Shock wave lithotripsy (SWL): outcomes from a national SWL database in New Zealand

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1 Shock wave lithotripsy (SWL): outcomes from a national SWL database in New Zealand Cameron E. Alexander*, Stuart Gowland, Jon Cadwallader, John M. Reynard and Benjamin W. Turney *Academic Urology Unit, University of Aberdeen, Aberdeen, Scotland, Mobile Medical Technology, Christchurch, New Zealand, Mobile Medical Technology, Auckland, New Zealand, and Oxford Stone Group, Department of Urology, Nuffield Department of Surgical Sciences, The Churchill Hospital, Oxford, England Objectives To present the national outcomes for New Zealand of over stone cases treated with SWL at 21 centres over a 20 year period. Subjects/patients and methods Stone cases treated with SWL on board the Mobile Medical Technology (MMT) vehicle between 19 June 1995 and 1 December 2014 were identified, and data collection undertaken prospectively for patient, stone and treatment characteristics, and retrospectively for treatment outcomes. The primary outcome was treatment success, defined as complete stone clearance or clinically insignificant residual fragments (CIRFs) of 4mm. Secondary outcomes were stone free rate, complications and auxiliary procedures, and all statistical analyses were descriptive. Results stone cases (7 769 patients) were included. The overall, cumulative success rate was 58.7%; this included 45.1% that were stone free and 13.5% in which there were CIRFs 4mm. Success rates varied widely by stone size and location. Overall rates of urinary tract infection, perinephric haematoma, hospital admission and ureteral stent placement were 1.1%, 0.2%, 6.8% and 4.1%, respectively. Variations in SWL protocols across centres limits the overall reliability of our findings. Conclusion SWL remains a low morbidity management option requiring careful patient selection. This study provides valuable data for patient counseling and the formation of evidence based guidelines in SWL. The MMT SWL service has demonstrated that is it possible to deliver a high volume specialist stone service without requiring patients to travel further for treatment. Keywords Kidney stones, Nephrolithiasis, Lithotripsy Introduction Urolithiasis comprises a significant and growing proportion of urological practice, with international epidemiological data demonstrating a global increase in its incidence and prevalence in recent decades [1 3]. This has important economic implications for healthcare services: a recent analysis estimated that the cost of stone disease will be >$5 billion per annum by 2030 in the USA [4]. Since its inception in the 1980s, shock wave lithotripsy (SWL) has become a well established treatment option for urolithiasis, demonstrating superior outcomes in morbidity and postoperative recovery than surgery, with relatively few contraindications [5,6]. The European Association of Urology (EAU) guidelines recommend SWL as the first line management option for proximal ureteral stones <10mm, and an equivalent first line option to endourology for renal stones <20mm, proximal ureteral stones >10mm and distal ureteral stones <10mm [7]. In spite of this, reports indicate that the rate of SWL use has plateaued or decreased in recent years alongside a surge in the use of ureteroscopy with the holmium laser [8 11], and despite evidence suggesting similar success rates between management options [7]. The current evidence examining the use of SWL demonstrates wide variation in clinical outcomes, with overall stone free rates (SFRs) ranging from 40.2% to 96.8%, and is limited to studies reporting small cohorts or in which multiple models of SWL machine has been used [12]. The accurate estimation of the probability of successful treatment outcome or of associated complications and auxiliary procedures is essential if patients are to be appropriately selected and counseled regarding SWL treatment: it is a great failure that 30 years after the BJU Int 2016; 117: Supplement 4, wileyonlinelibrary.com BJU International 2016 BJU International doi: /bju Published by John Wiley & Sons Ltd.

