Operator experience and adequate anesthesia improve treatment outcome with third-generation lithotripters

Optimisation of shock wave lithotripsy: a systematic review of technical aspects to improve outcomes

Shock wave lithotripsy (SWL) remains an important treatment option for the management of upper urinary tract stones. The optimisation of certain technical principles can help to improve the results of SWL. We performed a systematic review based on preferred reporting items for systematic review and meta-analysis (PRISMA) standards for studies reporting on technical aspects of SWL. A literature search was conducted on the PubMed database between January 1984 and November 2018 using 'shockwave lithotripsy' and 'stone' as keywords. Summaries and manuscripts of relevant articles were reviewed in order to select studies with the best level of evidence in each theme covered during the review. From 4,135 titles, 165 abstracts and full-text articles were reviewed. Overall, SWL has good outcomes in the treatment of upper urinary tract stones. It remains the only truly non-invasive stone treatment. While stone-free rate (SFR) might not be equivalent to ureteroscopy or percutaneous nephrolithotomy outcomes, SWL can be optimised by changing several technical factors, including type of machine, patient position, number, rate and energy of shocks, stone targeting, and patient analgesia. For each of these included SWL themes, relevant and selected studies with the highest level of evidence were described and discussed. Paired with these improved technical factors and appropriate patient selection, SWL, with its low complication rates, remains an excellent treatment option in 2019.

Extracorporeal shock wave lithotripsy under intravenous sedation for treatment of urolithiasis

BACKGROUND

In contrast to treatment with oral or intramuscular analgesics, extracorporeal shock wave lithotripsy (E.S.W.L.) can be performed with patients under sedation too. Besides the advantage of increased shock energy, patients tend to have more constant breathing excursions and are more idle during treatment, potentially increasing the stone-free ratio (S.F.R.) after treatment.

METHODS

This study presents the results of 310 patients who underwent 400 E.S.W.L. procedures under sedation, with a stationary lithotripter.

RESULTS

After one procedure, the S.F.R. was 54.8% (170/310). A second treatment was successful in 42.1% (32/76), a third treatment in 21.4% (3/14). Therefore, 66.1% (205/310) of patients eventually became stone-free. Kidney stones were successfully treated in 65.4% (161/246), ureteral stones in 68.8% (44/64) of cases. Patients with stones ≤15 mm were successfully treated in 67.4% (194/288), patients with stones >15 mm in 50% (11/22) of cases. Considering each procedure individually, 45.3% (181/400) of procedures were successful after 3 weeks. Extending follow-up to 3 months is important, since 26.7% of stones (24/90) eventually still disappeared, increasing S.F.R. to 51.3% after one procedure. Complications occurred after 5.5% E.S.W.L.-procedures.

CONCLUSIONS

E.S.W.L. is a well-tolerated, non-invasive procedure that produces reasonable stone clearance of both upper and lower urinary tract calculi. Performing the procedure whilst patients are intravenously sedated results in an acceptable S.F.R. Strong selection based on unfavourable factors could increase the chance on successful treatment and spare patients a pointless procedure. However, considering E.S.W.L.'s elegant nature, sometimes a more tolerant approach seems justifiable.

Listening to music during shock wave lithotripsy decreases anxiety, pain, and dissatisfaction : A randomized controlled study

BACKGROUND

We analyzed the effects of music on pain, anxiety, and overall satisfaction in patients undergoing a shock wave lithotripsy (SWL) procedure.

METHODS

A total of 200 patients scheduled to undergo SWL were included in this study. Group 1 consisted of 95 patients who listened to music during the SWL session while group 2 included 105 patients who did not listen music during the procedure. State-Trait Anxiety Inventory (STAI) was used to assess state and trait anxiety (STAI-S/T). A visual analog scale (VAS) was used at the end of the session in order to assess pain, willingness to repeat the procedure, and overall patient satisfaction. Hemodynamic parameters including systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were recorded before and after the session.

