Single-Use Digital Flexible Ureteroscopes as a Safe and Effective Choice for the Treatment of Lower Pole Renal Stones: Secondary Analysis of a Randomized-Controlled Trial

Abstract

Objective:

To compare the efficacy and safety of a single-use digital flexible ureteroscope (FURS) and a reusable FURS for the treatment of lower pole stones (LPS) smaller than 20 mm.

Patients and Methods:

We analyzed the data of 49 patients with LPS from our previous multicenter, randomized, open-label clinical trial in four hospitals in China. All patients underwent FURS for LPS with a single-use FURS ZebraScope™ (trial group) or a reusable FURS URF-V (control group). The efficacy endpoints assessed were the 1-month postsurgical stone-free rate (SFR), operative time, length of postoperative hospital stay, and mean reduction in hemoglobin level. The safety outcomes assessed were the presence of adverse events (AEs), severe AEs (SAEs), and postoperative complications.

Results:

The demographic and preoperative parameters were comparable between the two groups. The 1-month SFR was 84.00% for the ZebraScope group and 58.33% for the reusable flexible ureteroscope (URF-V) group (p < 0.05). There was no difference between the two groups in the operative time (p = 0.665), length of hospital stay (p = 0.308), presence of postoperative complications (p = 0.307), presence of AEs (p = 0.483), and the presence of SAEs (p = 0.141).

Conclusions:

This study demonstrates that single-use digital FURS is a safe and effective option and can offer higher SFR than the reusable FURS in the treatment of LPS smaller than 20 mm. We recommend single-use digital FURS as an alternative to reusable FURS for the treatment of LPS.

The Clinical Trial Registration number: ChiCTR1900021615.

Introduction

Poor clearance of fragments and difficulty accessing lower pole calices account for differences in treatment outcomes compared with stones in other locations in the kidney. It has been reported that the stone-free rate (SFR) after extracorporeal shockwave lithotripsy (SWL) for lower pole stones (LPS) is 25%–90%.^1
–3 The residual fragments of LPS still play a negative role in stone formation, which can become the core for further growth and formation of new stones.⁴

The choice of treatment for patients with LPS remains controversial. SWL is a better choice for LPS less than 1 cm in diameter, while percutaneous nephrolithotomy (PCNL) is the first choice for LPS larger than 2 cm.^5,6 For LPS 10–20 mm, Raman and Pearl recommended that PCNL is the best management, although ureteroscopy is an option in patients who are not considered candidates for PCNL.⁵ Likewise, a survey of 205 urologists reported by Gerber revealed that 65% preferred SWL and 30% would advise PCNL.⁷

Technical improvements, the introduction of a wide range of disposables, and improvements in digital imaging quality for flexible ureteroscope (FURS) have led to increased use and shorter operating times.⁴ Grasso and Ficazzola⁸ used FURS to treat LPS. The SFRs of LPS were 82%, 71%, and 65% with stone less than 1 cm, 1–2 cm, and greater than 2 cm, respectively.

In recent years, single-use FURS was introduced and has been favored by urologists. Single-use FURS allows doctors to use laser lithotripsy with higher power and longer time. In addition, LPS is one of the high-risk factors for damage caused by the repeated use of FURS. Single-use FURS can reduce the psychological pressure on doctors caused by damage to medical equipment. Therefore, single-use FURS may have more advantages in the treatment of LPS. However, there are few clinical studies on whether single-use FURS has unique advantages over reusable FURS and can provide a higher SFR for LPS treatment. Therefore, we analyzed the data of LPS treatment using single-use FURS and evaluated the effectiveness and safety to provide the basis for clinical treatment of LPS.

Patients and Methods

Data source and trial process

We analyzed the data of 49 patients with LPS from our previous multicenter, randomized, open-label clinical trial in four hospitals in China (Registration No.: ChiCTR1900021615).⁹ The clinical study was approved by the Ethics Committees of the Lanzhou University Second Hospital (2018-QX-029), the Second Hospital of Tianjin Medical University (2018K032), Peking University Shougang Hospital (IRB-2018-016-02), and Beijing Xuanwu Hospital (2018-007-1).