2 Shock wave lithotripsy introduction of SWL patients can t be given more reliable answers to such questions. Furthermore, the immediate need to provide greater clarity regarding SWL outcomes and to define its role in the management of urological stone disease can be seen within the context of the increasing range of minimally invasive techniques available for stone management. This study presents the national outcomes for New Zealand of over stone cases treated with the Dornier DoLi-S1 lithotripter and its sister model, the DoLi- S2, across 21 centres over a 20 year period. Subjects/patients and methods Study Design and Participants In this retrospective observational study patients with urolithiasis treated with SWL on the Mobile Medical Technology (MMT) vehicle between 19 June 1995 and 01 December 2014 were identified through an electronic search of the New Zealand wide SWL database. Those patients who were 18 years and underwent SWL for kidney or ureteral stones were included. Patients who received treatment for stones which were classified as partial or complete staghorns, or as parenchymal or diverticular, were excluded. Moreover, patients who refused to return for follow up or for which treatment outcomes could not be ascertained were excluded from the final analysis. Data Collection Data collection was undertaken prospectively from 19 June 1995 for patient demographics, stone and treatment characteristics and entered into the national SWL database (Microsoft Access, Redmond, Washington, USA) by the radiographer responsible for the respective patient s treatment. A data nurse was responsible for contacting radiology departments within respective centres to confirm treatment outcomes, and for contacting urology departments to confirm postoperative complications or need for auxiliary procedures. The diagnosis of stone disease, and confirmation of treatment outcomes, was made with non-enhanced computer tomography (CT), abdominal x-ray of kidney, ureter and bladder (KUB) or with intravenous urography according to local treatment protocols over the 20 year study period. Stone size was measured in terms of its maximal diameter (mm). Study variables were defined according to the classifications used within published guidelines on nephrolithiasis. SWL Service Provision The MMT SWL vehicle serves a patient population of approximately 4.4 million in 21 hospitals across 14 cities throughout New Zealand. The fixed, Dornier DoLi-S1 (Dornier MedTech GmbH, Wessling, Germany) lithotripter, and its sister successor DoLi-S2 (Germany), were used throughout the period of study. The first machine was used from 19 June 1995 to 15 September 2005, and the second from 27 September 2005 to 01 December Whilst each individual treatment session was delivered by a single radiographer and urologist, a total of 45 radiographers and 85 urologists delivered treatment over the study period. The diagnoses of acute urinary tract infection, abdominal aortic aneurysm, pregnancy, uncorrected coagulopathy, pelviureteric junction obstruction and ureteric strictures, or the use of a pacemaker, were considered contraindications for SWL. Furthermore, the suitability of individual patients for treatment with SWL on the MMT vehicle was subject to an assessment by the duty anaesthetist. The use of anaesthesia or sedation was selected according to the skills and preferences of the individual anaesthetist, as was the use of prophylactic antibiotics, ureteric stenting, and the rate of shock wave delivery by the urologist. The monitoring of target points was undertaken using fluoroscopy or ultrasound scanning, and treatment stopped when stone fragmentation was identified or the maximum number of shocks had been delivered in accordance with local protocols. Where there were multiple stones present, a single stone would be selected as the primary target and the remaining stones would receive targeted shocks where fragmentation of the primary stone had been observed. Patients were treated on an outpatient basis and discharged home on the same day where there was no evidence of treatment complications requiring hospital admission. The use of auxiliary stent or nephrostomy tube placement was not dictated by national protocols but according to local centre protocols or at the discretion of the surgeon. The date of follow-up was determined by individual centres, with the MMT SWL service recommending radiological imaging at 1 3 months postoperatively to confirm stone status and determine treatment outcome. Where first SWL treatment was unsuccessful, a second session would be offered, after which an alternative management option would be considered by the urologist. Outcome Measurements and Statistical Analysis The primary outcome was treatment success, where success was defined as complete stone clearance (stone free) or clinically insignificant residual fragments (CIRFS) of 4mm on radiological imaging at the time of first follow-up appointment. Treatment failure was defined as stone fragments >4mm or no stone change on radiological imaging. Secondary outcomes included postoperative complications, such as pain requiring analgesia use, perinephric haematoma, urinary tract infection, and postoperative auxiliary procedures, such as the need for nephrostomy tube or ureteric stent placement, ureteroscopy, percutaneous nephrolithotomy or open surgery. All statistical analyses were descriptive and performed using SPSS software, version 22.0 (SPPS Inc, Chicago, IL, USA). 