Burst wave lithotripsy and acoustic manipulation of stones

PURPOSE OF REVIEW

Burst wave lithotripsy and ultrasonic propulsion of kidney stones are novel, noninvasive emerging technologies to separately or synergistically fragment and reposition stones in an office setting. The purpose of this review is to discuss the latest refinements in technology, to update on testing of safety and efficacy, and to review future applications.

RECENT FINDINGS

Burst wave lithotripsy produced consistent, small passable fragments through transcutaneous applications in a porcine model, while producing minimal injury and clinical trials are now underway. A more efficient ultrasonic propulsion design that can also deliver burst wave lithotripsy effectively repositioned 95% of stones in 18 human participants (18 of 19 kidneys) and clinical trials continue. Acoustic tractor beam technology is an emerging technology with promising clinical applications through the manipulation of macroscopic objects.

SUMMARY

The goal of the reviewed work is an office-based system to image, fragment, and reposition urinary stones to facilitate their natural passage. The review highlights progress in establishing safety, effectiveness, and clinical benefit of these new technologies. The work is also anticipating challenges in clinical trials and developing the next generation of technology to improve on the technology as it is being commercialized today.

[Current status of extracorporeal shock wave lithotripsy in urinary lithiasis.]

Over the last decade, urinary lithiasis' prevalence has dramatically increased due to diet and lifestyle changes, growing 10.6% and 7.1% in men and women respectively. Extracorporeal shock wave lithotripsy has lost relevance in current practice due to endoscopic device development and unpredictability of results. Instrument miniaturization is leading to an increase of the percutaneous approach of increasingly smaller stones, while most flexible ureteroscopes durability and digitalization has allowed urologists to address larger stones. So that, decision algorithm is now impossible to define, but what is clear is that ESWL has declined worldwide. Can it disappear as a urinary lithiasis treatment modality? If we don't improve appropriate candidate selection and optimize disintegration efficiency, guidelines are going to replace the more "boring" ESWL by popular and more attractive endoscopes. Shock wave technology has evolved in the last two decades, however lithotripsy fundamental principle has not changed. ESWL has passed the test of time and centers dedicated to stone treatment should have a lithotripter in order to offer an appropriate balance in different options for different clinical situations. New developments will be focused on improvements in location (in-line navigation systems; Vision track system) and automatic ultrasound location on a robotic arm; monitoring and stone fixation, implementation of different focal sizes with new acoustic lenses, multitask working stations that allow endourological approach, coupling control (avoiding microbubbles) and low cost devices for different applications. On the other hand, optimizing outcomes by: slower pulse rates, ramping strategies and patient selection with soft stones, short stone-skin distance, low BMI and favorable collecting system anatomy, allow us to achieve better outcomes in shock wave treatments. SWL still represents a unique non invasive method of stone disease treatment with no anesthesia and low complication rates; and a high proportion of stones could still be treated with shock waves and remains among patient's first options. This update objective has been to review the evolution, identify shock wave new developments and clarify their impact on our daily practice in urinary stones treatment.

National Practice Pattern and Time Trends in Treatment of Upper Urinary Tract Calculi in Korea: a Nationwide Population-Based Study

Despite high prevalence of upper urinary tract calculi (UUTC), there are few studies regarding patterns of care in Asian populations. We investigated treatment patterns and time trends in patients with newly diagnosed UUTC in Korea using the National Health Insurance database that includes de-identified claims from a random 2% sample of the entire population (> 1 million people). A total of 14,282 patients who received active treatments, including shock wave lithotripsy (SWL), ureteroscopic surgery (URS), percutaneous nephrolithotomy (PNL), and uretero/pyelolithotomy (UPL), for newly diagnosed UUTC between 2003 and 2013 were included. The number of primary and all treated cases of UUTC significantly (43% and 103.3%, respectively) increased over the 10-year period. While patients undergoing SWL, URS, PNL, and UPL as primary treatment increased by 43.7%, 31.9%, 87.5%, and 0%, respectively, the relative proportion undergoing each treatment remained constant over the 10 years (SWL > 90%, URS 4.5% to 7.8%, PNL 0.4% to 1.0%, and UPL < 0.4%, respectively). Multinomial logistic regression analysis showed that age > 40 years (compared to age < 30 years) was significantly associated with URS, PNL, and UPL, rather than SWL, while patients living in urban or suburban/rural areas (compared to metropolitan) were significantly less likely to undergo URS and PNL. In summary, the majority of Korean patients underwent SWL as primary treatment for UUTC, and the predominant use of SWL remained steady over a 10-year period in Korea. Our results will be valuable in examining treatment patterns and time trends in Korean UUTC patients.

