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The mechanics of urine during its transport from the renal pelvis to the bladder is of great interest for urologists. The knowledge of the different physical variables and their interrelationship, both in physiologic movements and pathologies, will help a better diagnosis and treatment. The objective of this chapter is to show the physics principles and their most relevant basic relations in urine transport, and to bring them over the clinical world. For that, we explain the movement of urine during peristalsis, ureteral obstruction and in a ureter with a stent. This explanation is based in two tools used in bioengineering: the theoretical analysis through the Theory of concontinuous media and Ffluid mechanics and computational simulation that offers a practical solution for each scenario. Moreover, we review other contributions of bioengineering to the field of Urology, such as physical simulation or additive and subtractive manufacturing techniques. Finally, we list the current limitations for these tools and the technological development lines with more future projection. CONCLUSIONS: In this chapter we aim to help urologists to understand some important concepts of bioengineering, promoting multidisciplinary cooperation to offer complementary tools that help in diagnosis and treatment of diseases.
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The use of double J catheters is usual in urologist`s daily practice. The indication can be divided in prophylactic or therapeutic. Prophylactically, they prevent complications derived from endourological procedures, such as ureteral lesion or obstructive uropathy secondary to residual lithiasis or edema. Therapeutically, they treat obstructive uropathy of many different pathologies, either in an emergency setting or scheduled, such as lithiasis, stenosis, extrinsic compression of any nature or urinary tract tumors among others. Although they add clear benefits in both cases, they are not free from side effects. The most frequent symptoms they cause are: voiding urgency and increase in voiding frequency, macroscopic hematuria and suprapubic and lumbar pain. The physiopathological mechanism is explained by a mechanical and inflammatory effect or due to vesicoureteral reflux depending on the symptom. This causes patient`s quality of life disturbance that may vary from mild degree to very severe. Thus, several strategies have emerged with the aim of diminishing or palliate the intensity of such symptoms: alpha-blocker drugs, design modifications or reduction of their use.
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OBJECTIVE: Double J ureteral stents are frequently used to allow free diuresis from the kidney to the bladder, but their presence has a major impact on patient`s quality of life (QoL). Our aim is to describe such impact, and to describe possible solutions that can alleviate the symptoms associated with their use.METHODS: Systematic search in bibliographic sources including Cochrane library, UpToDate, Pubmed, Tripdatabase, selecting publications between 2000-2015, and also the EAU European guidelines (2016). Studies that assessed QoL with double J stents and possible solutions were selected.RESULTS: We included 6 qualitative studies on QoL, 6 clinical trials of double J catheters new designs, and 3 systematic reviews. Most studies used the USSQ (QoL) questionnaire and main problems are described, being storage symptoms and pain the most frequent and important. Possible solutions include modifications in design and composition of the catheter and specially, the use of alpha-blockers and anticholinergics to improve QoL.CONCLUSION: Double J stents have an important symptomatic impact that impairs QoL. They should be used under appropriate indication; their duration should be limited and we must employ all the technological and pharmacological approaches to mitigate their effects.
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OBJECTIVES: We review the literature oninfections associated with ureteral stents and new technologiesaimed at preventing them.Ureteral stent placement is one of the most commonurologic procedures, but carries a comparatively highmorbidity. Infection is one of the most common stent-associatedmorbidities. Several new stent materials andcoatings have been proposed and tested to reducestent-associated infections.METHOD: We review the current methods of preventingbacterial infection, including antibiotic prophylaxis andminimising dwell time. We look at the science underlyinginfection and biofilm formation on stents. Severalnew stent materials and coatings are described, as wellas the studies underlying their mechanism of action.RESULTS AND CONCLUSIONS: While many promisingideas for new stent coatings and materials havebeen tested, no significant improvement to current polyurethanestent technology is commonly available or used.The basic principles of antibiotic prophylaxis at time ofinsertion, avoiding contamination, and minimising dwelltimes remain the best methods to prevent stent-associatedinfections.
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Ureteral stents are the most commonly used urological implants. They are used for temporary as well as for long-term ureteral stenting.Amongst others, complications of ureteral stenting are encrustation and cellular adherence which, in turn, promotes urinary tract infection and can induce impaired healing in case of ureteral damage. Biofilm formation on urological implants leads to the protection of persisting bacteria from local defense mechanisms, thereby rendering persistent urinary tract infections more common. It seems clear that antibiotics cannot penetrate into biofilms adequately. Also, bacteria persist in biofilms in a state of reduced metabolism which further reduces antibiotic efficacy. Furthermore, bacteria develop resistance more quickly in biofilms. This paper tries to give an overview of the complex pathophysiological mechanisms that underlie stent encrustation as far as we know to date.
