Lithotripter outcomes in a community practice setting: comparison of an electromagnetic and an electrohydraulic lithotripter.

PURPOSE: We assessed patient outcomes using 2 widely different contemporary lithotripters. MATERIALS AND METHODS: We performed a consecutive case series study of 355 patients in a large private practice group using a Modulith® SLX electromagnetic lithotripter in 200 patients and a LithoGold LG-380 electrohydraulic lithotripter (TRT, Woodstock, Georgia) in 155. Patients were followed at approximately 2 weeks. All preoperative and postoperative films were reviewed blindly by a dedicated genitourinary radiologist. The stone-free rate was defined as no residual fragments remaining after a single session of shock wave lithotripsy without an ancillary procedure. RESULTS: Patients with multiple stones were excluded from analysis, leaving 76 and 142 treated with electrohydraulic and electromagnetic lithotripsy, respectively. The stone-free rate was similar for the electrohydraulic and electromagnetic lithotripters (29 of 76 patients or 38.2% and 69 of 142 or 48.6%, p = 0.15) with no difference in the stone-free outcome for renal stones (20 of 45 or 44.4% and 33 of 66 or 50%, p = 0.70) or ureteral stones (9 of 31 or 29% and 36 of 76 or 47.4%, respectively, p = 0.08). The percent of stones that did not break was similar for the electrohydraulic and electromagnetic devices (10 of 76 patients or 13.2% and 23 of 142 or 16.2%) and ureteroscopy was the most common ancillary procedure (18 of 22 or 81.8% and 30 of 40 or 75%, respectively). The overall mean number of procedures performed in patients in the 2 groups was similar (1.7 and 1.5, respectively). CONCLUSIONS: We present lithotripsy outcomes in the setting of a suburban urology practice. Stone-free rates were modest using shock wave lithotripsy alone but access to ureteroscopy provided satisfactory outcomes overall. Although the acoustic characteristics of the electrohydraulic and electromagnetic lithotripters differ substantially, outcomes with these 2 machines were similar.

Focused ultrasound to expel calculi from the kidney: safety and efficacy of a clinical prototype device.

PURPOSE: Focused ultrasound has the potential to expel small stones or residual stone fragments from the kidney, or move obstructing stones to a nonobstructing location. We evaluated the efficacy and safety of ultrasonic propulsion in a live porcine model. MATERIALS AND METHODS: Calcium oxalate monohydrate kidney stones and laboratory model stones (2 to 8 mm) were ureteroscopically implanted in the renal pelvicalyceal system of 12 kidneys in a total of 8 domestic swine. Transcutaneous ultrasonic propulsion was performed using an HDI C5-2 imaging transducer (ATL/Philips, Bothell, Washington) and the Verasonics® diagnostic ultrasound platform. Successful stone relocation was defined as stone movement from the calyx to the renal pelvis, ureteropelvic junction or proximal ureter. Efficacy and procedure time was determined. Three blinded experts evaluated histological injury to the kidney in the control, sham treatment and treatment arms. RESULTS: All 26 stones were observed to move during treatment and 17 (65%) were relocated successfully to the renal pelvis (3), ureteropelvic junction (2) or ureter (12). Average ± SD successful procedure time was 14 ± 8 minutes and a mean of 23 ± 16 ultrasound bursts, each about 1 second in duration, were required. There was no evidence of gross or histological injury to the renal parenchyma in kidneys exposed to 20 bursts (1 second in duration at 33-second intervals) at the same output (2,400 W/cm(2)) used to push stones. CONCLUSIONS: Noninvasive transcutaneous ultrasonic propulsion is a safe, effective and time efficient means to relocate calyceal stones to the renal pelvis, ureteropelvic junction or ureter. This technology holds promise as a useful adjunct to surgical management for renal calculi.

Fragility of brushite stones in shock wave lithotripsy: absence of correlation with computerized tomography visible structure.

PURPOSE: Brushite stones were imaged in vitro and then broken with shock wave lithotripsy to assess whether stone fragility correlates with internal stone structure visible on helical computerized tomography. MATERIALS AND METHODS: A total of 52 brushite calculi were scanned by micro computerized tomography, weighed, hydrated and placed in a radiological phantom. Stones were scanned using a Philips® Brilliance iCT 256 system and images were evaluated for the visibility of internal structural features. The calculi were then treated with shock wave lithotripsy in vitro. The number of shock waves needed to break each stone to completion was recorded. RESULTS: The number of shock waves needed to break each stone normalized to stone weight did not differ by HU value (p = 0.84) or by computerized tomography visible structures that could be identified consistently by all observers (p = 0.053). Stone fragility correlated highly with stone density and brushite content (each p <0.001). Calculi of almost pure brushite required the most shock waves to break. When all observations of computerized tomography visible structures were used for analysis by logistic fit, computerized tomography visible structure predicted increased stone fragility with an overall area under the ROC curve of 0.64. CONCLUSIONS: The shock wave lithotripsy fragility of brushite stones did not correlate with internal structure discernible on helical computerized tomography. However, fragility did correlate with stone density and increasing brushite mineral content, consistent with clinical experience with patients with brushite calculi. Thus, current diagnostic computerized tomography technology does not provide a means to predict when brushite stones will break well using shock wave lithotripsy.

