Impact on Active Scope Deflection and Irrigation Flow of All Endoscopic WorkingTools during Flexible Ureteroscopy

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1 European Urology European Urology 45 (2004) Impact on Active Scope Deflection and Irrigation Flow of All Endoscopic WorkingTools during Flexible Ureteroscopy Federico Pasqui, Francis Dubosq, Kessile Tchala, Mohamed Tligui, Bernard Gattegno, Philippe Thibault, Olivier Traxer * Department of Urology, Hopital Tenon, 4, rue de la Chine, Paris, France Accepted 28 August 2003 Published online 21 September 2003 Abstract Objective: Flexible ureteroscopy is nowadays an alternative effective option for treatment of upper urinary tract stones, especially in the lower renal pole. Access in this case is often limited by active deflection capabilities of the instrument which is always deteriorated by the passage of different tools through the working channel. Insertion of them limits also the irrigation flow and so that the visibility. These deteriorations vary largely following the tool inserted. We performed an in vitro evaluation of deterioration of active deflection, possibility of tool insertion in maximal active deflection and irrigation flow in 6 different flexible ureteroscopes with almost all of tools available. Methods: A total of 546 measures of maximal deflection, test of passage of tools in maximal deflection and measures of irrigation flow passage through the working channel were made on 6 different ureteroscopes, the ACMI DUR-8, the ACMI DUR-8 Elite, the Karl Storz AA, the Karl Storz AU1 Flex-X, the Wolf and the Olympus URF/P-3 without any tool inserted and with 22 different tools (14 extraction devices and 8 lithotripsy probes). Results: Larger caliber tools resulted in more deflection degradation than smaller ones but it is more evident in case of use of non-nitinol tools instead of the nitinol ones. Generally lithotripsy probes affected active deflection more than nitinol extractions tools but different brand laser fibres present different results. Usually 1.6 and 1.9F electro hydraulic probes offer a slightly better deflection than does the 200m laser fibre. Ballistic shock probes are so stiff that can not be used for treating lower renal pole stones. Conclusions: An array of different instruments are nowadays available for upper renal endoscopic treatment but they differ largely on stiffness and on obstruction to irrigation flow. Laser probes are very problematic to insert in the already deflected instruments, something that is less evident with the EHL probes and the smaller nitinol extraction tools. Irrigation flow is inversely proportional to the diameter of the tool inserted. Tools with a diameter of 3 French or more block totally the flow. # 2003 Elsevier B.V. All rights reserved. Keywords: Ureterorenoscopy; Irrigation flow; Laser; Basket; Equipment; Supplies 1.Introduction In the current practice treatment of moderately-sized upper urinary tract stones relies mostly on ESWL. But when a poor fragmentation is noted or the residual * Corresponding author. Tel. þ ; Fax: þ address: olivier.traxer@tnn.ap-hop-paris.fr (O. Traxer). stones are located in the lower pole calyx, a by far more efficient way of treating the stones is by endoscopic procedures. While for ureteral access a semirigid ureteroscope could be sufficient, in case of intrarenal and especially in case of lower pole calyx stones, an actively deflectable flexible ureteroscope is required. A review of the literature shows that successful fragmentation with complete stone clearance or presence of /$ see front matter # 2003 Elsevier B.V. All rights reserved. doi: /j.eururo

