Prospective,Randomized Comparison of Dual-Lumen vs Single-Lumen Flexible Ureteroscopes in Proximal Ureteral and Renal Stone Management

Abstract

Introduction:

We sought to compare the safety, efficacy, efficiency, and surgeon experience during upper urinary tract stone management with single-lumen (SLFU) vs dual-lumen flexible ureteroscopes (DLFU).

Materials and Methods:

Seventy-nine patients with proximal ureteral or renal stone burden <2 cm were randomized to a SLFU or DLFU. We recorded times for ureteroscopy (URS), laser lithotripsy, stone basketing, as well as intraoperative and postoperative complications. The rate of stone clearance and stone free status were calculated using CT imaging. Surgeons completed a survey after each procedure rating various metrics regarding ureteroscope performance.

Results:

Thirty-five patients from the single-lumen group and 44 patients from the dual-lumen group had comparable median URS time (37 vs 35 minutes, p = 0.984) and basketing time (12 vs 19 minutes; p = 0.584). Median lithotripsy time was decreased in the dual-lumen group (single: 6 vs dual: 2 minutes, p = 0.017). The stone clearance rate was superior in the dual-lumen group (single: 3.7 vs dual: 7.1 mm³/min, p = 0.025). The absolute stone-free rate (SFR) was superior for the dual-lumen group (single: 26% vs dual: 48%, p = 0.045). No differences in intraoperative (single: 0% vs dual: 2%; p = 0.375) and postoperative complications (single: 7% vs dual: 11%, p = 0.474) were observed. Surgeons' ratings of the dual-lumen ureteroscope was superior for visibility, comfort, ease of use, and overall performance.

Conclusions:

The use of the dual-lumen ureteroscope in patients with renal and proximal ureteral stones <2 cm provided shorter lithotripsy time, higher stone clearance rates, improved SFR, and superior surgeon ratings when compared with SLFUs.

Introduction

Since flexible ureteroscopy (fURS) was introduced in 1964, improvements in endoscopic technology have led to the development of actively deflectable flexible fiberoptic ureteroscopes, which have been further enhanced by the development of distal sensor technology.^1,2 In the upper urinary tract, these advances have led to a shift from rigid to flexible ureteroscopes; expanding the variety of pathology that can be managed endoscopically. In 2010, the dual-lumen flexible ureteroscope (DLFU) (Cobra; Richard Wolf Endoscopy^®, Vernon Hills, IL) was introduced. Whereas the majority of single-lumen flexible ureteroscopes (SLFU) have a single 3.6F channel, the novel DLFU contains two channels, each measuring 3.3F.³

The benefit of dual channels was first corroborated in an ex vivo study conducted by Bach and colleagues, which reported enhanced irrigant flow compared with SLFU; improvements were potentiated as the diameter of the working tools increased.⁴ In addition to improved endoscopic visibility, Haberman and colleagues' benchtop laboratory study showed the ability to use two instruments at once resulted in fewer instrument exchanges and passes of the ureteroscope into the kidney.⁵

Our hypothesized benefits from using a dual-lumen ureteroscope included faster and higher stone clearance. To the best of our knowledge, there has not been a head-to-head clinical comparison of safety, efficacy, and efficiency of SLFU vs DLFU for upper tract stone management. As such, we performed a prospective, randomized study of SLFU vs DLFU.

Materials and Methods

Study design

We obtained Institutional Review Board approval to conduct a prospective, randomized controlled trial comparing SLFU and DLFU in a single-center trial of patients undergoing fURS for stones in the kidney and ureter. This study was registered with www.ClinicalTrials.gov (NCT02123082) in April of 2014.

Participants and randomization

All eligible patients presenting to the Department of Urology at the University of California, Irvine, between November 2016 and October 2020, requiring a flexible ureteroscope for treatment of their kidney or proximal ureteral stone disease were approached for enrollment in this study. Patients ≥18 years of age with ≤2 cm total burden in the proximal ureter or kidney were randomized to fURS using either a single-lumen or a dual-lumen ureteroscope. Exclusion criteria included: ≤18 years of age, inability to give consent, urinary tract infection, anticoagulant therapy, chronic pain disorders, pregnancy, abnormal renal anatomy (horseshoe kidney, duplicated collecting system), and prior procedure (ureteroscopy [URS], shockwave lithotripsy, or percutaneous nephrolithotomy) for the targeted stone.