Size and location of defects at the coupling interface affect lithotripter performance.

UNLABELLED: Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? In shock wave lithotripsy air pockets tend to get caught between the therapy head of the lithotripter and the skin of the patient. Defects at the coupling interface hinder the transmission of shock wave energy into the body, reducing the effectiveness of treatment. This in vitro study shows that ineffective coupling not only blocks the transmission of acoustic pulses but also alters the properties of shock waves involved in the mechanisms of stone breakage, with the effect dependent on the size and location of defects at the coupling interface. OBJECTIVE: • To determine how the size and location of coupling defects caught between the therapy head of a lithotripter and the skin of a surrogate patient (i.e. the acoustic window of a test chamber) affect the features of shock waves responsible for stone breakage. MATERIALS AND METHODS: • Model defects were placed in the coupling gel between the therapy head of a Dornier Compact-S electromagnetic lithotripter (Dornier MedTech, Kennesaw, GA, USA) and the Mylar (biaxially oriented polyethylene terephthalate) (DuPont Teijin Films, Chester, VA, USA) window of a water-filled coupling test system. • A fibre-optic probe hydrophone was used to measure acoustic pressures and map the lateral dimensions of the focal zone of the lithotripter. • The effect of coupling conditions on stone breakage was assessed using gypsum model stones. RESULTS: • Stone breakage decreased in proportion to the area of the coupling defect; a centrally located defect blocking only 18% of the transmission area reduced stone breakage by an average of almost 30%. • The effect on stone breakage was greater for defects located on-axis and decreased as the defect was moved laterally; an 18% defect located near the periphery of the coupling window (2.0 cm off-axis) reduced stone breakage by only ~15% compared to when coupling was completely unobstructed. • Defects centred within the coupling window acted to narrow the focal width of the lithotripter; an 8.2% defect reduced the focal width ~30% compared to no obstruction (4.4 mm vs 6.5 mm). • Coupling defects located slightly off centre disrupted the symmetry of the acoustic field; an 18% defect positioned 1.0 cm off-axis shifted the focus of maximum positive pressure ~1.0 mm laterally. • Defects on and off-axis imposed a significant reduction in the energy density of shock waves across the focal zone. CONCLUSIONS: • In addition to blocking the transmission of shock-wave energy, coupling defects also disrupt the properties of shock waves that play a role in stone breakage, including the focal width of the lithotripter and the symmetry of the acoustic field • The effect is dependent on the size and location of defects, with defects near the centre of the coupling window having the greatest effect. • These data emphasize the importance of eliminating air pockets from the coupling interface, particularly defects located near the centre of the coupling window.

Optimising an escalating shockwave amplitude treatment strategy to protect the kidney from injury during shockwave lithotripsy.