2 F. Pasqui et al. / European Urology 45 (2004) insignificant residual fragments with ureteropyeloscopy in a single session is 86%, and can be higher after a second-look procedure [1]. Moreover, while in case of ESWL the success rate of lower pole calyx stone removal is lower [2], smaller ureteroscopes combined with holmium laser lithotripsy increased the singleprocedure success rate to 97% for ureteral stones and 79% for intrarenal stones [3]. Flexible ureteral endoscopes have become a readily available urological instrument. The standard flexible ureteroscope is now an actively deflectable ureteroscope of approximately 8.5F on the body shaft with a smaller bevelled tip of about 7.5F. Cross sections of such endoscope show the presence of the light and vision fiber-optics on a side and a working and irrigating channel of at least 3.6F, which allows the passage of most of the currently available instruments [4]. This now standard endoscope has a primary actively deflectable segment which can be deflected by a moving thumb liver on the handle. The tip deflects from 160 to 270 degrees in one direction and 130 to 270 degrees in the opposite direction in the same plane depending on the model. There is also a secondary or passively deflecting segment, which is a segment in the shaft which is relatively more flexible than the other portions of the shaft. An evolution of the flexible ureteroscope DUR8 was recently introduced by ACMI (DUR8 Elite ), this model has a double lever system for a secondary more proximal active deflection which allows even more manoeuvrability. Another new ureteroscope recently available is the Storz model AU1 ( Flex-X ), with an active flexion of 270 degrees on both ways. The most important aspect of endourologic management of the ureter and the intrarenal collecting system is also the availability of an appropriate array of instruments. These instruments can be used for specific applications to optimise stone retrieval. Special ones are required for diagnosis, stone disintegration and/or extractions and tissue ablation. Unfortunately when placed into the channel within the flexible ureteroscope, all instruments variably limit the deflection of the tip. Moreover, the irrigation and working channel is essential not only for passing instruments but also for irrigation flow. Irrigation flow determines visibility but it is usually reduced by the introduction of different instruments. However, both deflection and irrigation flow depend largely by the probe inserted and the ureteroscope used. The aim of this study was an exhaustive in-vitro testing of all the materials currently available in our country. 2. Material and methods 2.1. Flexible ureteroscopes Six currently available flexible ureterorenoscopes were used for this study: the ACMI DUR-8, the ACMI DUR-8 Elite, the Karl Storz AA, the Karl Storz AU1 Flex-X, the Wolf and the Olympus URF/P-3 (which represent the totality of ureteroscopes available at the moment in our country) (Table 1). Another model, the Wolf , with a working channel of 4.5F, was not available for our test and the Mitsubishi model is not yet commercialised in our country. It should be mentioned that, while the other brands produce ureteroscopes with an angle of view of zero degrees, the ACMI models present an angle of view of about 12 degrees. Moreover, while all the other ureteroscopes have an intuitive control of the active deflection (thumb lever down ¼ tip down) the Olympus model present an inverted control. The ACMI DUR-8 Elite is a recent evolution of the ACMI DUR-8 which adds the possibility of a contemporary double active deflection and a total downward deflection of about 270 degrees. The Storz Flex-X is a new model capable of a bigger active deflection on both directions. All of the instruments have a 3.6F working channel diameter. All of the ureteroscopes have the possibility of passive deflection Endoscopic tools Most working instruments are now available in sizes 3F or less to fit through the working channel of the flexible ureteroscopes. Table 1 Ureteroscopes specifications Brand ACMI ACMI Olympus Storz Storz Wolf model DUR-8 DUR-8E Elite TM URF/P AA AU1 Flex-X TM Length (mm) Total Working Channel diameter (F) Direction of view (8) Field of view (mm) n.a. n.a n.a. Control Intuitive Intuitive Non intuitive Intuitive Intuitive Intuitive Outer diameter (F) Tip Body Active deflection (8) Up Down Active secondary def. Down 130