Renal calculi: trends in the utilization of shockwave lithotripsy and ureteroscopy

INTRODUCTION

To assess trends in the usage of extracorporeal shockwave lithotripsy (SWL) and ureteroscopy (URS) in the treatment of renal calculi.

MATERIALS AND METHODS

An analysis of the 5% Medicare Public Use Files (years 2001, 2004, 2007 and 2010) was performed to evaluate changes in the use of SWL and URS to treat renal calculi. Patients were identified using ICD-9 (cm) and CPT codes. Statistical analyses, including the Fisher, 2 tests, and multivariate logistic regression analysis were performed using SAS 9.3 (SAS Institute Inc., Cary, NC, USA) and SPSS v20 (IBM Corp., Armonk, NY, USA).

RESULTS

The absolute number of patients diagnosed with (+85.1%) and treated for (+31.5%) kidney calculi increased from 2001 to 2010. The ratio of diagnosed/treated patients declined from 15.2% in 2001 to 10.8% in 2010. Whites (OR = 1.27, p < 0.0001), patients in the South (OR = 1.16, p < 0.0001) and those ≤ 84 years of age were more likely to be treated. The utilization of SWL (84.7%) was greater than URS (15.3%), but the utilization of URS increased over time from 8.4% in 2001 to 20.6% of cases by 2010 (p < 0.0001). Treatment via URS was more likely in women (OR = 1.28, p < 0.0001), in patients living outside the South (OR = 1.29-1.45, p ≤ 0.006) and in later years of the study (OR = 2.87, p < 0.0001).

CONCLUSIONS

Treatment patterns for renal calculi changed from 2001 to 2010. The usage of URS increased at the cost of SWL. Multiple sociodemographic factors correlated with the likelihood of being treated surgically as well as the choice of the surgical approach.

Overview of therapeutic ultrasound applications and safety considerations

Applications of ultrasound in medicine for therapeutic purposes have been accepted and beneficial uses of ultrasonic biological effects for many years. Low-power ultrasound of about 1 MHz has been widely applied since the 1950s for physical therapy in conditions such as tendinitis and bursitis. In the 1980s, high-pressure-amplitude shock waves came into use for mechanically resolving kidney stones, and "lithotripsy" rapidly replaced surgery as the most frequent treatment choice. The use of ultrasonic energy for therapy continues to expand, and approved applications now include uterine fibroid ablation, cataract removal (phacoemulsification), surgical tissue cutting and hemostasis, transdermal drug delivery, and bone fracture healing, among others. Undesirable bioeffects can occur, including burns from thermal-based therapies and severe hemorrhage from mechanical-based therapies (eg, lithotripsy). In all of these therapeutic applications of ultrasound bioeffects, standardization, ultrasound dosimetry, benefits assurance, and side-effect risk minimization must be carefully considered to ensure an optimal benefit to risk ratio for the patient. Therapeutic ultrasound typically has well-defined benefits and risks and therefore presents a manageable safety problem to the clinician. However, safety information can be scattered, confusing, or subject to commercial conflicts of interest. Of paramount importance for managing this problem is the communication of practical safety information by authoritative groups, such as the American Institute of Ultrasound in Medicine, to the medical ultrasound community. In this overview, the Bioeffects Committee of the American Institute of Ultrasound in Medicine outlines the wide range of therapeutic ultrasound methods, which are in clinical use or under study, and provides general guidance for ensuring therapeutic ultrasound safety.

