Acoustic emission of kidney stones: a medical adaptation of statistical breakdown mechanisms.

Kidney stones have a prevalence rate of > 10% in some countries. There has been a significant increase in surgery to treat kidney stones over the last 10 years, and it is crucial that such techniques are as effective as possible, while limiting complications. A selection of kidney stones with different chemical and structural properties were subjected to compression. Under compression, they emit acoustic signals called crackling noise. The variability of the crackling noise was surprisingly great comparing weddellite, cystine and uric acid stones. Two types of signals were found in all stones. At high energies of the emitted sound waves, we found avalanche behaviour, while all stones also showed signals of local, uncorrelated collapse. These two types of events are called 'wild' for avalanches and 'mild' for uncorrelated events. The key observation is that the crossover from mild to wild collapse events differs greatly between different stones. Weddellite showed brittle collapse, extremely low crossover energies (< 5 aJ) and wild avalanches over 6 orders of magnitude. In cystine and uric acid stones, the collapse was more complicated with a dominance of local "mild" breakings, although they all contained some stress-induced collective avalanches. Cystine stones had high crossover energies, typically [Formula: see text] 750 aJ, and a narrow window over which they showed wild avalanches. Uric acid stones gave moderate values of crossover energies, [Formula: see text] 200 aJ, and wild avalanche behaviour for [Formula: see text] 3 orders of magnitude. Further research extended to all stone types, and measurement of stone responses to different lithotripsy strategies, will assist in optimisation of settings of the laser and other lithotripsy devices to insight fragmentation by targeting the 'wild' avalanche regime.

The Uniform grading tooL for flexIble ureterorenoscoPes (TULIP-tool): a Delphi consensus project on standardised evaluation of flexible ureterorenoscopes.

OBJECTIVE: To develop a standardised tool to evaluate flexible ureterorenoscopes (fURS). MATERIALS AND METHODS: A three-stage consensus building approach based on the modified Delphi technique was performed under guidance of a steering group. First, scope- and user-related parameters used to evaluate fURS were identified through a systematic scoping review. Then, the main categories and subcategories were defined, and the expert panel was selected. Finally, a two-step modified Delphi consensus project was conducted to firstly obtain consensus on the relevance and exact definition of each (sub)category necessary to evaluate fURS, and secondly on the evaluation method (setting, used tools and unit of outcome) of those (sub)categories. Consensus was reached at a predefined threshold of 80% high agreement. RESULTS: The panel consisted of 30 experts in the field of endourology. The first step of the modified Delphi consensus project consisted of two questionnaires with a response rate of 97% (n = 29) for both. Consensus was reached for the relevance and definition of six main categories and 12 subcategories. The second step consisted of three questionnaires (response rate of 90%, 97% and 100%, respectively). Consensus was reached on the method of measurement for all (sub)categories. CONCLUSION: This modified Delphi consensus project reached consensus on a standardised grading tool for the evaluation of fURS - The Uniform grading tooL for flexIble ureterorenoscoPes (TULIP) tool. This is a first step in creating uniformity in this field of research to facilitate future comparison of outcomes of the functionality and handling of fURS.

Impact of Ureteral Stent Material on Stent-related Symptoms: A Systematic Review of the Literature.

Context: Ureteral stents are essential implants that are used on a daily basis. Since their invention, advances in stent design have been directed towards alleviating stent-related symptoms. It remains unclear how the material composition of the stent affects stent-related symptoms. Objective: To review the literature and define the clinical impact of ureteral stent material on stent-related symptoms. Evidence acquisition: A literature search of the Embase, MEDLINE (PubMed), and Web of Science databases was conducted on December 17, 2021 to collect articles comparing stent composition materials regarding stent-related symptoms. Thirteen publications met the inclusion criteria, of which only one met the high-quality requirements of the Cochrane Collaboration tool for assessing the risk of bias in randomized trials. Evidence synthesis: Most trials, including the highest quality trial, seem to support that silicone double-J (DJ) stents reduce stent-related symptoms compared to nonsilicone DJ stents. Regarding physical properties, it seems that "soft" or "flexible" DJ stents reduce stent-related symptoms. However, since there was only one high-quality study with a low risk of bias, it is impossible to draw a definitive conclusion owing to the lack of quality data. Conclusions: Silicone DJ stents, and by extension "soft" DJ stents, appear to reduce stent-related symptoms compared to nonsilicone polymers and "hard" DJ stents. No definitive conclusion can be drawn owing to a lack of quality evidence. Creating a standard for measuring and reporting physical stent properties should be the first step for further research. Patient summary: A ureteral stent is a small hollow tube placed inside the ureter to help urine drain from the kidney. We reviewed the literature on the impact of stent material on stent-related symptoms. We found that silicone may reduce stent-related symptoms, but no definitive conclusion can be drawn and further studies are needed.

