Efficacy analysis of a flexible-tip vacuum sheath combined with a 7.5F single-use digital ureteroscope in the treatment of upper urinary tract stones

Abstract

Background

The management of upper urinary tract stones, particularly complex and lower pole calculi, remains a significant clinical challenge. This study aimed to evaluate the efficacy and safety of a novel technique combining a flexible-tip vacuum sheath with a 7.5F single-use digital ureteroscope, which is designed to overcome the limitations of traditional access sheaths.

Methods

We performed a retrospective analysis of 74 patients with upper urinary tract stones treated between September 2024 and May 2025. All procedures were performed by a single surgeon using the combined technique. Primary outcomes were stone-free rate (SFR) assessed by computed tomography (CT) on postoperative day 1 and at 1 month, categorized as Grade A (absolute stone-free), Grade B (fragments ≤2 mm), Grade C (fragments 2.1–4 mm), and Grade D (fragments >4 mm). Secondary outcomes included operative time, hospital stay, basket usage, and complication rates.

Results

The mean operative time was 105.95 minutes, and the mean postoperative hospital stay was 1.69 days. The SFR on postoperative day 1 was 75.68% for Grade A, 2.70% for Grade B, and 9.46% for Grade C. The final SFR at 1 month was 75.68% for Grade A, 2.70% for Grade B, and 16.21% for Grade C. A stone basket was used in 27 cases (36.5%), primarily for stone displacement (10 cases). No major complications occurred. Two patients (2.7%) experienced a transient fever below 38.5 ℃.

Conclusions

The combination of a flexible-tip vacuum sheath and a 7.5F single-use digital ureteroscope is proven to be a highly effective and safe treatment modality, demonstrating high SFRs, a low complication profile, and reduced reliance on ancillary instruments.

Highlight box.

Key findings

• A retrospective study of 74 patients with unilateral upper urinary tract stones evaluated the flexible-tip vacuum sheath + 7.5F single-use digital ureteroscope. Key results: 78.4% Grade A+B stone-free rate (SFR) at 1 month; mean operative time 105.95 minutes, hospital stay 1.69 days; only 36.5% basket usage; 2.7% complication rate (transient fever <38.5 ℃), no major adverse events. Most stones (56.8%) were lower pole, mean size 24.78 mm.

What is known and what is new?

• Upper urinary tract stones (especially lower pole/complex) are challenging; traditional ureteroscopy/extracorporeal shock wave lithotripsy has limitations, with high basket reliance.

• This combined technique achieves high SFR for complex stones, reduces basket use, and ensures safety via active suction and single-use scope consistency.

What is the implication, and what should change now?

• A preferred option for complex upper urinary tract stones, balancing efficacy, safety, and efficiency.

• Conduct large-scale randomized controlled trials; validate in diverse populations; develop standardized training; integrate into clinical guidelines.

Introduction

Recent epidemiological studies indicate a rising global prevalence of urolithiasis, with approximately 10% of the population experiencing a urinary stone episode in their lifetime (1). Incidence rates vary geographically, influenced by lifestyle and dietary factors, particularly in developed countries (2). The substantial financial burden on healthcare systems underscores the need for effective management strategies (2).

Despite advancements, treating upper urinary tract calculi—especially those in the lower pole and complex cases—remains challenging. Current standards, such as extracorporeal shock wave lithotripsy (ESWL) and ureteroscopy, have limitations: ESWL is less effective for lower calyceal stones, while ureteroscopy can be hindered by anatomical variations or stone size (3,4). Although flexible ureteroscopic lithotripsy is a key modality, its efficacy is often limited by sheath accessibility, irrigation efficiency, and stone clearance capacity. Traditional ureteral sheaths may struggle to access the lower pole and lack active fragment removal capability, frequently necessitating stone retrieval baskets, which prolongs surgery and increases costs. The development of distally deflectable negative-pressure sheaths and ultra-thin disposable ureteroscopes offers potential solutions (4,5). The former improves sheath placement success and provides continuous vacuum-assisted drainage, while the latter eliminates reprocessing and may enhance scope flexibility. This study aims to retrospectively analyze the stone-free rate (SFR) and complication rate of this combined technique for upper urinary tract calculi. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-aw-814/rc).

