A Comparative Study of Flexible Navigable Vacuum-Assisted Ureteral Access Sheath and Traditional Ureteral Access Sheath in Retrograde Intrarenal Surgery: Evaluating the Impact of Hydronephrosis on Stone-Free Rate and Complications

Abstract

Background:

Retrograde intrarenal surgery (RIRS) is a widely used minimally invasive technique for renal stone management. Recently, flexible navigable vacuum-assisted ureteral access sheaths (FV-UASs) have been introduced to enhance RIRS outcomes. This study aimed to evaluate the efficacy of FV-UAS compared with traditional UAS (T-UAS) in RIRS, with a specific focus on the impact of hydronephrosis.

Methods:

A retrospective multicenter study was conducted involving 207 patients undergoing RIRS for renal stones. Patients were divided into two groups based on the type of UAS used: FV-UAS (n = 105) or T-UAS (n = 102). Demographic data, stone characteristics, operative time, complications, and stone-free rates (SFRs) were analyzed. The degree of hydronephrosis was assessed using the Society of Fetal Urology grading system.

Results:

The FV-UAS group demonstrated significantly shorter operative times (median: 50 minutes vs 57.5 minutes, p = 0.039) and a higher SFR at 1-week postoperatively (47.6% vs 23.5%, p < 0.001) compared with the T-UAS group. However, there was no significant difference in SFR at 1 month (75.2% vs 68.6%, p = 0.290). Postoperative fever was significantly lower in the FV-UAS group (3.8% vs 18.6%, p = 0.001). Importantly, the degree of hydronephrosis did not significantly impact the outcomes that performed RIRS with FV-UAS.

Conclusion:

FV-UAS offers potential advantages over T-UAS in RIRS, including shorter operative times, improved early stone-free status, and reduced postoperative complications. Hydronephrosis did not appear to affect the efficacy of FV-UAS. These findings suggest that FV-UAS may be a valuable tool in optimizing RIRS outcomes.

Introduction

Urolithiasis is a worldwide common disease and nowadays, all symptomatic stones in the renal collecting system require active management with appropriate tools to limit the risk of obstruction, recurrent infection, and troublesome renal colic attacks that affect quality of life to a certain extent.^1

–4 Over the past two to three decades, the treatment of kidney stones has undergone significant advancements as a result of the innovations in instrument technology and evolving new management concepts. Regarding the options available for minimally invasive stone management, shock wave lithotripsy (SWL), retrograde intrarenal surgery (RIRS), and percutaneous nephrolithotomy have been applied with varying certain indications and success rates.⁵ Among these alternatives, RIRS has become a preferred option for renal stones sizing smaller than 20 mm, demonstrating better outcomes than SWL.^6,7 Current urolithiasis guidelines recommend both SWL and RIRS as the equally preferable treatment options for such stones.⁸ However, it is well known that the stone fragments left to spontaneous passage after RIRS may cause increased recurrence rates and reintervention especially when the stone size increases.^9,10 Taking this fact into account, to achieve all cases stone free after RIRS, some innovations in the consumables used during RIRS have been introduced to increase the stone-free rate (SFR) and reduce complications. Among these game changers, novel laser types, smaller scopes, and accompanying equipment such as baskets and access sheaths could be stated.¹¹

Concerning these instruments, in addition to enabling several entries of instruments into the ureter along with improved visualization, ureteral access sheaths (UASs) have been found to provide an effective drainage during RIRS, which certainly reduces the risk of infection, one of the most crucial complications following these procedures. In the light of the significantly increased SFR a due to the successful use of these access sheaths and the experience gained so far in these applications, novel design flexible navigable vacuum-assisted UASs (FV-UASs) were recently introduced into clinical practice. In addition to reducing intrarenal pressure compared with the traditional UAS (T-UAS), FV-UAS can move within the kidney with the flexible part at the tip, which gives the ability to suction smaller fragments and stone dust formed after lithotripsy.^12,13 Although the advantages of these new modalities have been evaluated and confirmed in some studies, their true potential in RIRS requires further investigation. Related to this critical issue, despite the successful outcomes in kidneys with normal characteristics reported so far, it needs to be kept in mind that the efficacy of the FV-UAS may change based on the anatomical characteristics, as well as the degree of hydronephrosis during the time of management.^12
–14 In other words, the true efficacy of these new game-changing modalities needs to be evaluated in stone as well as renal anatomy-related abnormal conditions. To our best knowledge, our current study is the first one focusing on the possible impact of both the presence and degree of hydronephrosis on the success as well as the complication rates of RIRS performed with FV-UAS.

