Endourological stone treatment
Beyond the scope of guidelines
Legemate, J.D.
Publication date
2019
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Final published version
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Legemate, J. D. (2019). Endourological stone treatment: Beyond the scope of guidelines.
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Voor het bijwonen van de openbare verdediging van het proefschrift
Endourological
Stone Treatment
Beyond the scope of guidelines door
Jaap Legemate
op woensdag 22 mei 2019 om 12.00 uur in de Agnietenkapel van de Universiteit van Amsterdam Oudezijds Voorburgwal 231
Amsterdam
Aansluitend bent u van harte welkom op de receptie ter plaatse
Paranimfen
Jan Erik Freund Christophe Mannaerts
Endour
ologic
al
Stone T
rea
tment:
B ey ond the sc ope of guidelines JAAP D . LEGEMA TEJ A A P D . L E G E M A T E
U I T N O D I G I N GEndourological
Stone Treatment
Endourological
Stone Treatment
Beyond the scope of guidelines
Endourological
Stone Treatment
Beyond the scope of guidelines
Title: Endourological stone treatment: beyond the scope of guidelines Author: Jaap D. Legemate
PhD thesis, University of Amsterdam, The Netherlands
Layout and cover design: Design Your Thesis, www.designyourthesis.com
Printing: Ridderprint B.V., www.ridderprint.nl
Text edit: Cambridge Proofreading (Chapters 1, 9, 10)
ISBN: 978-94-93108-01-1
Publication of this thesis was kindly supported by: Astellas Pharma B.V., Chipsoft, Coloplast, Eurocept Homecare, Stöpler Medical B.V., Universiteit van Amsterdam, Zambon Nederland B.V.
Endourological stone treatment:
beyond the scope of guidelines
A C A D E M I S C H P R O E F S C H R I F T
ter verkrijging van de graad van doctor aan de Universiteit van Amsterdam op gezag van de Rector Magnificus
prof. dr. ir. K.I.J. Maex
ten overstaan van een door het College voor Promoties ingestelde commissie, in het openbaar te verdedigen in de Agnietenkapel
op woensdag 22 mei 2019, te 12.00 uur
door
Jakob Dingeman Legemate geboren te Utrecht
Promotores: Dr. Th.M. de Reijke AMC-UvA
Prof. dr. R.J.A. van Moorselaar Vrije Universiteit Amsterdam
Overige leden: Prof. dr. H.P. Beerlage AMC-UvA
Prof. dr. P. Fockens AMC-UvA
Prof. dr. A.G.J.M. van Leeuwen AMC-UvA
Prof. dr. L.M.O. de Kort Universiteit van Utrecht
Dr. I.J.B. Spijkerman AMC-UvA
Dr. P.C.M.S. Verhagen Erasmus MC
Dr. F.C.H. d’Ancona Radboud MC
TABLE OF CONTENTS
Chapter 1 General introduction 7
PART I: URETEROSCOPIC STONE TREATMENT: OUTCOMES OF UNCOMMON CASES Chapter 2 Characteristics and outcomes of ureteroscopic treatment in 2650
patients with impacted ureteral stones
27
Chapter 3 Outcomes of ureterorenoscopic stone treatment in 301 patients with a solitary kidney
47
Chapter 4 Ureteroscopic urinary stone treatment among patients with renal anomalies: patient characteristics and treatment outcomes
67
PART II: DURABILITY OF THE FLEXIBLE URETEROSCOPE AND REPROCESSING EFFECTIVENESS Chapter 5 Durability of flexible ureteroscopes: a prospective evaluation of
longevity, the factors that affect it, and damage mechanisms
85
Chapter 6 Pre-use ureteroscope contamination after high level disinfection: reprocessing effectiveness and the relation with cumulative ureteroscope use
105
PART III: LIVE AND SEMI-LIVE SURGERY: PATIENTS’ SAFETY AND EDUCATIONAL VALUE Chapter 7 Outcome from 5-year live surgical demonstrations in urinary stone
treatment: are outcomes compromised?
125
Chapter 8 Surgical teaching in urology: patient safety and educational value of ‘LIVE’ and ‘SEMI-LIVE’ surgical demonstrations
147
PART IV: DISCUSSION AND SUMMARY
Chapter 9 Discussion and future perspectives 167
Chapter 10 English and Dutch summary 177
Supplements Authors contributions PhD portfolio List of publications About the author
Dankwoord/Acknowledgements 197 199 201 203 205
EAU European Association of Urology
Chapter 1
9
General introduction
1
GENERAL INTRODUCTION
Epidemiology and economics of urinary stone disease
Urolithiasis is a highly prevalent disease with a peak incidence present in adults aged 20 years to 60 years. Its prevalence ranges from 1% to 5% in Asia, 5% to 9% in Europe, 5.5% in the Netherlands, and 7% to 13% in North America. In the United States, up to 16% of men and 7% of women will have demonstrated at least one naturally-passing urinary stone by the age of 70 years. Recurrence is an important cause for the morbidity of urolithiasis. After a first stone episode, the risk of a recurrent symptomatic stone episode
is 11% at two years and 39% at 15 years.1–4
The prevalence of urolithiasis is growing. The increased prevalence has been attributed to the improvement of detection methods, alterations in dietary factors, and the
increasing prevalence of associated diseases like diabetes and obesity.2,4,5
In the light of the high prevalence and recurrence rates, urinary stone disease represents a significant burden to the global health care system. The annual direct and indirect cost for urolithiasis are estimated at more than 5 billion U.S. dollars. Furthermore, urolithiasis
is the second most expensive urological disease.6–8 Direct health care costs originate
from prevention and treatment. Moreover, considering the high recurrence rates and the peak incidence at middle age, urolithiasis also causes great indirect costs that
originate from illness-related absences from work.9,10
Management of upper urinary tract stones
Urinary stones can present as asymptomatic without the need for treatment, but they can also cause a high level of acute and chronic morbidity. Symptomatic stones can prompt pain complaints, urinary tract infections, and kidney function deterioration. It is estimated that 95% of stones measuring 4 mm or less in diameter will pass the ureter
spontaneously without the need for outside assistance.11 However, in cases of larger
stones, there is a low likelihood of spontaneous passage and active stone removal can be indicated.
