Introduction

Innovations in technology and surgical approach have rapidly changed the landscape of endourology, which has been a discipline particularly adept at advancing the status quo. In this chapter we present an overview of recent developments in the surgical management of nephrolithiasis including new laser technologies, the emerging role for disposable ureteroscopes, percutaneous nephrolithotomy (PCNL) positioning, percutaneous access technology, endoscopic combined intrarenal surgery, and “miniaturized” PCNL. It is our hope that the reader may apply some of these innovations and approaches in a practical manner to their current practice as well as gain an appreciation for what the future may hold.

Laser Technology

The newest generation of holmium: yttrium-aluminum-garnet (Ho:YAG) laser lithotripters allow the operator to control parameters including pulse energy, frequency, and pulse width in order to achieve optimal stone dusting or fragmentation during retrograde ureteroscopy and PCNL. Retropulsion and stone migration to difficult locations are common challenges during holmium laser lithotripsy. Recently, Lumenis has developed a new technology for the Lumenis Pulse 120H laser system designed to mitigate these issues [1]. Moses Technology (Lumenis, Yokneam, Israel) is a pulse modulation mode that improves holmium laser energy transmission through water. The wavelength of Holmium laser, 2100 nm, is near the 1940 nm absorption peak of water and in traditional pulse mode most of its energy forms a vapor bubble which generates pressure waves upon collapse [2]. With the “Moses effect”, first described almost 30 years ago [3], the laser-induced vapor bubble created during an initial pulse “parts the water”, allowing the subsequent pulse to be more efficiently delivered to the stone or tissue for enhanced ablation [4].

The effects of Moses Technology (delivery of a short, low-energy pulse to create a vapor bubble before delivery of a longer, higher energy pulse) were first investigated in a preclinical study by El Hilali and associates [5]. They found that stone movement in vitro was reduced by 50 times at a setting of 0.8 J and 10 Hz (p < 0.01), and observed a clear reduction in retropulsion with both fragmentation settings (high energy) and dusting settings (low energy, high frequency). In addition, stone fragmentation tests showed that the Moses modes resulted in a significantly higher ablation volume when compared with the regular mode at all settings tested. A subsequent in vitro study by the same investigators showed higher efficiency of stone fragmentation with the Moses mode compared to standard mode [6]. Recently, using an automated in vitro dusting model, Winship and colleagues demonstrated that the Moses Ho:YAG laser technology provided more efficient ablation of soft stones compared with standard long-pulse lithotripsy, both with the laser tip in contact with the stone surface and at a distance of 1 mm [7].

The thulium fiber laser is currently being explored as an alternative lithotripter to the gold standard Ho:YAG laser. This experimental fiber laser is not to be confused with the Thulium:YAG laser that has been in use for BPH procedures for over a decade. With fiber lasers, a chemically doped silica optical fiber is used as the gain medium instead of a bulk solid-state crystal (as used in Ho:YAG and Thulium:YAG). The light originates within the core of a small optical fiber and is pumped by another laser source, such as a diode laser, and then the light emitted from the fiber laser can be coupled into a separate, conventional, disposable silica surgical fiber [8].

The primary advantage of fiber lasers in general is their ability to deliver high power output from a small fiber core, resulting in high intensity or brightness [9]. The spatial beam profile of the thulium fiber laser is much smaller than the beam profile typically produced by Ho:YAG laser, allowing it to be coupled to a silica working fiber as small as 50 μm [10]. The thulium fiber laser emits light at a wavelength of 1940 nm, which more closely matches the water absorption peak in tissue and calculi than Ho:YAG (2100 nm), leading to higher ablation efficiency at the same power [11]. Several in vitro studies have supported this property. Using Begostone phantoms, Chiron et al. demonstrated that with a single impact, for an equivalent delivered energy, the area destroyed by the thulium fiber laser is four times higher than the effect of Ho:YAG laser [12]. Thulium fiber laser has also been shown to produce twice as much stone dust as Ho:YAG laser with Moses technology at the same settings [13]. Studies describing initial clinical experiences with thulium fiber laser suggest that it is safe and effective for use in retrograde ureteroscopy [14] and PCNL [15], however, to date there are no clinical studies with direct comparison to the Ho:YAG laser. Thulium fiber laser is currently not approved for clinical human use in the U.S. or Europe with the exception of Russia where the initial clinical investigations have taken place. Further clinical studies are needed to validate the performance and safety of this new technology.