UNLABELLED: Study Type--Therapy (case series) Level of Evidence 4. What's known on the subject? and What does the study add? Animal studies have shown that one approach to reduce SWL-induced renal injury is to pause treatment for 3-4 min early in the SWL-treatment protocol. However, there is typically no pause in treatment during clinical lithotripsy. We show in a porcine model that a pause in SWL treatment is unnecessary to achieve a reduction in renal injury if treatment is begun at a low power setting that generates low-amplitude SWs, and given continuously for ≈ 4 min before applying higher-amplitude SWs. OBJECTIVE: • To test the idea that a pause (≈ 3 min) in the delivery of shockwaves (SWs) soon after the initiation of SW lithotripsy (SWL) is unnecessary for achieving a reduction in renal injury, if treatment is begun at a low power setting that generates low-amplitude SWs. MATERIALS AND METHODS: • Anaesthetised female pigs were assigned to one of three SWL treatment protocols that did not involve a pause in SW delivery of >10 s (2000 SWs at 24 kV; 100 SWs at 12 kV + ≈ 10-s pause + 2000 SWs at 24 kV; 500 SWs at 12 kV + ≈ 10-s pause + 2000 SWs at 24 kV). • All SWs were delivered at 120 SWs/min using an unmodified Dornier HM3 lithotripter. • Renal function was measured before and after SWL. • The kidneys were then processed for quantification of the SWL-induced haemorrhagic lesion. Values for lesion size were compared to previous data collected from pigs in which treatment included a 3-min pause in SW delivery. RESULTS: • All SWL treatment protocols produced a similar degree of vasoconstriction (23-41% reduction in glomerular filtration rate and effective renal plasma flow) in the SW-treated kidney. • The mean renal lesion in pigs treated with 100 low-amplitude SWs delivered before the main dose of 2000 high-amplitude SWs (2.27% functional renal volume [FRV]) was statistically similar to that measured for pigs treated with 2000 SWs all at high-amplitude (3.29% FRV). • However, pigs treated with 500 low-amplitude SWs before the main SW dose had a significantly smaller lesion (0.44% FRV) that was comparable with the lesion in pigs from a previous study in which there was a 3-min pause in treatment separating a smaller initial dose of 100 low-amplitude SWs from the main dose of 2000 high-amplitude SWs (0.46% FRV). The time between the initiation of the low - and high-amplitude SWs was ≈ 4 min for these latter two groups compared with ≈ 1 min when there was negligible pause after the initial 100 low-amplitude SWs in the protocol. CONCLUSIONS: • Pig kidneys treated by SWL using a two-step low-to-high power ramping protocol were protected from injury with negligible pause between steps, provided the time between the initiation of low-amplitude SWs and switching to high-amplitude SWs was ≈ 4 min. • Comparison with results from previous studies shows that protection can be achieved using various step-wise treatment scenarios in which either the initial dose of SWs is delivered at low-amplitude for ≈ 4 min, or there is a definitive pause before resuming SW treatment at higher amplitude. • Thus, we conclude that renal protection can be achieved without instituting a pause in SWL treatment. It remains prudent to consider that renal protection depends on the acoustic and temporal properties of SWs administered at the beginning stages of a SWL ramping protocol, and that this may differ according to the lithotripter being used.

Evaluation of shock wave lithotripsy injury in the pig using a narrow focal zone lithotriptor.

UNLABELLED: What's known on the subject? and What does the study add? Of all the SW lithotriptors manufactured to date, more research studies have been conducted on and more is known about the injury (both description of injury and how to manipulate injury size) produced by the Dornier HM-3 than any other machine. From this information have come suggestions for treatment protocols to reduce shock wave (SW)-induced injury for use in stone clinics. By contrast, much less is known about the injury produced by narrow-focus and high-pressure lithotriptors like the Storz Modulith SLX. In fact, a careful study looking at the morphology of the injury produced by the SLX itself is lacking, as is any study exploring ways to reduce renal injury by manipulating SW delivery variables of this lithotriptor. The present study quantitates the lesion size and describes the morphology of the injury produced by the SLX. In addition, we report that reducing the SW delivery rate, a manoeuvre known to lower injury in the HM-3, does not reduce lesion size in the SLX. OBJECTIVE: • To assess renal injury in a pig model after treatment with a clinical dose of shock waves using a narrow focal zone (≈3 mm) lithotriptor (Modulith SLX, Karl Storz Lithotripsy). MATERIALS AND METHODS: • The left kidney of anaesthetized female pigs were treated with 2000 or 4000 shock waves (SWs) at 120 SWs/min, or 2000 SWs at 60 SWs/min using the Storz SLX. • Measures of renal function (glomerular filtration rate and renal plasma flow) were collected before and 1 h after shock wave lithotripsy (SWL) and the kidneys were harvested for histological analysis and morphometric quantitation of haemorrhage in the renal parenchyma with lesion size expressed as a percentage of functional renal volume (FRV). • A fibre-optic probe hydrophone was used to determine acoustic output and map the focal width of the lithotriptor. • Data for the SLX were compared with data from a previously published study in which pigs of the same age (7-8 weeks) were treated (2000 SWs at 120 or 60 SWs/min) using an unmodified Dornier HM3 lithotriptor. RESULTS: • Treatment with the SLX produced a highly focused lesion running from cortex to medulla and often spanning the full thickness of the kidney. Unlike the diffuse interstitial haemorrhage observed with the HM3, the SLX lesion bore a blood-filled core of near-complete tissue disruption devoid of histologically recognizable kidney structure. • Despite the intensity of tissue destruction at the core of the lesion, measures of lesion size based on macroscopic determination of haemorrhage in the parenchyma were not significantly different from kidneys treated using the HM3 (2000 SWs, 120 SWs/min: SLX, 1.86 ± 0.52% FRV; HM3, 3.93 ± 1.29% FRV). • Doubling the SW dose of the SLX from 2000 to 4000 SWs did not significantly increase lesion size. In addition, slowing the firing rate of the SLX to 60 SWs/min did not reduce the size of the lesion (2.16 ± 0.96% FRV) compared with treatment at 120 SWs/min, as was the case with the HM3 (0.42 ± 0.23% FRV vs 3.93 ± 1.29% FRV). • Renal function fell significantly below baseline in all treated groups but was similar for both lithotriptors. • Focal width of the SLX (≈2.6 mm) was about one-third that of the HM3 (≈8 mm) while peak pressures were higher (SLX at power level 9: P+≈90 MPa, P-≈-12 MPa; HM3 at 24 kV: P+≈46 MPa, P-≈-8 MPa). CONCLUSIONS: • The lesion produced by the SLX (narrow focal width, high acoustic pressure) was a more focused, more intense form of tissue damage than occurs with the HM3. • Slowing the SW rate to 60 SWs/min, a strategy shown to be effective in reducing injury with the HM3, was not protective with the SLX. • These findings suggest that the focal width and acoustic output of a lithotriptor affect the renal response to SWL.

