Abstract
To evaluate the safety and efficacy of the flexible vacuum-assisted ureteral access sheath combined with the single-use flexible ureteroscopy in the treatment of renal calculi. We prospectively analyzed the patients treated with single-use flexible ureteroscopy from January 2023 to December 2023, among which 113 cases were treated with flexible vacuum-assisted ureteral access sheath (FV-UAS group) and 113 cases were treated with conventional sheath (conventional sheath group). Patient data ofthe two groups were collected and recorded before and after operation. No significant differences were observed between the two groups regarding demographics and pre-operative clinical characteristics. The duration of the operation was significantly longer in the FV-UAS group (79.5 ± 6.8 min) compared to the conventional UAS group (65.2 ± 7.3 min). However, the stone free rate (SFR) at one day and one month post-operation in the FV-UAS group was 85.6% and 98.2%, respectively, significantly higher than that in the conventional UAS group (72.6%, 90.3%). Complications such as infection and urosepsis were more common in conventional UAS group. Notably, hospitalization costs were lower in the FV-UAS group. Flexible vacuum-assisted ureteral access sheath combined with flexible single-use ureteroscope is a feasible and effective method for treating renal calculi. It offers higher SFR and lower rate of infectious complications.
Keywords: Retrograde intrarenal surgery, Vacuum-assisted ureteral access sheath, Renal calculi, Infection
Introduction
The incidence rate of urinary calculi has been increasing year by year, and treatment methods have become progressively less invasive. Traditional open and laparoscopic surgeries have become relatively rare, while percutaneous nephrolithotomy (PCNL) has evolved from standard channels to miniaturized, and ultra-miniaturized approaches. With advancements in endoscopic technology coupled with the development of laser lithotripsy systems, flexible ureteroscopy with laser lithotripsy (FURL) has emerged as an increasingly popular treatment option for upper urinary tract stones, especially renal stones [1–5]. According to the European Association of Urology (EAU) and the American Urological Association (AUA) guidelines, FURL has become one of the preferred treatments for upper urinary tract stones < 2 cm [6]. A flexible ureteroscope paired with a ureteral access sheath (UAS) is currently the standard technique for flexible ureteroscopy lithotripsy (FURL).The conventional use of ureteral access sheath (UAS) facilitates entry and exit of the flexible ureteroscope into the urinary tract, improving the field of view through continuous drainage. However, conventional UAS has limitations, including uncontrollable intrarenal pressure (IRP) and suboptimal post-operative stone clearance rate. With the advent of flexible vacuum-assisted ureteral access sheath (FV-UAS), these issues are being addressed. FV-UAS can actively reduce IRP, allowing stone fragments to be removed from the renal calyx under the negative pressure. This study prospectively compares the clinical efficacy of FV-UAS and conventional UAS combined with single-use flexible ureteroscope in treating renal calculi.
Patients and methods
From January 2023 to December 2023, a total of 226 patients with renal calculi were enrolled and assigned to either the flexible vacuum-assisted ureteral access sheath group (FV-UAS, n = 113) or the conventional UAS group (UAS, n = 113) in our unit. Relevant patient data were collected and recorded pre- and postoperatively. Stone characteristics were obtained by the CT and intravenous urography (IVU) and stone size was calculated by measuring the maximum length diameter of the stone according to the CT 3D reconstruction images. Inclusion criteria: (1) renal stones (< 3 cm) as per the guidelines of Chinese Urology Association (CUA); (2) surgical risk < level II based on the score of the American Society of Anesthesiologists (ASA). Exclusion criteria: (1) History of ipsilateral ureteral stricture; (2) Severe hydronephrosis; (3) Cardiopulmonary insufficiency and severe liver dysfunction; (4) Abnormal coagulation function or bleeding tendency. Patients with urinary infection were treated with antibiotics preoperatively. All procedures were performed by the experienced surgeon following established guidelines of operation [7]. All procedures were in accordance with ethical standards of The Second Affiliated Hospital of Soochow University Ethics Committee, and all patients provided written informed consent to treatment.
Surgical procedure
All patients were placed in the lithotomy position and all operations were performed under general anesthesia. In the study, 30 cases in FV-UAS group and 35 cases in conventional UAS group received a 6 F double-J stent two weeks prior to the FURL procedure. During the operation, an F8.4 single-use flexible ureteroscope (Innovex Anqing Medical, Shanghai, China), the FV-UAS and UAS (Female: 36 cm, Male: 46 cm, F12/14, Wellead Medical, Guangzhou, China, Fig. 1) were used in the procedure.