How Reliable Is Endoscopic Stone Recognition? A Comparison Between Visual Stone Identification and Formal Stone Analysis.

Objective: To assess the diagnostic accuracy and intra-observer agreement of endoscopic stone recognition (ESR) compared with formal stone analysis. Introduction: Stone analysis is a corner stone in the prevention of stone recurrence. Although X-ray diffraction (XRD) and infrared spectroscopy are the recommended techniques for reliable formal stone analysis, this is not always possible, and the process takes time and is costly. ESR could be an alternative, as it would give immediate information on stone composition. Materials and Methods: Fifteen endourologists predicted stone composition based on 100 videos from ureterorenoscopy. Diagnostic accuracy was evaluated by comparing the prediction from visual assessment with stone analysis by XRD. After 30 days, the videos were reviewed again in a random order to assess intra-observer agreement. Results: The median diagnostic accuracy for calcium oxalate monohydrate was 54% in questionnaire 1 (Q1) and 59% in questionnaire 2 (Q2), whereas calcium oxalate dihydrate had a median diagnostic accuracy of 75% in Q1 and 50% in Q2. The diagnostic accuracy for calcium hydroxyphosphate was 10% in Q1 and 13% in Q2. The median diagnostic accuracy for calcium hydrogen phosphate dihydrate and calcium magnesium phosphate was 0% in both questionnaires. The median diagnostic accuracy for magnesium ammonium phosphate was 20% in Q1 and 40% in Q2. The median diagnostic accuracy for uric acid was 22% in both questionnaires. Finally, there was a diagnostic accuracy of 60% in Q1 and 80% in Q2 for cystine. The intra-observer agreement ranged between 45% and 72%. Conclusion: Diagnostic accuracy of ESR is limited and intra-observer agreement is below the threshold of acceptable agreement.

Quality of life in patients with kidney stones. / Calidad de vida en pacientes con litiasis urinarias.

Patient reported outcome measures (PROMs) are essential to fully understand the impact of diseases and the effectiveness of treatment from a patient's perspective. Generic and disease-specific tools have been used to assess the impact of nephrolithiasis on patients' quality of life (QoL), as well as the impact of various treatment modalities. Additionally, various studies have investigated the factors that might determine the impact of the disease on the patients' QoL. Here were view the available knowledge on this nascent topic and highlight the need for extensive future research in this crucial area.

Las mediciones de los resultados informados por los pacientes (PROMs) son esenciales para entender completamente el impacto de las enfermedades y la efectividad de los tratamientos desde la perspectiva del paciente. Se han utilizado herramientas genéricas y específicas de la enfermedad para evaluar el impacto de la nefrolitiasis en la calidad de vida de los pacientes (QoL) y también el impacto de varias modalidades de tratamiento. Además, varios estudios han investigado los factores que pueden determinar el impacto de la enfermedad sobre la QoL de los pacientes. Aquí revisamos el conocimiento disponible sobre este tema emergente y subrayamos la necesidad de una futura eintensa investigación en esta crucial área.

Double JJ Ureteral Stenting: Encrustation and Tolerability.

Indications for stenting should be considered and the stent indwelling time should be minimised. Silicone stents are superior in terms of lower rates of encrustation and stent symptoms. α-Blockers may have an off-label role in reducing both pain and urinary symptoms, while keeping an up-to-date stent register may help in ensuring that stents are not forgotten.

Survey on ureTEric draiNage post uncomplicaTed ureteroscopy (STENT).