Bubble proliferation in the cavitation field of a shock wave lithotripter.

Lithotripter shock waves (SWs) generated in non-degassed water at 0.5 and 2 Hz pulse repetition frequency (PRF) were characterized using a fiber-optic hydrophone. High-speed imaging captured the inertial growth-collapse-rebound cycle of cavitation bubbles, and continuous recording with a 60 fps camcorder was used to track bubble proliferation over successive SWs. Microbubbles that seeded the generation of bubble clouds formed by the breakup of cavitation jets and by bubble collapse following rebound. Microbubbles that persisted long enough served as cavitation nuclei for subsequent SWs, as such bubble clouds were enhanced at fast PRF. Visual tracking suggests that bubble clouds can originate from single bubbles.

Inaccurate reporting of mineral composition by commercial stone analysis laboratories: implications for infection and metabolic stones.

PURPOSE: We determined the accuracy of stone composition analysis at commercial laboratories. MATERIALS AND METHODS: A total of 25 human renal stones with infrared spectroscopy determined composition were fragmented into aliquots and studied with micro computerized tomography to ensure fragment similarity. Representative fragments of each stone were submitted to 5 commercial stone laboratories for blinded analysis. RESULTS: All laboratories agreed on the composition of 6 pure stones. Only 2 of 4 stones (50%) known to contain struvite were identified as struvite at all laboratories. Struvite was reported as a component by some laboratories for 4 stones previously determined not to contain struvite. Overall there was disagreement regarding struvite in 6 stones (24%). For 9 calcium oxalate stones all laboratories reported some mixture of calcium oxalate but the quantity of subtypes differed significantly among laboratories. In 6 apatite containing stones apatite was missed by the laboratories in 20% of samples. None of the laboratories identified atazanavir in a stone containing that antiviral drug. One laboratory reported protein in every sample while all others reported it in only 1. Nomenclature for apatite differed among laboratories with 1 reporting apatite as carbonate apatite and never hydroxyapatite, another never reporting carbonate apatite and always reporting hydroxyapatite, and a third reporting carbonate apatite as apatite with calcium carbonate. CONCLUSIONS: Commercial laboratories reliably recognize pure calculi. However, variability in the reporting of mixed calculi suggests a problem with the accuracy of stone analysis results. There is also a lack of standard nomenclature used by laboratories.

Micro-computed tomography for analysis of urinary calculi.

Micro-computed tomographic (micro CT) imaging has become an important tool for the study of urinary stones. The method involves the collection of a series of X-ray pictures of the stone as it is rotated, and the internal structure of the stone is computationally reconstructed from these pictures. The entire process takes from 30 min to an hour with present technology. Resulting images of the stone provide unprecedented detail of the mineral composition and its morphological arrangement within the stone. For smaller stones, reconstructions can easily have voxel sizes of <5 µm, making this a truly microscopic view of the stone. The micro CT reconstructions can be viewed with any of a number of existing methods for visualizing the structure of both the surface and internal features of the stone. Because the entire process is non-destructive, traditional analysis methods--such as dissection and spectroscopic examination of portions of the stones--can also be performed. Micro CT adds value to traditional methods by identifying regions of the stone to be analyzed, and also with its ability to scan a cluster of stones or stone fragments at once. Finally, micro CT has become a powerful tool to help investigate events in stone formation that distinguish different kinds of stone disease.

In vitro evaluation of the Lithoclast Ultra Vario combination lithotrite.