Fig. 1.
The structure of the FV-UAS
Initially, a 9.8 F semi rigid ureteroscope was used to access the ureter and place a guidewire. If the double-J stent was placed preoperatively, it was removed. In cases without preoperative double-J stents, if the ureters were in poor condition or there was ureteral stricture, a double-J stent would be placed and the FURS would be delayed for 2–4 weeks. For the conventional sheath group, the procedure followed the previously published paper [8]. At the conclusion of the operation, stone fragments with size > 2 mm were removed by a stone retrieval basket. For the FV-UAS group, the guidewire was placed first and then the FV-UAS was inserted along the guidewire through the junction of the renal pelvis and ureter. Meanwhile, the condition of renal calyces and the location of stones were evaluated. The surgeon then adjusted the working handle and positioned the sheath tip toward the renal calyces, where the stone was located. Stones were fragmented by the 200 μm holmium laser with energy settings of 1.0–1.5 J and a frequency of 20–30 Hz. During the process of the holmium laser lithotripsy, minimal stone fragments were aspirated through the gap between the flexible ureteroscope and the inner wall of the sheath, at the same time. Stone fragments smaller than the diameter of the sheath were washed out when the ureteroscope was withdrawn out of the sheath. At the end of the operation, a 6 F double-J stent was placed and stone fragments were collected in a container for analysis.
Postoperative evaluations, including blood routine, renal function and electrolytes were routinely conducted. Aradiograph on the first postoperative day assessed residual stones. A stone-free status was defined as no radiological evidence of stones or the presence of ≤ 2 mm asymptomatic fragments in the urinary system [9–11]. Primary study outcomes included the stone free rate(SFR) at 1 day and four weeks post-operatively. Other recorded parameters included operative time, postoperative hospital stay, and operation-related complications. Postoperative complications were graded retrospectively according to the modified Clavien-Dindo classification [12, 13]. Follow-up imaging (the KUB examination, B-ultrasound or CT scan) was performed at 1 month before the removal of the double-J stent.
Statistical analysis
Continuous variables were summarized as mean ± SD and compared by one-way ANOVA test. Categorical variables were analyzed using the chi-square test or Fisher’s exact test. The statistical package for the social science (SPSS Inc, Chicago, Illinois, USA) version 19.0 was used for statistical analysis with statistical significance set at P < 0.05.
Results
The baseline characteristic of the two groups are summarized in Table 1. No significant differences were observed between the two groups in terms of age, body mass index (BMI), gender distribution, stone location, degree of hydronephrosis or mean stone size.
Table 1.
The baseline characteristics of patients in two groups
| Variables, mean ± SD | FV-UAS group (n = 113) |
Conventional UAS group (n = 113) |
P value |
|---|---|---|---|
| Age(years) | 45.6 ± 11.8 | 46.2 ± 11.6 | P > 0.05 |
| BMI | 24.6 ± 2.8 | 24.1 ± 3.1 | P > 0.05 |
| Gender | |||
|
Male Female |
75(66.37%) 38(33.63%) |
80(70.8%) 33(29.2%) |
P > 0.05 P > 0.05 |
| ASA | |||
|
I II |
81(71.68%) 32(28.32%) |
88(77.88%) 25(22.12%) |
P > 0.05 P > 0.05 |
| Stone location | |||
|
Upper calyx Middle calyx Lower calyx |
42(37.17%) 56(49.56%) 15(13.27%) |
45(39.82%) 57(50.44%) 11(9.73%) |
P > 0.05 P > 0.05 P > 0.05 |
| Size of stones (cm) | 2.2 ± 0.5 | 2.1 ± 0.8 | |
|
Number of Stone Single Multiple |
49(43.36%) 64(56.64%) |
51(45.13%) 62(54.87%) |
P > 0.05 P > 0.05 |
| Degree of hydronephrosis | |||
|
Mild Moderate Severe |
48(42.48%) 49(43.36%) 16(14.16%) |
52(46.02%) 48(42.48%) 13(11.5%) |
P > 0.05 P > 0.05 P > 0.05 |
The surgical outcomes and post-operative clinical characteristics of the two groups are shown in Table 2. The mean operative time was 79.5 ± 6.8 min for FV-UAS group and 65.2 ± 7.3 min for conventional UAS group, respectively, with no statistically significant difference between the two groups. Similarly, there was no significant difference in the decrease in hemoglobin levels between the two groups. The SFR at one day after the operation in FV-UAS group is 85.8%, which is significantly higher than that in UAS group. Meanwhile, a significant difference in SFR was also observed in the two groups 4 weeks postoperatively. Regarding complications, significant hematuria occurred in 12 cases after surgery in FV-UAS group and 6 cases in conventional UAS group, with the difference reaching statistical significance. In terms of the rate of fever and urosepsis, conventional UAS group was significantly higher than that in the FV-UAS group. However, there was also no significant difference between the two groups. No significant difference was observed in hospitalization time between two groups. However, the cost of hospitalization was higher in conventional UAS group than that in FV-UAS group.