There are various interventional options for the treatment of urinary stones. A commonly used treatment option is shock wave lithotripsy (SWL), while another option is endourological treatment. Endourological options consist of percutaneous nephrolithotomy (PCNL) and ureterorenoscopy (URS), or the combination of both referred to as endoscopic combined intrarenal surgery (ECIRS). Open, laparoscopic or
The optimal treatment modality should achieve a 100% stone-free rate with a low risk of complications. There are several disease- and patient-specific factors that can influence the effectiveness of the different treatment modalities. Disease-specific factors include stone size, stone composition, and stone location. In the European Association of Urology (EAU) guidelines, stone size and stone location are the most important factors for the selection of an active treatment modality (Figure 1). Separately, the anatomy of the urinary tract and the patient’s habitus as well as comorbidities represent important patient-specific factors. Consequently, symptomatic urinary stone disease requires a personalized approach for treatment selection. The patient’s preferences and local expertise are also important factors in treatment selection.
Following active stone removal or spontaneous passage, the patient should be assigned to a stone formation risk group. A metabolic evaluation, including analysis of stone composition, must be performed to determine a prevention strategy for recurrent stone
formation.11
Ureteroscopy
This thesis focused on ureteroscopic stone treatment. In the past two decades, the management of urolithiasis has clearly shifted towards employing endourological
techniques and, in particular, towards ureteroscopy.12 Ureteroscopy is a type of
endoscopic surgery that relies on the patient’s existing anatomy to reach the upper urinary tract in a retrograde fashion. This means that, by inserting a ureteroscope via the urethra and the bladder and passing such through the ureteral orifices, the ureters and the renal collecting systems can be reached in a ‘minimally invasive’ manner.
The ureter has on average a diameter of 3 mm.13 With a rigid ureteroscope, typically only
the ureter can be visualized. Conversely, with a flexible ureteroscope, both the ureter and the collecting system of the kidney can be visualized (Figure 2). The images derived from a fibre-optic or digital imaging system are then projected on a digital screen. Stones can be fragmented into small parts using a laser fiber via the working channel of the ureteroscope. The small fragments can then be taken out actively using a stone retrieval device (Figure 3). Very small fragments will generally evacuate with the urine spontaneously.
11
General introduction
1
FIGURE 1. EAU guideline algorithms with recommended treatment options for active stone
FIGURE 2. A: semirigid ureteroscope, B: flexible ureteroscope © KARL STORZ SE & Co. KG,
Tuttlingen, Germany. Fr. = French (1 mm ≈ 3 Fr.).
FIGURE 3. Fragmentation of a calyceal stone with a holmium: yttrium–aluminum–garnet laser
and subsequent removal of the fragments with a stone retrieval basket.
A
13
General introduction
1
1854 1912 1953 1960 1964 1981 1987 1995 1998 2006
FIGURE 4. Landmarks in the evolution of ureteroscopy.
The first reported rigid ureteroscopic procedure was performed in 1912 by Hugh Hampton Young. Marshall performed a flexible ureteroscopy in 1964 after fiber optics became available. Actively deflectable flexible ureteroscopes with irrigation systems were subsequently introduced in the late 1980s. In 1992, Karl Storz was able to downsize the diameter of the flexible shaft from 9.8 French (Fr.) to 7.5 Fr. while maintaining the
original 3.6-Fr. working channel.14 The first digital ureteroscope was released in 2006,15,16
In 2015, the first disposable digital flexible ureteroscope was launched.17 Figure 4
presents the key landmarks in the evolution of ureteroscopy.
In the past decade, the technology of flexible ureteroscopes has evolved rapidly. Technological advances include the miniaturisation of the ureteroscope shaft, increased capability of deflection, and improved optics. Additionally, there has been progress in the development of accessory devices that can be used through the working channel of the ureteroscope. These advancements have expanded the indications for ureteroscopic
stone treatment.18–20 Conversely, however, the miniaturization and heat sensitivity may
make the device more prone to damages and wear and tear. Consequently, careful handling of the device during procedures and reprocessing are required to maintain a long usable life.
SPECIFICATION OF THESIS SUBJECTS AND STUDY AIMS
Guidelines play an important supportive role in the management of urolithiasis. Recommendations made in existing guidelines cover most aspects of urinary stone management, but not all. The approach of complex cases, economic aspects, quality control of ureteroscope reprocessing, and surgical education are issues that go beyond the scope of currently available clinical guidelines. Nonetheless, these issues are of importance in the context of everyday urological practice.
This thesis covers three of such issues. In the first part of this thesis, the outcomes of ureteroscopic stone treatment of uncommon cases were evaluated. Secondly, the durability and decontamination effectiveness of the latest and most frequently used flexible ureteroscopes is investigated. Lastly, this thesis evaluated the safety and educational value of live- and semi-live surgery demonstrations for ureteroscopic stone treatment physician education.
Ureteroscopic stone treatment: outcomes of uncommon cases
The international guidelines of the EAU, American Urological Association (AUA), and Société Internationale d’Urologie (SIU) provide evidence-based recommendations for urolithiasis management. These recommendations are mainly based on current reports that present the results of general cases with average complexity. However, there are various uncommon situations in which stone management may be a challenge to the urologist. Examples of such situations are impacted ureteral stones; stone treatment in patients with a solitary kidney; and stone treatment in patients with a deviant anatomy of the urinary tract, e.g., congenital renal anomalies.
The EAU guidelines provide some general recommendations, but no specific suggestions for managing uncommon or highly complex cases. For impacted ureteral stones, the EAU guidelines do state that SWL is unlikely to be successful. PCNL is an option for impacted stones in the proximal ureter. Furthermore, it is recommended to perform laparoscopic stone removal for large impacted stones when endoscopic lithotripsy or SWL have failed. Nonetheless, these recommendations are based on the outcomes of small studies, and the role of retrograde ureteroscopy is not clearly discussed. The EAU guidelines recommendations for the treatment of stones in anomalous kidneys are limited. In horseshoe kidneys, acceptable stone-free rates can be achieved with flexible ureteroscopy, while the passage of fragments after SWL might be poor. For stones in pelvic kidneys, SWL, retrograde intrarenal surgery (RIRS), PCNL, or laparoscopy are recommended, but without a clear preferred treatment choice identified. No specific
15
General introduction
1
Especially uncommon and complex cases require a thorough preparation as well as significant expertise and guidance. This thesis presents the outcomes of ureteroscopic treatment in a large cohort of patients with uncommon urinary stone cases. These outcomes provide valuable information for clinicians to consider in attempts to improve treatment selection. Furthermore, the information will help to inform patients about the outcomes of ureteroscopy during preoperative consultation.