Objectives: To assess the feasibility of conducting a randomised controlled trial (RCT) to assess whether avoiding ureteric drainage is superior to performing ureteric drainage after Uncomplicated Ureteroscopy and/or Flexible Ureterorenoscopy (URS/FURS) treatment of a urinary tract stone in improving patient reported outcome measures (PROMs) and 30-day unplanned readmission rates. A secondary objective was to understand current practice of urologists regarding ureteric drainage after uncomplicated URS/FURS (UU). Material and methods: We undertook an online survey of urologists, circulated amongst members of international urological societies and through social media platforms. Uncomplicated URS/FURS was defined as completion of URS/FURS treatment for a urinary tract stone, with the absence of: ureteral trauma, residual fragments requiring further lithotripsy procedures, significant bleeding, perforation, prior urinary tract infection or pregnancy. The ureteric drainage options considered included an indwelling stent, stent on a string or a ureteric catheter. The primary outcome was to determine the proportion of urologists willing to take part in a RCT, randomising patients after UU to a "no ureteric drainage" arm or ureteric drainage arm. Secondary outcomes included determining in their current practice, the proportion of clinicians performing routine ureteric drainage after UU, the reasons for performing ureteric drainage following UU and their preferred optimal duration for ureteric drainage if it is used. The study was reported according to the Checklist for Reporting Results of Internet E-Surveys (CHERRIES). Results: Total of 468 respondents from 45 countries took part in the survey, of whom 303 completed the entire survey (65%). The majority agreed that they would be willing to randomise patients (244/303, 81%) in the proposed RCT. Perceived lack of equipoise to randomise was the most common reason for not being willing to participate (59/303, 19%).92% (308/335) reported that they use ureteric drainage after UU. This was most often due to wanting to prevent possible complications from post-operative ureteric oedema (77%) or to aid passage of small fragments (43%). Complexity of the case (i.e. impacted stone 90%) and length of the procedure (46%) were the most important intraoperative factors influencing the decision to use ureteric drainage post procedure. If required, the median stated ideal duration of ureteric drainage was 5 days (IQR: 3-7 days) after UU. If having UU personally, 30% would want no stent postoperatively and over half would prefer a stent on a string. Conclusion: We have highlighted wide variation in practice regarding ureteric drainage after UU. Our results support the feasibility of an RCT evaluating if no ureteric drainage is superior to ureteric drainage in improving PROMs and 30-day unplanned readmission rates following UU.

Percutaneous Cystolitholapaxy Using the LithoClast Trilogy for Multiple Bladder Stones.

Background: Multiple large bladder calculi are traditionally managed through open cystolithotomy or transurethrally in patients who have an open bladder neck. Open procedures are technically challenging in patients who may have had multiple previous open surgeries, and may be associated with significant morbidity in patients with a high comorbid burden. Therefore, a percutaneous approach to such stones has been used especially when there is a closed bladder neck, and has been shown to be effective. There are a number of available devices for breaking stones in these approaches, the newest of which is the LithoClast Trilogy™ (EMS, Nyon, Switzerland) device, a probe that provides ultrasonic and mechanical calculi fragmentation and suction in a single instrument. Case Presentation: We describe the first reported case of percutaneous cystolitholapaxy using the LithoClast Trilogy device in a 41-year-old woman with spina bifida, and multiple large bladder calculi with a history of ileocystoplasty and Mitrofanoff formation, and a bladder neck closure for neuropathic bladder. The calculi measured 31 and 25 mm, and had a volume of 19.6 and 7.9 cm3 and average HU of 408 and 462, respectively. The calculi were composed of 37% calcium phosphate and 63% magnesium ammonium phosphate. Conclusion: We demonstrate that this approach can be used as a viable alternative to open surgery, which is of particular importance for complex patients who have undergone multiple previous open operations, and who may have a high comorbid burden.

Hexametaphosphate as a potential therapy for the dissolution and prevention of kidney stones.

The incidence of kidney stones is increasing worldwide, and recurrence is common (50% within 5 years). Citrate, the current gold standard therapy, which is usually given as potassium or sodium salts, is used because it raises urine pH and chelates calcium, the primary component of up to 94% of stones. In this study hexametaphosphate (HMP), a potent calcium chelator, was found to be 12 times more effective at dissolving calcium oxalate, the primary component of kidney stones, than citrate. HMP was also observed to be effective against other common kidney stone components, namely calcium phosphate and struvite (magnesium ammonium phosphate). Interestingly, HMP was capable of raising the zeta potential of calcium oxalate particles from -15.4 to -34.6 mV, which may prevent stone growth by aggregation, the most rapid growth mechanism, and thus avert occlusion. Notably, HMP was shown to be up to 16 times as effective as citrate at dissolving human kidney stones under simulated physiological conditions. It may thus be concluded that HMP is a promising potential therapy for calcium and struvite kidney stones.