Rigid intracorporeal lithotrites can be invaluable in the removal of large stone burdens during percutaneous nephrolithotomy. One such device, the Lithoclast Ultra Vario (LUV) has an outer ultrasound probe and inner pneumatic-ballistic probe. The ballistic probe can be advanced or retracted and run at 1-12 Hz. Since it can be difficult to predict optimal settings with any new device, we asked if in vitro testing could give insight into how best to operate this lithotrite. We tested the LUV under hands-free conditions that simulate treatment of fixed stones and freely movable stones. A fixed-stone test system measured the time to penetrate a gypsum model stone placed atop the probe and a movable-stone system determined time for comminution of a stone within a confined space. In addition, the time to evacuate 2-mm stone particles was measured. For hands-on testing, model stones were placed in a plastic dish submerged in water and the time to comminution was measured. Penetration time of fixed stones was faster with the ballistic probe extended 2.5 mm than when retracted (5.30 ± 0.85 vs. 8.75 ± 1.07 s, p < 0.0001). Comminution of free stones was faster with the ballistic probe retracted than when it was extended 1 mm or 2.5 mm (9.7 ± 0.9, 13.8 ± 1.3, 23.7 ± 3.2 s, p < 0.0001). In hands-on testing, extending the ballistic probe substantially reduced the efficiency of comminution (36.7 ± 6.4 vs. 131.3 ± 15.3 s, p < 0.0001). Clearance of fragments was considerably faster when the pneumatic-ballistic rate was 12 Hz compared to 1 Hz (12.3 ± 1.1 vs. 28.3 ± 2.2 s, p < 0.0001). These in vitro findings suggest ways to take advantage of the positive features while minimizing potential limitations of this lithotrite. Extending the ballistic probe is an advantage when the stone is immobile, as would be the case in treating a large stone that can be isolated against the wall of the pelvicalyceal system, but is a distinct disadvantage--due to retropulsion--when the stone is free to move. Operation of the LUV at fast ballistic rate significantly improved its ability to aspirate stone fragments.

Analysis of mixed stones is prone to error: a study with US laboratories using micro CT for verification of sample content.

This project sought to test the ability of commercial stone analysis laboratories to correctly analyze urinary stones. Human stone specimens were cleaved into pieces, and the pieces of each specimen were verified as being similar using micro-computed tomography (micro CT), a non-destructive method. Thus, similar specimens from 25 stones were sent to five laboratories, and a sixth piece was kept for analysis in our laboratory using Fourier-transform infrared spectroscopy (FT-IR). The results showed that laboratories were very good at analyzing pure specimens, but with mixed specimens the accuracy and consistency varied. In six stones containing apatite, a mineral easily identified using micro CT, apatite was missed 20% of the time. Struvite content in the specimens was inconsistently reported, with laboratories differing in their reports of the presence of struvite in six of the 25 stones (24%). A mixed stone containing atazanavir was not reported by any of the laboratories as containing that drug. Nomenclature differed among the laboratories, especially with regard to apatite, which was variously reported as hydroxyapatite, carbonate apatite, or as apatite with calcium carbonate. One laboratory reported protein in every stone, while for all others protein was reported in only one stone. We conclude that physicians need to be aware that reports on mixed stones, which represent >90% of all calculi, can be erroneous. It is likely that supplying a greater amount of stone material will assist a laboratory in making a correct analysis of mixed stones. Also, standardization of nomenclature could assist in analysis reproducibility, but this remains to be tested.

Assessment of renal injury with a clinical dual head lithotriptor delivering 240 shock waves per minute.

PURPOSE: Lithotriptors with 2 treatment heads deliver shock waves along separate paths. Firing 1 head and then the other in alternating mode has been suggested as a strategy to treat stones twice as rapidly as with conventional shock wave lithotripsy. Because the shock wave rate is known to have a role in shock wave lithotripsy induced injury, and given that treatment using 2 separate shock wave sources exposes more renal tissue to shock wave energy than treatment with a conventional lithotriptor, we assessed renal trauma in pigs following treatment at rapid rate (240 shock waves per minute and 120 shock waves per minute per head) using a Duet lithotriptor (Direx Medical Systems, Petach Tikva, Israel) fired in alternating mode. MATERIALS AND METHODS: Eight adult female pigs (Hardin Farms, Danville, Indiana) each were treated with sham shock wave lithotripsy or 2,400 shock waves delivered in alternating mode (1,200 shock waves per head, 120 shock waves per minute per head and 240 shock waves per minute overall at a power level of 10) to the lower renal pole. Renal functional parameters, including glomerular filtration rate and effective renal plasma flow, were determined before and 1 hour after shock wave lithotripsy. The kidneys were perfusion fixed in situ and the hemorrhagic lesion was quantified as a percent of functional renal volume. RESULTS: Shock wave treatment resulted in no significant change in renal function and the response was similar to the functional response seen in sham shock wave treated animals. In 6 pigs treated with alternating mode the renal lesion was small at a mean +/- SEM of 0.22% +/- 0.09% of functional renal volume. CONCLUSIONS: Kidney tissue and function were minimally affected by a clinical dose of shock waves delivered in alternating mode (120 shock waves per minute per head and 240 shock waves per minute overall) with a Duet lithotriptor. These observations decrease concern that dual head lithotripsy at a rapid rate is inherently dangerous.

