The Effect of Reusable Flexible Ureteroscope Aging on the Efficacy and Safety of Retrograde Intrarenal Surgery

Introduction

Owing to its high level of efficacy and safety, retrograde intrarenal surgery (RIRS) has become the first-line treatment for upper urinary system stones of <2 cm. ¹ The surgical preference for RIRS for upper urinary system stones has increased significantly during the past few decades. ² The main disadvantage of this surgery is its dependence on costly equipment, including flexible ureteroscopes. The historical evolution of flexible ureteroscopes started with the invention of reusable instruments, but their fragility and durability caused a significant maintenance cost for RIRS. The industry has tried to solve this problem with the invention of single-use flexible ureteroscopes. These flexible ureteroscopes have decreased the case-dependent cost of RIRS, but they have some limitations in terms of visual quality and mechanical abilities. For this reason, some clinicians still prefer to use the reusable ureteroscopes for RIRS.

The durability of reusable ureteroscopes varies between 3 and 159 cases with a median of 27 procedures.^3–8 Most of the damage occurs during the sterilization and transfer periods or because of intraoperative misuse of the flexible ureteroscope. Flexible ureteroscopes, which are able to perform a high number of cases, may also lose their mechanical properties over time. Legemate et al. documented a linear deflection loss in flexible ureteroscopes caused by ongoing surgical procedures. ⁸ This natural period is referred to as “aging of the flexible ureteroscope.” Although mechanical disability owing the aging of flexible ureteroscopes has been shown in in vitro studies, there is no study in the literature evaluating the effect of this situation on the efficacy and safety of RIRS. The aim of our study was to evaluate the effect of flexible ureteroscope aging on the efficacy and safety of RIRS.

Materials and Methods

With the approval of the local ethics committee (No: 2023.34.02.12), those patients who had undergone RIRS between 2017 and 2021 at a single center were included in the study. Although the study was designed retrospectively, the RIRSearch group database, which was formed prospectively, was used for the study. Serial surgeries were performed using the same reusable flexible ureteroscope (Storz X₂) until it was broken or malfunctioned because of the aging process. Flexible ureteroscopes that were broken by accidental mechanical damage, or during the sterilization process, were excluded from the study. In order to standardize the aging period of the instruments, flexible ureteroscopes that had performed <70 cases were also excluded from the study. The first 10 and the last 10 cases using each flexible ureteroscope were divided into two groups. Group 1 was formed by the first 10 cases in which the flexible ureteroscopes had been used, representing the youngest period of the instruments, whereas group 2 was composed of the last 10 cases in which the flexible ureteroscopes had been used, representing the oldest phase of the instruments. As we were evaluating the efficacy and safety of RIRS, we planned to exclude patients younger than 18 years of age, patients who had undergone bilateral surgery, patients who had a solitary kidney, a bleeding disorder or who were pregnant, but there was no such patient in either group.

All patients were evaluated through a physical examination, urinalysis, urine culture, serum creatinine level, and noncontrast abdominopelvic tomography before the surgery. Presurgical urine cultures were obtained, and any positive culture was treated according to the antibiogram. Second-generation cephalosporins were used for preoperative antibiotic prophylaxis. The patients gave written informed consent, and the surgical procedures were performed by the same experienced surgeon under general anesthesia. The surgery started with cystoscopy, and retrograde pyelography was performed to evaluate the upper urinary system. A 0.035-inch safety guidewire (Sensor, Boston Scientific) was routinely placed. Then, the ureteral access sheath (UAS) (10–12 Fr Bi-Flex™, Rocamed) was inserted over the working guidewire and placed 1 cm below the ureteropelvic junction, or just below the upper ureter stone, under fluoroscopic guidance. Any surgery that was performed without the insertion of a UAS was excluded from the study. The flexible ureteroscope (Storz Flex X2, Germany) was inserted through the UAS, and a holmium YAG laser with a 272 μm laser fiber was used to fragment the stones. Constant gravity-based irrigation was used at a height of 50 cm above the patient, and a hand-pumping system was used when necessary. The laser energy and pulse frequency were varied based on the stone burden, stone density, and surgeon’s preference. Stone fragments of >2 mm were extracted using a nitinol basket catheter (Dakota^®, Boston Scientific, Marlborough, MA, USA). A 4.7 Fr. double J stent was inserted into the urinary system and left in place for 3 weeks. Stone-free status was evaluated by noncontrast abdominopelvic tomography at the first month after the surgery. Stone-free status was defined as a residual stone of <3 mm. Surgical complications were evaluated by the Clavien–Dindo classification system.

The demographic and clinical properties of the patients—including age, gender, body mass index (BMI), presence of preoperative double J stent, Charlson Comorbidity Index, preoperative serum creatinine level, preoperative urine culture, presence of preoperative hydronephrosis, side of the surgery, stone location, stone size, stone volume, and stone density—were noted. The operative and postoperative data—including the operation time, hospitalization time, intraoperative complications, postoperative complications, and stone-free rates—were used to evaluate the efficacy and safety of RIRS.