This study aimed to compare two different types of UAS, namely FV-UAS and T-UAS, regarding the SFR and complication rates in patients undergoing RIRS. In addition, we aimed to assess whether the degree of hydronephrosis in patients undergoing this procedure could affect the outcomes.

Materials and Methods

This retrospective multicenter study was conducted in accordance with the principles outlined in the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines to ensure standardized and transparent reporting of the study design, methods, and results.¹⁵ A total of 207 patients across five tertiary centers in Turkey, 105 of whom were operated on with FV-UAS at three centers and 102 with T-UAS at two centers between March 2024 and October 2024, were included into the study program. The inclusion criteria were patients aged 18 years and older undergoing unilateral RIRS with the use of an access sheath for kidney stones sizing less than 2 cm. All patients underwent a preoperative computed tomography (CT) scan evaluation, and patients with abnormal renal anatomy, ureteral stones, or incomplete medical records were excluded from the study. Demographic data, type of UAS used, degree of hydronephrosis, stone characteristics (laterality, number, localization, size, and density with Hounsfield Unit measurement), operation time, perioperative and postoperative complications were all recorded. Stone size was recorded as the largest diameter (in mm) assessed in CT images, and stone surface area was also measured. Total stone burden was recorded in patients with multiple stones. The Society of Fetal Urology grading system was used to assess the severity of hydronephrosis based on CT imaging findings. Patients with hydronephrosis grade 0–1 were defined as low-grade hydronephrosis and grade 2–4 as high-grade hydronephrosis.

Operative details

All cases were performed at each center by a single surgeon with at least 5 years of experience in endourology and RIRS, with each surgeon performing a minimum of 50 RIRS cases annually. The decision to include patients was based on the availability of the FV-UAS device at the participating centers and the standardization of its use in clinical practice.

All patients had a negative urine culture before the procedure. In cases of urinary tract infection, appropriate antibiotic therapy was applied in accordance with the culture sensitivity tests. Following prophylactic antibiotic administration, two 0.035-inch flexible guidewires (one for working and one for safety) were placed into the collecting system during semirigid ureteroscope. FV-UAS or T-UAS was inserted over the guidewire under fluoroscopy control. After accessing with single-use flexible ureteroscope (Hugemed HU30, Shenzhen HugeMed Medical, China), the stone was fragmented with 272 μm Holmium YAG laser fiber with settings varying between 10 and 20 W energy. While a 10/12F hydrophilic access sheath (Plasti-med, Istanbul, Turkey) was used for T-UAS, a 10/12F ClearPetra (Well Lead Medical, China) access sheath was used for FV-UAS. When using FV-UAS, the suction channel was connected to the vacuum device, and negative pressure was set at a range of −50 to −150 mm Hg to maintain optimal suction conditions without causing any collapse. Following stone fragmentation, a 4.8F Double-J stent and a Foley catheter were placed in all patients. Operative time was calculated as the time between semirigid ureterorenoscopy and urethral catheter insertion.

Follow-up

Urethral catheter was removed on postoperative day 1, and the patients were discharged. At postoperative 1 week and 1 month, stone-free status was evaluated according to low-dose CT scan as grade A (no stones on CT scan), grade B (≤2 mm fragments), grade C (2.1–4 mm fragments), and not stone free (>4 mm fragments). Stone-free status was defined as if the patient was completely stone free that defined above as grade A. Double-J stent was removed within 2 weeks in all patients unless any other indication requiring prolonged stenting was not present.

Statistical analyses

The data were analyzed using SPSS version 26 (IBM Corp, Armonk, NY, USA). Categorical variables in the study were presented with frequency (n) and percentage (%). To assess the normality of quantitative data, a one-sample Kolmogorov–Smirnov test was employed. Normally distributed variables were presented as mean ± standard deviation, while nonnormally distributed variables were reported as median (range) for descriptive statistical analysis. Independent samples t-tests were used to compare means between groups for normally distributed variables. For nonnormally distributed variables, the Mann–Whitney U test was employed. Chi-squared and Fisher’s exact tests were used to compare categorical variables between groups. Statistical significance was set at a p-value of <0.05.