Patients were randomized to either the single-lumen or dual-lumen group, followed by randomization to a specific ureteroscope based on those available at the time of surgery. Patients scheduled to undergo bilateral fURS had both kidneys independently randomized. All other procedure metrics were performed as per surgeon's preferred standard of care.

All ureteroscopes were purchased new and dedicated to the study. The five SLFUs used in this study included the FLEX-X^C and FLEX-X² (Karl Storz Endoscopy-America Inc.^®, El Segundo, CA), the URF-V (Olympus^®, Olympus, MA), and the Viper and Boa Vision (Richard Wolf Endoscopy). Two DLFUs were used in this study, the Cobra and Cobra Vision (Richard Wolf Endoscopy). The FLEX-X^C, URF-V, Boa Vision, and Cobra Vision are digital ureteroscopes, whereas fiberoptic ureteroscopes used in this study were FLEX-X², Viper, and Cobra. Further specifications of the ureteroscopes used in this study can be found in Supplementary Table S1.

Intraoperative data collection and outcomes

The primary outcome variables included efficiency as defined by fURS time and secondarily, efficacy of the procedure measured by stone clearance/stone-free rate (SFR). Other factors considered were, lithotripsy time, basketing time, complications, and surgeon ratings of the flexible ureteroscope's visibility, comfort, ease of use, and overall performance.

At the time of surgery, fURS time, laser lithotripsy duration, and stone basketing time were recorded by a dedicated team member for each case. After each procedure, surgeons completed a questionnaire rating the following on a 1 to 10 scale (poor to excellent): image quality, visibility during the procedure, ergonomics, ease of use, and overall performance of the ureteroscope. Information on demographics, stone characteristics, and outcomes were recorded. Stone burden was calculated using the largest dimension of the target stone or by adding the largest dimension of each stone when more than one stone was to be treated. The Center of Artificial Intelligence in Diagnostic Medicine at The University of California, Irvine, was able to provide the file type needed to calculate stone volumes using 3D Slicer (National Institute of Health, Bethesda, MD) for patients with CT images stored in the Picture Archiving and Communication System.

Stone volumes were calculated by two separate members of the research team blinded to all details of each procedure. The average stone volume between the two volumes calculated was used in the data analysis. All calculated stone volumes for both researchers fell within 10% of the calculated average. Absolute SFR (Grade A) was defined as the absence of any stone fragment on postoperative CT imaging, whereas relative SFR was defined as stone fragments ≤2 mm (Grade B) or ≤4 mm (Grade C) on CT images. Following surgery, 30-day complications (emergency room visit or hospital readmission) were recorded.

Sample size calculation and statistical analyses

To detect a difference of fURS time of 10 minutes between the groups using a two-sample, two-sided t-test of mean with an alpha of 0.05% assuming a fURS time of 68 minutes (±25.1 minutes) in the SLFU, and a power of 93%, we needed to enroll 300 participants.⁶

Shapiro–Wilk test was used to assess normality of continuous variables. Normally distributed continuous data were analyzed using Student's t-test and represented using mean ± standard deviation, otherwise Wilcoxon rank-sum test, median, and range were used. Chi-square tests were used to compare categorical variables. Multiple variable linear regression models were used to evaluate the effect of DLFUs based on several parameters. All statistical analyses were performed using RStudio (Boston, MA).

Results

Study population

After excluding patients without a CT image within 6 months following their operation, 79 renal units remained with a median follow-up of 50 days (Fig. 1). There were no significant differences in the age, sex, body mass index, race, or ethnicity between the two groups (Table 1). Stone location, specifically the presence of lower pole stones, was similar in the SLFU and DLFU groups (34%, 50%; p = 0.161). There were no differences in the two-dimensional measurements of preoperative stone burden or density between the groups. However, calculated stone volumes showed the DLFU group (267 mm³) to have a larger median volume compared with the SLFU group (132 mm³, p = 0.029). Ureteral access sheaths (UASs) were used in 92% of SLFU cases and 98% of the DLFU cases (p = 0.205), with a 16F UAS being passed in 35% and 57% of those, respectively (p = 0.046). No differences were observed in the number of patients with indwelling ureteral stents at the time of surgery (8/35 SLFU vs 6/44 DLFU; p = 0.286).

FIG. 1.

Flowchart of patient enrollment and randomization. Color images are available online.

Table 1.