Durability of the flexible ureteroscope
Reusable flexible ureteroscopes have undergone technical improvements, but they remain fragile instruments. The reported durability for a single flexible ureteroscope varies
widely from three to 159 procedures.22,23 Flexible ureteroscopes present considerable
costs in both the initial purchase and maintenance processes.24,25 Consequently, the
device itself makes up a considerable part of the costs that arise from ureteroscopic stone treatment. The reported costs per case in the literature vary. Martin et al. reported
an amortized cost of 848 U.S. dollars per use, excluding the original purchasing cost.26
The overall cost per use described by Hennessey et al. and by Geraghty et al. varied from
1,785 to 2,801 U.S. dollars.27,28
In brief, the finite durability of flexible ureteroscopes and therefore the costs for repair
and replacement are a burden in urological practice.29–31 To shine more light on this
issue, the durability of commonly used flexible ureteroscopes is evaluated in this thesis. Also, factors that affect ureteroscope durability are assessed. This information can help to improve the durability of ureteroscopes and thereby limit costs.
Effectiveness of ureteroscope reprocessing
Infections have been linked to the cross-contamination of endoscopes in several
medical fields, including urology.32 An increasing number of outbreaks involving
multidrug-resistant organisms caused by contaminated duodenoscopes has been reported in the field of gastroenterology in both the United States and Europe. Over the last few years, gastro- and duodenoscope contamination has been studied in large cohorts. Outbreaks in Dutch gastroenterology centres encouraged Rauwers et al. to conduct a nationwide study to determine the prevalence of bacterial contamination of
reprocessed duodenoscopes in the Netherlands.33 They found that 15% of the
patient-ready duodenoscopes harboured microorganisms of gastrointestinal or oral origin. These results imply that the present reprocessing process is not adequate and safe. Flexible ureteroscopes are considered less complex instruments to decontaminate in comparison with duodenoscopes. However, ureteroscope reprocessing is a complex
multistep process that involves both automated and manual processes. These processes are assumed to have a high decontaminating effect. To date, the reprocessing effectiveness of flexible ureteroscopes was only investigated by one small study, to our knowledge; specifically, this study by Ofstead et al. tested the contamination of 16
patient-ready flexible ureteroscopes after sterilisation.34 They detected contamination
on all 16 scopes (13% microbial growth, 44% adenosine triphosphate, 63% haemoglobin, and 100% protein). The contamination levels found by Ofstead et al. exceeded the benchmarks for clean gastrointestinal endoscopes. Moreover, there are no benchmarks established at this time for the process control of ureteroscope reprocessing.
The miniaturization and heat sensitivity of modern flexible ureteroscopes may make these instruments more prone to experiencing wear and tear. Ureteroscope wear and tear can result in surface irregularities that may form a breeding ground for
microorganisms.34,35 Accordingly, we hypothesize that the reprocessing effectiveness
declines with cumulative ureteroscope use.
Improper ureteroscope reprocessing could potentially put patients at risk of ureteroscope-associated infections. In this thesis, the reprocessing effectiveness of ureteroscopes is evaluated. Furthermore, whether cumulative ureteroscope use results in increased ureteroscope contamination or not is investigated. Lastly, the possibility of cross-contamination of patients through contaminated ureteroscopes as well as eventual clinical effects is considered.
Live- and semi-live surgery: patients’ safety and educational value
Live surgical demonstrations (LSDs) are popular in the field of urology. However, the increased popularity of LSDs has fuelled the debate of whether the educational value of
such demonstrations comes at the cost of patient safety.36–38
Societies in different medical fields have published policy statements on the use of LSDs at meetings. Several societies have banned the use of live surgery, while others accept live surgery on the condition of strict adherence to the stated policies (Table 1).
In 2014, the EAU also published a policy on live surgical events to regulate their organisation. The key principle of this policy is that patient safety must take priority above all other considerations. The information presented in the policy is based on the consensus view of an expert panel. This expert panel recognised the educational value of LSDs and thus advocated for the abidance of a clearly regulated framework for the conduct of live surgical events. Prerequisites for an event with live surgery are described in the EAU policy. The local organising committee has to assign an experienced
17
General introduction
1
independent urologist who is responsible to look after the patient’s best interests (the patient’s advocate). Furthermore, results on treatment outcomes including data from a
follow-up period of at least one year should be provided to the EAU.37
TABLE 1. Policies regarding LSDs by organisation.36
Policy Organization
Banned American College of Obstetricians and Gynecologists
American College of Surgeons
Japanese Association for Thoracic Surgery Japanese Society for Cardiovascular Surgery Japanese Society for Vascular Surgery Japanese Urological Association Acceptable if guidelines are followed American Association for Thoracic Surgery
American College of Cardiology
American Society for Gastrointestinal Endoscopy Asian-Pacific Society of Interventional Cardiology European Association for Cardio-Thoracic Surgery European Society of Cardiology
Heart Rhythm Society
Society for Cardiovascular Angiography and Interventions Society of Thoracic Surgeons
European Association of Urology
Further literature on the safety and educational value of LSDs mainly consists of surveys and opinions. The conclusions of these publications are not based on treatment outcomes. Knowledge of the treatment outcomes of LSDs may help us to gain more objective insights into the safety of this educational tool.
In this thesis, the outcomes of live endourological procedures for stones are compared with the outcomes of treatments performed in a routine setting. Furthermore, the opinions of a large group of congress participants with regard to the safety and educational value of LSDs are evaluated. The information derived from such studies will help to assess whether or not there is still room for live endourological demonstrations in future surgical education.
OUTLINE OF THIS THESIS
Part I: ureteroscopic stone treatment: outcomes of uncommon cases
In Chapter 2, patient characteristics and outcomes of ureteroscopic stone treatment in a large group of patients with impacted ureteral stones are presented. These outcomes are compared with the treatment outcomes of a group of patients with non-impacted stones. Furthermore, possible predictors for stone impaction are evaluated.
In Chapter 3, patient characteristics and outcomes of ureteroscopic stone treatment in patients with a solitary functioning kidney are presented. The outcomes are divided into the following three groups: ureteroscopy for ureter stones, ureteroscopy for kidney stones, and ureteroscopy for the combination of ureter and kidney stones.