Results

Evaluation of our data revealed the following findings:

First of all, no significant difference was observed between the two groups regarding the demographic data and stone-related parameters (laterality, size, number, location, hardness) along with the degree of hydronephrosis (Table 1). Operative time was found to be significantly shorter in the FV-UAS group than in the T-UAS group, with a median value of 57.5 minutes in the T-UAS group and 50 minutes in the FV-UAS group, respectively (p = 0.039). Perioperative complications were similar between the T-UAS and FV-UAS groups where 96 (94.1%) and 99 (94.3%) of the patients in these groups experienced no complications, respectively (p = 0.999). However, the incidence of postoperative fever was significantly higher in the T-UAS group compared with the FV-UAS group (18.6% vs 3.8%; p = 0.001). Regarding the success rates, the SFR evaluated at 1 week was significantly higher in the FV-UAS group (47.6% vs 23.5%, respectively; p < 0.001), although this value was found to be higher in the FV-UAS group at 1-month evaluation, the difference was not statistically significant (75.2% vs 68.6%, p = 0.290) (Table 2). Finally, as the main focus of our current study, evaluation of both approaches based on the degree of hydronephrosis of the involved kidneys revealed that the efficacy of FV-UAS demonstrated similar SFR and complication rates in both groups, indicating no evident effect of hydronephrotic status of the kidney on this aspect (Table 3).

Table 1.

Demographic Data of Patients

	T-UAS (n = 102)	FV-UAS (n = 105)	p value
Age (years)	49.1 ± 15.04	46.58 ± 15.03	0.230
Gender (n, %)			0.550
Male	58 (56.9)	64 (61)
Female	44 (43.1)	41 (39)
Hydronephrosis grade			0.296
None	40 (39.2)	37 (35.2)
Grade 1	20 (19.6)	26 (24.8)
Grade 2	29 (28.4)	33 (31.4)
Grade 3	13 (12.7)	7 (6.7)
Grade 4	0	2 (1.9)
Laterality (n, %)			0.290
Right	58 (56.9)	52 (49.5)
Left	44 (43.1)	53 (50.5)
Stone type (n, %)			0.659
Single	67 (65.7)	72 (68.6)
Multiple	35 (34.3)	33 (31.4)
Stone location (n, %)			0.727
Upper calyx	7 (6.9)	4 (3.8)
Middle calyx	10 (9.8)	13 (12.4)
Lower calyx	19 (18.6)	18 (17.1)
Renal pelvis	66 (64.7)	70 (66.7)
Stone diameter (mm)	12 (6–20)	13 (7–20)	0.709
Stone surface (mm²)	100 (30–400)	110 (35–300)	0.500
Hounsfield unit of stone	956.6 ± 291.5	933.9 ± 326.4	0.599

T-UAS = traditional ureteral access sheath; FV-UAS = flexible navigable vacuum-assisted ureteral access sheath; n = number.

Table 2.

Complications and SFR^a

	T-UAS (n = 102)	FV-UAS (n = 105)	p value
Operative time, median (minutes)	57.5 (25–90)	50 (15–90)	0.039
Perioperative complications (n, %)			0.999
None	96 (94.1)	99 (94.3)
Hematuria	4 (3.9)	4 (3.8)
Mucosal damage	2 (2)	2 (1.9)
Fever (n, %)	19 (18.6)	4 (3.8)	0.001
First week SFR (n, %)	24 (23.5)	50 (47.6)	<0.001
First month SFR (n, %)	70 (68.6)	79 (75.2)	0.290

The stone-free designation indicates the absence of stones on CT scan (absolute stone free, grade A).

SFR = stone-free rate; T-UAS = traditional ureteral access sheath; FV-UAS = flexible navigable vacuum-assisted ureteral access sheath; n = number.

Statistically significant p-values are shown in bold.

Table 3.

