increase stone ablation efficiency and decrease stone retropulsion. A newly introduced thulium fiber laser (TFL) has been adapted to a very small laser fiber size and is able to generate very low pulse energy and very high pulse frequency. Both of these technologies promise to play a larger role in laser lithotripsy in the near future. However, more experimental and clinical studies are needed to expand on these early experimental findings. Even though laser lithotripsy is considered safe, precautions should be taken to avoid harmful or even catastrophic adverse events to the patient or the operating room staff. SUMMARY: The Ho:YAG laser remains the clinical gold standard for laser lithotripsy for over the last two decades. High-power Ho:YAG laser machines with Moses technology have the potential to decrease stone retropulsion and enhance efficiency of laser ablation. The new TFL has a potential to compete with and perhaps even replace the Ho:YAG laser for laser lithotripsy. Safety precautions should be taken into consideration during laser lithotripsy.

Evaluation of a synchronous twin-pulse technique for shock wave lithotripsy: a prospective randomized study of effectiveness and safety in comparison to standard single-pulse technique.

OBJECTIVE: To asses the efficacy and safety of bidirectional synchronous twin-pulse extracorporeal shock wave lithotripsy (ESWL) compared with standard ESWL. PATIENTS AND METHODS: Between March 2003 and December 2006, 240 patients with a radio-opaque single renal stone of 10 mm the rate for the failure of disintegration was 13.3% for the DLS vs 1.4% for the TH (P = 0.009). For stones of 10 mm it was 78.1% and 66.7%, respectively (P = 0.14). The median (range) number of sessions in both groups was 2 (1-5). After ESWL urinary NAG levels were increased significantly in both groups; in the TH group it declined below the level before ESWL after 2 days, while in the DLS group it remained high after 7 days. In the DLS group four patients developed subcapsular or parenchymal haematoma after ESWL, vs none in the TH group. There was loss of corticomedullary differentiation after ESWL in three patients in the DLS group and only one in the TH group. In the DLS group there was a statistically significantly decrease in bilateral renal perfusion after ESWL, but no changes in the TH group. CONCLUSIONS: Synchronous twin-pulse ESWL has clinical advantages over standard ESWL in terms of safety and efficacy.

Evaluation of retropulsion caused by holmium:YAG laser with various power settings and fibers.

The ideal intracorporeal lithotriper would comminute all types of calculi into small readily excreted particles. It would be small and flexible with an energy source safe for the uroepithelium. It should not break, should be inexpensive, and should not retropulse the stone up the urinary tract. This investigation was designed to quantify the last quality for the holmium:YAG laser. The mechanism of action of the pulsed Ho:YAG laser (wavelength 2100 nm) is the generation of a gas plasma at the stone-fluid interface causing a shockwave. The holmium laser was employed for lithotripsy of model stones composed of silicate with a ferrous coating. Stones were selected with a mass of 2 mg +/- 0.1 mg. We sequentially investigated three variables: energy (0.6, 0.8, and 1.0 J), frequency (10, 16, and 20 Hz), and fiber diameter (200, 365, 550, and 1000 microm). Ten stone trials were performed with each of the 36 possible combinations of energy, pulse frequency, and fiber diameter. Our model ureter consisted of a clear rigid polymer tube filled with 0.9% saline. The system was closed and permitted intertrial flushing of generated air bubbles. The laser fiber was maintained at constant extension from the ureteroscope, with stones positioned at the fiber tip before each trial. Laser energy was applied for 2 seconds, with maximum and net retropulsion recorded in millimeters. Each measurement series was recorded in a database for paired Student t-tests. Net retropulsion was then compared by statistically holding each of the three variables constant (fiber size constant with power and frequency varying; frequency constant with power and fiber size varying; and power constant with fiber size and frequency varying). Most retropulsion occurred with the 365-microm and 550-microm fibers. Most comminution was also noted with these fiber sizes. There was no statistical correlation between observed retropulsion and efficiency of comminution. This self-contained model for laser lithotripsy allowed us to measure retropulsion accurately. Silicate stones are not chemically similar to human uroliths but are of uniform composition. The irregular surface characteristics are similar to human stones, making them ideal for retropulsion investigations.

Efficacy of in vitro stone fragmentation by extracorporeal, electrohydraulic, and pulsed-dye laser lithotripsy.

Fragmentation has become the standard therapy for urinary calculi in the modern era. Stone fragility as well as position and size are important for the determination of a treatment program. To compare the efficacy of stone fragmentation, seven kinds of human urinary calculi with known composition (calcium oxalate monohydrate and dihydrate, dibasic calcium phosphate, uric acid, struvite, calcium phosphate, and cystine) were treated by three fragmentation techniques commonly used, namely extracorporeal shock wave (SWL), electrohydraulic (EHL), and pulsed-dye laser lithotripsy. Uric acid, calcium oxalate dihydrate, and calcium phosphate stones could be destroyed easily by any of these methods. Struvite was soft but sticky and not easy to break into tiny particles. Both dibasic calcium phosphate and calcium oxalate monohydrate stones were resistant to the laser and EHL; SWL is the treatment of choice. For cystine stones, none of the treatments was satisfactory; SWL was the only way to break them into large pieces.