RESULTS

No statistically significant difference was found between the two groups in terms of stone characteristics, SWL parameters, pre-SWL STAI-T/S scores, and pre-SWL hemodynamic parameters. Post-SWL STAI-S scores were found to be lower in patients who listened to music (p = 0.006). At the end of the SWL, VAS scores of pain, satisfaction, and willingness to repeat procedure were significantly different in favor of the music group (p = 0.007, p = 0.001, p = 0.015, respectively). SBP, DBP, and HR were significantly higher in patients who did not listen to music (p = 0.002, p = 0.024, p = 0.001, respectively).

CONCLUSION

Music can be an ideal adjunctive treatment modality for patients undergoing SWL treatment. It has the potential to enhance patient compliance and treatment satisfaction by reducing the procedure-related anxiety and pain perception.

Shockwave Lithotripsy Practice Pattern Variations Among and Between American and Canadian Urologists: In Support of Guidelines

PURPOSE

Shockwave lithotripsy (SWL) is a widely utilized form of treatment for urolithiasis. There are new evidence-based recommendations regarding pre-SWL patient work-up and the performance of SWL. The purpose of this study is to determine practice patterns for SWL and to determine if regional variation exists between Canada and the United States.

MATERIALS AND METHODS

A 19-question survey was prepared. Canadian urologists were surveyed through e-mail correspondence. In the United States, members of the Endourologic Society and members of two large stone management groups were surveyed. Canadian and American results were compared using the chi-square and Fisher's exact tests.

RESULTS

Ninety-four Canadian urologists and 187 U.S. urologists completed the survey. Practice patterns differed between countries. Intravenous sedation was more commonly used in Canada (Canada 94.7% vs United States 17.9%, p < 0.001); routine antibiotics were more commonly given in United States (Canada 2.1% vs United States 78.1%, p < 0.001); a shock rate of 2 Hz was more common in Canada (Canada 76.6% vs United States 16.2%, p < 0.00001); rate of discontinuing ASA for renal and ureteral stone treatment was higher in the United States (renal Canada 88.3% vs United States 95.7%, p < 0.02; ureteral Canada 62.4% vs 90.3%, p < 0.0001); and ureteral stents were more commonly used if treating a large stone or patients with solitary kidneys in the United States (large stones Canada 58.2% vs United States 88.8%, p = 0.0001; solitary kidney Canada 50.6% vs 66.3%, p = 0.02).

CONCLUSIONS

This study highlights the absence of standardization of SWL. Significant regional differences exist in practice patterns and performance of SWL between Canadian and American urologists.

The effect of music therapy during shockwave lithotripsy on patient relaxation, anxiety, and pain perception

OBJECTIVES

To research the effect of listening to music during shock wave lithotripsy (SWL) on the patient's pain control, anxiety levels, and satisfaction.

PATIENTS AND METHODS

The study comprised 400 patients from three hospitals. Half of patients listened to music during their first SWL session but not during their second session. The other half had no music for the first session but the second session was accompanied by music. During all sessions, with and without music, pulse rates, blood pressure, State-Trait Anxiety Inventory-State Anxiety scores (STAI-SA), Visual Analog Scale (VAS scores for pain), willingness to repeat procedure (0 = never to 4 happily), and patient satisfaction rates (0 = poor to 4 = excellent) were assessed.

RESULTS

There was no statistical difference between the two groups in terms of blood pressure and pulse rates. In both groups, the STAI-SA and VAS pain scores were lower in the session when music was listened to (p < 0.001). The patients requested more SWL treatment be completed while listening to music and their satisfaction was greater.

CONCLUSION

Music lowered the anxiety and pain scores of patients during SWL and provided greater satisfaction with treatment. Completing this procedure while the patient listens to music increases patient compliance greatly and reduces analgesic requirements.