Advances in Ureteroscope Technology

Since the first description of therapeutic flexible ureteroscopy for stone extraction in 1987 [16–18], there has been a revolution in the treatment options for stone disease. In one population based cross-sectional time series analysis, Ordon et al. showed a significant increase in the use of ureteroscopy between 1991 and 2010 (25–59% of all stone procedures, p < 0.0001) and a reciprocal decrease in the use of shock wave lithotripsy (69% to 34% of all procedures, p < 0.0001) [19]. The versatility of the ureteroscope in both percutaneous and retrograde stone intervention is attributable to incredible technological developments over the past decades such as the introduction of the digital ureteroscope and its improved image quality in 2008 [20].

Single-use (disposable) flexible ureteroscopes represent not only a new innovation in endourology but a paradigm shift in operating room workflow and efficiency, bypassing the issues of sterilization and the need for repair of fragile, costly instruments. The Polyscope (Polydiagnost, Germany) was the first single-use system described in the literature by Bader et al. in 2010 [21]. This 8F, fiber optic ureteroscope had a syringe-like handle to allow for one-sided deflection, and required both a reusable image fiber and light source connected outside of the sterile field. In this series, a stone-free rate of 87.5% was achieved in the completed cases, however in 5 out of the 40 cases the instrument broke. Single-use ureteroscope technology has continued to evolve and as of 2017 there had been seven devices developed [22]. Only two of these devices are approved by the U.S. Food and Drug Administration for use in patients – the LithoVue (Boston Scientific, Massachusetts, USA) and the Uscope UE3022 (Zhuhai Pusen Medical Technology Co, Ltd., Zhuhai, China).

The LithoVue is a single-use flexible digital ureteroscope with a similar structure to reusable digital ureteroscopes as well as a built-in LED light source and camera (Fig. 24.1). The device has a 7.7F tip and 9.5F shaft, 3.6F working channel, 270° deflection in both directions, and connects with a built-in cable to its own touchscreen monitor or to an operating room screen through DVI connection [23]. Since the LithoVue was introduced to the U.S. market in 2015 there have been numerous clinical studies comparing its performance to reusable digital ureteroscopes.

The Pusen Uscope was approved by the FDA in 2017 and is a single-use, flexible digital ureteroscope with a 9F tip and 9.5F shaft, 3.6F working channel, and an advertised 270° deflection in both directions [24]. Like the LithoVue, it has an integrated fixed camera that is connected using a cable to its own monitor or to an operating room screen. To date, there is minimal published clinical data on Uscope performance. In a recent case series, Emiliani et al. described successful completion of standard ureteroscopy and laser lithotripsy using the Uscope in four out of five procedures, with scope replacement required in one procedure due to leaking at the handle-shaft junction [25]. In another series of 71 procedures (with no comparison group), Salvadó et al. reported no device failure and clinical outcomes comparable to ureteroscopy with reusable instruments [26].