Extracorporeal shock wave lithotripsy at 60 shock waves/min reduces renal injury in a porcine model.

OBJECTIVE: To determine if extracorporeal shock wave lithotripsy (ESWL) at 60 shock waves (SWs)/min reduces renal damage and haemodynamic impairment compared to treatment at 120 SWs/min. MATERIALS AND METHODS: One kidney in each of 19 juvenile pigs (7-8 weeks old) was treated at 120 or at 60 SWs/min (2000 SWs, 24 kV) with an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, GA, USA). Renal function was determined before and after ESWL treatment by inulin clearance, extraction and clearance of para-aminohippuric acid. Both kidneys were then removed to measure parenchymal lesion size by sectioning the entire kidney and quantifying the size of the haemorrhagic lesion in each slice. RESULTS: ESWL at 60 SWs/min significantly reduced the size of the acute morphological lesion compared to 120 SWs/min (0.42% vs 3.93% of functional renal volume, P = 0.011) and blunted the decrease in glomerular filtration rate and renal plasma flow normally seen after treatment at 120 SWs/min. CONCLUSIONS: Treatment at a firing rate of 60 SWs/min produces less morphological injury and causes less alteration in renal haemodynamics than treatment at 120 SWs/min in the pig model of ESWL-induced renal injury.

Treatment protocols to reduce renal injury during shock wave lithotripsy.

PURPOSE OF REVIEW: Growing concern over the acute and long-term adverse effects associated with shock wave lithotripsy calls for treatment strategies to reduce renal injury and improve the efficiency of stone breakage in shock wave lithotripsy. RECENT FINDINGS: Experimental studies in the pig model show that lithotripter settings for power and shock wave rate and the sequence of shock wave delivery can be used to reduce trauma to the kidney. Step-wise power ramping as is often used to acclimate the patient to shock waves causes less tissue trauma when the initial dose is followed by a brief (3-4 min) pause in shock wave delivery. Slowing the firing rate of the lithotripter to 60 shock waves/min or slower is also effective in reducing renal injury and has the added benefit of improving stone breakage outcomes. Neither strategy to reduce renal injury -- not power ramping with 'pause-protection' nor delivering shock waves at reduced shock wave rate --- have been tested in clinical trials. SUMMARY: Technique in lithotripsy is critically important, and it is encouraging that simple, practical steps can be taken to improve the safety and efficacy of shock wave lithotripsy.

The acute and long-term adverse effects of shock wave lithotripsy.

Shock wave lithotripsy (SWL) has proven to be a highly effective treatment for the removal of kidney stones. Shock waves (SWs) can be used to break most stone types, and because lithotripsy is the only noninvasive treatment for urinary stones, SWL is particularly attractive. On the downside SWL can cause vascular trauma to the kidney and surrounding organs. This acute SW damage can be severe, can lead to scarring with a permanent loss of functional renal volume, and has been linked to potentially serious long-term adverse effects. A recent retrospective study linking lithotripsy to the development of diabetes mellitus has further focused attention on the possibility that SWL may lead to life-altering chronic effects. Thus, it appears that what was once considered to be an entirely safe means to eliminate renal stones can elicit potentially severe unintended consequences. The purpose of this review is to put these findings in perspective. The goal is to explain the factors that influence the severity of SWL injury, update current understanding of the long-term consequences of SW damage, describe the physical mechanisms thought to cause SWL injury, and introduce treatment protocols to improve stone breakage and reduce tissue damage.

Effect of firing rate on the performance of shock wave lithotriptors.