Characteristics of current digital single-use flexible ureteroscopes versus their reusable counterparts: an in-vitro comparative analysis.

BACKGROUND: Single-use flexible ureterorenoscopes (fURSs) have been recently introduced aiming to offer solutions to the sterilization, fragility and cost issues of the reusable fURSs. In order to be a viable alternative, the single-use scopes must prove similar capabilities when compared to their reusable counterparts. The goal of our in-vitro study was to compare the current reusable and single-use digital fURSs regarding their deflection, irrigation and vision characteristics. METHODS: We compared in-vitro 4 single-use fURSs-LithoVue™ (Boston Scientific, Marlborough, Massachusetts, USA), Uscope™ (Zhuhai Pusen Medical Technology Co. Ltd., Zhuhai, Guangdong Province, China), NeoFlex™ (NeoScope Inc, San Jose, California, USA) and ShaoGang™ (YouCare Technology Co. Ltd., Wuhan, China) versus 4 reusable fURSs-FLEX-Xc (Karl Storz SE & Co KG, Tuttlingen, Germany), URF-V2 (Olympus, Shinjuku, Tokyo, Japan), COBRA vision and BOA vision (Richard Wolf GmbH, Knittlingen, Germany). Deflection and irrigation abilities were evaluated with different instruments inserted through the working channel: laser fibres (200/273/365 µm), retrieval baskets (1.5/1.9/2.2 Fr), guide wires [polytetrafluoroethylene (PTFE) 0.038 inch, nitinol 0.035 inch] and a biopsy forceps. A scoring system was designed to compare the deflection impairment. Saline at different heights (40/80 cm) was used for irrigation. The flow was measured with the tip of the fURS initially straight and then fully deflected. The vision characteristics were evaluated (field of view, depth of field, image resolution, distortion and colour representation) using specific target models. RESULTS: Overall, the single-use fURSs had superior in-vitro deflection abilities than the reusable fURSs, in most settings. The highest score was achieved by NeoFlex™ and the lowest by ShaoGang™. PTFE guide wire had most impact on deflection for all fURSs. The 200 µm laser fibre had the lowest impact on deflection for the single-use fURSs. The 1.5 Fr basket caused the least deflection impairment on reusable fURSs. At the end of the tests, deflection loss was noted in most of the single-use fURSs, while none of the reusable fURSs presented deflection impairment. ShaoGang™ had the highest irrigation flow. Increasing the size of the instruments occupying the working channel led to decrease of irrigation flow in all fURSs. The impact of maximal deflection on irrigation flow was very low for all fURSs. When instruments were occupying the working channel, the single-use fURSs had slightly better in-vitro irrigation flow than the reusable fURSs. The field of view was comparable for all fURSs, with LithoVue™ showing a slight advantage. Depth of field and colour reproducibility were almost similar for all fURSs. ShaoGang™ and Uscope™ had the lowest resolution. FLEX Xc had the highest image distortion while LithoVue™ had the lowest. Partial field of view impairment was not for Uscope™ and ShaoGang™. CONCLUSIONS: In-vitro, there are differences in technical characteristics of fURSs. It appears that single-use fURSs deflect better than their reusable counterparts. Irrespective of deflection, the irrigation flow of the single-use fURSs was slightly superior to the flow of the reusable fURSs. Overall, reusable fURSs had better vision characteristics than single-use fURSs. Further in-vivo studies might be necessary to confirm these findings.

Development of a Disease-Specific Ureteral Calculus Patient Reported Outcome Measurement Instrument.