EAU Guidelines on Interventional Treatment for Urolithiasis

CONTEXT

Management of urinary stones is a major issue for most urologists. Treatment modalities are minimally invasive and include extracorporeal shockwave lithotripsy (SWL), ureteroscopy (URS), and percutaneous nephrolithotomy (PNL). Technological advances and changing treatment patterns have had an impact on current treatment recommendations, which have clearly shifted towards endourologic procedures. These guidelines describe recent recommendations on treatment indications and the choice of modality for ureteral and renal calculi.

OBJECTIVE

To evaluate the optimal measures for treatment of urinary stone disease.

EVIDENCE ACQUISITION

Several databases were searched to identify studies on interventional treatment of urolithiasis, with special attention to the level of evidence.

EVIDENCE SYNTHESIS

Treatment decisions are made individually according to stone size, location, and (if known) composition, as well as patient preference and local expertise. Treatment recommendations have shifted to endourologic procedures such as URS and PNL, and SWL has lost its place as the first-line modality for many indications despite its proven efficacy. Open and laparoscopic techniques are restricted to limited indications. Best clinical practice standards have been established for all treatments, making all options minimally invasive with low complication rates.

CONCLUSION

Active treatment of urolithiasis is currently a minimally invasive intervention, with preference for endourologic techniques.

PATIENT SUMMARY

For active removal of stones from the kidney or ureter, technological advances have made it possible to use less invasive surgical techniques. These interventions are safe and are generally associated with shorter recovery times and less discomfort for the patient.

Strategies to optimize shock wave lithotripsy outcome: Patient selection and treatment parameters

Shock wave lithotripsy (SWL) was introduced in 1980, modernizing the treatment of upper urinary tract stones, and quickly became the most commonly utilized technique to treat kidney stones. Over the past 5-10 years, however, use of SWL has been declining because it is not as reliably effective as more modern technology. SWL success rates vary considerably and there is abundant literature predicting outcome based on patient- and stone-specific parameters. Herein we discuss the ways to optimize SWL outcomes by reviewing proper patient selection utilizing stone characteristics and patient features. Stone size, number, location, density, composition, and patient body habitus and renal anatomy are all discussed. We also review the technical parameters during SWL that can be controlled to improve results further, including type of anesthesia, coupling, shock wave rate, focal zones, pressures, and active monitoring. Following these basic principles and selection criteria will help maximize success rate.

Management patterns of medicare patients undergoing treatment for upper urinary tract calculi

PURPOSE

We conducted this study to identify differences in the re-treatment rates and ancillary procedures for the two most commonly utilized stone treatment procedures in the Medicare population: ureteroscopy (URS) and shock wave lithotripsy (SWL).

MATERIALS AND METHODS

A retrospective claims analysis of the Medicare standard analytical file 5% sample was conducted to identify patients with a new diagnosis of urolithiasis undergoing treatment with URS or SWL from 2009-2010. Outcomes evaluated: (1) repeat stone removal procedures within 120 days post index procedure, (2) stent placement procedures on the index date, 30 days prior to and 120 days post index date, and (3) use of general anesthesia.

RESULTS

We identified 3885 eligible patients, of which 2165 (56%) underwent SWL and 1720 (44%) underwent URS. Overall, SWL patients were 1.73 times more likely to undergo at least one repeat procedure than URS patients, and twice as likely to require multiple re-treatments compared to URS. Among those with ureteral stones, SWL patients were 2.27 times more likely to undergo repeat procedures. The difference was not statistically significant in renal stone patients. Overall, SWL patients were 1.41 times more likely than URS patients to have a stent placed prior to index procedure, and 1.33 times more likely to have a stent placed subsequent to the index procedure. The majority of URS patients (77.8%) had a stent placed at the time of index procedure. There was no significant difference in anesthetic approaches between SWL and URS.

CONCLUSIONS

Patients undergoing SWL are significantly more likely to require re-treatments than URS patients. SWL patients are also significantly more likely to require ureteral stent placement as a separate event. SWL and URS patients have similar rates of general anesthesia.