In Chapter 4, the patient characteristics and outcomes of ureteroscopic stone treatment in patients with renal anomalies are presented. The three specific renal anomalies evaluated are horseshoe kidneys, ectopic kidneys, and malrotated kidneys.
Part II: ureteroscope durability and reprocessing effectiveness
In Chapter 5, the durability of flexible ureteroscopes is evaluated. Damage mechanisms are evaluated and possible factors that affect ureteroscope durability are assessed. In Chapter 6, the decontaminating effectiveness of flexible ureteroscope reprocessing with high-level disinfection is investigated. Furthermore, it is analysed whether or not cumulative ureteroscope use is associated with an increased preoperative ureteroscope contamination probability. Additionally, the possible clinical effects of ureteroscope contamination on infectious complications are determined.
Part III: safety and educational value of live surgery
In Chapter 7, the treatment outcomes of LSDs for endourological stone treatment in the Amsterdam University Medical Centers (AMC location) are presented. Both the outcomes of ureteroscopic and percutaneous stone removal are presented. The outcomes of live demonstrations are compared with the outcomes of procedures performed in a routine setting.
Chapter 8 provides a survey study on the educational value and safety of both LSDs
and semi-LSDs in endourology. The results for this study are derived from a survey conducted among attendees of the congress ‘Challenges in Endourology 2017’ in Paris, France.
19
General introduction
1
Part IV: discussion and summary
Chapters 9 and 10 finalize this thesis, providing a general discussion, with future
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Part I
Ureteroscopic stone treatment:
outcomes of uncommon cases
ASA American Society of Anesthesiologists
Chapter 2
Characteristics and outcomes of
ureteroscopic treatment in 2650 patients
with impacted ureteral stones
Jaap D. Legematea, Nienke J. Wijnstoka, Tadashi Matsudab, Willem
Strijbosc, Tibet Erdogrud, Beat Rothe, Hidefumi Kinoshitab, Judith
Palacios-Ramosg, Roberto M. Scarpah, Jean J.M.C.H. de la Rosettea
a Department of Urology, AMC University Hospital, Amsterdam, the Netherlands b Department of Urology and Andrology, Kansai Medical University, Osaka, Japan c Department of Urology, Zuyderland Medisch Centrum Parkstad, Heerlen, the Netherlands d Department of Urology, Memorial Istanbul Atasehir Hospital, Istanbul, Turkey
e Department of Urology, University Hospital Bern, Bern, Switzerland g Department of Urology, Hospital Galdakao-Usansolo, Vizcaya, Spain h Department of Urology, University of Turin, Turin, Italy
ABSTRACT
Purpose: To describe stone-free rates and complications of ureteroscopic treatment
for impacted compared with non-impacted ureteral stones and evaluate predictive variables for impaction.
Methods: The Clinical Research Office of the Endourological Society (CROES)
prospectively collected one consecutive year of data from 114 centers worldwide. Patients eligible for inclusion were patients treated with ureteroscopy for ureteral stones. Patient characteristics, treatment details and outcomes were compared with regard to stone impaction. Logistic regression analyses were conducted to explore predictive variables for ureteral stone impaction and to analyse the effect of impaction on outcomes.
Results: Of the 8543 treated patients, 2650 (31%) had impacted and 5893 (69%)
non-impacted stones. The stone-free rate was 87.1% for non-impacted stones, which is lower compared with 92.7% for non-impacted stones (p<0.001). Intra-operative complication rates were higher for impacted stones (7.9% versus 3.0%, p<0.001). Significantly higher ureteral perforation- and avulsion rates were reported in the impacted stone group compared with the non-impacted stone group. No association between stone impaction and post-operative complications could be shown. Female gender, ASA- score >1, prior stone treatment, positive pre-operative urine culture, and larger stones showed to be predictive variables for stone impaction.
Conclusions: Ureteroscopic treatment for impacted stones is associated with lower
stone-free rates and higher intra-operative complication rates compared with treatment for non-impacted stones. The predictive variables for the presence of stone impaction may contribute to the identification of stone impaction during the diagnostic process. Moreover, identification of stone impaction may aid the selection of the optimal treatment modality.
29 Impacted stones
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INTRODUCTION
Impacted ureteral stones are stones that remain unchanged at the same location for
a prolonged time period causing local inflammation.1 Confirmation of ureteral stone
impaction can be done during ureteroscopy, displaying a stone enveloped in a, frequently, inflamed oedematous mucosa. The impeded stone exposure and lack of expansion space around the stone make disintegration more difficult. Patients with impacted ureteral stones are considered to be at risk for a less effective initial treatment
and a higher complication rate if compared with patients with non-impacted stones.2
For the treatment of distal and mid-ureteral stones, ureteroscopy is the approach of choice. For proximal ureter stones < 10 mm, both ureteroscopy and shock wave lithotripsy (SWL) are appropriate options. Although SWL is a non-invasive modality it is unlikely to be successful for impacted stones. For the treatment of large proximal stones, percutaneous lithotomy is an alternative, whereas laparoscopic or open lithotomy may
be a rarely necessary option.3–5
Daily practice and the literature show that the prevalence of impacted ureteral stones is
high.2 Last decades research on ureteral stone treatment has been extensive. However,
the literature focused on the outcomes of ureterolithotripsy for impacted ureteral stones is limited. Furthermore, stone impaction is a neglected topic in preeminent guidelines. The aim of this study is to compare the stone-free rate (SFR) and complication rates of ureteroscopic lithotripsy between patients with and without impacted ureteral stones and evaluate predictive variables for impaction.
PATIENTS AND METHODS
Primary objective
To assess the differences in SFR and intra- and short-term post-operative complications rates between patients treated for impacted stones compared with patients treated for non-impacted stones.
Secondary objective
Study organization and data collection
This study examining impacted stones is a sub-analysis of the CROES URS Global Study which is a prospective, observational, international multicenter study. The CROES URS started between January 2010 and October 2011, collecting data on consecutive patients treated with ureteroscopy for urolithiasis at each participating center over a one-year period.
114 Centers participated in 32 countries and a total of 11.885 patients were included. Data were collected and stored in the online available CROES data management system (www.croesoffice.org). Participating centers treated patients according to their local
protocols. More detailed data containing the global URS study is described elswere.6
Study population
Patients eligible for inclusion were all patients treated with ureteroscopy for ureteral stones, as a primary or secondary treatment. Patients with ureteral stones in combination with renal stones were excluded to preclude possible influence on outcomes of renal stone treatment in the same session. Patients were divided into an impacted and a
non-impacted stone group. Impaction had to be verified endoscopically.1,2 Whether a stone
was impacted or not was determined by the surgeon and answered with the option yes or no. If stone impaction information was absent, patients were excluded from analysis.