Evaluation the Effect of Hydronephrosis

	FV-UAS with low-grade HN (n = 63)	FV-UAS with high-grade HN (n = 42)	p value
Stone location (n, %)			0.092
Upper calyx	3 (4.8)	1 (2.4)
Middle calyx	10 (15.9)	3 (7.1)
Lower calyx	14 (22.2)	4 (9.5)
Renal pelvis	36 (57.1)	34 (80.9)
Stone diameter (mm)	13 (7–20)	12.5 (7–20)	0.660
Hounsfield unit value	940.7 ± 326.8	923.7 ± 329.6	0.795
Operative time (minutes)	50 (15–90)	50 (30–81)	0.645
Perioperative complications (n, %)			0.408
None	58 (92)	41 (97.6)
Hematuria	3 (4.8)	1 (2.4)
Mucosal damage	2 (3.2)	0
Fever (n, %)	4 (6.3)	0	0.096
First week SFR^a (n, %)	29 (46)	21 (50)	0.690
First month SFR (n, %)	47 (74.6)	32 (76.2)	0.854

The stone-free designation indicates the absence of stones on CT scan (absolute stone free, grade A).

FV-UAS = flexible navigable vacuum-assisted ureteral access sheath; HN = hydronephrosis; n = number; SFR = stone-free rate.

Discussion

RIRS has emerged as a common treatment modality for renal stones smaller than 20 mm, particularly over the past two to three decades, mainly based on advances in technology and emerging new concepts in treatment strategies. Although the technique is being applied with a widespread use in all parts of the world, detailed clinical outcome analyses of RIRS often fall short of expectations. Reported SFRs for this modality vary significantly, ranging from 61.4% to 97.3%. The above-mentioned limited success in achieving complete stone clearance, along with the potential requirement for multiple interventions and the risk of severe complications linked to increased intrarenal pressure, seems to pose considerable challenges for RIRS, especially when managing larger stones.^16,17 In addition to its suction capability, FV-UAS is a novel device characterized by exceptional flexibility at its tip. Preliminary data suggest that the use of FV-UAS could enable the surgeons to provide a complete stone clearance chance during RIRS.¹⁸ Taking the goal of modern urolithiasis management as outlined to achieve the maximum SFR in one session of a minimally invasive procedure into account, the importance of such studies evaluating the actual role of such game-changing modalities gains more importance.

The main finding of this study was that SFR after RIRS in FV-UAS group was significantly higher during postoperative 1-week evaluation. However, our results also showed that although SFR was again higher in FV-UAS group compared with T-UAS group at postoperative 1 month, no statistical significance difference was found in this aspect. In a 2019 study by Zhu et al., a comparative analysis was conducted to evaluate the SFRs of 165 patients undergoing RIRS using either FV-UAS or T-UAS within the first 4 weeks of postoperative period, and the results indicated no statistically significant difference in SFR between the two groups (p = 0.13).¹⁹ Similarly, Qian et al. reported comparable SFRs between FV-UAS and T-UAS procedures during the same follow-up period (p = 0.368).²⁰ However, a study by Zhang et al. reported a significantly higher SFR of 91.2% in the FV-UAS group compared with 81.3% in the T-UAS group during this period (p = 0.037).²¹ When the SFRs of the groups at the first postoperative month were analyzed, no significant difference was found in our study (p = 0.290). A comparison of the procedural times between the groups in the studies by Zhang et al. and Zhu et al. revealed a significantly shorter surgical time in FV-UAS group (p = 0.028, p < 0.001).^19,21 The results of our study were consistent with those of the studies, with the FV-UAS group exhibiting a shorter surgical time (p = 0.039). It is possible to explain this phenomenon by removing stone dust from the collecting system with the effect of suction, thereby providing a better field of vision and reducing the fragment load. Regarding the duration of hospitalization, similar to our findings, no statistically significant difference was identified between the two groups in the studies conducted by Zhu et al. and Zhang et al. (p = 0.13, p = 0.57).^19,21 Our study demonstrated a significantly lower rate of postoperative fever in the FV-UAS group compared with the T-UAS group (3.8% vs 18.6%, p = 0.001). This finding aligns with the results of previous studies by Zhu et al., Zhang et al., and Qian et al., who reported similar trends in complication rates and postoperative fever or sepsis between FV-UAS and T-UAS groups. The results of these studies indicate that the suction effect helps maintain stable intrarenal pressure during the procedure and suggests a potential reduction in the risk of infection.^19
–21 In their study, Erkoc et al. reported that the use of FV-UAS reduced the incidence of postoperative fever following RIRS. Additionally, they achieved higher SFR, along with decreased operative time and a reduction in the incidence of sepsis in the FV-UAS group for renal stones >20 mm in diameter.²²