Patient Demographics and Stone Characteristics

	Single lumen (n = 35)	Dual lumen (n = 44)	p
Age (years), mean (SD)	56.6 (±13.9)	60.1 (±13.0)	0.252
Gender, n (%)			0.237
Females	19 (54)	18 (41)
Males	16 (46)	26 (59)
Body mass index, median (range)	29.2 (19.1–62.3)	27.4 (18.8–73.4)	0.234
American Society of Anesthesiologists Score, n (%)			0.627
One	0 (0)	0 (0)
Two	21 (60)	24 (55)
Three	14 (40)	20 (45)
Cumulative stone burden (mm), median (range)	8 (2–15)	8 (2–20)	0.448
Preoperative stone volume (mm³)^*, median (range)	132 (17–1297)	267 (34–1791)	0.029
Number of stones, median (range)	2 (1–10)	2 (1–7)	0.668
HU, median (range)	733 (150–1582)	661 (178–2024)	0.421
Laterality, n (%)			0.293
Left	19 (54)	29 (66)
Right	16 (46)	15 (34)
Stone location, n (%)
Renal
Lower pole	6 (17)	15 (34)	0.090
Upper pole	2 (6)	4 (9)	0.574
Renal pelvis	6 (17)	5 (11)	0.461
Proximal ureter	12 (34)	9 (21)	0.167
Multiple locations	9 (26)	11 (25)	0.942
Flexible ureteroscope used			—
URF-V (digital)	5 (14)	—
FLEX-X² (fiberoptic)	12 (35)	—
The Viper (fiberoptic)	8 (23)	—
BOA Vision (digital)	5 (14)	—
FLEX-X^C (digital)	5 (14)	—
The Cobra (fiberoptic)	—	32 (73)
COBRA Vision (digital)	—	12 (27)
UAS used, n (%)	32 (92)	43 (98)	0.205
UAS size, n (%)
11F	5 (14)	N/A	—
14F	15 (43)	18 (42)	0.861
16F	12 (35)	25 (57)	0.046

Values in bold indicate statistically significant results.

Only patients with calculated stone volumes included.

N/A = not applicable; SD = standard deviation; UAS = ureteral access sheath.

Outcomes

The median fURS time, stone clearance time, and number of cases requiring lithotripsy were comparable between the groups (Table 2). Among cases requiring lithotripsy, the median lithotripsy time was longer in the SLFU group (6 minutes) compared with the DLFU group (2 minutes, p = 0.017). All cases requiring lithotripsy utilized Holmium:YAG laser technology. The absolute SFR was 26% in the SLFU group vs 48% in the DLFU group (p = 0.045). The relative SFR for fragments ≤2 mm (i.e., Grade B) was 51% in the SLFU group and 61% in the DLFU group (p = 0.376). Relative SFR for fragments ≤4 mm (Grade C) was 63%, in the SLFU group, compared with 77% in the DLFU group (p = 0.161).

Table 2.

Intraoperative Parameters and Surgical Outcomes

	Single lumen (n = 35)	Dual lumen (n = 44)	p
Ureteroscopy time (minutes), median (range)	37 (9–119)	35 (3–140)	0.984
Basketing time (minutes), median (range)	12 (0–81)	19 (0–56)	0.584
Cases requiring lithotripsy, n (%)	29 (83)	34 (77)	0.540
Lithotripsy time (minutes), median (range)	6 (1–35)	2 (1–61)	0.017
Clearance rate (mm³/min)^*, median (range)	3.7 (0.1–34)	7.1 (1.4–190)	0.025
Intraoperative complications, n (%)	0 (0)	1 (2)	0.375
Postoperative complications, n (%)	4 (11)	3 (7)	0.474
Stone-free outcomes, n (%)
Absolute (Grade A)	9/35 (26)	21/44 (48)	0.045
Fragments ≤2 mm (Grade B)	18/35 (51)	27/44 (61)	0.376
Fragments ≤4 mm (Grade C)	22/35 (63)	34/44 (77)	0.161

Values in bold indicate statistically significant results.

Only patients with calculated stone volumes included.

When looking at the 57 patients with both preoperative and postoperative CT images, the median stone clearance rate (mm³ of stone removed/fURS time in minutes) was greater for DLFU (7.1 mm³/min) than for SLFU (3.7 mm³/min, p = 0.025). One intraoperative complication occurred, a urothelial tear in the upper ureter of a DLFU group participant. The patient had the stent removed 2 weeks after surgery and had no further complications or stricture with over 2-year follow-up. Four patients in the SLFU group, and three patients in the DLFU group had an Emergency Department visit within 30 days after their surgery; these complications were all Clavien–Dindo Grade II (Table 2).