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3 Alexander et al. Results In the 20 year period between 19 June 1995 and 01 December 2014, urological stones (8 215 patients) were treated using the Dornier DoLi-S machines on the MMT vehicle in New Zealand. In accordance with the predefined selection criteria, stone cases were excluded, and (7 769 patients) were included in the final analysis. 16.6% (n = 1 962) of stone cases were excluded due to loss to follow up, and 2.9% (n = 341) because they were classified as staghorn, diverticular or parenchymal stones. The overall follow up rate for stone cases was 83.4% (n = 9 879/11 841). The mean age of the included patient sample was years, and 66.1% were male. The mean stone size was mm, and renal and ureteric stones comprised 80.3% (n = 7 663) and 19.7% (n = 1 875), respectively. Patient demographics and stone characteristics are described in Table 1. The majority of patients were treated in the supine position (98.9%), under general anaesthetic (86.8%), using only intraoperative fluoroscopic imaging (91.1% vs ultrasound 8.9%) and received prophylactic antibiotics (62.1%) (Table 2). In the period between 2004 and 2014 the use of ultrasound imaging for renal stones increased from 3.2% (n = 16/507) to 19.8% (n = 49/248). Furthermore, significant variation was observed between centres in choice of anaesthetic; whilst neuroleptic sedation was used in 13.1% of stone cases overall, centres in Christchurch used sedation in 90.5% of cases. The number of stones treated with SWL on the MMT vehicle increased in each successive 5 year period between 1995 and the end of 2009 (n = 2 305, 2 488, 2 673), but decreased for the first time in the period between 2010 and the end of 2014 (n = 2 072) (Fig. 1). Table 1 Patient demographics and stone characteristics. Patient demographics and Stone characteristics Value Mean age (SD) (years) 52.2 (14.7) Gender (male:female, n) 1.9:1 (5133:2636) Mean stone size (SD) (mm) 9.9 (4.9) Stone size category, n (%) <5 667 (7.0) (59.0) (30.6) > (3.3) Side (left:right, n) 1.3:1 (5427:4111) Stone location, n (%) Upper calyx 1011 (10.6) Middle calyx 1731 (18.1) Lower calyx 3381 (35.4) Renal pelvis 1540 (16.1) Pelviureteric (PUJ) 691 (7.2) Upper ureter 683 (7.2) Middle ureter 268 (2.8) Lower ureter 233 (2.4) Multiple stones, n (%) 2921 (30.6) Table 2 Characteristics of delivered SWL treatment. Characteristics of SWL Treatment Value Patient position, n (%) Supine 9433 (98.9) Prone 105 (1.1) Anaesthetic type, n (%) General anaesthesia 8282 (86.8) Epidural 11 (0.1) Neuroleptic sedation 1245 (13.1) Mean number of shocks (SD) (1397.5) Intraoperative imaging Fluoroscopy 8690 (91.1) Ultrasound 848 (8.9) Median fluoroscopy time (IQR) (mins) 4.0 (1.0) Prophylactic antibiotics (n, yes:no) (%) 5921 (62.1): 3617 (35.9) Gentamicin 4567 (47.9) Cefotaxime 465 (4.9) Ceftriaxone 397 (4.2) Other 492 (5.2) The median follow-up time for radiological confirmation of stone status after SWL was 4.4 months (IQR:7.6). The overall, cumulative success rate was 58.7% (n = 5 597); this included 45.1% (n = 4 305) that were stone free at follow up and 13.5% (n = 1 292) in which there were CIRFS 4mm. When only considering the first SWL session, the treatment success rate was 52.6% (n = 5 018), with a stone free rate (SFR) of 40.8% (n = 3 890). Of those patients who had an unsuccessful outcome after first treatment (n = 4 520), 28.1% (n = 1 271) subsequently received a second SWL session (i.e. retreatment); the success rate in the retreatment group was 46.6% (n = 579), with a SFR of 32.7% (n = 414). On excluding those stones cases >20mm (n = 319), the cumulative success rate was 59.5% (n = 5 486); this included 45.7% (n = 4 216) that were stone free at follow up and 13.8% (n = 1 270) in which there were CIRFs 4mm. For the first SWL session, the treatment success rate was 53.3% (n = 4 916), with a SFR of 41.3% (n = 3 809). Of those patients who had stones 20mm and an unsuccessful outcome after first treatment (n = 4 306), 26.2% (n = 1 227) subsequently received a second SWL session (i.e. retreatment); this success rate in the retreatment group was 46.5% (n = 570), with a SFR of 33.2% (n = 407). Table 3 describes cumulative treatment success rates by stone size and location. The highest cumulative success rates were observed for those stones <5mm in the lower ureter (100%, n = 14/14) and upper ureter (91.7%, 33/36), and the lowest success rates for those stones >20mm in the upper calyx (23.3%, 7/30) and PUJ (29.4%, 10/34). The frequency of post-swl complications and need for auxiliary procedures is described in Table 4. In approximately 1/3 of stone cases (33.0%, n = 3 147), pain after SWL required analgesia: oral, suppository or intravenous analgesic agents were used in 82.0% (n = 2 579), 9.9% (n = 313) and 78 BJU International 2016 BJU International