3 60 F. Pasqui et al. / European Urology 45 (2004) We have tested all the tools that are normally required for stone disintegration and/or extraction, i.e. a total of 22 instruments: ACMI/Circon Laser probe 200m, World of Medicine (WoM) Freddy 1 Laser probe 273m and 420m, Lumenis Holmium Coherent Laser probe 1 200m and 365m, EMS Swiss Lithoclast Master 1 probe 0.8F, Storz Electro hydraulic (EHL) probe 1.6F, ACMI/ Circon Electro hydraulic (EHL) probe 1.9F, Boston Scientific Zerotip basket and 3.0F and Stone Cone 1, Cook NCircle 1 basket 2.2, 2.4, 3.0 and 3.2F, Bard ureteral stone basket 1.9F, Bard Dimension basket 1 3F, Boston Scientific Graspit and 3.2F, Boston Scientific Tricep 1 3.0F, Circon Surecatch 1 3.0F, and Bard Grasper 1 2.4F Methodology The active deflection was evaluated firstly considering the maximal active deflection angle on one direction measured on the intersection between the tangent to the active deflection segment and the deflected tip with a standard protractor. This has been performed without any instrument inserted with the scope blocked in a straight alignment. After this phase it was tested the possibility of inserting a working tool (a probe, a basket or a grasper) at the maximal deflection (a situation often seen during the clinical practice while trying to treate a non mobile lower pole calyx stone) and finally it was measured the downward deflection with the instrument already inserted and passed 1 cm beyond the tip (another possible clinical situation). We simplified the measurements not considering the opposite active deflection angle of each ureteroscope (usually the smaller one). We have also avoided to test the passive deflection because of our impossibility of providing a in-vitro reproducible evaluation of the stiffness of the endoscope just proximal to the active deflection segment. However it should be stressed that passive deflection without any tool inserted is something that is referable to the elastic characteristics of the scope. The irrigation flow was measured in millilitres per minute in a straight alignment with the irrigation bag placed in two positions, at 60 cm and at 100 cm above the height of the instrument, with and without all of the instruments inserted, for evaluating the situation of an extra pressure for the irrigation flow. Always we have used a special screw biopsy port seal at the inner opening of the working channel manufactured by ACMI/Circon, as we are used to do in our clinical practice. 3. Results 3.1. Maximal active deflection A total of 138 measures of maximal deflection were made with 6 different ureteroscopes. In all cases ureteroscope deflection was the greatest with an empty working channel. Larger caliber tools resulted in more deflection degradation than smaller ones. For example, maximum downward ureteroscope deflection of the DUR8E was 270 degrees. The ureteroscope maximum deflection degraded sequentially with the passage of 2.2F, 3F and 3.2F Cook baskets from 270 to 260, 258 and 250 degrees, respectively. Table 2 and Fig. 1 show the deterioration in active ureteroscope deflection with different caliber nitinol basket and other endoscopic tools. Generally the newer tools like baskets and graspers, which are made of nitinol, affect much less the Table 2 Alteration in ureteroscope deflection inserting different tools Brand Model DUR8 DUR8E URF/P AA 11278AU Channel empty Extraction tools Boston Scientific Zerotip TM 3F Boston Scientific Zerotip TM 2.4F Cook Ncircle 1 3.2F Cook Ncircle 1 3.0F Cook Ncircle 1 2.4F Cook Ncircle 1 2.2F ACMI/Circon Surecatch 1 3.0F Bard Dimension 1 3.0F Bard Basket 1.9F Boston Scientific Graspit TM 3.2F Boston Scientific Graspit TM 2.6F Boston Scientific Tricep 3F Bard Grasper 2.4F Boston Scientific Stone Cone 1 3.0F Probes ACMI/Circon Laser 200m Lumenis Coherent Holmium Laser 200m Lumenis Coherent Holmium Laser 365m EMS Swiss Lithoclast Master Storz EHL 1.6F ACMI/Circon EHL 1.9F W o M Freddy 1 Laser 273m W o M Freddy 1 Laser 420m