OBJECTIVE: To determine the mechanism that underlies the effect of shock wave (SW) rate on the performance of clinical lithotripters. MATERIALS AND METHODS: The effect of firing rate on the pressure characteristics of SWs was assessed using a fibre-optic probe hydrophone (FOPH 500, RP Acoustics, Leutenbach, Germany). Shock waves were fired at slow (5-27 SW/min) and fast (100-120 SW/min) rates using a conventional high-pressure lithotriptor (DoLi-50, Dornier MedTech America, Inc., Kennesaw, GA, USA), and a new low-pressure lithotriptor (XX-ES, Xi Xin Medical Instruments Co. Ltd, Suzhou, PRC). A digital camcorder (HDR-HC3, Sony, Japan) was used to record cavitation fields, and an ultrafast multiframe high-speed camera (Imacon 200, DRS Data & Imaging Systems, Inc., Oakland, NJ, USA) was used to follow the evolution of bubbles throughout the cavitation cycle. RESULTS: Firing rate had little effect on the leading positive-pressure phase of the SWs with the DoLi lithotriptor. A slight reduction ( approximately 7%) of peak positive pressure (P+) was detected only in the very dense cavitation fields (approximately 1000 bubbles/cm(3)) generated at the fastest firing rate (120 SW/min) in nondegassed water. The negative pressure of the SWs, on the other hand, was dramatically affected by firing rate. At 120 SW/min the peak negative pressure was reduced by approximately 84%, the duration and area of the negative pressure component was reduced by approximately 80% and approximately 98%, respectively, and the energy density of negative pressure was reduced by >99%. Whereas cavitation bubbles proliferated at fast firing rates, HS-camera images showed the bubbles that persisted between SWs were very small (<10 microm). Similar results were obtained with the XX-ES lithotriptor but only after recognizing a rate-dependent charging artefact with that machine. CONCLUSION: Increasing the firing rate of a lithotriptor can dramatically reduce the negative pressure component of the SWs, while the positive pressure remains virtually unaffected. Cavitation increases as the firing rate is increased but as the bubbles collapse, they break into numerous microbubbles that, because of their very small size, do not pose a barrier to the leading positive pressure of the next SW. These findings begin to explain why stone breakage in SWL becomes less efficient as the firing rate is increased.

Independent assessment of a wide-focus, low-pressure electromagnetic lithotripter: absence of renal bioeffects in the pig.

OBJECTIVE: To assess the renal injury response in a pig model treated with a clinical dose of shock waves (SWs) delivered at a slow rate (27 SW/min) using a novel wide focal zone (18 mm), low acoustic pressure (<20 MPa) electromagnetic lithotripter (Xi Xin-Eisenmenger, XX-ES; Xi Xin Medical Instruments Co. Ltd., Suzhou, PRC). MATERIALS AND METHODS: The left kidneys of anaesthetized female pigs were treated with 1500 SWs from either an unmodified electrohydraulic lithotripter (HM3, Dornier MedTech America, Inc., Kennesaw, GA, USA; 18 kV, 30 SW/min) or the XX-ES (9.3 kV, 27 SW/min). Measures of renal function (glomerular filtration rate, GFR, and renal plasma flow) were collected before and after SW lithotripsy, and kidneys were harvested for histological quantification of vascular haemorrhage, expressed as a percentage of the functional renal volume (FRV). A fibre-optic probe hydrophone was used to characterize the acoustic field, and the breakage of gypsum model stones was used to compare the function of the two lithotripters. RESULTS: Kidneys treated with the XX-ES showed no significant change in renal haemodynamic function and no detectable tissue injury. Pigs treated with the HM3 had a modest decline from baseline ( approximately 20%) in both GFR (P > 0.05) and renal plasma flow (P = 0.064) in the treated kidney, but that was not significantly different from the control group. Although most HM3-treated pigs showed no evidence of renal tissue injury, two had focal injury measuring 0.1% FRV, localized to the renal papillae. The width of the focal zone for the XX-ES was approximately 18 mm and that of the HM3 approximately 8 mm. Peak positive pressures at settings used to treat pigs and break model stones were considerably lower for the XX-ES (17 MPa at 9.3 kV) than for the HM3 (37 MPa at 18 kV). The XX-ES required fewer SWs to break stones to completion than did the HM3, with a mean (sd) of 634 (42) and 831 (43) SWs, respectively (P < 0.01). However, conditions were different for these tests because of differences in physical configuration of the two machines. CONCLUSION: The absence of renal injury with the wide focal zone XX-ES lithotripter operated at low shock pressure and a slow SW rate suggests that this lithotripter would be safe when used at the settings recommended for patient treatment. That the injury was also minimal using the Dornier HM3 lithotripter at a slow SW rate implies that the reduced tissue injury seen with these two machines was because they were operated at a slow SW rate. As recent studies have shown stone breakage to be improved when the focal zone is wider than the stone, a wide focal zone lithotripter operated at low pressure and slow rate has the features necessary to provide better stone breakage with less tissue injury.

Potential for cavitation-mediated tissue damage in shockwave lithotripsy.