[Clinical results of transurethral ureterolithotripsy using pulsed-dye laser: primary ureteral stones versus secondary ureteral stones after ESWL].

Between September 1993 and December 1996, 138 patients underwent transurethral ureterolithotripsy (TUL) either as primary treatment or as a second-line therapy after extracorporeal shock wave lithotripsy. In all patients, a semirigid 6.0 F ureteroscope was used. Lithotripsy was performed using a pulsed-dye laser. The overall success rate was 82.6%. The success rates according to the location of stones were as follows, 76.9% for stones in the upper ureter (U1), 96.0% for those in the midureter (U2), and 86.2% for those in the distal ureter (U3). In 68 patients treated with TUL as primary therapy, the success rate was 88.2% and efficiency quotient, which was modified for TUL was 0.75. Complications were rare: no ureteral perforations and no major bleeding occurred, but urosepsis developed in 2 patients. In conclusion, transurethral ureterolithotripsy using a small caliber ureteroscope with pulsed-dye laser is recommended as the primary treatment for mid- and distal ureteral stones, because of its superior success rate. In addition, for upper ureteral stones, laser tripsy is recommended as a helpful auxiliary procedure.

A comparison of holmium:YAG laser with Lithoclast lithotripsy in ureteral calculi fragmentation.

PURPOSE: Among various intracorporeal lithotriptors, Lithoclast (EMS, Switzerland) has become the widely used tool for the treatment of urinary stones. Recently, the holmium:YAG laser has been used with a wide range of potential urological applications, including intracorporeal lithotripsy of urinary calculi. The purpose of the present study is to compare Lithoclast with holmium:YAG laser lithotripsy in ureteral calculi fragmentation. METHODS: Out of 51 patients with ureteral calculi, 26 underwent Lithoclast lithotripsy and 25 holmium:YAG lithotripsy using a 8/9.8F rigid ureteroscope. There were no changes to the ureteroscopes, video monitors, baskets or irrigation devices during the study period. RESULTS: There were no differences in patient age, sex, stone size and location of stones between these groups. The immediate stone-free rates were 96.0% in the holmium:YAG group and 73.1% in the Lithoclast group (P < 0.05). The 3-month stone-free rates were 96.0% and 84.6%, respectively (P = 0.350). The mean operation time and mean period of postoperative hospitalization in the holmium:YAG group (49.8 min and 1.0 days, respectively) were shorter than those of the Lithoclast counterpart (76.9 min and 2.5 days, respectively). Post-treatment complications, such as ureteral perforation, were encountered in only two patients who underwent Lithoclast. CONCLUSIONS: Holmium:YAG lithotripsy was associated with shorter operation time and postoperative hospitalization period. These data also suggest that holmium:YAG lithotripsy was safe and more effective than Lithoclast lithotripsy in the aspect of immediate stone free rate. We believe that holmium:YAG laser is an excellent treatment modality for managing ureteral calculi.

Retrograde flexible ureterorenoscopic holmium-YAG laser lithotripsy: the new gold standard.

To demonstrate the efficacy of flexible retrograde ureterorenoscopic holmium-YAG intracorporeal laser lithotripsy for the treatment of renal calculi, a total of 86 patients presenting to our hospital with renal calculi underwent flexible retrograde ureterorenoscopic holmium-YAG intracorporeal laser lithotripsy of their stones, and the data were collected prospectively. As extracorporeal shock wave lithotripsy is not available at our institution, all patients with renal calculi in this study were treated in a retrograde fashion using the Richard Wolf 6.0F semirigid ureteroscope, the 7.5F flexible ureterorenoscope, and the holmium-YAG laser by Coherent Inc. Except for inhospital consults or patients requiring admission secondary to infection, all cases were performed on an ambulatory basis. All renal calculi 3 cm or smaller were approached in a retrograde fashion. Where possible, the stones were initially debulked using the semirigid ureteroscope and the 550-microm fiber followed by the flexible ureterorenoscope in combination with the 360- or 200-microm laser fiber depending on stone position. Stones were fragmented until they were small enough to be removed by hydrocleansing. Using this technique, stone-free success rates for calculi 2.5 cm or smaller after a single treatment, regardless of stone composition or location, are superior to those of extracorporeal shock wave lithotripsy. For calculi between 2.5 and 3 cm, the results also are noted to be superior. We conclude that for calculi larger than 3 cm or for partial staghorn calculi, the treatment of choice appears to be a percutaneous approach.