INTRODUCTION: Patient reported outcome measures (PROMs) are powerful instruments to assess the impact of a disease on health from the patient's perspective. We describe the process of designing, testing, and validating the Cambridge Ureteral Stone PROM (CUSP). MATERIALS AND METHODS: Patients recently diagnosed with ureteral stones were approached for participation in focus groups, structured interviews, and test-retest validation studies. Statistical tests included Cronbach's alpha for internal consistency, Spearman's and Pearson's correlation coefficients for test-retest validity, permutation tests of equality of means and Spearman's correlation coefficients for discriminant validity. RESULTS: Forty-three patients participated in the development of the CUSP. Twenty-two patients were involved in the focus groups and structured interviews and a further 21 participated in the prospective test-retest study. Expressed comments were grouped into seven broad health domains: pain, fatigue, sleep disturbance, work and daily activities, anxiety, gastrointestinal (GI) symptoms, and urinary symptoms. Items were selected from established PROM platforms to form the draft (dCUSP) instrument, which was then used for test-retest validation and item reduction. All domains scored highly for Cronbach's alpha (>0.8), with the exception of GI symptoms. Large Spearman's (>0.76) and Pearson's correlation estimates (>0.83) were obtained for test-retest validity, suggesting that answers were reliable through the time period tested. The estimates of the Spearman's correlation coefficient between each pair of domains ranged from 0.17 to 0.78 and the upper bounds of the corresponding 95% confidence intervals were all smaller than 0.95, suggesting that each domain measures something different. The tests of equality of the mean of scores of the control (n = 25) and patient groups were all significant, suggesting that CUSP successfully discriminated patients suffering from ureteral stones for every domain. CONCLUSION: CUSP is a patient-derived ureteral stone PROM, which can be used to measure ureteral stone disease health outcomes from the patient's point of view.

The Role of Medical Expulsive Therapy for Ureteral Stones: Against MET.

We no longer advocate the use of medical expulsive therapy in our patients. We also believe that the European Association of Urology guidelines group should believe the findings of the SUSPEND study and stop advocating the use of medical expulsive therapy.

Do renal stones that fail lithotripsy require treatment?

The rates of extracorporeal shock wave lithotripsy (SWL) appear stable in the UK. However, there is little evidence on the natural history of these calculi if SWL fails. We set to look at the effectiveness of SWL in patients with a single, previously untreated renal stone and the natural history of those stones that failed treatment. We retrospectively reviewed all data from our prospectively collected database of patients undergoing a first treatment for a single renal stone between October 2010 and November 2013. Outcomes after SWL were categorised as success, subsequent intervention needed or conservative management. The medical records of patients managed conservatively were reviewed to determine whether further intervention was required and why. We further sought to define, in those patients where SWL failed, whether subsequent active intervention was needed. For the remainder, we examined whether conservative management was a reasonable management option. 313 patients fitted the inclusion criteria. Of these, 144 were treated successfully. Of the 170 patients with a residual stone, 51 went on to flexible ureteroscopy directly at their next clinical review mainly due to persistent symptoms. 79 patients were managed conservatively, and for 39 follow-up data were unavailable as their follow-up was at a different hospital. 63 patients (80%) were successfully managed conservatively with no recurrence of symptoms over the follow-up period (mean 2 years 4 months). 16 (20%) patients that were initially managed conservatively required subsequent intervention. Of these, 87% had a stone in an upper pole calyx. Conservative management of renal stones after failed SWL is a suitable option for asymptomatic patients with stones not located in the upper pole. For patients with upper pole stones, early intervention is warranted due to the high risk of requiring intervention.

Percutaneous nephrolithotomy access by urologist or interventional radiologist: practice and outcomes in the UK.

OBJECTIVE: To compare outcomes of urologist vs interventional radiologist (IR) access during percutaneous nephrolithotomy (PCNL) in the contemporary UK setting. PATIENTS AND METHODS: Data submitted to the British Association of Urological Surgeons PCNL data registry between 2009 and 2015 were analysed according to whether access was obtained by a urologist or an IR. We compared access success, number and type of tracts, and perceived and actual difficulty of access. Postoperative outcomes, including stone-free rates, lengths of hospital stay and complications, including transfusion rates, were also compared. RESULTS: Overall, percutaneous renal access was undertaken by an IR in 3453 of 5211 procedures (66.3%); this rate appeared stable over the entire study period for all categories of stone complexity and in cases where there was predicted or actual difficulty with access. Only 1% of procedures were abandoned because of failed access and this rate was identical in each group. IRs performed more multiple tract access procedures than urologists (6.8 vs 5.1%; P = 0.02), but had similar rates of supracostal punctures (8.2 vs 9.2%; P = 0.23). IRs used ultrasonograhpy more commonly than urologists to guide access (56.6% vs 21.7%, P < 0.001). There were no significant differences in complication rates, lengths of hospital stay or stone-free rates. CONCLUSIONS: Our findings suggest that favourable PCNL outcomes may be expected where access is obtained by either a urologist or an IR, assuming that they have received the appropriate training and that they are skilled and proficient in the procedure.

Alpha blockers should no longer be used for ureteric stones.