How to improve results with extracorporeal shock wave lithotripsy

OBJECTIVE

Shock wave lithotripsy (SWL) has greatly revolutionized the treatment of patients suffering from stone disease. There are a number of patient- and device-specific factors that can affect treatment outcome. Herein, we review practices that can increase the likelihood of SWL treatment success.

METHODS

A systematic literature review was performed to identify studies of SWL treatment parameters.

RESULTS

Among the factors affecting the outcome of SWL were patient selection criteria, such as stone burden, stone location, and anatomic features. Additionally, technical aspects of the SWL procedure also can affect outcome; these factors include the acoustic output of the lithotripter, the coupling of the lithotripter to the patient, and the power, total number, and rate of shock wave delivery.

CONCLUSIONS

The outcome of SWL can be optimized with close attention to patient selection criteria as well as the manner in which the treatment is performed.

ESWL and Triple Fire Lithotripter

The ideal lithotripter which all companies hope to achieve in the near future, should be characterized by high efficacy, low impact on the patient's sensitivity to pain and least detrimental action on the surrounding tissues. Yet, even the most modern technology seems to be still very far from achieving these goals. For around 1 year our Department has been using the last generation lithotripter Piezolith 3000® (variable triple-focus). Compared to its predecessor, this machine has some changes such as: a) triple focus module that allows to adjust the focal distance to the size of the calculation, b) greater focal depth ranging from 15 cm in Piezolith 3000® fixed focus to 16.5 cm in the new lithotripter, allowing for an easier and more effective treatment of obese patients, c) increase in power by opening the SW variable focal length (F1: 0.20–3.26 mJ/mm2, F2: 0.08–1.64 mJ/mm2, F3: 0.030–0.41 mJ/mm2). The objective of our work is to assess whether the technical characteristics of the new Piezolith 3000® determine a real improvement in management of urinary calculi.

Methods

265 patients undergoing ESWL with variable triple-focus lithotripter from January 2008 to January 2009 (Group A) were compared to 265 patients treated with an equal lithotripter Piezolith 3000® fixed focus (Group B). The two groups were homogeneous as for the following variables: age, size and location of the calculi, which are distributed as follows: superior calyx (6), medium (20), inferior (32), renal pelvis (36), pyeloureteral junction (12), lumbar ureter (50), iliac (12), pelvis (6), iuxtavesical (70), bladder (7), multiple sites (14). The ESWL was performed in both groups with ultrasound exclusive point.

Results

In Group A the time of fragmentation is lower compared to Group B (p<0.01), with fewer days required for fragment expulsion and lower number of re-treatments (p<0.05). The latter result is probably due to increased average energy applied (2.35 mJ/mm2). However, the increase of this energy results in parallel increased perception of pain during ESWL.

Conclusions

Piezolith 3000® represents a real improvement in the effectiveness of fragmentation but there is, compared to the previous model, a significant reduction in the time of expulsion. This suggests that this variable is affected by other factors.

Effect of initial shock wave voltage on shock wave lithotripsy-induced lesion size during step-wise voltage ramping

OBJECTIVE

To determine if the starting voltage in a step-wise ramping protocol for extracorporeal shock wave lithotripsy (SWL) alters the size of the renal lesion caused by the SWs.

MATERIALS AND METHODS

To address this question, one kidney from 19 juvenile pigs (aged 7-8 weeks) was treated in an unmodified Dornier HM-3 lithotripter (Dornier Medical Systems, Kennesaw, GA, USA) with either 2000 SWs at 24 kV (standard clinical treatment, 120 SWs/min), 100 SWs at 18 kV followed by 2000 SWs at 24 kV or 100 SWs at 24 kV followed by 2000 SWs at 24 kV. The latter protocols included a 3-4 min interval, between the 100 SWs and the 2000 SWs, used to check the targeting of the focal zone. The kidneys were removed at the end of the experiment so that lesion size could be determined by sectioning the entire kidney and quantifying the amount of haemorrhage in each slice. The average parenchymal lesion for each pig was then determined and a group mean was calculated.