On multiple variable linear regression, the odds ratio for the absolute SFR of those undergoing fURS by DLFU was 9.17 when compared with SLFU (p = 0.050) (Table 3). The predicted absolute SFR and lithotripsy times from this regression model of various stone locations, ureteroscope type, and UAS size is seen in Table 4.

Table 3.

Multiple Variable Linear Regression Models of Single-Lumen vs Dual-Lumen Flexible Ureteroscopes for Absolute Stone-Free (Grade A) Status and Lithotripsy Time

Group	Absolute stone-free (Grade A), mean (95% CI)	p	Lithotripsy time, mean (95% CI)	p
Lower pole stones	9.17 (1.00–83.7)	0.050	0.59 (0.29–1.23)	0.164
Non-lower pole stones	1.87 (0.57–6.21)	0.304	0.73 (0.40–1.33)	0.302
16F UAS	1.85 (0.44–7.75)	0.402	0.86 (0.42–1.75)	0.682
<16F UAS	3.24 (0.85–12.4)	0.085	0.54 (0.29–1.01)	0.057

Values in bold indicate statistically significant results.

CI = confidence interval.

Table 4.

Predicted Absolute Stone-Free Rate and Lithotripsy Time Based on Ureteroscope (Single vs Dual Lumen), Stone Location and Ureteral Access Sheath Size

Group	Absolute stone free (%) (Grade A), mean (95% CI)	Lithotripsy time (minutes), mean (95% CI)
SLFU non-lower pole stones	34.8 (18.4–55.8)	4.16 (2.36–6.93)
DLFU non-lower pole stones	50.0 (30.2–69.8)	2.75 (1.41–4.81)
SLFU lower pole stones	8.3 (1.2–41.3)	3.62 (1.55–7.38)
DLFU lower pole stones	45.4 (26.5–65.9)	1.74 (0.77–3.26)
SLFU <16F UAS	21.7 (9.3–42.8)	4.66 (2.68–7.69)
DLFU <16F UAS	47.3 (26.8–68.9)	2.04 (0.90–3.88)
SLFU 16F UAS	33.3 (13.1–62.4)	2.88 (1.14–6.02)
DLFU 16F UAS	48.0 (29.6–66.9)	2.34 (1.21–4.04)

DLFU = dual-lumen flexible ureteroscope; SLFU = single-lumen flexible ureteroscope.

Surgeon comfort, visibility, ease of use, and overall performance of the flexible ureteroscope were all significantly greater for DLFU (Table 5).

Table 5.

Postoperative Survey Responses for Single-Lumen and Dual-Lumen Flexible Ureteroscopes

	Single lumen (n = 35)	Dual lumen (n = 44)	p
Comfort, median (range)	7 (1–10)	9 (2–10)	0.001
Visibility, median (range)	5 (1–10)	9 (4–10)	0.001
Ease of deflection, median (range)	8 (2–10)	9 (7–10)	0.001
Overall, median (range)	6 (1–9)	9 (3–10)	0.001

Values in bold indicate statistically significant results.

Discussion

As of April 2021, the only investigation of dual-lumen URS in primary medical literature has come from in vitro, ex vivo, and in vivo laboratory studies. Haberman and colleagues demonstrated no significant differences in deflection angles between SLFU and DLFU, while Bach and colleagues' ex vivo study showed irrigation through a DLFU resulted in better irrigant flow than SLFU.^4,5 Lusch and colleagues compared three SLFU with DLFU; demonstrating superior irrigation flow and higher maximum illumination in their in vitro models, as well as significantly shorter evacuation times of a standardized blood-filled field during in vivo URS.⁷ The current study represents the first prospective randomized comparison of clinical efficiency and effectiveness between SLFU and DLFU, reporting lower median lithotripsy times, higher median stone clearance rates, and higher SFRs when using a DLFU.