Alpha-blockers have been used as medical expulsive therapy for ureteric stones for a number of years. Conventional wisdom supporting their use has recently been challenged by the publication of a large, multi-centre, randomised double-blinded, placebo-controlled study, SUSPEND, which showed that they were ineffective. This paper looks at the evidence behind the use of alpha-blockers, and discusses why we should believe the evidence we have from SUSPEND, rather than other published studies, and therefore stop using them as medical expulsive therapy.

In Vitro Assessment of Three Clinical Lithotripters Employing Different Shock Wave Generators.

OBJECTIVE: To test the hypothesis that shock wave lithotripsy machines vary in their ability to fragment standardized artificial urinary calculi. MATERIALS AND METHODS: An in vitro test configuration was used to fragment synthetic U-30 Gypsum (U.S. Gypsum, Chicago, IL) stones (mean length 7.1 ± 0.2 mm, mean diameter 6.5 ± 0.07 mm, mean mass 299 ± 16 mg) using the Sonolith i-sys (EDAP TMS, Vaulx-en-Velin, France), Modulith SLX F2 (Storz Medical AG, Tägerwilen, Switzerland), and Piezolith 3000 (Richard Wolf GmbH, Knittlingen, Germany) lithotripters. Gypsum stones were placed at the nominal focus and treated with 250, 500, or 1000 shocks. The residual mass following passage through a 2-mm wire mesh was measured and compared using ANOVA and the Tukey-Kramer HSD test. RESULTS: There was no statistically significant difference between the Modulith SLX F2 and Piezolith 3000 lithotripters for 250 and 1000 shock treatments (p = 0.34 and 0.31, respectively). The Piezolith 3000 demonstrated the most favorable stone mass reduction for 500 shock treatments (187.4 ± 45.2 mg). The Sonolith i-sys was found to be significantly less effective than the other lithotripters for all shockwave conditions. Furthermore, performance of the Sonolith i-sys decreased beyond a threshold generator electrode age of 6000 shocks. CONCLUSIONS: This in vitro study found considerable variability in the ability of lithotripters to fragment synthetic urinary calculi. Synthetic stones were employed to provide a repeatable means of assessing variability in fragmentation efficiency of lithotripters. The Modulith SLX F2 and Piezolith 3000 are broadly equal and resulted in greater fragmentation efficiencies than the Sonolith i-sys. The performance of the Sonolith i-sys deteriorates at 6000 shocks, before the specified lifetime of 20,000 shocks.

Hospital Volume Does Not Influence the Safety of Percutaneous Nephrolithotomy in England: A Population-Based Cohort Study.

PURPOSE: This study aims to investigate the relationship between hospital case volume and safety-related outcomes after percutaneous nephrolithotomy (PCNL) within the English National Health Service (NHS). PATIENTS AND METHODS: The study used the Hospital Episode Statistics (HES) database, a routine administrative database, recording information on operations, comorbidity, and outcomes for all NHS hospital admissions in England. Records for all patients undergoing an initial PCNL between April 1, 2006 and March 31, 2012 were extracted. NHS trusts were divided into low-, medium-, and high-volume groups, according to the average annual number of PCNLs performed. We used multiple regression analyses to examine the associations between hospital volume and outcomes incorporating risk adjustment for sex, age, comorbidity, and hospital teaching status. Postoperative outcomes included: Emergency readmission, infection, and hemorrhage. Mean length of stay was also measured. RESULTS: There were 7661 index elective PCNL procedures performed in 163 hospital trusts, between April 2006 and March 2012. There were 2459 patients who underwent PCNL in the 116 units performing fewer than 10 PCNL procedures per year; 2643 patients in the 37 units performing 10 to 19 procedures per year; and 2459 patients in the 9 hospitals performing more than 20 procedures per year. For low-, medium-, and high-volume trusts, there was little variation in the rates of emergency readmission (L 9.7%, M 9.3%, H 8.4%), infection (3.0%, 4.2%, 3.8%), or hemorrhage (1.3%, 1.5%, 1.5%), and there was no statistical evidence that volume was associated with adjusted outcomes. Mean length of stay was slightly shorter in the medium- (5.0 days) and high-volume (5.0) groups compared with the low-volume group (5.3). The effect remained statistically significant after adjusted for confounding. CONCLUSION: Hospital volume was not associated with emergency readmission, infection, or hemorrhage. Length of stay appears to be shorter in higher volume units.