Image quality of digital single-use flexible ureteroscopes, critical to the success and efficiency of endoscopic procedures, has been demonstrated to rival that of reusable digital instruments. Talso et al. compared image resolution and quality of seven different flexible ureteroscopes by filming standardized grids and stones of different composition in a simulated fluid setting and showing the videos to 103 subjects (51 urologists and 52 non-urologists) who rated image quality on a 5-point scale. Image quality of the LithoVue was rated as better than that of the two fiberoptic ureteroscopes (Olympus URF-P6 and Storz Flex-X2) as well as two of the digital ureteroscopes (Wolf Cobra Vision and Olympus URF-V2), but inferior to image quality of the reusable digital ureteroscopes Storz Flex-XC and Olympus URF-V [27]. Additionally, in a blinded ex-vivo study using porcine kidneys, 13 experienced endourologists rated the image quality of the LithoVue as significantly better than that of six commonly used reusable flexible ureteroscopes (Storz Flex-X2, Storz Flex-Xc, Olympus URF-P5, Olympus URF-P6, Olympus URF-V2, Wolf Cobra), and similar to the image quality of the Wolf Boa [28].

Deflection properties of the LithoVue have been shown to meet or exceed those of conventional ureteroscopes. Dale et al. examined performance characteristics and found that with an empty working channel, the LithoVue had bidirectional maximal deflection of 276°, compared to 263° for the Flex-Xc and 253° for the Cobra fiberoptic ureteroscope. Furthermore, the LithoVue ureteroscope had minimal loss of deflection, only 2–5°, with the 200 μm laser fiber, 1.9F nitinol basket, and 2.0F and 2.4F nanoelectric pulse lithotripsy probes in the working channel. The Flex-Xc and Cobra ureteroscopes showed loss of deflection ranging from 2 to 27°, depending on the instrument placed [29]. In a study using human cadavers, Proietti et al. found no significant differences between the LithoVue, Olympus URF-P5, and Olympus URF-V in lower pole access and deflection angle. Surgeons participating in the study also rated the overall maneuverability of the LithoVue as higher than the reusable ureteroscopes [30].

The overall clinical performance of the LithoVue was recently assessed by Usawachintachit et al. in prospective case–control study [31]. Study cases included 115 consecutive flexible ureteroscopic procedures in which the LithoVue was utilized over a 6 month period at a single institution, and study controls included 65 consecutive cases in which reusable fiberoptic flexible ureteroscopes (Olympus URF-P6) were utilized over a previous six month period. There were no significant differences in indication for procedure (stone removal, diagnostic, urothelial carcinoma), total stone burden, and lower pole stone burden treated between the two groups. Scope failure occurred in 4.4% of LithoVue cases and 7.7% of reusable cases (p = 0.27). The overall mean procedure duration was 10.4 min shorter in the LithoVue cohort (64.5 vs. 54.1 min, p < 0.05) compared with the reusable ureteroscope cohort. For stone removal cases only, mean procedural duration was also significantly shorter in the LithoVue cohort (70.3 vs. 57.3 min, p < 0.05) compared to the reusable ureteroscope cohort. Stone-free rates were higher in the LithoVue cohort (60% vs. 44.7%), but not significantly (p = 0.36). The authors speculate that the decreased procedure time in the LithoVue cohort may be explained by better image quality than the fiberoptic reusable ureteroscopes as well as by ergonomics and operator fatigue—the LithoVue (with integrated light source and camera) weighs only 277.5 g, while the combination of the URF-P6 scope plus camera head and light cord weighs between 838 g and 1378 g, depending on which camera and light cord model is attached [32].

It is debatable at this time whether the cost of a disposable instrument will mitigate the significant costs associated with sterile processing and maintenance of reusable flexible ureteroscopes. In addition to the initial expense of acquiring the reusable instruments ($23,000–$58,000), there is the cost of repair, which has been shown to be necessary approximately every 5–22 cases [33, 34]. Tosoian et al. calculated that at a large-volume academic center, the cost of flexible ureteroscope repair averages to $605 per case [35]. Recently, Martin et al. developed an algorithm to evaluate the potential economic cost of single use, flexible digital ureteroscopes compared to reusable flexible digital ureteroscopes. All cases using the Storz Flex-XC digital ureteroscope were prospectively recorded over a 12 month period, and cost assessment was performed based on the original purchasing cost and repair-exchange fees divided by the number of cases. Ureteroscopes required repair after an average of 12.5 cases. Excluding original purchasing costs, the analysis revealed an average cost of $848 per case. Based on an approximate cost of $1500 per disposable ureteroscope, after 99 ureteroscopy cases the cost-benefit analysis favored reusable ureteroscopes. The authors included that exclusive disposable ureteroscope use may be cost beneficial at only at centers with a lower case volume per year [36]. In contrast, in a prospective, single-center micro-costing analysis, Taguchi et al. demonstrated comparable overall cost per case between disposable and reusable flexible ureteroscopes [37]. This study accounted for the initial cost of reusable ureteroscope acquisition (Olympus URF-P6) in addition to costs of sterile processing and repair costs per case. Of note, the authors included the labor costs for disposal of used LithoVue ureteroscope and recycling of the packaging in this analysis.