Optimizing Shock Wave Lithotripsy in the 21st Century

OBJECTIVE

Shock wave lithotripsy (SWL) has radically changed treatment of stone disease and appears to be the first option for the majority of patients. This review of current literature focused on suggestions for optimising technique, patient selection, results, and lithotriptor comparison for SWL.

METHODS

Literature search for SWL was performed for recently published papers in English language. Topics of interest were treatment protocols; patient evaluation; pre-SWL prediction of outcome; lithotriptor technology; efficacy; and methods to assess the effects, decrease complications, and compare lithotriptors. Earlier classic papers on SWL and guidelines for stone disease were also reviewed.

RESULTS

Recent literature contained important recommendations about SWL concerning (1) methods to predict stone fragmentation; (2) identification of factors contributing to treatment failure for lower pole and ureteric calculi; (3) guidelines from urological associations; (4) manoeuvres and changes in SWL delivery (slower rate, twin-pulse technique) to increase efficacy and decrease complications; (5) clarification of the role of medical treatment (antibiotics, alpha-blockers); (6) role of SWL in calyceal stones, CIRF, and abnormal kidneys; (7) obesity and SWL; and (8) methods to evaluate and compare lithotriptors.

CONCLUSIONS

SWL delivered in an outpatient setting as an anaesthesia-free treatment is still considered the first option for the majority of stones with a minimal number of complications. Better understanding of the physics of shockwave delivery is required, together with treatment optimisation by limiting renal damage and better selection of patients because this approach will offer maximum benefit to patients and physicians, as well as more cost-effective treatment.

Therapeutic applications of ultrasound

Therapeutic applications of ultrasound predate its use in imaging. A range of biological effects can be induced by ultrasound, depending on the exposure levels used. At low levels, beneficial, reversible cellular effects may be produced, whereas at high intensities instantaneous cell death is sought. Therapy ultrasound can therefore be broadly divided into "low power" and "high power" applications. The "low power" group includes physiotherapy, fracture repair, sonophoresis, sonoporation and gene therapy, whereas the most common use of "high power" ultrasound in medicine is probably now high intensity focused ultrasound. Therapeutic effect through the intensity spectrum is obtained by both thermal and non-thermal interaction mechanisms. At low intensities, acoustic streaming is likely to be significant, but at higher levels, heating and acoustic cavitation will predominate. While useful therapeutic effects are now being demonstrated clinically, the mechanisms by which they occur are often not well understood.

Extracorporeal shock wave lithotripsy 25 years later: complications and their prevention

OBJECTIVE

We review the pathophysiology and possible prevention measures of complications after extracorporeal shock wave lithotripsy (ESWL).

METHODS

A literature search was performed with the Medline database on ESWL between 1980 and 2004.

RESULTS

ESWL application has been intuitively connected to complications. These are related mostly to residual stone fragments, infections, and effects on tissues such as urinary, gastrointestinal, cardiovascular, genital, and reproductive systems. Recognition of ESWL limitations, use of alternative therapies, correction of pre-existing renal or systemic disease, treatment of urinary tract infection, use of prophylactic antibiotics, and improvement of ESWL efficacy are the most important measures of prevention. Decrease of shock wave number, rate and energy, use of two shock-wave tubes simultaneously, and delivery of two shock waves at carefully timed close intervals improve ESWL efficacy and safety.

CONCLUSION

ESWL is a safe method to treat stones when proper indications are followed. The need for well-designed prospective randomised trials on aetiology and prevention of its complications arises through the literature review.