One of the main parameters evaluated in our current trial was the possible impact of the presence and degree of hydronephrosis on the success rates of FV-UAS. The number of studies focusing on this critical parameter is highly limited in the literature, and in a study conducted by Ergani et al., RIRS success rate was found to be lower in patients with relatively higher degree (grade 2 and higher) of hydronephrosis during the procedure.²³ Among the possible reasons for this finding could be the clustering of fragments in the dilated lower calyceal space, delayed passage of fragments and missing stone fragments in the dilated parts of the collecting system could be stated. However, this was not the case in our trial and careful evaluation of the effect of hydronephrosis on the success rate in patients managed with FV-UAS, SFR demonstrated similar success and complication in patients with low- (grade 0–1) and high-grade (grade 2–4) hydronephrosis in our study. In addition, hydronephrotic kidneys may collapse more easily during suctioning with FV-UAS, but the controlled suction pressure (−50 to −150 mm Hg) applied during the use of the FV-UAS is likely to have prevented excessive collapse while maintaining optimal visibility and fragment removal, and the extended anatomical conditions may have contributed to the flexibility and navigability of the FV-UAS.

Our present study is not free of limitations. Retrospective nature of the methodology and the relatively small number of patients included in the analysis could be accepted as potential limitations. Another limitation of our study is the potential impact of variations in experience and technique among surgeons at different centers. Although all surgeons had at least 5 years of experience in RIRS, this is particularly unavoidable in procedures that rely on surgical skill and may affect our findings. However, in the light of the limited data dealing with the true efficacy of the FV-UAS in the complete removal of disintegrated stone fragments and dust particularly focusing on the possible role of collecting system dilation, we believe that our current findings will be contributive enough to the existing information in the published literature.

Conclusions

Our study findings showed that FV-UAS offers potential advantages over T-UAS in RIRS, including shorter operative times, improved early stone-free status, and reduced postoperative complications. Hydronephrosis did not appear to affect the efficacy of FV-UAS. These findings suggest that FV-UAS may be a valuable tool in optimizing RIRS outcomes.

Footnotes

Authors’ Contributions

O.A., E.E., M.E.A., F.Y.S., M.U., A.I., and C.S. contributed to the conceptualization and design of the study, and collected and analyzed the data. C.S., A.Y., and K.S. contributed to the writing of the article, and K.S. contributed to the editing. O.A., A.I., and E.B.S. contributed to the data collection and writing of the article. All the authors approved the final article in its existing form.

Ethical Considerations

This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki and adhered to the Good Clinical Practice guidelines. Ethical approval for the study was granted by the Institutional Ethics Committee (Approval No: 68/03.13.2024). Patient data were anonymized to ensure confidentiality, and all procedures were performed in compliance with institutional and national ethical standards.

Author Disclosure Statement

The authors declare that they have no conflict of interest.

Funding Information

The authors declared that this study has received no financial support.

Abbreviations Used

References

Hill

, Basourakos

, Lewicki

, et al. Incidence of kidney stones in the United States: The continuous national health and nutrition examination survey. J Urol, 2022; 207(4):851–856; doi: 10.1097/JU.0000000000002331

Zeng

, Mai

, Xia

, et al. Prevalence of kidney stones in China: An ultrasonography based cross-sectional study. BJU Int, 2017; 120(1):109–116; doi: 10.1111/bju.13828

New

, Somani

. A complete world literature review of Quality of Life (QOL) in patients with Kidney Stone Disease (KSD). Curr Urol Rep, 2016; 17(12):88; doi: 10.1007/s11934-016-0647-6

Assimos

, Krambeck

, Miller

, et al. Surgical management of stones: American urological association/endourological society guideline, PART II. J Urol, 2016; 196(4):1161–1169; doi: 10.1016/j.juro.2016.05.091

Pradère

, Doizi

, Proietti

, et al. Evaluation of guidelines for surgical management of urolithiasis. J Urol, 2018; 199(5):1267–1271; doi: 10.1016/j.juro.2017.11.111

Setthawong

, Srisubat

, Potisat

, et al. Extracorporeal shock wave lithotripsy (ESWL) Versus Percutaneous Nephrolithotomy (PCNL) or Retrograde Intrarenal Surgery (RIRS) for kidney stones. Cochrane Database Syst Rev, 2023; 8(8):CD007044; doi: 10.1002/14651858.CD007044.pub4

Bosio

, Alessandria

, Dalmasso

, et al. Flexible ureterorenoscopy versus shockwave lithotripsy for kidney stones ≤2 cm: A randomized controlled trial. Eur Urol Focus, 2022; 8(6):1816–1822; doi: 10.1016/j.euf.2022.04.004

Akram

, Jahrreiss

, Skolarikos

, et al. Urological guidelines for kidney stones: Overview and comprehensive update. J Clin Med, 2024; 13(4):1114; doi: 10.3390/jcm13041114

Senel

, Ceviz

, Ozden

, et al. The fate of clinically insignificant residual fragments following retrograde intrarenal surgery and factors affecting spontaneous passage. Urolithiasis, 2024; 52(1):39; doi: 10.1007/s00240-024-01544-9

10.