Patient characteristics
Patient baseline characteristics include age in years, gender, ASA-score (American Society of Anaesthesiologists score), BMI, medical history, prior stone treatment and anticoagulant use. Stone characteristics are captured in stone width and length in mm and measured on the imaging modality that was used for pre-operative evaluation. Stone burden was calculated using the formula: length*width*0.25*3.14159.
Intra-operative characteristics are operation time in minutes, intra-operative complications, and stone-free status.
Patient follow-up and secondary treatment
Imaging consisted of x-ray and ultrasound of kidneys, ureter, and bladder, or computed tomography scan of the abdomen. Classification of a stone-free status was attained by the overall absence of stones or fragments larger than one mm based on imaging techniques available, and left to the discretion of the treating physician.
31 Impacted stones
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Post-operative characteristics, used as study outcomes, are long hospital stay (defined as longer versus shorter than one day), readmission (any possible procedure related hospital visit, including retreatment), and post-operative complications according to
the Clavien-Dindo Grading system.7 The follow-up period for the registration of
post-operative complications was three months.
Statistical analysis
Descriptive information is presented as mean with standard deviation for continuous normally distributed variables, and median with inter-quartile ranges for continuous skewed variables. Categorical variables are presented as percentages. Descriptive data and percentages were based on available data. To compare outcomes between groups, Pearson’s chi-square or Fisher’s exact test was used for dichotomous and categorical variables. A Student’s t-test was used for continuous normally distributed variables and a Mann-Whitney U test for skewed variables.
Logistic regression analyses were used to determine which variables could predict stone impaction and to evaluate the association between stone impaction and outcomes after ureterolithotripsy. Outcomes tested were SFR and intra- and postoperative complications. Outcomes were adjusted for possible confounders, including gender, ASA-score, positive pre-operative urine culture, prior stone treatment, stone burden, ureteroscopy type, difference in fragmentation device, operation time, pre-operative stent placement, and postoperative ureteral stent placement, and for differences in evaluation modalities uses to determine absence of residual fragments.
For all analysis the level of statistical significance was set at p < 0.05. Statistical analyses were performed using IBM SPSS statistics version 23.0.
RESULTS
Patient characteristics
Of 11885 patients in the URS CROES database, 8630 patients were treated for ureter stones only. Information on stone impaction was missing for 87 patients, remaining 8543 patients for analysis. 2650 (31.0%) Patients were treated for impacted stones and 5893 (69.0%) for non-impacted stones.
Patients with impacted stones had higher ASA II and III scores more often, higher rates of cardio vascular disease, higher rates of prior SWL treatment (20.9% versus 14.7%) and a higher stone burden. In the 6 months before the surgery SWL in the ureteral renal unit was performed in 12.6% in the impacted stone group and 6.9% in the non-impacted stone group (p<0.001). A prior ureteroscopy within 6 months before the current ureterolithotripsy was performed in 2.9% in the impacted stone group and 3.5% in the non-impacted stone group (p=0.15). A pre-operative ureteral stent was less often placed (13.7% versus 15.8%, p=0.013) in patients with impacted stones.
Operative characteristics
The operative characteristics, presented in table 2, show notable higher median operation time, more frequent use of laser fragmentation and post-operative stents in patients with impacted stones.
Stone-free rate
The overall SFR was 87.1% for impacted ureteral stones, which is significantly lower compared with 92.7% for non-impacted stones (table 2). For both groups SFRs declined with an increase in stone burden (figure 1 supplementary material).
For the distal and proximal locations, SFR were lower with a larger burden. For the mid-ureter, SFRs were higher than 80%, even with an increased stone burden (figure 2 supplementary material). Stones migrated in 14.4% of the impacted stone group and in 7.9% of the non-impacted stone group. SFR for procedures were migration occurred were 52.4% for impacted stones and 86.6% for non-impacted stones.
A sub-analysis was performed to show the difference between outcomes after semirigid and flexible ureteroscopy for impacted stones in the proximal ureter. A ureteral access sheath was used in 61.7% of the flexible ureteroscopy cases. The SFR was 88.2% for flexible ureteroscopy and 76.4% for semi-rigid ureteroscopy. Though the average stone burden was lower in the flexible ureteroscopy group. More specified results with respect to semirigid versus flexible ureteroscopy can be found in Table S1 in the supplementary material.
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TABLE 1. Baseline characteristics.