Strategies for improved shock wave lithotripsy

Research in lithotripsy that started with the effort to characterize acute shock wave damage to the kidney has led to advances on several fronts, including discovery of strategies that have improved clinical treatment. It is appreciated now that shock wave trauma is primarily a vascular lesion, that injury is dose dependent, and that hemorrhage can be severe and can lead to a permanent loss of functional renal mass. Studies of the renal functional response to lithotripsy have shown that shock wave treatment triggers vasoconstriction in the kidney. This finding has been turned to advantage, and it is now known that when treatment is begun using low amplitude pulses, subsequent high amplitude shock waves are far less damaging. Thus, when shock waves are delivered judiciously, treatment can have a protective effect. The finding that cavitation is a key mechanism in vessel rupture has led to the development of novel experimental methods of shock wave delivery that can suppress bubble expansion and minimize tissue damage. Progress has also been made in understanding the physical mechanisms involved in stone comminution, and it is seen that the forces generated by cavitation, shear stress and circumferential squeezing act synergistically to fragment stones. Recent work suggests that a broad focal zone may be an advantage, allowing stones to be broken with lower amplitude pulses. Cavitation has been shown to play a critical role in reducing stone fragments to a size that can be voided. Cavitation is also the factor that limits the rate at which treatment can be performed, as stones break significantly better at slow rate than at fast ratean observation from basic research that is now appreciated in clinical practice. The current environment in lithotripsy research is encouraging. There is great interest in developing new technology, and in finding ways to improve how lithotripsy is performed.

Nephrolithiasis: "Scope," Shock or Scalpel?

PURPOSE

To evaluate treatment preferences for complex urinary calculi.

MATERIALS AND METHODS

A questionnaire was sent to 174 members of the Minnesota Urological Society. Three case scenarios were presented: a 1.5-cm lower-pole calculus with unfavorable anatomy, a 1.4-cm proximalureteral calculus, and a staghorn calculus. The treatment options offered were extracorporeal shockwave lithotripsy (SWL), ureteral stenting, ureteroscopy (URS), percutaneous nephrolithotomy (PCNL), and open surgery.

RESULTS

Our survey response rate was 49%. A PCNL for staghorn calculi was more likely to be offered by urologists in metropolitan (100%; P<0.001) and urban (100%; P=0.003) settings than rural settings (57%). Whereas only 22% of urban and metropolitan urologists would offer anatrophic nephrolithotomy, 43% of rural urologists would include this among their treatment options. A PCNL was more likely to be offered by urologists trained after 1980 (100%) than by urologists trained before 1980 (81%; P=0.004). For a large lower-pole calculus with unfavorable anatomy, urologists with >50% managed-care practices were more likely (91%) than urologists with <50% managed-care practices (65%) to select PCNL for such stones (P=0.034). Whereas 82% of metropolitan urologists would select PCNL, 43% of rural urologists would consider SWL as initial therapy. A URS was more likely to be offered by urologists trained after 1980 (16%) than by urologists trained before 1980 (0; P=0.044). For a large proximal-ureteral calculus, metropolitan urologists were most likely (64%) to use stents initially (urban 28%; P=0.014; rural 14%; P=0.017). Rural urologists were more likely to offer SWL (100%) than were metro urologists (55%; P=0.024).

CONCLUSIONS

Initial therapy for nephrolithiasis differs significantly according to geographic location, year of residency completion, and the percentage of managed-care patients in a urologist's practice. Future emphasis should be placed on increasing the availability of endoscopic techniques in rural settings.

Calculus fragmentation in laser lithotripsy

The intracorporeal treatment of urinary calculi with lasers is presented, which describes laser-calculus interactions associated with lithotripsy. Reliable fragmentation of calculi with diverse compositions and minimal collateral tissue damage are primarily contingent upon laser parameters (wavelength, pulse duration, and pulse energy) and physical properties of calculi (optical, mechanical, and chemical). The pulse duration governs the dominant mechanism in calculi fragmentation, which is either photothermal or photoacoustical/photomechanical. Lasers with long pulse durations (i.e. > tens of micros) induce a temperature rise in the laser-affected zone with minimal acoustic waves; material is removed by means of vaporization, melting, mechanical stress, and/or chemical decomposition. Short-pulsed laser ablation (i.e. < 10 micros), on the other hand, produces shock waves, and the resultant mechanical energy fragments calculi. Work continues throughout the world to evaluate the feasibility of advanced lasers in lithotripsy and to optimize laser parameters and light delivery systems pertinent to efficient fragmentation of calculi.