4 Shock wave lithotripsy Fig. 1 Number of stone cases treated on the MMT vehicle each year between 1995 and Number of stones Year Table 3 Cumulative treatment success rate (i.e. clearance or fragmentation <4mm) (%) by stone size (mm) and location (*highlights those stones for which SWL is currently recommended as the first line management option, or an equivalent first line management option compared to other management strategies, in EAU Guidelines 2015, **recommendation dependent on other factors related to favorability of SWL). < >20 Total (n) Stone location Upper Calyx 52.5* 53.2* 50.4* Middle Calyx 57.4* 57.2* 50.7* Lower Calyx 65.9** 61.5** 48.9** Renal Pelvis 82.4* 67.0* 56.4* Pelviureteric Junction 73.9* 68.6* 61.0* 29.4* 691 Upper Ureter 91.7* 72.2* 56.7* 60.0* 683 Middle Ureter 78.6* 72.1* Lower Ureter 100.0* 71.2* Total (n) Key Colour Success rate (%) Dark Green >70 Light Green Orange Red <50 8.1% (n = 255) of cases, respectively. The placement of a ureteric stent after SWL was undertaken in 4.1% (n = 394) of stone cases. Moreover, in those patients admitted to hospital following SWL (6.8%, n = 647), the median duration of hospital stay was one night (range = 1 26 nights). Discussion This study has presented the SWL outcomes for more than 9,000 stone cases treated with the Dornier DoLi-S lithotripters on the MMT vehicle at 21 centres in New Zealand over a 20 year period. The MMT SWL service has demonstrated that it is possible to deliver a high-volume specialist stone service without requiring patients to travel further for treatment, but has also uniquely facilitated the prospective, centralised collection of national data to reliably inform the future selection and counseling of suitable patients for SWL. The observed variation in cumulative treatment success rates by stone size and site within this study (e.g. 100% for <5mm lower ureter vs 23.3% for >20mm upper calyx) reinforces the importance of careful patient selection if SWL outcomes are to be maximised. The outlined data supports current understanding that SWL outcomes are inversely proportional to stone size [13 15], and reinforces EAU guidance that stones >20 mm are generally unsuitable for SWL therapy [7]: for the majority of stone locations, there was a consecutive decrease in success rate for each increase in stone size category, with an overall success rate of 30.8% for all stones BJU International 2016 BJU International 79

5 Alexander et al. Table 4 Post-SWL complications and auxiliary procedures. Variable Frequency, n (%) Post-SWL complications (Clavien-Dindo grade) Grade 1 Postoperative pain (requiring analgesia) 3147 (33.0) Grade 2 Perinephric haematoma 23 (0.2) Urinary tract infection (UTI) 107 (1.1) Grade 4 Urosepsis 3 (0.04) Other Hospital admission (any complication) 647 (6.8) Post-SWL auxiliary procedures Ureteric stent placement 394 (4.1) Percutaneous nephrostomy placement 66 (0.7) Ureteroscopy (URS) 359 (3.8) Percutaneous nephrolithotomy (PCNL) 135 (1.4) Open surgery 104 (1.1) >20mm. This descriptive analysis has clearly confirmed important trends in SWL outcomes, but is of more limited use for rarer stone categories in which there is a smaller case volume, including lower ureteral stones >20mm. This study does, however, challenge current opinion regarding the impact of stone location on SWL outcomes. Indeed, whilst previous studies have described poorer outcomes for renal stones located in the lower calyx [8,14,16], this study has demonstrated similar outcomes for stones in this location compared to the upper and middle calyces across all stone size categories. Sensitivity analysis demonstrated that this remained true when considering only the SFR, with overall cumulative SFRs of 36.7%, 42.1% and 41.5% for the upper, middle and lower calyces, respectively. Whilst it may be that other factors related to the management of lower calyceal stones in New Zealand, such as more stringent patient selection, have facilitated such results, other studies have also failed to demonstrate a clear relationship between the collecting system anatomy and SWL outcomes [15]. This study reaffirms that SWL continues to represent a safe, low morbidity management option for urolithiasis. The slightly lower success rates of SWL compared to other management options [17] must be considered within the context of its ability to offer a less invasive approach and to reduce patient morbidity. In particular, SWL offers an effective treatment option for those patients who would not be considered fit for general anaesthesia. Patients should be made aware of the available treatment options and their associated risks in order to facilitate informed decision making. Whilst current EAU guidelines do not consider SWL as a first line management option for stones in the middle and lower ureter, this study suggests that stones under 10mm at all sites in the ureter have excellent outcomes with SWL. Previous studies have also shown superior SFRs for ureteral compared to renal stones with SWL [8,10], but the small number of ureteral stones has frequently limited the applicability of such