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Urinary tract catheters are hollow andflexible tubes used to facilitate urine output or to achieveurine transit through them. We can find different typesof catheters depending on the purpose they have beendesigned for: urethral, cystostomy and ureteral cathetersamong others. We review the indications for insertionof these catheters, their designs, composition, coveringmaterials, insertion techniques and associated complications.Pediatric catheters are behind what is producedfor adults, so we perform a bibliographic review abouturinary catheters in general with emphasis on the pediatricpatient.
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OBJECTIVE: To describe the different therapeutic alternatives in malignant ureteral obstruction (MUO), and to analyze short and long-term results.METHODS: We conducted a bibliographic search about MUO in Spanish and English languages in PubMed and Google Scholar. We examined the most relevant reviews, original manuscripts and their respective citations. Last search was on April 2016.RESULTS: Polymeric double J stent is the cheapest and most accessible internal urinary diversion, but has also the shortest duration. Early and late failure rates were 0-35% and 14-49% respectively. Mean time to late failure was 3-12 months. Percutaneous nephrostomy is the safest alternative in terms of failure rates, though it has frequent complications such as tube dislodgement, and may have a negative effect on quality of life. The only metallic double J stent with enough bibliographic background is the Resonance® stent. Early failure was 0-15% and late failure 4-41%, with a mean time to late failure of 2.6-13 months. Regarding metallic stents, Memokath 051® has obtained the best results, with 0-5% early failure rates, 19-49% late failures and mean time to late failure of 7-11 months. In patients with polymeric double J stent failure, patients benefited from tandem double J stents, metallic double J catheters or metallic stents, avoiding the need of a percutaneous nephrostomy. The evidence level was low in all cases.CONCLUSIONS: Results in MUO are very heterogeneous and have a low evidence level. Factors that influence results include stent characteristics, status and prognosis of the obstructive condition and probably patient and physician’s preferences. Polymeric double J stents seem to have higher early and late failure rates than metallic double J catheters and metallic stents. Even though, the difference is not clearly evident. Prospective, multicenter, multidisciplinary trials are necessary to elucidate convenience and adequate selection of each type of stent.
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Double J stents are used in Urology in an important number of pathologies. These devices contribute to solve very prevalent pathologies such as upper urinary tract lithiasis. However, there are very frequent symptoms associated with double J catheters that may produce a very important constraint on the quality of life of patients. Although theses symptoms are not severe in most cases, they require medical treatment to be solved in certain patients. Several types of drugs such as analgesics, anti-inflammatories, antibiotics, anticholinergics and alpha-blockers have been used for this pathology, with variable results depending on the authors. We consider the use of certain drugs may help patients to solve the symptoms associated with double J catheters, mainly the first days after insertion. In the mid term, urinary symptoms are associated with problems related to double J catheter, so it is necessary to establish the proper measures to have this devices not loose their physical characteristics, that may condition these adverse symptoms.
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The insertion of a double J catheter (DJ) has widespread, becoming a usual procedure and standard of care in urology. Despite its relative simplicity it is not free from intraoperative risks or problems during the weeks after the implant. Conversely, despite great advances in design of these catheters the ideal material has not been discovered yet, one that is perfectly biocompatible with urine and avoids completely the advent of complications.The range of problems associated with DJs is variable: from mild self-limited dysuria or hematuria to more complex situations with higher risk, such as catheter migration, complete calcification, breakage, obstruction and renal unit loss.The treatment of theses complications must combine maximal efficacy for their resolution with the least possible surgical aggression. Accordingly, the different options of endourological approach become very important and they are the cornerstone for the treatment of the complications associated with ureteral catheters.The objective of this review is to present the main complications derived from the insertion of a DJ, their diagnosis, prevention and treatment, focusing mainly in the different endourological techniques.