PURPOSE: Shockwave lithotripsy (SWL) injures renal tissue, and cavitation has been reported to mediate some of these effects. Much of the work characterizing the cavitation injury of SWL has been performed in small animals or in vitro. We describe experiments that promote cavitation during SWL and estimate the spatial distribution of the resulting hemorrhagic lesion in a large-animal (porcine) model of clinical lithotripsy. MATERIALS AND METHODS: The lower pole calix of the left kidney in female farm pigs was targeted for SWL with a Dornier HM3 lithotripter. Intraventricular injections of polystyrene microspheres were made before and at intervals during lithotripsy to blanket systemic circulation with cavitation nuclei. Following SWL, the abdominal viscera were inspected and the kidneys were processed for morphologic analysis. RESULTS: Extensive surface hemorrhage occurred over both the targeted and contralateral kidneys, along with widespread petechial hemorrhage over the spleen, intestines, and peritoneum. The targeted kidneys developed subcapsular hematomas. Histology revealed focal and diffuse damage to the targeted kidneys and vascular rupture in both kidneys with complete necrosis of the walls of intralobular arteries and veins. CONCLUSIONS: These results demonstrate the potential for unfocused shockwaves to damage blood vessels outside the focal zone of the lithotripter when the vasculature is seeded with cavitation nuclei. The wide distribution of damage suggests that the acoustic field of a lithotripter delivers negative pressures that exceed the cavitation threshold far off the acoustic axis. The findings underscore that conditions permissive for cavitation can lead to dramatic sequelae during SWL.

Why stones break better at slow shockwave rates than at fast rates: in vitro study with a research electrohydraulic lithotripter.

BACKGROUND AND PURPOSE: Stones break better when the rate of shockwave (SW) delivery is slowed. It has been hypothesized that the greater cavitation accompanying a fast rate shields pulse propagation, thus interfering with the delivery of SW energy to the stone. We tested this idea by correlating waveforms measured at the SW focus with cavitation viewed using high-speed imaging. MATERIALS AND METHODS: A series of U30 gypsum stones held in a 2-mm mesh basket were exposed to 200 SWs at 30 or 120 SW/min from a research electrohydraulic lithotripter (HM3 clone). Waveforms were collected using a fiberoptic probe hydrophone. High-speed imaging was used to observe cavitation bubbles in the water and at the stone surface. RESULTS: Stone breakage was significantly better at 30 SW/min than at 120 SW/min. The rate had little effect on SW parameters in the water free field. In the presence of particulates released from stones, the positive pressure of the SW remained unaffected, but the trailing tensile phase of the pulse was significantly reduced at 120 SW/min. CONCLUSIONS: Cavitation bubbles do not persist between SWs. Thus, mature bubbles from one pulse do not interfere with the next pulse, even at 120 SW/min. However, cavitation nuclei carried by fine particles released from stones can persist between pulses. These nuclei have little effect on the compressive wave but seed cavitation under the influence of the tensile wave. Bubble growth draws energy from the negative-pressure phase of the SW, reducing its amplitude. This likely affects the dynamics of cavitation bubble clusters at the stone surface, reducing the effectiveness of bubble action in stone comminution.

Variability of protein content in calcium oxalate monohydrate stones.

BACKGROUND AND PURPOSE: Urinary stones are heterogeneous in their fragility to lithotripter shockwaves. As a first step in gaining a better understanding of the role of matrix in stone fragility, we measured extractible protein in calcium oxalate monohydrate (COM) stones that were extensively characterized by micro-computed tomography (micro CT). MATERIALS AND METHODS: Stones were scanned using micro CT (Scanco mCT20, 34 microm). They were ground, and the protein extracted using four methods: 0.25M EDTA, 2% SDS reducing buffer, 9M urea buffer, and 10% acetic acid. Protein was measured using NanoOrange. The SDS extracts were also examined using polyacrylamide electrophoresis (PAGE). RESULTS: Extracted protein was highest with the SDS or urea methods (0.28% +/- 0.13% and 0.24% +/- 0.11%, respectively) and lower using the EDTA method (0.17% +/- 0.05%; P < 0.02). Acetic acid extracted little protein (0.006 +/- 0.002%; P < 0.001). Individual stones were significantly different in extractability of protein by the different methods, and SDS-PAGE revealed different protein patterns for individual stones. Extracted protein did not correlate with X-ray-lucent void percentage, which ranged from 0.06% to 2.8% of stone volume, or with apatite content. CONCLUSIONS: Extractible stone-matrix protein differs for individual COM stones, and yield is dependent on the extraction method. The presence of X-ray-lucent voids or minor amounts of apatite in stones did not correlate with protein content. The amounts of protein recovered were much lower than reported by Boyce, showing that these methods extracted only a fraction of the protein bound up in the stones. The results suggest that none of the methods tested will be useful for helping to answer the question of whether matrix content differs among stones of differing fragility to lithotripter shockwaves.