Clinical Evaluation of Miniature Flexible Scope for Diagnosis of Ureteroscope Working Channel Defects

Introduction

In recent decades, the prevalence of stone disease in the United States has increased, now affecting 10.6% of men and 7.1% of women. ¹ As a result, associated health care costs with the management of nephrolithiasis have increased. ² Flexible ureteroscopes are often utilized during the management of nephrolithiasis for both diagnosis and treatment of stones. However, because of ureteroscope design and the narrow working channel, there can be significant risks of damage to these ureteroscopes with each use. Increased utilization of ureteroscopes leads to increased repair and replacement costs from associated wear and tear, passing costs to both the patient and health care systems alike. ³

To date, there have been limited prior studies examining the use of a miniature flexible ureteroscope to evaluate endoscope damage during urologic procedures. ⁴ Prior investigations have largely examined ureteroscopes in the gastroenterology literature and discovered a high prevalence of debris, residue, visual irregularities, and damage. ⁵ These findings have been implicated in persistent ureteroscope contamination and recurrent infection outbreaks. ⁶ Herein, we not only examine ureteroscope damage but also report the first study assessing the feasibility of detecting direct damage to flexible ureteroscopes during urologic procedures. We also describe the predominant factors contributing to working channel damage over time.

Materials and Methods

Imaging review

Two investigators (T.T.C. and M.V.N.) independently reviewed and compared all videos and images to quantify and record average pre- and postprocedural damage. Damage types assessed included total damage, shavings, scratches/dents, pinhole/disruptions, and discoloration as shown in Figure 1. Since the ureteroscopes used in this study were all not-first use ureteroscopes, pre-existing markings or damages were used as landmarks to compare damages acquired after the procedure. Any discrepancies were resolved through consensus discussion and video review with a third reviewer (C.C. or J.H.B.).

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FIG. 1.

Ureteroscope damage by category.

Results

We analyzed a total of 25 procedures from August 2021 to February 2022 for patients undergoing surgery for renal stone disease using flexible ureteroscopy. Table 1 demonstrates patient demographics and clinical disease characteristics. Of the 25 patients, 8 (32%) were men and 17 (68%) were women with a mean age of 62.32 ± 13.95. Mean BMI was 30.56 ± 7.37 kg/m². Twenty-four (96%) of patients received preoperative CT imaging and 1 (4%) had ultrasound. On preoperative imaging, mean axial stone size (intended as axial width × axial length) was 14.1 ± 8.4 mm and mean stone density was 923.4 ± 458.1 HU. Table 2 depicts the number of unique ureteroscopes examined in the 25 cases. Nine unique Boa digital flexible ureteroscopes (Richard Wolf, Germany) and 1 Viper ureteroscopes (Richard Wolf) were analyzed.

Table 3 represents the intraoperative data collected. Mean operative time was 63.8 ± 34.0 min. The average number the instrument passes through the working channel was 2.1 ± 1.6. Sixteen out of 25 cases used an access sheath, 16 out of 25 cases used a basket for stone retrieval, and 11 out of 25 cases used a laser intraoperatively. The average laser time was 18.8 ± 19.7 minutes for an average total energy of 5.8 ± 4.2 KJ.

Table 4 highlights acquired ureteroscope damage. On preoperative assessment, all ureteroscopes had some form of damage (24% shave, 32% pinhole, 96% dents and scratches, and 28% discolorations). During postoperative assessment, 23/25 (92%) ureteroscopes showed additional damage with an average of 14.2 ± 8.8 imperfections found per ureteroscope (including baseline imperfections). An average of 3.7 ± 2.8 imperfections were acquired after one use. Significant differences were seen in acquired shavings (p = 0.028) and scratches or dents (p = 0.018). Of the 355 imperfections seen in total on postoperative evaluation, 0.4% were shave, 3% were pinhole, 85.8% were dents and scratches, and 10.8% were discolorations (Fig. 1). No significant differences in imperfections were seen in subgroup analyses of stone location (lower pole vs non-lower pole stone), laser energy settings (>0.8 J, ≤0.8 J, no laser), and surgery (PCNL vs ureteroscopy) (Table 5). Of note, none of the imperfections led to clinically significant events, including the need for a new ureteroscope.

Discussion

The advent of novel consumer borescopes has enabled study of the damage, debris, and residue within the working channels of endoscopes. Prior studies have suggested the utility and role of these borescopes in helping to guide reprocessing of ureteroscopes to address and prevent persistent ureteroscope contamination and infection. ⁴ Since then, various associations including the European Society of Gastrointestinal Endoscopy and International Association of Healthcare Central Service Material Management have endorsed visual inspection as a required step for reprocessing ureteroscopes. ⁷ Although borescopes have been used to examine post-use cross-contamination and infection, to date, there remain limited efforts to investigate and describe the damage caused by intraoperative manipulation to ureteroscope working channels over time. This is an important area of investigation considering on average, a new ureteroscope will require repair or replacement after just 27 uses or 14 hours of procedure time. ^{8 –11}

In our study, postprocedural review of the working channel in ureteroscopes revealed a high number of visible defects, leftover debris, as well as scratches and dents, which could be because of ureteroscope bending, laser firing, or basket passages. Consistent with prior reports, our investigation also demonstrated that every ureteroscope had visible irregularities, spanning from residual debris and discolorations to more specific damages, including pinhole defects, dents, and scratches. We also found that some damages, namely dents and scratches, might contribute to working channel deterioration overtime and significantly accumulate from a single endoscopic case alone.