4 F. Pasqui et al. / European Urology 45 (2004) Degrees None Zerotip 3.0F Zerotip2.4F NCircle 3.2F NCircle 3.0F NCircle 2.4F NCircle 2.2F Surecatch 3.0F Dimension 3.0F Basket 1.9F Graspit 3.2F Graspit 2.6F Tricep 3.0F Grasper 2.4F Stone Cone Tool Laser 200µ Holmium Laser 200µ Holmium Laser 365µ Lithoclast Master 0.8F EHL 1.6 F FreddyLaser 273µ FreddyLaser 420µ AA URF/P-3 DUR8 DUR8E 11278AU1 Fig. 1. Alteration in ureteroscope deflection inserting different tools. deflection of the instrument. So that Bard Grasper 2.4F was an old model and was not made of this material and demonstrates its stiffness. Electro hydraulic probes show less deterioration in active deflection than the laser probes Passage of instruments A total of 132 tests of passage of 22 different tools on the 6 different ureteroscopes in maximal active deflection were made. The impossibility of insertion of the instrument in this situation has been noted as no in Table 3. It should be noticed that paradoxically there are some kind of tool that can t even emerge from the tip of the scope, even if they can pass through it when in maximal deflection. This is due to the shortness of the tool and the length of the working channel of some models of ureteroscopes with the port seal. This is true in case of use of the Lithoclast Master Probe into the Olympus URF/P-3 and the Storz 11274AA. The use of smaller seals could obviate the problem Irrigation flow A total of 276 measurements, as shown in Table 4,of water solution flow passage through the working channel of the six models of ureteroscopes in straight position with and without the different tool inserted in two pressure condition was performed. But, bearing in mind that even in an extra pressure condition the irrigation flow is quite weak trough a channel 3.6F width, our study demonstrates that in case of the insertion of bigger instruments (usually over 3F) flow drops to zero, determining a major loss of visibility. It should be noted that with the augmentation of the diameter of a same tool the flow is inversely proportional. In any case the application of this extra pressure,as mentioned above, often seems useful. Table 3 Passage of instrument while in active deflection Brand Model DUR8 DUR8E URF/P AA AU Extraction tools Boston Scientific Zerotip TM 3.0F yes no yes yes yes yes Boston Scientific Zerotip TM 2.4F yes no yes a yes yes yes Cook Ncircle 1 3.2F yes yes yes yes yes yes Cook Ncircle 1 3.F yes yes yes yes yes yes Cook Ncircle 1 2.4F yes yes yes yes yes yes Cook NCircle 1 2.2F yes yes yes yes yes yes ACMI/Circon Surecatch 1 2.4F yes no yes yes no yes Bard Dimension 3.F yes yes yes yes yes yes Bard Basket 1.9F yes no yes no no no Boston Scientific Graspit TM 3.2F yes no no no no yes Boston Scientific Graspit TM 2.6F yes no no no yes yes Boston Scientific Triceps 3.0F yes yes yes a yes a yes a yes Bard Grasper 2.4F no no no no yes no Boston Scientific Stone Cone 1 no no no no no no Probes ACMI/Circon Laser 200m no no no no no no Lumenis Coherent Holmium Laser 200m no no no no no no Lumenis Coherent Holmium Laser 365m no no no no no no EMS Swiss Lithoclast Maste. no no no a no a no no Storz EHL 1.6F yes yes yes yes yes yes ACMI/Circon EHL 1.9F yes no yes no yes yes W o M Freddy 1 Laser 273m no no no no no no W o M Freddy 1 Laser 420m yes no yes yes no no a Short.

5 62 F. Pasqui et al. / European Urology 45 (2004) Table 4 Irrigation flow (ml/min) at 60 cmh 2 O [at 100 cmh 2 O] Brand Model DUR8 DUR8E URF/P AA AU Empty channel 42 [54] 42 [54] 36 [46] 46 [56] 40 [48] 44 [54] Extraction tools Boston Scientific Zerotip TM 3.0F 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] Boston Scientific Zerotip TM 2.4F 10 [18] 10 [18] 5 [5] 6 [6] 5 [5] 7 [9] Cook Ncircle 1 3.2F 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] 0 [2] Cook NCircle 1 3.F 4 [8] 4 [8] 3 [4] 3 [4] 3 [4] 4 [6] Cook NCircle 1 2.4F 12 [16] 12 [16] 8 [10] 12 [12] 6 [8] 11 [14] Cook NCircle 1 2.2F 15 [19] 15 [19] 8 [9] 11 [13] 9 [10] 13 [15] ACMI/Circon Surecatch 1 2.4F 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] 0 [2] Bard Dimension 3.F 0 [0] 0 [0] 0 [0] 0 [0] 0 [3] 0 [3] Bard Basket 1.9F 16 [22] 16 [22] 11 [13] 13 [15] 11 [13] 12 [15] Boston Scientific Graspit TM 3.2F 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] Boston Scientific Graspit TM 2.6F 10 [10] 10 [10] 4 [5] 4 [5] 4 [5] 5 [6] Boston Scientific Triceps 3.0F 12 [18] 12 [18] 6 [7] 7 [9] 4 [5] 8 [9] Bard Grasper 2.4F 8 [8] 8 [8] 5 [7] 7 [9] 6 [7] 7 [9] Boston Scientific Stone Cone 1 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] 0 [0] Probes ACMI/Circon Laser 200m 30 [40] 30 [40] 22 [30] 26 [36] 22 [30] 26 [32] Lumenis Coherent Holmium Laser 200m 26 [36] 26 [36] 20 [28] 22 [29] 20 [25] 24 [29] Lumenis Coherent Holmium Laser 365m 18 [23] 18 [23] 13 [18] 16 [18] 14 [18] 19 [22] EMS Swiss Lithoclast Maste. 