Before the procedure, all patients signed an informed consent form and were enrolled in the study after a routine preoperative evaluation, including urinalysis, urine culture, complete blood count, renal function, electrolyte determination, and nonenhanced CT. We carried out the randomization using computerized random numbers. The allocated treatment for each patient was recorded in concealed envelopes. After achieving the patients' consent, the concealed envelopes were opened to identify patients for each group. All patients underwent FURS for LPS with a single-use FURS ZebraScope™ (trial group) or a reusable FURS URF-V (control group). All patients received plain abdominal kidney, ureter, and bladder radiograph (KUB) and CT scans at 1 month postoperatively. KUB was performed before the stent removal to determine whether Double-J stent becomes displaced and if prolonged the dwelling time due to the existence of residual stones. CT scan was performed after the stent removal to assess whether residual stones exist and the allocation and size of them. The radiologists who performed the CT scan and the KUB were blinded to the study objectives and protocols.

The structures and major parameters of the ZebraScope were introduced in our previous study.⁹ The comparison of the performance of the two ureteroscopes used in this study is shown in Table 1. Intraoperative endoscopic images of retrograde intrarenal surgery (RIRS) using single-use and reusable digital FURS are shown in Figure 1.

FIG. 1.

Intraoperative endoscopic images of RIRS using single-use (A) and reusable digital FURS (B). FURS = flexible ureteroscope; RIRS = retrograde intrarenal surgery.

Table 1.

The Comparison of the Performance of the Two Ureteroscopes Used in This Study

FURS	Country	Outer diameter (F)	Tip diameter (F)	Working channel (F)	Range of deflecting	Weight (g)	Length (mm)
ZebraScope™	China	8.7	7.4	3.6	Upward 275° Downward 275°	185	670
URF-V	Japan	9.9	8.5	3.6	Upward 180° Downward 275°	NA	680

FURS, flexible ureteroscope; NA, not available; URF-V, reusable flexible ureteroscope.

Surgical technique

All the procedures were performed by skilled surgeons with the use of FURS. Before the surgery, the surgeon checked the device to confirm that the FURS was in good working order. The surgeries were performed in the lithotomy position under general anesthesia. An F8/9.8 rigid ureteroscope was placed into the ureter to dilate the ureter to facilitate the placement of a ureteral access sheath (UAS). Then, a 0.038-inch Zebra guidewire was passed through the involved ureter as the safety guidewire. After that, a 12F/14F Flexor UAS was placed in the ureter of every patient. The ZebraScope or URF-V FURS was placed into the pelvis through the UAS. Lithotripsy was performed with a holmium laser using 200 μm fibers at 0.8–1.5 J and 10–20 Hz. All stones are broken into powder as much as possible. A 1.7F or 2.4F nitinol basket was used to extract larger fragments. A 6F Double-J stent was indwelled for 4 weeks, and a Foley catheter was placed in the site postoperatively. We completed every case with a single ZebraScope in the trial group.

Inclusion and exclusion criteria

The inclusion criteria were as follows:

Maximum stone diameter of 6–20 mm confirmed by a CT scan.

Stones located in the lower pole of the kidney.

Adults aged 18 to 75 years.

The exclusion criteria were as follows:

Coagulopathy or current anticoagulation therapy.

Anatomic abnormalities such as horseshoe kidneys, caliceal diverticula, ureteral strictures, ureteropelvic junction obstructions, infundibular stenoses, and impassable urethral strictures.

Comorbidities that interfere with participation in or completion of the study, for example, myocardial infarction, stroke, congestive heart failure, severe chronic respiratory lung disease, cancer, uncontrolled diabetes mellitus, pregnancy, mental illness, and severe systemic diseases or psychosis.