Atis

, Pelit

, Culpan

, et al. The fate of residual fragments after retrograde intrarenal surgery in long-term follow-up. Urol J, 2019; 16(1):1–5; doi: 10.2203/7/uj.v0i0.4124

11.

Inoue

, Okada

, Hamamoto

, et al. Retrograde intrarenal surgery: Past, present, and future. Investig Clin Urol, 2021; 62(2):121–135; doi: 10.4111/icu.20200526

12.

Yuen

SKK

, Traxer

, Wroclawski

, et al. Scoping review of experimental and clinical evidence and its influence on development of the suction ureteral access sheath. Diagnostics (Basel), 2024; 14(10):1034; doi: 10.3390/diagnostics14101034

13.

Jahrreiss

, Nedbal

, Castellani

, et al. Is suction the future of endourology? Overview from EAU section of urolithiasis. Ther Adv Urol, 2024; 16:17562872241232275; doi: 10.1177/17562872241232275

14.

Solano

, Chicaud

, Kutchukian

, et al. Optimizing outcomes in flexible ureteroscopy: A narrative review of suction techniques. J Clin Med, 2023; 12(8):2815; doi: 10.3390/jcm12082815

15.

von Elm

, Altman

, Egger

, et al.; STROBE Initiative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: Guidelines for reporting observational studies. J Clin Epidemiol, 2008; 61(4):344–349; doi: 10.1016/j.jclinepi.2007.11.008

16.

Liu

, Zhang

, Wen

, et al. Efficacy and safety of minimally invasive percutaneous nephrolithotomy versus retrograde intrarenal surgery in the treatment of upper urinary tract stones (>1 cm): A systematic review and meta-analysis of 18 randomized controlled trials. BMC Urol, 2023; 23(1):171; doi: 10.1186/s12894-023-01341-3

17.

Sanguedolce

, Bozzini

, Chew

, et al. The evolving role of retrograde intrarenal surgery in the treatment of urolithiasis. Eur Urol Focus, 2017; 3(1):46–55; doi: 10.1016/j.euf.2017.04.007

18.

Zeng

, Wang

, Zhang

, et al. Modified access sheath for continuous flow ureteroscopic lithotripsy: A preliminary report of a novel concept and technique. J Endourol, 2016; 30(9):992–996; doi: 10.1089/end.2016.0411

19.

Zhu

, Cui

, Zeng

, et al. Comparison of suctioning and traditional ureteral access sheath during flexible ureteroscopy in the treatment of renal stones. World J Urol, 2019; 37(5):921–929; doi: 10.1007/s00345-018-2455-8

20.

Qian

, Liu

, Hong

, et al. Application of suctioning ureteral access sheath during flexible ureteroscopy for renal stones decreases the risk of postoperative systemic inflammatory response syndrome. Int J Clin Pract, 2022; 2022:9354714; doi: 10.1155/2022/9354714

21.

Zhang

, Xie

, Li

, et al. Comparison of traditional and novel tip-flexible suctioning ureteral access sheath combined with flexible ureteroscope to treat unilateral renal calculi. World J Urol, 2023; 41(12):3619–3627; doi: 10.1007/s00345-023-04648-w

22.

Erkoc

, Bozkurt

, Sezgin

, et al. Efficacy of aspiration-assisted ureteral access sheath (ClearPETRA) in retrograde intrarenal surgery. J Laparoendosc Adv Surg Tech A, 2024; 34(5):420–424; doi: 10.1089/lap.2024.0076

23.

Ergani

, Ozbilen

, Yalcın

, et al. The effect of hydronephrosis grade on stone-free rate in retrograde intrarenal stone surgery with flexible ureterorenoscopy. Am J Clin Exp Urol, 2021; 9(2):194–201.