Table 2.
Comparisons of surgical outcomes and post-operative clinical characteristics between two groups
| Variables, mean ± SD | FV-UAS group (n = 113) |
Conventional UAS group (n = 113) |
P value |
|---|---|---|---|
| Operative time (min) | 79.5 ± 6.8 | 65.2 ± 7.3 | P > 0.05 |
| Hemoglobin decrease | 3.4 ± 1.2 | 3.2 ± 1.5 | P > 0.05 |
| Stone free rate (%) | |||
| 1 day after operation | 85.8%(97/113) | 72.6%(82/113) | P < 0.05 |
| 1 month after operation | 98.2%(111/113) | 90.3%(102/113) | P < 0.05 |
| Complications | |||
| Fever | 2(1.8%) | 6(5.31%) | P > 0.05 |
| Bleeding | 12(10.6%) | 6(5.3%) | P < 0.05 |
| Urospesis | 0 | 4(3.54%) | P < 0.05 |
| Post-operative hospitalization time (days) | 2.1 ± 1.1 | 2.2 ± 1.3 | P > 0.05 |
Discussion
Renal calculi are a common urological disease with increasing incidence rate year by year. Currently, PCNL and FURL are the primary surgical methods for treating kidney stones. Over the past decade, FURL has become widely used to treat renal stones due to its advantages, including low invasiveness, minimal bleeding, and shorter hospitalization time [14]. In clinical practice, some patients with renal stones even refused the PCNL and choose multiple FURLs [15]. However, two significant drawbacks of FURL are challenges in controlling intrarenal pressure and managing residual fragments [16, 17]. The widespread application of vacuum-assisted ureteral access sheath in clinical practice has shown promise in addressing these issues. Multiple studies have confirmed that it could significantly and effectively reduce IRP, shorten surgical time, lower postoperative infection rates, and improve SFRs [18, 19].
IRP remains a critical factor in RIRS. The main reason is that traditional or vacuum-assisted UAS is difficult to be smoothly placed in the renal pelvis through the UPJ [20]. According to relevant literature reports, the obstacle to control IRP is the relatively narrow or twisted UPJ, which acts as a functional valve between the renal pelvis and proximal ureter [21]. To mitigate high IRP, reducing the fluid irrigation flow rate is an option, but this compromises the intra-operative visual field. In addition, continuous perfusion is essential to maintain a clear visual field in the process of lithotripsy. If the drainage is inadequate or perfusion pressure is excessively high, it can lead to high IRP, raising the risk of the incidence of post-operative infections. According to the published literature [22], we set the fluid irrigation flow rate to 100 ml/min and the negative pressure to 100cmH2O in order to control the IRP at a lower level during the operation. In our present study, no cases of sepsis or urinary infection-related complications occurred postoperatively in the FV-UAS group, underscoring its efficacy in IRP control.
While the stone retrieval basket can reduce the residual fragments effectively in the process of FURL, they often fail to completely remove all the stone residual fragments from the kidney. A study showed that among 32 patients with lower pole caliceal calculi who underwent FURL with traditional UAS, only 16 (50%) patients achieved complete stone free status during follow-up period [23].Traditional UAS, positioned at the junction of the renal pelvis and ureter, struggles to clear intrarenal stones, particularly in the lower calyx due to limited suction capacity. Additionally, the application of negative pressure suction sheath also requires a special surgical position (such as contralateral oblique supine position) to optimize suction effects. In some cases, it is necessary to use gravity and external force to pat the renal area to encourage the stone movement, allowing the stone to fall into the renal pelvis and be aspirated away during surgery, which limited the broader application of vacuum UAS. In contrast, the FV-UAS can directly reach each renal calices, providing better suction effect even in narrow spaces which enhances stone removal. Furthermore, the FV-UAS does not require a special position and facilitates the visualization of standard anatomical structures during surgery. Its application can achieve a higher rate of complete stone clearance. The literature results have indicated e a mean stone volume clearance rate of 98.5% with FV-UAS with seven cases achieving complete SFS [22]. In our study, the SFRs in FV-UAS group were 85.8% and 98.2% at 1 day and one month postoperatively, compared to 72.6% and 90.3% in conventional UAS group, demonstrating significant differences between the two groups. However, the operative time in FV-UAS group was longer than that in conventional UAS group, likely due to the additional time required for extracting stone fragments.