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Double-J ureteral stents disposal is associated with the appearance of side effects in up to 90% of the patients. The main causes of these symptoms are related to stent`s design and the materials they are manufactured from. Vesicoureteral reflux and bladder trigone irritation are the etiopathogenic causes of ureteral stents associated morbidity. Due to this, and in order to improve patients’ quality of life, stents that avoid reflux have been developed. Among anti-reflux designs, the first was a double-J stent the bladder tip of which is provided with a polymeric membrane that prevents retrograde flow of urine through its internal drainage channel. This design showed satisfactory results, although not statistically significant. Their use in renal transplantation has also been assessed not only to decrease morbidity and ascending infection but also to improve graft survival.Other designs try to thin the distal end and even change it to a surgical suture thread, with the aim of eliminating the internal drainage channel in order to cause the minimum interference with the UVJ. Recently, two prototypes were evaluated in animal models and have achieved reduction of VUR. The first consists of a valve attached to the distal end of a traditional double-J stent, acting as a backflow prevention device. The second design is an intra-ureteral stent that acts like a double-J stent, but without crossing the UVJ and therefore preventing reflux completely. Nowadays, the use of these devices is not implemented in hospitals due to the absence of scientific evidence supporting the superiority of these designs over conventional stents.
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One of the main wishes in the fieldof urinary catheters and stents is to arm them withbiodegradable characteristics because we considera failure of these devices the need for retrieval, theforgotten catheter syndrome as well as the adverseeffects permanent devices cause after fulfilling theiraim. The efforts focused in new designs, coatings andbiomaterials aim to increase the biocompatibility oftheses internal devices. Lately, there have been correctadvances to answer the main challenges regardingbiodegradable ureteral devices. Thus, modulation of therate of degradation has been achieved thanks to newbiomaterials and the use of copolymers that enable tochoose the time of permanence as it is programmedwith conventional double J catheters. Biocompatibilityhas improved with the use of new polymers that adaptbetter to the urine. Finally, one of the main problems iselimination of degraded fragments and experimentally ithas be demonstrated that new designs elicit controlleddegradation, from distal to proximal; using strandingand combination of copolymers degradation may becaused by dilution, reducing fragmentation to the laststages of life of the prosthesis. Moreover, it has beendemonstrated that biodegradable catheters potentiallymay cause less urinary tract infection, less encrustationand predictably they will diminish catheter morbidity,since their degradation process reduces adverse effects.Regarding the development of biodegradable urethralstents, it is necessary to find biomaterials that enablemaintaining their biomechanical properties in the longterm, keeping open the urethral lumen both in patientswith BPH and urethral stenosis. Modulation of the time ofdegradation of the prosthesis has been achieved, but theappearance of urothelial hyperplasia is still a constant inthe initial phases after implantation. The development ofdrug eluting stents, anti-proliferative or anti-inflammatory,as well as biodegradable stents biocoated is a fieldfrom which it is expected the arrival of the solution oftheses adverse effects.Therefore, many features need to be improved to obtainbiodegradable stents, but over the last years someturning points have been accomplished thanks to theadvances in Bioengineering, allowing to foresee safeand effective solutions in the nearest future.
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OBJECTIVE: The development of smaller diameter ureteroscopes, along with the advance in surgical techniques has allowed ureteroscopy to be progressively less traumatic. The considerable morbidity produced by a ureteral stent makes it advisable to question routine placement.METHODS: We performed a review of the literature searching for systematic reviews, meta-analysis and prospective randomized clinical trials.RESULTS: Three systematic reviews and meta-analysis along with 14 clinical trials were included in our review. Most of the consulted articles show a higher incidence of irritative urinary symptoms, and hypogastric and flank pain in patients carrying a JJ stent. No differences were observed in postoperative complication rates.DISCUSSION: Apparently, there is little benefit in ureteral stenting regarding postoperative complications after uncomplicated ureteroscopy, with a few exceptions. The challenge regarding ureteral stenting after ureteroscopy is to identify the cases that will benefit from it. An interesting alternative, that requires further study, is the placement of a ureteral catheter (internal-external) during the first 24 hours after procedure.CONCLUSIONS: It seems advisable to place a JJ stent in complicated cases or in those considered to have a higher risk of postoperative complications. In the rest of cases it seems that stenting after ureteroscopy involves more problems tan benefits.