10 [10] 10 [10] 4 [5] 4 [6] 4 [6] 6 [7] Storz EHL 1.6F 18 [26] 18 [26] 16 [24] 16 [24] 16 [18] 16 [24] ACMI/Circon EHL 1.9F 23 [26] 23 [26] 11 [15] 14 [16] 12 [15] 14 [18] W o M Freddy 1 Laser 273m 26 [36] 26 [36] 20 [28] 22 [29] 20 [25] 24 [29] W o M Freddy 1 Laser 420m 9 [11] 9 [11] 7 [12] 7 [12] 7 [10] 10 [12] 4. Discussion Retrograde ureteroscopy was initially used for the distal ureteral calculi. The development of smaller calibre rigid ureteroscopes, flexible ureteroscopes, and improved flexible contact lithotriptors has allowed for its application to the more proximal portions of the ureter. Ureteroscopic treatment of proximal ureteral calculi is best reserved for patients who are unsuitable for ESWL or as a salvage procedure in patients who fail ESWL. Actually other classical indications for an endoscopic lithotripsy are well defined [5]: renal stones of more than 2 cm in diameter cystine renal stones stones with an associated renal malformation which could rise the risk of failure by ESWL (diverticulae, obstructions etc.). With the development of rigid and flexible ureteroscopes, ureteroscopy has been also used increasingly in diagnosis of upper tract urothelial tumours. As a matter of fact, when in 1971, Takagi and co-workers, developed a 6F, 75 cm long, actively deflectable, flexible ureteroscope it had only a diagnostic, not a therapeutic potential, because the lacking of working or an irrigating channel [6]. Visualization was facilitated only by mannitol diuresis. Once the diagnostic is posed nowadays there is also room for a purely endoscopic treatment of upper urinary tract tumours, when a nephron-sparing technique is advocated. Various energetic sources are available for in-situ lithotripsy: acoustic (ultrasonic shocks), electric (hydroelectric shocks), mechanic (ballistic shocks), and light (lasers). With the advent of flexible ureteroscopes and ancillary equipments like laser and electro hydraulic probes, the stone free rate achieved by ureteroscopy for upper ureter stones has been reported to be as high as 80 to 95% [7]. Not all the lasers available on urology are the same. Holmium YAG (Yttrium-Aluminium-Garnet is the more efficient and it is capable to break all kind of stones but unfortunately there is the risk to damage endoscopic tools, to burn the ureter and to rebound the stone [8]. Recently a new model of laser has been developed, the Frequency-doubled dual-pulse Neodymium YAG laser ( Freddy ). This laser, exclusively developed for lithotripsy, is constituted of 80% of infrared component (1064 nm) and of a green component (532 nm) obtained with a partial doubling of the frequency of the infrared component [9]. Regardless the type of laser, laser beams are transferred via glass fibres covered by polymeric sheaths of

6 F. Pasqui et al. / European Urology 45 (2004) different materials and diameter. Usually for clinical use are available fibres from 200 to 720 mm. Several new retrieval baskets have been introduced. Different designs and materials have different purposes and advantages. The helical basket can be rotated to engage a stone impacted within the ureter. The presence of a tip can be useful for maintaining purchase over an ureteral impacted calculus. Other tipless baskets are more useful for extracting stones in lower renal calices. While stainless steel extractors are sculpted to the desired shape, nitinol baskets are heat set, allowing permanent memory of the wire shape. Moreover nitinol will not kink or deform during use. Other baskets have increased the radial expansion strength by using wires with shaped cross section in the form of triangle or Delta rather than the usual flat or round wires. It should be noted that 2.4F Cook baskets is different from the other models being made of delta wires capable of a radial force equivalent to the 3.2F model