The common complications after FURL surgery are hematuria and infection. In our study, the incidence of hematuria in FV-UAS group is higher than that in conventional UAS group, which is attributed to the FV-UAS repeatedly rubbing against the mucosa of renal pelvic and calyx, causing mucosa damage. During the peri-operation of FURL, surgeons should pay particular attention to the risk of infection. Our findings showed that there are significant differences between two groups in terms of infection and urosepsis, suggesting that the application of FV-UAS could decrease the incidence of these complications effectively.
The present study also has some limitations. For renal calyx stone, the FV-UAS relies on the flexible ureteroscope to navigate into the renal calyx. While this is beneficial for aspirating stones and controlling IRP through the negative pressure, it is less effective for certain renal lower calyx, particularly those with an IPA < 30°. In these cases, the FV-UAS may struggle to reach the lower calyces, limiting its ability to remove stones effectively. In our study, the residual stones were detected and SFRs were lower than that in other renal calices. Additionally, the study was a single-center study with a relatively small sample size, and a short follow-up period. Future research with larger cohorts and extended follow-up is necessary to further validate the clinical value and long-term outcomes of FV-UAS.
In conclusion, single-use flexible ureteroscopy combined with FV-UAS is a safe and effective alternative for the treatment of renal calculi offering improved r SFRs and safety of operation, and reduced IRP and postoperative complications, making it a valuable tool in modern urological practice. Further clinical studies with large sample sizes are needed to validate our findings.
Acknowledgements
No.
Author contributions
Wei Tao: Data Collection, Manuscript writing Ming Xu: Data Collection, Manuscript writingLu Jin: Data Collection Dongrong Yang: Data management Boxin Xue: Project development Chuanyang Sun: Data management, Manuscript writing. All authors reviewed the manuscript.
Funding
Support: No.
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
Yes.
Competing interests
The authors declare no competing interests.
Clinical trial number
Not applicable.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Desai M, Sun Y, Buchholz N et al (2017) Treatment selection for urolithiasis: percutaneous nephrolithotomy, ureteroscopy, shock wave lithotripsy, and active monitoring. World J Urol 35(9):1395–1399. 10.1007/s00345-017-2030-8 [DOI] [PubMed] [Google Scholar]
- 2.Grasso M (2000) Ureteropyeloscopic treatment of ureteral and intrarenal calculi. Urol Clin North Am 27(4):623–631. [DOI] [PubMed]
- 3.Galvin DJ, Pearle MS (2006) The contemporary management of renal and ureteric calculi. BJU Int 2006;98(6):1283–1288.10.1111/j.1464-410X. 2006. 06514.x [DOI] [PubMed]
- 4.Vanlangendonck R, Landman J (2004) Ureteral access strategies: pro-access sheath. Urol Clin North Am 31(1):71–81. 10.1016/S0094-0143 [DOI] [PubMed] [Google Scholar]
- 5.Honey RJ (1998) Assessment of a new tipless nitinol stone basket and comparison with an existing flat-wire basket. J Endourol 12(6):529–531. 10.1089/end.1998.12.529 [DOI] [PubMed] [Google Scholar]
- 6.Alenezi H, Denstedt JD (2015) Flexible ureteroscopy: technological advancements, current indications and outcomes in the treatment of urolithiasis. Asian J Urol 2(3):133–141. 10.1016/j.ajur.2015.06.002 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Chinese Urological Association (2016) Consensus of Chinese experts on flexible Ureteroscopy. Chin J Urol 37(8):561–565. 10.3760/cma.j.issn1600- 6702.2016.08.001 [Google Scholar]
- 8.Tao W, Zhang ZZ, Zhang YY, Xu M, Sun CY (2022) Superselective renal arterial embolization in treatment for severe renal hemorrhage after flexible ureterorenoscopy and laser lithotripsy (FURSL). J X-ray Technol 30(5):1047–1056. 10.3233/XST-221214 [DOI] [PubMed] [Google Scholar]