analyses. Although these findings do not, in isolation, identify SWL as the best available management strategy for ureteral stones, there remains no strong evidence, in the form of prospective randomised controlled trials, to demonstrate the superiority of ureteroscopy (URS) over SWL in managing such stones. The overall cumulative treatment success rate reported for our patient cohort (58.7%, with a SFR of 45.1%), represents a more conservative value than the those described in other large series within the literature [8,18 20]. There may be a number of factors which have contributed to this, including the loss of patients with successful outcomes to follow up, and that the majority of patients in New Zealand with an unsuccessful outcome after one session of SWL will go on to receive an alternative management strategy. In particular, the delivery of SWL to remote locations in New Zealand acted to make the routine follow up of patients with successful outcomes more difficult. Whilst the overall number of stone cases treated on the MMT SWL vehicle has decreased in the last 5 year period, this does not reflect an overall reduction in the use or popularity of SWL in New Zealand. Indeed, this result can be attributed to the lower number of cases treated in 2014 (n = 260) due to an incomplete financial year at the time of data analysis (01 December 2014), and the development and planning of a new MMT SWL vehicle for future use,. The potential differences in SWL treatment protocols across centres in New Zealand over the 20 year period, and any changes in these over time, as well as the individual practices and experience of a large number of urologists and radiographers, meant that it was not possible to assess the impact of other potential confounding factors on outcomes in this study. Incomplete data on a number of factors, including patient BMI, the use of medical expulsive therapy, stone density or skin to stone distance, also prevented a valid multivariate analysis. Furthermore, the lack of data on stone composition, including patients with cystine urolithiasis, or of concurrent stone obstruction prevented any conclusions in the use of SWL in such patient groups [21,22]. These limitations were a consequence of the retrospective, observational nature of this study, but it also allowed for the inclusion of a larger stone case series and longer follow-up period. Furthermore, whilst variation in the time of follow-up for radiological confirmation of stone status reduces the overall reliability of our findings, the median follow-up time of 4.4 months is similar to that selected by prospective RCTs [13]. Moreover, although the definition of SWL treatment success remains controversial, our inclusion of CIRFs 4mm has also been described by other studies [23] and was selected 80 BJU International 2016 BJU International

6 Shock wave lithotripsy on the basis that it represents a more comprehensive measure of success than SFR alone, and because the available evidence suggests that only a small proportion of such fragments will require retreatment [24]. Conclusions This study has presented the outcomes of a national series of over 9,000 stone cases treated with SWL across 21 centres in New Zealand over a 20 year period. The MMT SWL service has demonstrated that is it possible to deliver a high volume specialist stone service without requiring patients to travel further for treatment. It offers valuable data on treatment success, complication, and auxiliary procedure rates that can be directly applied in the clinical setting to facilitate appropriate patient selection and counseling, as well as in the development of future evidence based guideline recommendations in SWL. Acknowledgements The authors are extremely grateful to Dave Hopkins, software developer at Mobile Medical Technology, for his invaluable advice regarding the use and organisation of the SWL database. Conflicts of Interest None declared for all authors. References 1 Turney BW, Reynard JM, Noble JG, Keoghane SR. Trends in urological disease. BJU Int 2011; 109: Curhan GC. Epidemiology of stone disease. Urol Clin North Am 2007; 34: Romero V, Akpinar H, Assimos D. Kidney stones: a global picture of prevalence, incidence, and associated risk factors. Rev Urol 2010; 12: e Antonelli JA, Maalouf NM, Pearle MS, Lotan Y. Use of the National Health and Nutrition Examination Survey to calculate the impact of obesity and diabetes on cost and prevalence of urolithiasis in Eur Urol 2014; 66: Chaussy C, Schmiedt E, Jocham D, Brendel W, Forssmann B, Walther V. First clinical experience with extracorporeally induced destruction of kidney stones by shock waves. 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J Urol 2011; 186: Osman MM, Alfano Y, Kamp S et al. 5-Year follow-up of patients with clinically insignificant residual fragments after extracorporeal shockwave lithotripsy. Eur Urol 2005; 47: 860 Correspondence: Cameron E. Alexander, FY1, First Floor, Teaching and Learning Centre, New South Glasgow University Hospital (NSGUH), Glasgow, G51 4TF, United Kingdom. cameron.alexander.09@aberdeen.ac.uk BJU International 2016 BJU International 81