Characteristics All patientsn = 8543
Impacted stones n = 2650 (31.0)
Non-impacted stones
n = 5893 (69.0) Differencep-value of test Type
Age, mean in years (SD) 47.9 (15.9)
(n = 7328) 49.8 (15.4) (n = 2412) 47.0 (16.1) (n = 4916) < 0.001 C Gender Male n (%) Female n (%) 5660 (66.3) 2875 (33.7) (n = 8535) 1867 (63.7) 962 (36.3) (n = 2649) 3973 (67.5) 1913 (32.5) (n = 5886) 0.001 A BMI mean(SD) 26.6 (4.6) (n = 7147) 26.9 (4.9) (n = 2392) 26.4 (4.5) (n = 4753) < 0.001 C ASA score n (%) I II III IV 4795 (59.3) 2670 (33.0) 587 (7.3) 31 (0.4) (n = 8083) 1254 (49.4) 982 (38.6) 288 (11.3) 17 (0.7) (n = 2541) 3514 (63.9) 1688 (30.5) 299 (5.4) 14 (0.3) (n = 5542) < 0.001 A
Comorbidity & medication n (%) DM CVD Crohn’s disease Prednisone Anticoagulation 840 (9.9) (n = 8485) 2364 (27.7) (n = 8543) 31 (0.4) (n = 8476) 58 (0.7) (n = 8479) 393 (4.6) (n = 8481) 306 (11.6) (n = 2634) 910 (34.3) (n = 2650) 11 (0.4) (n = 2632) 23 (0.9) (n = 2635) 166 (6.3) (n = 2633) 534 (9.1) (n = 5851) 1454 (24.7) (n = 5893) 20 (0.3) (n = 5844) 35 (0.6) (n = 5844) 227 (3.9) (n = 5848) < 0.001 < 0.001 0.59 0.16 < 0.001 A A A A A Previous stone treatment n (%)
URS PCNL SWL Ureterolithotomy Pyelolithomy 880 (10.4) (n = 8491) 264 (3.1) (n = 8494) 1407 (16.6) (n = 8471) 90 (1.1) (n = 8492) 94 (1.1) (n = 8500) 269 (10.2) (n = 2635) 81 (3.1) (n = 2636) 548 (20.9) (n = 2622) 49 (1.9) (n = 2635) 37 (1.4) (n = 2639) 611 (10.4) (n = 5856) 183 (3.1) (n = 5858) 859 (14.7) (n = 5849) 41 (0.7) (n = 5857) 57 (1.0) (n = 5861) 0.75 0.090 < 0.001 < 0.001 0.080 A A A A A Pre-operative positive urine
culture n (%) 488 (5.9) (n = 8264) 214 (8.3) (n = 2569) 274 (4.8) (n = 5695) < 0.001 A Total stone burden (mm2)
median, [IQR] 53, [28-85] (n = 8539) 59, [33-95] (n = 2650) 50, [27-79] (n = 5889) < 0.001 D
TABLE 1. (Continued)
Characteristics All patientsn = 8543
Impacted stones n = 2650 (31.0)
Non-impacted stones
n = 5893 (69.0) Differencep-value of test Type
Stone location ureter n (%) Proximal ureter Mid ureter Distal ureter Multiple locations 2336 (27.3) 1784 (20.9) 4140 (48.5) 283 (3.3) (n = 8543) 772 (29.1) 601 (22.7) 1172 (44.2) 105 (4.0) (n = 2650) 1564 (26.5) 1183 (20.1) 2968 (50.4) 178 (3.0) (n = 5893) < 0.001 A Preureteral stent n (%) 1285 (15.1) (n = 8496) 361 (13.7) (n = 2637) 924 (15.8) (n = 5859) 0.013 A
ASA: American Society of Anesthesiologists, DM: Diabetes Mellitus, CVD: Cardio Vascular Disease, PCNL: Percutaneous Nephrolithotomy, ESWL: Extra Corporeal Shockwave Lithotripsy, URS: Ureterorenoscopy, UPJ: uretero-pelvic junction. NS = not significant. Data are n (%) of patients for whom data were available. Percentages exclude missing values from denominators. Statistical test: A) Pearson’s Chi-square test, B) Fishers exact test, C) Student’s t-test, D) Mann-Whitney U test.
Complications
Descriptive information on intra- and post-operative complications is shown in table 3. The overall intra-operative complication rate was higher in patients with impacted stones. More specifically, there was a significant difference in bleeding, ureteral perforations and avulsions, unfavourable to the impacted stone group. Although there was a significantly higher overall post-operative complication rate in patients who had impacted stones, there were no differences between severity of the post-operative
complications, measured by the Clavien-Dindo grades 7.
During the follow-up period of 3 months, 11 (0.4%) patients in the impacted stone group and 15 (0.3%) patients in the non-impacted stone group were re-admitted because of a ureteral stricture (p=0.21).
Post-operative outcomes
Data on length of hospital stay, re-treatment rate, and re-admission rate are shown in table 3. Patients in the impacted stone group had a longer hospital stay, a higher re-treatment rate, and a higher readmission rate compared with the non-impacted stone group.
Multivariable logistic regression analysis
Logistic regression analyses, presented in table 4, were conducted to evaluate the association between stone impaction and primary outcomes.
35 Impacted stones
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TABLE 2. Operation data comparing impacted stones with non-impacted stones.
Outcomes Impacted stones (n = 2650) Non-impacted stones
(n = 5893) Differencep-value Type of test
Overall stone-free rate (SFR) n (%) 2293 (87.1) (n = 2634) 5423 (92.7) (n = 5850) < 0.001 A Proximal ureter SFR n (%) 605 (79.3) (n = 763) 1364 (88.3) (n = 1544) < 0.001 A Midureter SFR n (%) 520 (86.8) (n = 599) 1090 (92.8) (n = 1174) <0.001 A Distal ureter SFR n (%) 1089 (93.2) (n = 1168) 2831 (95.8) (n = 2956) 0.001 A
Multiple ureteral locations SFR n (%) 79 (76.0) (n = 104) 138 (78.4) (n = 176) 0.66 A Method of evaluation CT Ultrasound X-ray/KUB IVU Retrograde pyelogram Intra-operative confirmation Other None 353 (13.5) 1363 (52.1) 1509 (57.7) 197 (7.5) 24 (0.9) 480 (18.3) 30 (1.1) 132 (5.0) (n = 2617) 437 (7.5) 3218 (54.9) 2835 (48.4) 135 (2.3) 138 (2.4) 723 (12.3) 33 (0.6) 253 (4.3) (n = 5863) < 0.001 0.017 < 0.001 < 0.001 < 0.001 < 0.001 0.004 0.14 A A A A A A A A Type of ureteroscope n (%) Semirigid Flexible Both 2295 (87.0) 137 (5.2) 207 (7.8) (n = 2639) 5523 (93.9) 179 (3.0) 181 (3.1) (n = 5883) < 0.001 A
Type of fragmentation device Laser Pneumatic Other No device 1392 (52.6) 856 (32.4) 171 (6.5) 227 (8.6) (n = 2646) 2055 (35.0) 2540 (43.3) 150 (2.6) 1121 (19.1) (n = 5866) < 0.001 A Peroperative antibiotics n(%) 2313 (88.0) (n = 2628) 4739 (80.9) (n = 5856) < 0.001 A
Anti-retropulsion device used 411 (15.5)
(n= 2644)
824 (14.0) (n= 5888)
0.062 A
Operation time minutes, median, [IQR] 40, [30-60] (n = 2612)
30, [21-60] (n = 5781)
< 0.001 D
Postoperative ureteral stent n (%) 2333 (88.2)
(n = 2644)
2492 (76.2) (n = 5893)
< 0.001 A
Data are n (%) of patients for whom data were available. Percentages exclude missing values from denominators. IVU: intravenous urography, KUB: kidneys, ureters, bladder. Statistical test: A) Pearson’s Chi-square test, B) Fishers exact test, C) Student’s t-test, D) Mann-Whitney U test.