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Mayor urological complications,fistulae and stenosis, mainly affect the vesicoureteralanastomosis and present in the early post-transplantperiod. The systematic use of ureteral catheters keeps being controversial with many groups using them onlyselectively depending on the existence of pretransplantor intraoperative risk factors.METHODS: We performed a bibliographic reviewthrough automatized search in the Medline bibliographicdatabase, as the main bibliographic source, and also inClinical Key. The search strategy included the followingterms: “stent” AND “kidney transplantation”.RESULTS: The bibliographic search revealed theprotective effect of the use of ureteral catheters in thetransplant ureteroneocystostomy for both development offistulae (RR 0.29, 0.12 to 0.74, p=0.009) and stenosis(RR 0.27, 0.09 to 0.81, p=0.02). The use of cathetersin immunosuppressed patients was associated withsignificant increase of the incidence of post-transplanturinary tract infections (RR 1.49 IC 95% 1.04 to 2.15,p=0.03) that was prevented by antibiotic prophylaxiswith cotrimoxazole directed against pneumocistiscarinii.The rates of permeability of self-expandable metallicstents and extra-anatomic bypasses in the treatmentof ureteral stenosis after renal transplantation in highsurgical risk patients or after the failure of previoussurgery, has varied from 50% to 100%, with a limitednumber of patients included.CONCLUSIONS: The use of ureteral catheters in theextravesical ureteroneocystostomy reduces the incidenceof anastomotic complications. Surgery is the treatmentof choice of post-transplant ureteral stenosis. The useof metallic stents and extra-anatomic bypasses shouldbe limited to complex ureteral stenosis when primarytherapy has failed, in high surgical risk patients orchronic graft dysfunction
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The management of ureteral obstruction of malignant origin or complicated benign obstruction continues to be a challenge for the urological community. In this sense, the use of metallic stents could be considered a useful alternative to the conventional drainage techniques, because it accomplishes the resolution of obstruction in a single procedure, without external diversions and without the adverse effects of current diversions. Another important advantage they offer is that they do not need replacement as frequently as double J catheters or nephrostomy tubes require.From their first applications in the upper urinary tract until now the design of metallic stents has experienced a notable evolution. The main obstacle at the beginning was the use of stents intended for other organic territories, which caused a high rate of failures, since they did not take into consideration in their designs the hostile environment represented by urine for this type of devices, neither the existence of ureteral peristaltism. Thanks to subsequent metallic designs (Memokath, Uventa, Allium Medical URS-stent, Resonance), the current generation of ureteral metallic stents has improved the success rate in comparison to classical designs, accommodating to ureteral dynamics and improving the coating and alloys. Despite these advances, today, their application is limited to very selected patients due to the onset of undesirable effects still associated with theses stents, such as obstructive urothelial hyperplasia, encrustation or migration.The precise knowledge of the physiopathological mechanisms responsible for the cited adverse effects, together with the application of Bioengineering enabling the development of drug eluting metallic stents, biocoated stents, or new biodegradable metallic materials that mitigate or diminish their effects, may be the key to allow the development of the ideal metallic stent.
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The Drug eluting stents (DESs) are the most commonly used stents in interventional cardiology. DESs have been shown to minimize the restenosis rate after stenting the coronary vessels by addressing the phenomena of smooth muscle proliferation and inflammation. The effect of the DESs is attributed to the anti-proliferative drugs which are coated onto the stent and are released in controlled fashion. The anti-proliferative drugs reduce the hyperplastic reaction by inhibiting the smooth muscle cell cycle and their proliferation. Urological stents are important instruments of the everyday urological practice with a variety of indications for their use. Nevertheless, their use is hampered by a number of complications such as infection, patient discomfort, encrustation, migration and hyperplastic reaction. In an attempt to reduce the complications, the concept of DESs was introduced to Urology. DESs for ureteral or urethral as well as polymeric or metal have been evaluated in experimental studies. The clinical evaluation of DESs is limited only to polymeric stent with results that require further investigation and confirmation. The development of stent designed for the urinary tract, the selection of the appropriate substances combined with the appropriate experimental and clinical investigation would provide DESs acceptable for the urological practice.
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Urethral stents were first introduced in 1988, and since then, they have undergone significant improvements. However, they did not gain a wide popularity and their use is limited to a small number of centers around the world. Urethral stents can be used in the entire urethra and for various and diverse indications. In the anterior urethra, it can be used to treat urethral strictures. In the prostatic urethra, they can be used for the treatment of prostatic obstruction, including benign, malignant and iatrogenic prostatic obstruction. Moreover, although not widely used, it can be also applied for the treatment of posterior urethral stricture and bladder neck contracture, usually resulting in urinary incontinence and the need for subsequent procedures.Our main experience are with Allium urethral stents, and as such, we provide the latest updates in urethral stents with special emphasis on the various types of Allium urethral stents: bulbar, prostatic and bladder neck stents.