- 9.Ghani KR, Wolf JS Jr (2015) What is the stone-free rate following flexible ureteroscopy for kidney stones? Nat Rev Urol 12(5):281–286. 10.1038/nrurol.2015 [DOI] [PubMed] [Google Scholar]
- 10.Dauw CA, Simeon L, Alruwaily AF et al (2015) Contemporary practice patterns of flexible ureteroscopy for treating renal stones: results of a worldwide survey. J Endourol 29(11):1221–1230. 10.1089/end.2015.0260 [DOI] [PubMed] [Google Scholar]
- 11.Huang ZC, Fu FJ, Zhong ZH, Zhang L, Xu R, Zhao XK (2012) Flexible ureteroscopy and laser lithotripsy for bilateral multiple intrarenal stones: is this a valuable choice? Urology 80:800–804. 10.1016/j.urology.2012.05.013 [DOI] [PubMed] [Google Scholar]
- 12.Mamoulakis C, Efthimiou I, Kazoulis S, Christoulakis L, Sofras F (2011) The modified clavien classification system: a standardized platform for reporting complications in transurethral resection of the prostate. World J Urol 29(2):20. 10.1007/s00345-010-0566-y [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Mitropoulos D, Artibani W, Graefen M et al (2012) Reporting and grading of complications after urologic surgical procedures: an ad hoc EAU guidelines panel assessment and recommendations. Eur Urol 61(2):341–349. 10.1016/j.eururo.2011.10.033 [DOI] [PubMed] [Google Scholar]
- 14.Tokas T, Herrmann TRW, Skolarikos A, Nagele U, T.R.U.S.T.-Group (2019) Pressure matters: intrarenal pressures during normal and pathological conditions, and impact of increased values to renal physiology. World J Urol 37:125–131. 10.1007/s00345-018-2378-4 [DOI] [PubMed] [Google Scholar]
- 15.Zhu M, Wang XY, Shi ZQ, Ding M, Fan DY, Wang X, Jiang R (2019) Comparison between retrograde intrarenal surgery and percutaneous nephrolithotripsy in the management of renal stones: a meta-analysis. Exp Ther Med 18(2):1366–1374. 10.3892/etm.2019.7710 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Doizi S (2021) Intrarenal pressure: what is acceptable for flexible ureteroscopy and percutaneous nephrolithotomy? Eur Urol Focus 7(1):31–33. 10.1016/j.euf.2021.01.010 [DOI] [PubMed] [Google Scholar]
- 17.Guven S, Yigit P, Tuncel A et al (2021) Retrograde intrarenal surgery of renal stones: a critical multi-aspect evaluation of the outcomes by the Turkish academy of urology prospective study group (ACUP study). World J Urol 39(2):549–554. 10.1007/s00345-020-03210-2 [DOI] [PubMed] [Google Scholar]
- 18.Wu ZH, Wang YZ, Liu TZ et al (2022) Comparison of vacuum suction ureteroscopic laser lithotripsy and traditional ureteroscopic laser lithotripsy for impacted upper ureteral stones. World J Urol 40(9):2347–2352. 10.1007/s00345-022-04075-3 [DOI] [PubMed] [Google Scholar]
- 19.Lai DH, He YZ, Li X, Chen ml, Zeng XR (2020) RIRS with vacuum-assisted ureteral access sheath versus MPCNL for the treatment of 2–4 cm renal stone. Biomed Res Int 2020(8052013). 10.1155/2020/8052013 [DOI] [PMC free article] [PubMed]
- 20.Zhu ZW, Cui Y, Zeng F, Li Y, Chen ZY, Chen HQ (2019) Comparison of suctioning and traditional ureteral access sheath during fexible ureteroscopy in the treatment of renal stones. World J Urol 37(5):921–929. 10.1007/s00345-018-2455– 8 [DOI] [PubMed] [Google Scholar]
- 21.Oratis AT, Subasic JJ, Hernandez N, Bird JC, Eisner B (2018) A simple fluid dynamic model of renal pelvis pressures during ureteroscopic kidney stone treatment. PLoS ONE 13(11):e0208209. 10.1371/journal.pone.0208209 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Chen YJ, Li C, Gao L et al (2022) Novel fexible vacuum-assisted ureteral access sheath can actively control intrarenal pressure and obtain a complete stone-free status. J Endourol 36(9):1143–1148. 10.1089/end.2022.0004 [DOI] [PubMed] [Google Scholar]
- 23.Pearle MS, Lingeman JE, Leveillee R et al (2008) Prospective randomized trial comparing shock wave lithotripsy and ureteroscopy for lower Pole caliceal calculi 1 cm or less. J Urol 179(5 Suppl):S69–73. 10.1016/j.juro.2008.03 [DOI] [PubMed] [Google Scholar]
Associated Data
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Data Availability Statement
No datasets were generated or analysed during the current study.