without sacrificing irrigation. Generally lithotripsy probes affected active deflection more than nitinol extraction tools but it is obvious that not all the laser fibres present the same characteristics of flexibility. It has been noted that, for some lower pole stones, 1.6 and 1.9F electro hydraulic probes offer a slightly better deflection than does the 200m laser fibre [10]. Our work clearly confirms that. Actually, as we showed on Fig. 1, the new Freddy Laser fibres demonstrate exceptional flexibility. On the contrary, the only ballistic-shocks energy driven probe, the EMS Lithoclast Master is so stiff that it is suitable only for ureteral stone removal, but hardly in case of upper stone localisations, especially the renal lower pole. As a matter of fact when trying to treat a lower pole renal stone one of the most important think to consider is the flexibility of the instrument. Usually, after having bent the tip of the instrument thanks to an active, lever controlled mechanism, the possibility of actually arrive on the stones is granted also by the use of the secondary passive deflection. But usually, apart from the case of diagnostic procedure, the passage of a tool inside of the working channel is necessary but stiffens the instrument and tends to pull out the position of its tip. Interestingly, Storz Flex-X ureteroscope showed less appreciable change in deflection with different instruments inserted than the DUR8 Elite, suggesting a stronger force in the active deflection (Fig. 2). Usually lithotripsy of lower pole renal stones is performed after having positioned on direct visual control the tip onto the stone itself. Unfortunately often in this position (maximal deflection) it is actually impossible to enter the scope with the desired tool. Fig. 2. Maximal ureteroscope deflection with different tools inserted: DUR8E with Zerotip 3F (A), DUR8 with Circon Laser 200m (B), Flex-X with Zerotip 3F (C) and Flex-X with Holmium 200m (D). For example, this is almost constant in case of laser probes, making quite a though task to perform the lithotripsy of the lower pole renal stones. EHL probes proved to be more suitable for the task. It has already been stated that the flexible ureterorenoscopy should be planned by measuring the infundibulopelvic angle (IVP) [11], but also considering the individual capability of using a certain flexible ureteroscope and the influence of the selected tool on deflection and irrigation flow. An interesting technique has been proposed to reduce the deterioration of active deflection and irrigation flow in case of insertion of ureteroscopic nitinol stone baskets: the use of disassembled ones (unsheathed) did allow an addition of flexibility and irrigation flow of 15 20% and 2 to 30 folds respectively [12]. The working channel is used for entering all the tool necessary to endoscopic manipulation and fragmentation but it is also the channel used for irrigation. A good irrigation flow is of paramount importance for improving the visibility during the procedure. Surprisingly with different ureteroscopes tested in our study, despite the same diameter of the working channel (3.6F), the irrigation flow seems a lot different. As a matter of fact in case of the ACMI DUR8 Elite the flow is the double compared with the one measured in the Storz Flex-X in case of NCircle Baskets 2.2, 2.4

7 64 F. Pasqui et al. / European Urology 45 (2004) and 3.0F. Maybe an explication can be found in different friction of different sheathing polymers. As regards the fragility of the ureteroscopes, it used to be conventionally accepted that URS equipment had to be checked after in-vivo procedures. In our invitro study, no optical fibres were broken after the tests for all ureteroscopes and we did not observe damage of the irrigation channel and/or deflection mechanism. The in-vitro testing usually did not evaluate the fragility of the ureteroscopes and it represents a limitation of this kind of tests. However, ureteroscopes are still fragile instruments and precautions must be taken to safeguard them. We recommend in particular that the instructions for use of ureteroscopes are followed, avoiding maximum deflection and avoiding working continuously in the lower caliceal group as far as possible. All the authors recommend mobilizing lower caliceal calculi in the renal pelvis or upper caliceal group to achieve fragmentation, if possible. 