Stone impaction gives an odds ratio of 0.57 on a stone-free status, and an odds ratio of 3.23 on intra-operative complications. This suggests that patients with impacted stones are less often stone free, but these patients also experience more intra-operative complications. No association between ureteral stone impaction and short-term post-operative complication rate was found.
TABLE 3. Intra- and postoperative complications and outcomes.
Outcomes Impacted stones (n = 2650) Non impacted stones
(n = 5893) Differencep-value Type of test
Intra-operative complications n (%) Overall Bleeding Perforation Failed procedure Conversion Avulsion Other 209 (7.9) 65 (2.5) 59 (2.2) 55 (2.1) 7 (0.3) 9 (0.3) 14 (0.5) (n =2643) 177 (3.0) 37 (0.6) 31 (0.5) 83 (1.4) 5 (0.08) 1 (0.02) 20 (0.3) (n = 5887) < 0.001 < 0.001 < 0.001 0.023 0.057 < 0.001 0.20 A A A A B B A Intra-operative migration n (%) 380 (14.4) (n = 2643) 463 (7.9) (n = 5887) < 0.001 A Post-operative complications n (%) Overall Bleeding Fever (> 38.0) UTI Sepsis Other 75 (2.8) 15 (0.6) 23 (0.9) 20 (0.8) 7 (0.3) 10 (0.4) (n = 2650) 106 (1.8) 15 (0.3) 33 (0.6) 24 (0.4) 10 (0.2) 24 (0.4) (n = 5893) 0.002 0.53 0.10 0.038 1.0 0.84 A A A A B A Clavien grading score n (%)
I II IIIa-b IVa-b V 31 (40.3) 33 (42.9) 10 (13.0) 3 (3.8) 0 (0) (n =2573 ) 41 (38.3) 48 (44.9) 13 (12.1) 3 (2.8) 2 (1.9) (n =5786) 0.68 A
Post-operative hospital stay longer than 24 hours n(%) 1211 (45.8) (n = 2643) 1757 (29.9) (n = 5873) < 0.001 A Re-treatment n(%) 307 (11.6) (n = 2647) 491 (8.1) (n= 5886) < 0.001 A Readmission < 3 months n(%) 241 (9.6) (n = 2518) 346 (6.2) (n = 5615) < 0.001 A
UTI = urinary tract infection. NS = not significant. Data are n (%) of patients for whom data were available. Percentages exclude missing values from denominators. Statistical test: A) Pearson’s Chi-square test, B) Fishers exact test, C) Student’s t-test, D) Mann-Whitney U test.
37 Impacted stones
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Prediction of impaction
Table 5 shows univariate and multivariate prediction models of stone impaction. Female gender, ASA-score >1, a positive pre-operative urine culture, prior treatment and a larger stone burden showed to be predictive variables for stone impaction.
TABLE 4. Examining the effect of ureteral stone impaction on outcomes corrected for confounders
using multivariate logistic regression.
Outcomes Odds ratio 95% confidence interval p-value Model 1- Association of stone impaction and outcomes after ureteroscopy (univariate analysis).
Stone-free rate Intra-operative complications Post-operative complications 0.53 2.77 1.59 0.46-0.62 2.26-3.40 2.65-5.98 <0.001 <0.001 <0.001
Model 2 - Association of impaction on outcomes after ureteroscopy corrected for baseline characteristics and stone characteristics found significant in the prediction model.
Stone-free rate Intra-operative complications Post-operative complications 0.57 2.71 1.43 0.48-0.67 2.17-3.38 1.04-1.98 <0.001 <0.001 0.030
Model 3 - Association of impaction on outcomes after ureteroscopy corrected for baseline characteristics and clinically possible confounders.
Stone-free rate Intra-operative complications Post-operative complications 0.57 3.23 1.34 0.48-0.68 2.54-4.11 0.95-1.90 <0.001 <0.001 0.095
TABLE 5. Logistic regression model for predictors of stone impaction.
Predictive variable univariate multivariate Odds ratio 95% confidence
interval p-value Odds ratio
95% confidence interval p-value Female Gender 1.18 1.08-1.30 0.001 1.15 1.03-1.27 0.01 ASA-score* II III IV 1.64 2.72 3.43 1.48-1.82 2.29-3.24 1.69-6.98 <0.001 <0.001 0.001 1.59 2.58 3.58 1.43-1.77 2.14-3.11 1.72-7.45 < 0.001 < 0.001 0.001 Pre-operative positive urine culture 1.87 1.55-2.26 <0.001 1.21 1.14-1.29 < 0.001
Total stone burden (> 1 cm) 1.29 1.23-1.36 <0.001 1.26 1.19-1.33 < 0.001
Previous treatment 1.34 1.22-1.48 <0.001 1.23 1.11-1.36 < 0.001
DISCUSSION
The main outcome of this study is that the treatment of impacted stones with ureterolithotripsy is associated with lower SFRs and a higher intra-operative complication rate compared with non-impacted stones. No association between stone impaction and short-term post-operative complications was found. Female gender, ASA-score > 1, a positive pre-operative urine culture, prior stone treatment, and larger stone burdens were found to be predictive variables for impacted ureteral stones.
Stone-free rate
In this study stone impaction was associated with lower SFR. Comprehensive work analysing ureteroscopic treatment for impacted stones with the semirigid Ho: YAG-laser was done by Seitz et al. in 2007, they report an overall SFR of 82% with a SFR of
67.2% for stones in the proximal ureter.2 A possible explanation for the fact that we
found higher SFRs could be the expansion in use of flexible ureteroscopy, increased
experience and improved techniques in endourological surgery over the past decade.8
Another study presented by Binbay et al. showed SFRs of 80% using a pneumatic lithotripter and 97.5% for the Ho:YAG-laser. This high effectiveness can be explained by excluding patients with stones >20 mm, using permanent anticoagulants, those with ureteral strictures, multiple stones, anatomical abnormalities, renal insufficiency, and
a previously unsuccessful ureteroscopic procedures.9 In this study we found a lower
SFR for the treatment of larger (> 80 mm2) impacted stones in the proximal ureter. The
average SFR for larger stones drops to 71.4%.