Results

A total of seven flexible ureteroscopes were used during the study period. Among these flexible ureteroscopes, one was broken during transportation, and one was disabled during sterilization, so five flexible ureteroscopes were able to reach >70 cases. The number of cases for each flexible ureteroscope ranged between 87 and 133, with a median number of 107 cases. The ureteroscopes were used until the deflection mechanism was totally lost. We observed deterioration of deflection mechanisms in all the flexible ureteroscopes during the aging process, but we were not able to measure the degree of deflection loss. As we evaluated the cases of the five flexible ureteroscopes, both group 1 and group 2 were composed of 50 patients. The mean ages of the patients in group 1 and group 2 were 48.7 ± 13.6 and 50.5 ± 11.9 years, respectively (p = 0.475). The demographic and clinical properties—including gender, body mass index, renal malformation, surgical side, stone volume, stone density, and stone location—were similar between the groups (Table 1).

The operation time, lasering time, and total laser pulse were similar between the groups. The stone-free rates in group 1 and group 2 were 82.0% and 78.0%, respectively (p = 0.304). The complication rates were similar between the groups (p = 0.591) (Table 2). When we evaluated the complications according to the Clavien classification system, there were four patients with Clavien I and two patients with Clavien II complications in group 1, whereas there were three patients with Clavien I, two patients with Clavien II, and one patient with Clavien IIIb complications in group 2. The most frequent complications were clinically insignificant bleeding and postoperative fever in both the groups. The Clavien IIIb complication was stent migration, which required repositioning under general anesthesia.

Discussion

Reusable flexible ureteroscopes are costly instruments because of their fragility. The industry has tried to solve this problem with the invention of single-use flexible ureteroscopes. However, studies comparing the reusable and single-use flexible ureteroscopes have documented that the cost–benefit analysis favors the reusable ureteroscopes, as the number of cases per instrument is increased. ⁹ Martin et al. reported that the cost–benefit analysis favored reusable flexible ureteroscope after 99 cases. ¹⁰ Such studies show that the durability of a reusable flexible ureteroscope may be increased with the surgeon’s experience and the attention of the operation team. Multescu et al. reported a total of 159 cases with a single reusable flexible ureteroscope. ⁶ We were able to perform 133 cases with a single reusable ureteroscope. These data showed that, with experience and intense attention, these instruments can perform more than 100 cases.

As the durability of reusable flexible ureteroscopes has increased, the functional capacity could be diminished. Legemate et al. showed that the deflection capacity of the flexible ureteroscope deteriorated over time, reaching a significant level that could prevent the instrument from reaching the lower pole stones. They also reported that the handling of the ureteroscope was medium or difficult during the last 13 cases. ⁸ Although in vitro studies have documented these aging-related flexible ureteroscope disabilities, there is no study evaluating the effect of this process on the efficacy and safety of RIRS. We evaluated the performance of five flexible ureteroscopes during RIRS. The first 10 cases represented the youngest period, whereas the last 10 cases represented the oldest period of the flexible ureteroscopes. None of the intraoperative variables—such as operation time, lasering time, and total laser pulse—were different between the groups. Surgical time and lasering time were two important variables remarking the surgeon’s technical comfort and ability. We proposed that the mechanical disabilities of the flexible ureteroscope may interfere with the technical ability of surgeons. However, our study showed that aging-related mechanical disability of flexible ureteroscopes did not affect the technical comfort and ability of an experienced surgeon.

The stone-free rates of the first 10 and the last 10 cases were similar between the groups. These data showed that aging of the flexible ureteroscopes did not negatively affect the efficacy of RIRS. The presence of renal stones at the lower calyx and at multiple calyces is challenging localizations for flexible ureteroscopes. There were 17 patients with multiple calyx stones and six patients with lower calyx stones in group 2. That means nearly half of the patients in group 2 had challenging stone localizations for RIRS. Despite these challenging stone localizations and aged flexible ureteroscopes, the surgical success was comparable between the groups. The complication rates of both groups were also similar. There was only one patient with a Clavien IIIb complication in the aged flexible ureteroscope group, which was because of stent migration and was not directly related to the aging of the instrument. The aging of the flexible ureteroscopes did not negatively affect the safety of RIRS.

Our study had some limitations. The main limitation was related to its retrospective design, but the data of the RIRsearch study group, which were prospectively obtained, were used for the study. The second limitation was related to the objective evaluation of the aging-related flexible ureteroscope disability. We did not measure the exact degree of deflection deterioration of each flexible ureteroscope. We were able to perform more than 100 cases with reusable ureteroscopes, which was a logical number of cases after which to expect significant mechanical deterioration of the instrument to occur.

Conclusion

The aging of reusable flexible ureteroscopes did not negatively affect the efficacy and safety of RIRS. Therefore, surgeons may use the reusable types of flexible ureteroscopes until they malfunction and become totally unusable.

Author's Contributions

C.M.Y.: article writing (lead), methodology, project development, data management (lead), and conceptualization; H.C.: methodology; O.O.: resources; C.B.: article editing (equal); H.M.A.: article editing (lead); O.C.: article editing (equal); D.S.: data collection and analysis (lead); E.B.S.: data collection and analysis (equal); B.B.: data management (equal); A.K.: data collection and analysis (equal), investigation; B.O.: project administration and supervision; H.A.: project administration and supervision.