RESULTS

Kidneys that received the standard clinical treatment had a mean (sem) lesion size of 3.93 (1.29)% functional renal volume (FRV). The mean lesion size for the 18 kV ramping group was 0.09 (0.01)% FRV, while lesion size for the 24 kV ramping group was 0.51 (0.14)% FRV. The lesion size for both of these groups was significantly smaller than the lesion size in the standard clinical treatment group.

CONCLUSIONS

The data suggest that initial voltage in a voltage-ramping protocol does not correlate with renal damage. While voltage ramping does reduce injury when compared with SWL with no voltage ramping, starting at low or high voltage produces lesions of the same approximate size. Our findings also suggest that the interval between the initial shocks and the clinical dose of SWs, in our one-step ramping protocol, is important for protecting the kidney against injury.

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.

ESWL Prediction of Outcome and Failure Prevention

Based on our own experiences and a review of the recent literature, this article evaluates recent developments in predicting outcomes and failures of shockwave lithotripsy when treating patients with urinary tract stones. After a detailed MEDLINE research, the authors identified several variables that influence and predict extracorporeal shockwave lithotripsy (ESWL) success. These variables may be categorized as stone variables, patient variables and operator variables. Only multivariate analysis on a large number of homogenous patients may offer an objective evaluation of the factors conditioning ESWL outcome.

Effect of modification of shock-wave delivery on stone fragmentation

PURPOSE OF REVIEW

Shock-wave lithotripsy has been the mainstay of urinary-stone treatment over the past 20 years, with three generations of lithotripters now in the market place. Little improvement, however, has been made in the overall efficiency, since the original Dornier HM3 lithotripter. Over the past 5 years much progress has been made in the basic research of shock-wave lithotripsy, with better understanding of the mechanisms involved in stone fragmentation. This progress has led to new modifications in the way shock-wave pulse is generated and delivered.

RECENT FINDINGS

Clinical studies, reflecting improved understanding of basic mechanisms of stone comminution, are being published. Two recent prospective clinical trials have shown the higher efficiency of slow-rate compared with fast-rate shock-wave lithotripsy. A very practical solution requiring no hardware upgrade albeit at longer procedure times. Other promising developments include the use of twin-head technology, with either simultaneous or sequential shock waves. In addition, chemolytic pretreatment and dose-escalation techniques have shown early encouraging results. This review provides an update of the latest shock-wave technology and delivery strategies.

SUMMARY

Long-term studies, to document anticipated improved safety with slow shock-wave rate, are needed. Future in-vivo and clinical studies of twin-head technology and dose-escalation strategy of shock-wave lithotripsy may initiate new lithotripter designs that will lead to improved stone-free rates, while simultaneously reducing associated renal trauma.

Shockwave lithotripsy: dose-related effects on renal structure, hemodynamics, and tubular function

BACKGROUND AND PURPOSE

Shockwave lithotripsy (SWL) predictably damages renal tissue and transiently reduces function in both kidneys. This study characterized the effects on renal function of a supraclinical dose of shockwaves (SWs) (8000) in porcine kidneys and tested the hypothesis that such excessive treatment would intensify and prolong the resulting renal impairment.

MATERIALS AND METHODS

Pigs aged 6 to 7 weeks were anesthetized and assigned to one of three groups. Groups 1 (N=8) and 2 (N=6) each received 8000 SWs at 24 kV (Dornier HM3) to the lower-pole calix of one kidney. Group 3 (7 pigs) received sham treatment. Renal function was monitored for the first 4 hours after SW treatment in Group 1 and for 24 hours in Group 2. Plasma renin activity was measured in Groups 2 and 3.