Severe deformity of the hip joint that prevents meeting the requirement of the operation position.

Patients who participated in other clinical trials within 3 months.

Outcome assessment and statistical analysis

The efficacy endpoints assessed were the 1-month postsurgical SFR, operative time, length of postoperative hospital stay, and mean reduction in hemoglobin level. The safety outcomes assessed were the presence of adverse events (AEs), severe AEs (SAEs), and postoperative complications, including pain, fever, renal hematoma, hematuria, pelvicaliceal system injury, urinary sepsis, and Steinstrasse formation. An AE was defined as any untoward medical occurrence in the trial. A serious AE was defined as any event that results in death or life-threatening events, or which results in inpatient hospitalization or prolongation of existing hospitalization. When AEs or SAEs occurred, the surgeon investigated whether these were associated with the use of the device. The operative time was defined as the time from ureteroscope insertion until the end of Foley cauterization. “Stone-free” status was defined as no residual stone or stones ≤4 mm by a plain CT scan 1 month after stent removal.

The data were analyzed by using Statistical Package for the Social Sciences, V. 22.0 (SPSS; SPSS, Inc., Chicago, IL, USA). Continuous variables were compared by independent samples t-tests. Categorical variables were compared by the chi-square or Fisher's exact test, as appropriate. All analyses were planned as the intention to treat.

Results

Patients and stone characteristics

Both groups were comparable. The patient and stone characteristics are shown in Table 2. The mean age of the patients in the trial group was 52.72 years, with a mean body mass index (BMI) of 25.32 kg/m². The mean age of the patients in the control group was 54.00 years, with a mean BMI of 26.47 kg/m². The mean stone sizes were 11.35 and 11.40 mm in the trial and control groups, respectively. The mean CT values were 927.56 and 967.53 HU in the trial and control groups, respectively. The mean levels of serum creatinine were 84.83 and 94.81 μmol/L in the trial and control groups, respectively. No difference was observed among the trial and control groups in terms of anatomical factors, including infundibulopelvic angle (IPA) (53.96° vs 52.08°, p = 0.638), infundibular width (IW) (5.79 mm vs 5.91 mm, p = 0.540), and IL (26.74 mm vs 26.42 mm, p = 0.796). The mean levels of blood urea nitrogen were 5.07 and 5.21 mmol/L in the trial and control groups, respectively. Ten (40%) patients in the trial group and 12 (50%) patients in the control group were prestented preoperatively. No significant differences were observed between the groups in terms of age, sex, stone size, CT value, procedural laterality, anatomical factors, renal function, or rate of preoperative ureteral stenting (all parameters p > 0.05).

Table 2.

Baseline Demographics and Clinical Characteristics

Characteristics	Trial group (n = 25)	Control group (n = 24)	p
Age (years), mean ± SD	52.72 ± 11.79	54.00 ± 12.69	0.716
Sex, n (%)
Male	21 (84)	19 (79.17)	0.662
Female	4 (16)	5 (28.83)
BMI (kg/m²), mean ± SD	25.32 ± 3.92	26.47 ± 3.49	0.282
CT value (HU), mean ± SD	927.56 ± 323.72	967.53 ± 279.35	0.670
Stone size (mm), mean ± SD	11.35 ± 5.19	11.40 ± 4.53	0.974
Procedural laterality, n (%)
Left	15 (60.00)	15 (62.5)	0.858
Right	8 (32.00)	6 (25.00)	0.588
Bilateral	2 (8.00)	3 (12.50)	0.603
Anatomical factors
IPA (°), mean ± SD	53.96 ± 14.25	52.08 ± 13.42	0.638
IW (mm), mean ± SD	5.79 ± 0.78	5.91 ± 0.68	0.540
IL (mm), mean ± SD	26.74 ± 4.86	26.42 ± 3.60	0.796
Renal function, mean ± SD
Serum creatinine (μmol/L)	84.83 ± 18.41	94.81 ± 19.68	0.206
Blood urea nitrogen (mmol/L)	5.07 ± 1.15	5.21 ± 1.52	0.713
Preoperative ureteral stenting, n (%)	10 (40)	12 (50)	0.482

BMI, body mass index; IL, infundibular length; IPA, infundibulopelvic angle; IW, infundibular width.