[Extracorporeal shock-wave lithotripsy. An established treatment]

Extracorporeal shock wave lithotripsy (ESWL) is the most required urinary stone therapy in our country and in the rest of the world. In a way it has replaced the alternative treatments (open surgery, percutaneous nephrolithectomy, ureteroscopy). Nevertheless these therapeutic approaches have still its own indications. Although there is no a definitive agreement, it should be desirable a world-wide consensus where each therapy will have a exactly defined land with all potential of each management improved. We review ESWL technical aspects, its literature-based most accepted indications, adverse bioeffects and last, future improvements are considered.

Current management of urolithiasis: progress or regress?

PURPOSE

To assess the impact of the development of less powerful second- and third-generation shockwave lithotripters on surgical stone therapy in light of recent advances in ureteroscopy and laser lithotripsy. As such, we sought to identify current trends in the treatment of stone disease, both at our university medical center and nationally, and to contrast them with the corresponding data from 1990.

PATIENTS AND METHODS

All urolithiasis procedures (ureteroscopy, SWL, open surgery, and percutaneous stone removal) performed in 1998 were compared with all urolithiasis procedures performed 8 years earlier (1990) at a single institution (Washington University, St. Louis). In addition, Medicare data for each year from 1988 through 2000 were collected from the Health Care Financing Administration to assess the national trends for open stone surgery, ureteroscopic stone removal, SWL, and percutaneous nephrolithotomy.

RESULTS

At Washington University, the number of percutaneous stone removals remained stable; however, the overall number of ureteroscopies increased by 53%, while the number of SWLs, decreased by 15%. The Medicare data likewise reflect a marked decrease in open stone surgery and a marked increase in ureteroscopic stone surgery with a slight increase in SWL. Utilization of percutaneous nephrolithotomy remained unchanged.

CONCLUSIONS

We believe this trend toward ureteroscopy is attributable to several factors: improved, smaller rigid and flexible ureteroscopes; the availability of more effective intracorporeal lithotripters (e.g., pneumatic and holmium laser), and the lack of development of lower cost, more effective SWL. This is an unfortunate trend, as we are moving away from the noninvasive treatment that was the hallmark of urolithiasis therapy at the beginning of the last decade toward more invasive endoscopic therapy. Increased research efforts in SWL technology are sorely needed.

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.

10-year experience with extracorporeal shockwave lithotripsy in the state of Colorado

PURPOSE

To evaluate trends in the utilization of extracorporeal shockwave lithotripsy (SWL) and the potential need for medical prophylaxis of urolithaisis in the state of Colorado.

MATERIALS AND METHODS

We examined patient and stone characteristics of individuals undergoing SWL for renal or upper-ureteral stones over a 10-year period (1987-1996) at the Kidney Stone Center of the Rocky Mountains. There were no significant changes in the in-state physician referral patterns nor SWL treatment criteria over this time interval. All patients were treated on the Dornier HM3 lithotripter. From September 1999 to December 1999, 198 consecutive patients undergoing SWL filled out a 10-point questionnaire regarding their interest in medical prophylaxis of urolithiasis.

RESULTS

The number of patients from Colorado rose 32.5%: from 15.7 per 100,000 population in 1987 to 20.8 per 100,000 in 1996. Patient demographics such as sex, race, age, and history of nephrolithiasis did not change. Furthermore, there were no significant changes in the treated stone size or stone location. The overall increase in treatment numbers was attributable equally to increases in the number of upper ureteral and renal stones. Of the 198 patients questioned, 114 (58%) were recurrent stone formers, but only 52 (45%) of these had been offered a metabolic evaluation.

CONCLUSIONS

Over the 10 years since the introduction of WSL in Colorado, there has been a gradual increase in its utilization. This higher utilization is probably multifactorial. Patients undergoing SWL have a strong desire to prevent future stone episodes and are very interested in medical prophylaxis of their stone disease.