RESULTS

The renal lesions produced by 8000 SWs comprised 13.8%+/-1.4% of the renal mass. In the 4-hour protocol, this injury was associated with marked reduction of the glomerular filtration rate (GFR), renal plasma flow (RPF), and urinary sodium excretion in both kidneys, although fractional sodium excretion was reduced only in the shocked kidneys. In the 24-hour protocol, GFR and RPF remained below baseline in shocked kidneys at 24 hours. Evidence of progressive ischemic injury was noted in shocked tissue at 24 hours after SW treatment.

CONCLUSIONS

These findings support the hypothesis that the severity of the renal injury caused by SWL is related to the number of SWs administered and demonstrate the connection in this relation between renal structure and function.

IS NEWER ALWAYS BETTER? A COMPARATIVE STUDY OF 3 LITHOTRIPTOR GENERATIONS

PURPOSE

At a single center we compared the efficacy of 3 generations of lithotriptors using identical protocol inclusion and followup criteria but with different modes of anesthesia.

MATERIALS AND METHODS

We compared stone disintegration and dilatation of the pyelocaliceal system achieved in a prospective, randomized trial comparing the original HM3 (Dornier Medtech, Kennesaw, Georgia) and Lithostar Plus (LSP) lithotriptors, and a matched, consecutive series of 107 treatments with the Modulith SLX. Stone disintegration and dilatation of the pyelocaliceal system were evaluated by abdominal plain x-ray and renal ultrasonography 1 day and 3 months after treatment.

RESULTS

A total of 82 treatments with the HM3, 75 with the LSP and 107 with the SLX were analyzed, matched for stone burden and location within the pyelocaliceal system. On postoperative day 1, 91%, 65% and 48% patients treated with the HM3, LSP and SLX, respectively, were stone-free or had fragments that were 2 mm or less (HM3 vs LSP p <0.001, HM3 vs SLX p <0.001 and LSP vs SLX p = 0.015). Three to 5 mm fragments were found in 7%, 21% and 35% of patients (p = 0.006, <0.001 and 0.06), and fragments 6 mm or greater were found in 1%, 14% and 15% (p = 0.002, <0.001 and 0.1, respectively). The re-treatment rate was 4% in the HM3 group, 13% in the LSP group and 38% in the SLX group (HM3 vs LSP p = 0.05, HM3 vs SLX p <0.001 and LSP vs SLX p <0.001). Obstructive pyelonephritis occurred in 1% of the HM3 group, 8% of the LSP group and 5% of the SLX group (HM3 vs LSP p = 0.02, HM3 vs SLX p = 0.12 and LSP vs SLX p = 0.4). All re-treatments except those in 5 patients were performed with the HM3. Therefore, the 3-month stone-free rate was comparable in all 3 groups (HM3 87%, LSP 80% and SLX 81%).

CONCLUSIONS

This study indicates that the HM3 lithotriptor disintegrates caliceal and renal pelvic stones better than the LSP and SLX machines, resulting in fewer complications and re-treatments. Disintegration with the LSP machine was also superior to that of the SLX with a need for fewer re-treatments.

Shockwave Lithotripsy: Anecdotes and Insights

Shockwave lithotripters have evolved considerably since the introduction of the Dornier HM3 machine 20 years ago. Although shockwave lithotripsy (SWL) remains the preferred treatment for the majority of symptomatic upper urinary-tract calculi, newer lithotripters are not as effective and may have a higher risk of side effects. Lack of progress in lithotripter evolution is attributable to inadequate understanding of how and why shockwaves produce effects on stone and tissue. Current knowledge suggests that stones fragment by the mechanisms of compression fracture, spallation, squeezing, and acoustic cavitation, while tissue damage from shockwaves is secondary to cavitation and non-cavitational forces such as sheer stress. It appears likely that most tissue damage from shockwaves is caused by cavitation. As the understanding of SWL matures, new lithotripter designs may emerge that truly represent an improvement on the original Dornier HM3 machine.