In Vitro Evaluation of Single-Use Digital Flexible Ureteroscopes

Since its introduction in the 1960’s, flexible ureteroscopy (fURS) has evolved significantly. Advancements in tip control deflection, miniaturization of scopes and the introduction of a working channel for small-caliber instruments and fluid irrigation have made fURS a commonly selected approach for patients undergoing treatment of upper urinary tract calculi. In the last decade, the insertion of the digital sensors improved image quality and shortened operative time. However, despite significant advancements in the scopes technology, there are numerous concerns associated with the reusable devices, such as durability, potential for cross infection and the high cost of a permanent flexible ureteroscopes. To overcome these obstacles, there has been growing interest in single-use flexible ureteroscopes. After the LithoVue, the first single-use digital flexible ureteroscope, the concept has gained in popularity and other single-use flexible ureteroscopes have been introduced in the market, prompting the need for comprehensive evaluation.

The purpose of our study was to systematically compare the manufacturing and in vitro performance of two single-use flexible ureteroscopes (LithoVue and Pusen) with a reusable optical flexible ureteroscope (Flex-X²) in terms of technical characteristics, optics, deflection mechanism and irrigation flow, as well as performance and safety. By knowing the particulars of each device, the surgeon might optimize a patient-centered approach, increasing the chance of success while preserving safety.

Pusen is half the weight of LithoVue, though both may be considered light compared to reusable scopes. For instances in which the ureteral sheath fails to reach the upper ureter, a flexible ureteroscope with a longer working length might be more effective. LithoVue is 5cm longer than Pusen and 1cm longer than the Flex-X². In terms of maneuverability, the handle control for deflection of Pusen requires surgeons to train in an unusual position for the dominant hand. All surgeons were more comfortable with standard scopes (LithoVue and Flex-X²) since they were trained in that manner. LithoVue was even easier to handle since is much lighter than the permanent one. We did not include this data since it is completely subjective and if surgeons trained with the other handling technique performed the trials results would be probably different.

The entrance of the working channel is very close to this handle control and extra care should be taken when using a laser fiber while moving the scope, since no fiber lock mechanism is available for this model. We must highlight that the new version of Pusen has a similar handle control compared to LithoVue and Flex-X² and further tests should be performed.

Conversely, because of the stiffer shaft of Pusen, it could also be used as a substitute for the standard semi rigid ureteroscope. In addition, although it is not our practice, for surgeons who perform upper urinary tract stone dusting without an access sheath, Pusen might be of great interest since it can be used as a semirigid and flexible ureteroscope, possibly reducing operative time.

Complete stone free status remains the ultimate outcome surgeons seek when performing flexible ureteroscopy for stone removal, regardless of stone composition. It is intuitive that adequate irrigation in combination with good optics is essential to allow efficient lithotripsy and to warrant complete stone fragment removal in a fast and secure manner. If one or the other is compromised, the final surgical result is suboptimal. LithoVue has a higher resolution and larger field of view. Conversely, Flex-X² was the scope with better color representation. In terms of irrigation, Pusen had the best results when no instruments were used through the working channel. This was probably a consequence of the stiffer shaft of Pusen that prevents bending and therefore avoids compression of the inner diameter of the working channel. No difference was seen between Pusen and LithoVue when small caliber instruments were in place. Conversely, with larger instruments, e.g. the 1.9F basket, LithoVue outperformed Pusen, probably because of the back leak from the working channel entrance seen for this scope.

The LithoVue scope deflection did not deteriorate even with larger instruments and only the 375μm laser fiber offered resistance for ureteroscope deflection. This is in accordance with previous clinical and in vitro studies. By having the tightest loop diameter (radius of deflection), the LithoVue may offer greater dexterity to access lower pole stones. A lower pole location is a common indication for intra-renal flexible ureteroscopy as shock wave lithotripsy offers poor results. This is especially true if an acute and long infundibulum-pelvic angle is present and if stone fragmentation has to be done in situ, with significant risk for scope damage. Though both Pusen and LithoVue allowed passage of a 200μm laser fiber in the complete deflected position, we do not recommend this maneuver to be done routinely and the Pusen achieved only 222⁰ deflection in that setting compared to 270^o for the LithoVue.

Study limitations are present. The scopes were tested in a clear endoscopic environment. The impact of blood or stone debris on image quality deserves further study. The durability of the scopes was not tested. While the ability to reach all calyces was tested, multiple users were not timed to evaluate the ease of access. Further clinical testing along with cost analysis modeling for utilization in low-volume and high-volume settings will further define the utility and potential impact of single-use scopes.

In conclusion, LithoVue, Pusen and Flex-X² have distinguishable baseline physical and optical characteristics. LithoVue outperformed the other ureteroscopes in terms of optical resolution, field of view, deflection capacity, and irrigation flow with larger instruments. Pusen is the lighter scope and showed better results in terms of irrigation when no instruments are in place. Flex-X² was superior in terms of color representation. By knowing the specifics of each flexible scope, a patient-centered approach might be optimized by the surgeon.

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Written By: Carlos Alfredo Batagello, M.D.¹ and Giovanni Scala Marchini, Ph.D.¹

1. Section of Endourology, Division of Urology, Hospital das Clínicas, University of Sao Paulo Medical School, Sao Paulo, Brazil. Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, Ohio, USA.

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