Aside from the use of retrograde ureterolithotripsy, PCNL is an alternative option for the removal of larger proximal ureter stones. Previous studies compared PCNL with antegrade ureterolithotripsy for the treatment of larger (≥ 10 mm) impacted proximal ureteral stones. Reported SFR for PCNL varied from 96-100% which is higher than the
SFR of 58-89% achieved with retrograde ureterolithotripsy.10–13
The difference in SFR using ureteroscopy for impacted stones compared with non-impacted stones may be explained by several factors. The impeded stone exposure
makes the surgical procedure technically more difficult.2,14 Further, a higher
intra-operative complication rate, in particular bleeding, can lead to early cessation of the procedure resulting in an incomplete stone disintegration. Moreover, in this study stone migration also seems to influence SFRs. The prevalence of migration for impacted stones was much higher with much lower SFRs compared to migrated non-impacted stones. It could be that patients with impacted stone were more likely to have hydronephrosis or
39 Impacted stones
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Lastly, the usage of diverse intracorporeal lithotripter devices could be a factor affecting effectiveness of ureterolithotripsy for impacted stones. In this study this was not investigated. Previous studies revealed that the use of the Ho:YAG-laser is more effective
than pneumatic lithotripsy.9,16,17
Complications
Intra- and post-operative complications rates were found to be significantly related to ureteral stone impaction. The current study shows a higher intra-operative complication rate for impacted stones.
Seitz and colleagues found higher intra- and post-operative complication rates in patients with impacted stones compared to those without impacted stones. Although in both the current study and the study by Seitz, complication rates are low, the actual number may be different due to differences in patient selection and definition of
complications.2 Currently reported complication rates for ureteroscopic treatment are
comparable with complication rates in overall populations.14,18,19
Predictors of stone impaction
Predictive variables could help us identify which patients have impacted stones, but may also help clarify the process of impaction. The process of stone impaction causes an inflammatory reaction of the ureteral mucosa with the genesis of oedema and fibrosis
of the ureteral wall.2,20
We did not find literature elucidating our finding that female gender predicts impaction. Subsequently, we do not assume that there is a causal relation between female gender and impaction.
We found that patients with an ASA-score >1 are more often affected. An explanation may be the higher prevalence of comorbidity affecting the quality and regenerative capacity of ureteral tissue which can result in a higher risk of inflammation and fibrosis and thereby impaction.
Another predictor for stone impaction is prior stone treatment in the same ureteral-renal-unit. We found that SWL was more often performed in patients with impacted stones. In earlier publications it has been reported that the effect of SWL is reduced in
impacted stones.1,3,21 Moreover, prior SWL could increase inflammation and oedema of
the ureteral wall.22 This inflammatory reaction may contribute in the process of stone
impaction. To that end, we suggest that if suspicion of impaction, SWL treatment should only be provided reluctantly and may even be contra-indicated.
We found that a positive pre-operative urine culture is a predictor for impaction. Positive urine cultures are well known as a consequence of obstructive uropathy due to impaction of ureteral stones. Moreover, infection of the urinary tract may aggravate the inflammatory reaction leading to further impaction. Whether urinary tract infections are a cause or consequence is not elucidated in this study.
Larger stones also show to be impacted more often. This is likely because stone with
a larger burden have a low likelihood of spontaneous passage.3 They get stuck in the
ureter thereby causing pressure on the ureteral wall. This stone-induced ureteral wall pressure is suggested to induce ischemia, which stimulates ureteral oedema and fibrosis
leading to impaction.1,2
The identified predictors for stone impaction may not directly be supportive to explicate preventive strategies for the reduction of stone impaction prevalence. Even so, outcomes may support future prevention strategies. Predicting characteristics contribute in the estimation which patients will be affected and help to determine the most effective and safest treatment option. However, other factors, not measured in current analyses could have predictive value. For example, a recent study by Sarica et al. showed that assessment of the acute phase reactants CRP and ESR values along with the
measurement of ureteral wall thickness are predictive parameters for stone impaction.23
Limitations
A limitation of this study is the relatively short follow up period of 3 months. A known complication after the treatment of impacted stones is the formation of ureteral
strictures. In literature stricture rates vary from 8-24%.14,24–27 We assume that the reported
short-term stricture rate in this study firmly underestimates the long-term stricture rate. Extension of the follow-up is needed to evaluate the long-term stricture rate.
Secondly, we are aware that the subjectivity of defining stone impaction is an important limitation in this study. In this study stone impaction was confirmed endoscopically. Still, the assessment was made by a large number of clinicians using their own interpretation assessing impaction.
In literature the definition of stone impaction is still not clarified. Most articles state an impacted stone as a stone that remains at the same location for at least 2 months. Further adduced criteria for impaction are the inability to pass the stone with a guidewire and
failure to visualize contrast beyond the stone.1,9,28 With the lack of one global standard,
consensus on criteria to define stone impaction is suggested to optimize quality of research and compare outcomes in the literature.
41 Impacted stones
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CONCLUSIONS
Ureteroscopic treatment for impacted stones showed lower SFR and higher intra-operative complication rates compared with ureteroscopic treatment for non-impacted stones. The predictive variables for the presence of stone impaction may contribute to the identification of stone impaction during the diagnostic process which may aid the selection of the optimal treatment modality.
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SUPPLEMENTARY MATERIAL
TABLE S1. Intra and postoperative outcomes according to type of ureteroscopy for patients who
had impacted stones located in the proximal ureter.
Type of ureteroscopy
Parameter Semirigid(n=541) Flexible(n=81) Difference p-value Type of test
Stone free rate, n (%) 410 (76.4)
(n = 537)
67 (88.2) (n = 76)
0.018 A
Stone burden (mm2),median, [IQR] 63.6, [44-115]
(n = 541) 43.2, [16-93] (n = 81) < 0.001 D Intraoperative complications n (%)* Overall Bleeding Perforation Failed procedure 58 (10.8) (n = 539) 10 (1.8) (n = 541) 16 (3.0) (n = 541) 24 (4.4) (n = 541) 5 (6.2) (n = 81) 2 (2.5) (n = 81) 0 (0) (n = 81) 1 (1.2) (n = 81) 0.24 0.66 0.25 0.23 B B B B Postoperative complications n (%) 16 (3.0) (n = 541) 3 (3.7) (n = 81) 0.73 B Re-treatment n (%) 114 (21.1) (n = 540) 10 (12.3) (n = 81) 0.074 B
NS = not significant (p ≥ 0.05). Data are n (%) of patients for whom data were available. Percentages exclude missing values from denominators. Statistical test: A) Pearson’s Chi-square test, B) Fishers exact test, C) Student’s t-test, D) Mann-Whitney U test. * Not all intraoperative complications were specified.