The environmental impact of single-use ureteroscopes is another factor to consider. Davis et al. recently quantified this cost in an analysis of the typical life cycle of the LithoVue compared to the Olympus URF-V. To measure the carbon footprint, data were obtained on manufacturing of single-use and reusable flexible ureteroscopes, repairs and processing of reusable scopes, and ultimate disposal of both ureteroscopes. The authors found that environmental impacts of the LithoVue and the reusable ureteroscope were similar; 4.43 kg vs. 4.47 kg of CO2 per endourologic case [38].

Following implementation of the algorithm at their institution, the number of annual ureteroscope repairs decreased from 47 to 35 (despite an overall increase in number of cases), for a direct cost savings of 21%. The authors also noted that the LithoVue was used in 26 additional procedures where an acceptable reusable digital ureteroscope was not available in order to prevent surgery delay or cancellation [40].

In conclusion, current data suggests that single-use flexible ureteroscopes provide an acceptable alternative to conventional ureteroscopes in terms of performance, may help avoid damage to reusable ureteroscopes, and will help increase patient access to ureteroscopy in situations where sterile, reliable reusable equipment is not readily available.

Innovations in Percutaneous Nephrolithotomy

Prior to the 1970s, open stone surgery was the standard treatment for patients with renal calculi [41]. In 1955, Goodwin et al. described the first successful nephrostomy tube placement and in 1976 Fernström and Johansson described the first extraction of renal calculi through a percutaneous nephrostomy tract under radiologic guidance in three patients unfit for open surgery [42]. Initially described as a procedure that occurred over several days of serial dilation with risk of high morbidity [43], PCNL can now be performed with a short hospitalization, or in select cases, as an outpatient. Continuous innovation and refinement in renal access, radiology, instruments, and lithotripsy techniques have all contributed to improving the safety and efficacy of the modern day PCNL. Even after the advent of less invasive treatment modalities such as shock wave lithotripsy and flexible ureteroscopy , PCNL remains the gold standard treatment for large or complex renal stones and a mainstay of modern endourology. Despite these advances, PCNL still remains a challenging procedure and the most morbid procedure performed by endourologists, with opportunity for continued improvement. The goal of this section is to discuss established advances that led to the modern PCNL as well as some experimental technologies that have the possibility to impact what PCNL may look like in the future.

Patient Positioning

While PCNL has classically been performed with the patient in the prone position, there has been renewed interest in alternative patient positions, namely the supine position and its variations. Advantages of the supine position include less risk of positioning-related injuries, reduced operative time related to patient positioning, and ability to simultaneously access the urethra for retrograde access. Disadvantages include a restricted working space, difficulty in performing an upper pole puncture, and an awkwardness in manipulation of the rigid nephroscope created by the downward angle of the access tract. Since the original description of supine PCNL in 1990 by Valdivia Uria and colleagues in a series of 287 patients [44], there have been numerous modifications to the basic supine position including the split-leg [45], flank [46], oblique supine lithotomy [47], and prone flex [48], to name a few (Fig. 24.2). Modifications to the supine position were primarily borne out of the need to make the position more comfortable for the surgeons whilst still ensuring access to the urethra.