During this study, standard stone measurements (largest linear dimension) as well as calculated stone volumes were considered. Although similar standard measurements were observed between the two groups, stone volume calculations demonstrated that the DLFU group had a significantly larger stone volume but significantly shorter lithotripsy time. This discrepancy could be due to a few observations, including a trend toward a greater proportion of lower pole calculi (DLFU: 50% vs SLFU: 34%, p = 0.161); it is well established that lower pole calculi are more challenging and time-consuming to treat than calculi in other areas of the kidney.^8,9 This could well be the reason for the coexistence of a similar overall URS time. In this regard, minimizing laser lithotripsy time is important as longer laser lithotripsy times are associated with myriad concerns: increased risk of intraoperative and postoperative bleeding (e.g., renal subscapular hematomas),^10
–12 increased intracaliceal pressure, temperature spikes that potentially could result in urothelial injury or long-term renal tissue damage,^13
–15 higher rates of ureteroscope damage, and safety concerns for the surgeon and operating room staff.^16,17

A new stone protocol CT-based “grading” system was created and employed to accurately evaluate procedural efficiency and allow comparison in future studies. In this system, absolute stone free (Grade A) is defined as no stones present on the CT scan. Relative stone free refers to either fragments remaining that are ≤2 mm (Grade B) or ≤4 mm (Grade C).^18,19 A more widely adopted postprocedural CT-based efficacy rating system would enable consistent comparisons between studies in the future, empowering the development of meaningful meta-analyses. The CT scans in the current study were standard of care and done at numerous sites. As such, the depth of the cuts in this study varied (2, 3, or 4 mm).

In the current study, using CT-based assessments, the absolute SFR was 48% in the DLFU group; significantly greater than the absolute SFR for the SLFU group, despite a larger stone volume in the DLFU group. Of note, unlike other reports, any stone noted on the postoperative CT scan excluded the patient from being categorized in the absolute stone-free group. As such, those with calculi deemed by the surgeon to be in inaccessible calices were not excluded.^20,21

There are several confounders that need to be considered in a study of this nature, including lithotripsy vs direct extraction of a stone, fiberoptic vs digital endoscopy, and the use of an UAS. Additional analyses examining if digital vs fiberoptic technology impacted the measured outcomes of this study showed no differences. The presence and the size of the UAS deployed were the only two significant differentiating surgical factors between the two groups. Over one-third of study participants were also consented to participate in another study at our institution investigating the force required to place an UAS.²² Of those not consented to participate in our “force” study, UAS placement and size was at the discretion of the surgeon.

DLFU scored consistently higher on the surgeons' questionnaire for all four metrics. Surgeons reported that the DLFU provided significantly better endoscopic visibility. The second variable that the surgeons subjectively reported was the comfort in using the DLFU. Overall, the surgeons uniformly preferred the DLFU to SLFU.

There are several limitations to this study, the most obvious being the premature termination before enrolling the 300 patients that would have tested the hypothesis of decreasing operative time by 10 minutes with DLFU vs SLFU. This was due to several factors, the most important being the favorable DLFU results after an interim analysis and desire of our institutions' surgeons to use the DLFUs when available. Further limitations included the necessity of postoperative CT imaging to calculate stone volumes and absolute/relative stone clearance rates; 45 enrolled patients had to be dropped from the study due to lack of a postoperative CT scan. Other limitations include the usage of seven different ureteroscopes by eight different surgeons and the reliance on questionnaires to assess surgeon ureteroscope preference. Also, in a study of this nature, there are myriad confounders: fiberoptic vs digital endoscopes, presence, or absence of laser lithotripsy, as well as size of the UAS used.

Conclusions

The use of DLFU in patients undergoing fURS for proximal ureteral and/or renal stone burden ≤2 cm provided several clinically significant advantages regarding the efficiency and efficacy of the procedure vs SLFU: shorter lithotripsy time, more rapid stone clearance, and a trend toward improved absolute SFR for renal stones.

Footnotes

Authors' Contributions

The authors confirm contribution to the article as follows: Conceptualization and methodology: D.L., S.S., Z.O., R.M.P., and J.L. Data collection: A.B., A.P., R.K., L.X., R.B.A., J.M.S., F.A.J., and E.P. Software and data curation: A.B., A.P., L.L., and E.P. Writing (original draft, review, and editing): A.B., A.P., Z.O., A.S.A., R.B., R.K., L.X., R.B.A., L.L., J.M.S., F.A.J., E.P., D.L., S.S., P.J., R.M.P., and J.L. Supervision and project administration: R.M.P., P.J., and J.L. Funding acquisition: J.L.

Author Disclosure Statement

The authors have no financial interest to declare in relation to the content of this article.

Funding Information

Richard Wolf Endoscopy provided funding to purchase ureteroscopes.

Supplementary Material

Supplementary Table S1

Abbreviations Used

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