5. Conclusion Our goal was to present en exhaustive review of the characteristics of the majority of working tool nowadays available for flexible ureteroscopy and to test them within almost all the ureteroscopes without any alteration on the commercialised tool, as it has been already partially done [13]. This will be useful for future pre-operative planning of the specific procedure, lowering the risk of damaging this extraordinary but really fragile instruments. As it noted by Afane, treatment procedures, especially those involving lower pole intrarenal calculi, are particularly hard on flexible ureteroscopes because it is difficult to manoeuvre the instrument into the lower infundibulum. The most common reason for endoscope repair was poor or complete loss of deflection, which acquainted for 40% of all repairs [14]. This fragility of the deflection unites in this new generation of ureteroscopes has been also reported by White and Moran [15]. On the other side luminosity and irrigation flow remained almost unchanged during consecutive applications [14]. Actually when thinking about buying a flexible ureteroscope the knowledge that we can take from these tests could be useful, but only if laboratory data are compared with other very important factors: durability and the initial and maintenance costs involved, that can vary considerably among different instruments. A new concept in the design of endoscopic tools for flexible ureteroscopic treatments should be aware of the necessity of both the greatest flexibility and the smallest possible diameter. References [1] Walsh PC, Retik AB, Sauders WB, Vaughan ED. Campbell s urology. 8th ed. Amsterdam: Elsevier; [2] Talic RF, Faqih SR. Extracorporeal shock wave lithotripsy for lower pole nephrolithiasis: efficacy and variables that influence treatment outcome. BJU Int 1999;51:544. [3] Grasso M, Bagley D. Small diameter, actively deflectable, flexible ureteropyeloscopy. J Urol 1998;160:1648. [4] Grasso M, Bagley DH. A 7.5/8.2F actively deflectable, flexible ureteroscope: a new device for both diagnostic and therapeutic upper urinary tract endoscopy. Urology 1994;43:435. [5] Tiselius HG, Ackermann D, Alken P, Buck C, Conort P, Gallucci M. Guidelines on urolithiasis. Working Party on Lithiasis, European Association of Urology. Eur Urol 2001;40:362. [6] Takagi T, Go T, Takayasu H, Aso Y. Fiberoptic pyeloureteroscope. Surgery 1971;70:661. [7] Abdel Razak OBD. The 6.9F semirigid ureteroscope in clinical use. Urology 1993;41:45. [8] Spore SS, Teichman JM, Corbin NS, Champion PC, Williamson EA, Glickman RD. Holmium: YAG lithotripsy: optimal power settings. J Endourol 1999;13:559. [9] Del Vecchio F, Auge BK, Brizuela RM, Weizer AZ, Zhong P, Preminger GM. In vitro analysis of stone fragmentation ability of the Freddy Laser. J Endourol 2003;17:177. [10] Tawfiek ER, Bagley DH. Management of upper urinary calculi with ureteroscopic techniques. Urology 1999;53:25. [11] Michel M, Knoll T, Ptaschnyk T, Kohrmann KU, Alken P. Flexible ureterorenopyeloscopy for the treatment of lower pole calyx stones: influence of different lithotripsy probes and stone extraction tools on scope deflection and irrigation flow. Eur Urol 2002; 41:312. [12] Landman J, Monga M, El-Gabry EA, Rehman J, Lee DI, Bhayani S, et al. Bare naked baskets: ureteroscope deflection and flow characteristics with intact and disassembled ureteroscopic nitinol stone baskets. J Urol 2002;167:2377. [13] Parkin J, Keeley Jr FX, Timoney AG. Flexible ureteroscopes: a user s guide. BJU Int 2002;90:640. [14] Afane JS, Olweny EO, Bercowsky E, Sundaram CP, Dunn MD, Shalav AL, et al. Flexible ureteroscopes: a single center evaluation of the durability and function of the new endoscopes smaller than 9 Fr. J Urol 2000;164:1164. [15] White MD, Moran ME. Fatigability on the latest generation ureteropyeloscopes: Richrad Wolf vs Karl Storz. J Endourol 1998; 182(Suppl 12).