Surgical outcomes

The surgical outcomes are shown in Table 3. The 1-month SFR was 84.00% for the ZebraScope group and 58.33% for the URF-V group (p < 0.05). The mean operative times were 40.52 and 42.88 minutes in the trial and control groups, respectively (p = 0.665). During surgery, the ureteroscopic basket was used in 96.00% of patients in the trial group and in 83.33% of patients in the control group, and the difference was not significant (p = 0.257). The mean decreases in hemoglobin were 8.68 and 7.75 g/L in the trial and control groups, respectively (p = 0.748). The mean lengths of hospital stay were 7.52 and 8.42 days in the trial and control groups (p = 0.308), respectively. The mean lengths of postoperative hospital stay were 1.76 and 2.08 days in the trial and control groups, respectively (p = 0.307).

Table 3.

Comparison of the Efficacy and Safety Between the Trial and Control Groups

Surgical outcomes	Trial group (n = 25)	Control group (n = 24)	p
SFR, n (%)	21/25 (84.00)	14/24 (58.33)	0.047
Operative time (minutes), mean ± SD	40.52 ± 17.63	42.88 ± 20.14	0.665
Use of basket, n (%)	24/25 (96.00)	20/24 (83.33)	0.257
Mean drop in hemoglobin level (g/L), mean ± SD	8.68 ± 10.37	7.75 ± 9.72	0.748
Hospital stay (days), mean ± SD	7.52 ± 2.86	8.42 ± 3.23	0.308
Postoperative hospital stay (days), mean ± SD	1.76 ± 1.13	2.08 ± 1.06	0.307
Presence of postoperative complications, n (%)	2 (8)	0 (0)	0.157
Adverse events, n (%)	8 (32)	10 (41.67)	0.483
Serious AEs, n (%)	0 (0)	2 (8.33)	0.141

AEs = adverse events; SFR = stone-free rate.

Postoperative complications occurred in 0 (0%) patient in the control group and 2 (8%) patients in the trial group (p = 0.157), including fever and renal colic caused by the expulsion of fragments. The AE rates were 32% and 41.67% in the trial and control groups, respectively (p = 0.483). The SAE rates were 0% and 8.33% in the trial and control groups, respectively (p = 0.141). AEs included hematuria, lower urinary tract symptoms, fever, lung infection, and nausea. SAEs included ureteral stent migration and postrenal acute renal failure.

Discussion

Our results show that the 1-month SFR following a single-use FURS was significantly higher than that after a reusable FURS for LPS (84.00% vs 58.33%, p < 0.05). The possible explanations are as follows. The single-use FURS used in the study can deflect 275° in the upward and downward directions, and the deflection loss is small when the operating instruments are placed. To a certain extent, it can overcome the lithotripsy difficulty caused by acute IPA. Abdelsehid and colleagues¹⁰ demonstrated that deflection was impaired when different instruments were placed in the working channels. With 200 μm laser fiber or 365 μm laser fiber, the FURS showed a decrease in deflection by 3.1%–22.7% or 25.9%–46.3%. In the same case, single-use FURS outperformed fiber-optic FURS for all other settings in terms of deflection loss.¹¹ In addition, the outer diameter of the ZebraScope is less than that of URF-V (8.7F vs 9.9F). Higher irrigation flow and a clearer field of vision brought by a smaller outer diameter are favorable to the enhancement of operative efficiency and effect. Furthermore, the use of single-use products allowed doctors to boldly attempt procedures, without the concern of damage to reusable ureteroscopes with high purchase costs. LPS was one of the significant risk factors for FURS damage, which increased the psychological pressure on doctors.