Interestingly, when comparing ureteroscope discoloration preoperatively (1.74 ± 4.09) vs postoperatively (1.54 ± 3.64) we noted a decrease in discoloration (p = 0.225). The decrease in discoloration noted here is likely caused by the use of irrigation to clear the work channel of debris in the postoperative borescope assessment, which altered the quality of the video compared with the preoperative assessment coupled with possible reviewer discrepancy from our two independent investigators. As this difference was not significant (p = 0.225), we did not further investigate this finding in our study.

Although working channel defects are common and these defects increase after every use, it remains to be determined how this impacts the eventual need for ureteroscope repair or replacement, an important consideration when the average cost of each ureteroscope repair can be as high as $6,808. ¹² Cumulative damage is more than just expensive; case reports have described adverse events involving retained ureteroscopes caused by device damage during surgery requiring escalation of care and further intervention, including conversion to open surgery, additional endoscopic procedures, and use of heavy machinery such as bolt cutters. Legemate et al. in their case of retained ureteroscope discovered a damaged inner shaft, whereas Huynh et al. reported retained ureteroscopes had damages, including damage of the distal end and compromise in integrity leading to buckling. ^8,13 Manufacturers of the ureteroscopes have separately reported a variety of patient injuries caused by dysfunction and damaged ureteroscopes. ¹⁴

Hence, a consideration for the management of complex nephrolithiasis with challenging anatomy may be the use of single-use ureteroscopes. Although these disposable ureteroscopes help to ensure that ureteroscopes are free of damage and/or contamination, they can also help address the costs of acquisition, reprocessing, repair, and maintenance of reusable ureteroscopes. Several groups have highlighted the comparable clinical efficacy of single-use ureteroscopes without compromise in procedural performance with almost comparable range of costs per case ($121 to $1743 for reusable ureteroscopes vs $700 to $3180 for single-use ureteroscopes). ³ However, resource-conscious practice may preclude this form of practice conversion.

If reusable ureteroscopes remain the primary working tool of endoscopy, the introduction of novel advanced deep learning artificial intelligence (AI) has the potential to automatize the routine examination of flexible ureteroscopes before clinical use. This quality improvement endeavor may help flag ureteroscopes that have accumulated an unacceptable level of damage that may adversely impact clinical care. Although the software needs to continue to be refined to address efficiency, reliability, and automation, the overall sensitivity for AI-based detection on borescope evaluation has been reported to be as high as 91.4% when compared with the gold standard, or expert endoscopists. ¹⁵ Building multidisciplinary teams involving clinicians, endoscope manufacturing experts and AI software developers may create a predictive maintenance model making the borescope examination widely adopted to screen endoscopes and identify those in need of maintenance or repair. ⁴

Several important limitations of this study include the interobserver variability in identification and rating degree of damage and the small sample size of ureteroscopes evaluated. For future studies, assembling a multidisciplinary team of collaborators between surgeons, manufacturing experts, repair technicians, reprocessing personnel, and researchers may help improve interobserver variability and improve concordance when performing analysis of defects. In this way, ureteroscope damages induced by an excessive bending in the sheath, or those that might be induced by the extra-body manipulation such as backtable management and processing, could be evaluated too. However, these goals were beyond the scope of this study.

Secondarily, we did not use out of the box or single-use ureteroscopes, although use of single-use endoscopes would limit the exposure variables to those occurring in a single surgical setting, we sought to adhere to a pragmatic approach and proceed with the reusable endoscopes typically utilized in our institution. Future studies may benefit from examination of both single-use and reusable endoscopes with strict tracking to determine if any damage were to occur in the sterilization process as well as the operating room. Another consideration for limitation is that our study was conducted at a large academic center and teaching institution, where residents and fellows are actively engaged in clinical care.

As a result, there are variations in technical expertise in appropriate handling of ureteroscopes based on training level, affecting the wear and tear. Given the short time frame of this study, it also remains unclear when dents and scratches accumulate to form more significant defects such as shavings and pinhole disruptions. In addition, at the time of this study we used the only available on the market borescopes (to our knowledge) small enough to fit into the working channel. The devices were preproduction borescope units, that have been modified with improved reliability since the study began. Nevertheless, the quality of the video was adequate to accomplish the goal of the study.

Conclusions

The borescope visually demonstrated damage after the majority of flexible ureteroscopy procedures for nephrolithiasis. Although such disruptions may not immediately render ureteroscopes nonfunctional, they are more common than previously described and can increase maintenance costs. Further studies are needed to investigate the burden of unit damage per procedure to raise operator awareness and reduce preventable ureteroscope imperfections.