In our study, we found that the SFR after reusable FURS treatment for LPS was similar to the prior studies. Koo and coworkers¹² evaluated the clinical outcomes of reusable FURS compared with those of SWL in 88 patients, and the results showed that the SFR of FURS was 59.4%, which is similar to the present study. Bozzini and colleagues¹³ prospectively evaluated the efficacy and safety of RIRS, SWL, and PCNL in the treatment of 1–2 cm LPS. The SFR was 82.1%, and the complication rate was 14.5% after RIRS. In addition, the results of our previous study showed that when the stone location is factored out, the 1-month total SFR was 77.78% for the single-use FURS group and 68.25% for the reusable FURS group.⁹ Compared with the total SFR, the SFR of LPS was lower in the URF-V group and was similar in the single-use FURS group. A possible reason for this is less outer diameter and deflection loss of the single-use FURS.

The present study indicates that there is no significant difference between the trial and control groups in the rate of complications (8% vs 0%, p = 0.157), AEs (32% vs 41.67%, p = 0.483), and SAEs (0% vs 8.33%, p = 0.141). There were no device-related AEs and SAEs in the present study. So, single-use FURS ZebraScope may be a safe option for LPS and worth further clinical application and promotion.

The measured value of the IPA correlated in a statistically significant manner with the overall success of FURS for LPS.¹⁴ Berkan and coworkers¹⁵ evaluated 67 patients with LPS who received RIRS, and the results showed that the lower pole anatomy, especially IPA, had a significant effect on the SFR of LPS after RIRS. Studies conducted by Jessen and colleagues¹⁶ showed that IPA and IL have adverse effects on SFR. Stephanie and coworkers¹⁷ retrospectively reviewed 243 patients with LPS treated with FURS and analyzed the univariate and multivariate influencing factors of SFR. The results showed that the residual stone fragments were negatively related to the more acute IPA and the larger stone diameter. Anatomical factors, including IPA (53.96° vs 52.08°, p = 0.638), IW (5.79 mm vs 5.91 mm, p = 0.540), and IL (26.74 mm vs 26.42 mm, p = 0.796), were similar statistically between the groups in our study. The data of anatomical factors in the two groups were consistent and comparable.

Based on the present study, we propose the following suggestions for the treatment of LPS using FURS. First, if feasible, the LPS can be moved to the pelvis to lower the complexity barrier of lithotripsy. Second, it is necessary to evaluate the parameters of renal anatomy before surgery, including IPA, IW, and IL. For patients with LPS whose IPA of the involved kidney is acute, FURS with greater deflection should be selected. Third, the stones should be powdered as much as possible during surgery. For larger stone fragments, the nitinol basket should be used to extract or relocate from the lower calix. In addition, combined with the physical stone removal method, the SFR after lithotripsy can be improved.

This study has several limitations. Further follow-up was not conducted to evaluate the recurrence rates and 3-month SFR of LPS after FURS treatment. Besides, the sample size in this study was relatively small.

Conclusion

Our study demonstrates that single-use digital FURS (ZebraScope) is a safe and effective option and can offer a higher SFR than the reusable digital FURS in the treatment of LPS smaller than 20 mm. We recommend single-use digital FURS as an alternative to reusable digital FURS for the treatment of LPS.

Footnotes

Acknowledgment

The authors would like to thank Ms. Juan Deng for providing assistance with calculating the IPA, IW, and IL.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

This work is supported by the National Natural Science Foundation of China (NSFC: 81874088), the Fundamental Research Funds for the Central Universities (lzujbky-2018-kb14), the Science and Technology Project of Tianjin (17ZXMFSY00060), the Education Commission Research Project of Tianjin (2017KJ208), and the Key Laboratory Fund Project of the Second Hospital of Tianjin Medical University (2017ZDSYS14).

Abbreviations Used

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