Methods

Study design and population

This retrospective study analyzed consecutive patients with upper urinary tract calculi of Peking University People’s Hospital treated between September 2024 and May 2025 using a distally deflectable negative-pressure sheath combined with a 7.5F disposable digital ureteroscope. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Peking University People’s Hospital (No. 2024PHB170-001) and informed consent was taken from all the patients. Inclusion criteria comprised symptomatic stone patients aged ≥18 years. Exclusion criteria included pregnancy, uncorrected coagulation disorders, bilateral calculi, or a history of ipsilateral renal surgery.

Surgical technique

All surgeries were performed by a single senior surgeon under general anesthesia to ensure technical consistency. After routine guidewire placement, an 11/13F distally deflectable negative-pressure sheath was positioned near the renal pelvis or target calyceal entrance. A 7.5F disposable digital ureteroscope (PUSEN™ or Zebra™) was introduced, and holmium laser lithotripsy was performed. Continuous negative-pressure suction (−50 to −100 mmHg) was applied to evacuate fragments, maintain a clear visual field, and assist in intracorporeal cooling. Laser settings (0.3J 80 Hz for dust and 1.2J 20 Hz for fragment) were adjusted based on stone location and hardness. Fluid rate ranges from 100 to 200 mL/min. Following lithotripsy, the collecting system was inspected, perfusion was reduced, and suction was discontinued. A second inspection was performed during ureteroscope withdrawal over a safety guidewire. A 6F double-J stent was routinely placed. Stone fragments were collected from the suction bottle for analysis.

Data collection and outcomes

Demographic and perioperative data—including age, gender, stone characteristics [size, location, computed tomography (CT) value], preoperative stenting, operative time, and hospital stay—were retrieved from electronic medical records. The mean stone size was determined from preoperative imaging, measured by the maximal diameter. In cases with more than one stone in the same renal unit, the stone burden was calculated as the sum of the longest diameter of each stone. The primary outcome was SFR on postoperative day 1 and at 1 month, assessed by CT. Secondary outcomes included the rate and indications for basket use and complications, graded by the Clavien-Dindo system. Postoperative fever was defined as a body temperature >38.5 ℃.

Statistical analysis

The results were expressed as mean ± standard error of the mean (SEM). We adopted the complete case analysis method to handle missing data, where only cases with complete records of all variables were included in the final statistical analysis.

Results

A total of 74 patients were included. Baseline characteristics are summarized in Table 1. The mean age was 53.39 years, and 68.9% were male. The mean maximum cumulative stone diameter was 24.78 mm, with a mean CT value of 857.6 Hounsfield units (HU), indicating moderate hardness. Calculi involved the inferior calyx in 42 patients (56.8%), and 2 patients (2.7%) had partial staghorn stones. Preoperative ureteral stents were placed in 31 patients (41.9%) due to obstruction or infection.

Table 1. The preoperative characteristic of upper urinary tract stones treatment of upper urinary tract stones.

Parameters	Values (n=74)†
Kidney
Left	47 (58.75)
Right	33 (41.25)
Gender
Male	51 (68.92)
Female	23 (31.08)
Age (years)	53.39±12.20 [30–80]
Stone type
Single	33 (44.59)
Multiple	41 (55.41)
Partially staghorn	2 (2.70)
Low pole	42 (56.76)
Stone size (mm)	24.78±12.85 [8–65]
Hydronephrosis (side)	59 (79.73)
BMI (kg/m2)	26.36±3.97 [17.72–48.07]
CT (HU)	857.60±279.3 [357–1,548]
Preoperative ureteral stent placement	31 (41.89)

^†, a total of 74 patients, including 6 cases have bilateral stones. Data are presented as n (%) or mean ± standard deviation [range]. BMI, body mass index; CT, computed tomography; HU, Hounsfield units.

All procedures were completed successfully. The mean operative time was 105.95 minutes, and the mean postoperative hospital stay was 1.69 days. Stone clearance outcomes are detailed in Table 2. The SFR on postoperative day 1 was 75.68% for Grade A, 2.70% for Grade B, and 9.46% for Grade C. The final SFR at 1 month was 75.68% for Grade A, 2.70% for Grade B, and 16.21% for Grade C. Stone retrieval baskets were used in 27 cases (36.5%), primarily for displacing inferior calyceal stones to more accessible locations (10 cases) or extracting larger fragments. No intraoperative complications occurred.

Table 2. The outcome of flexible-tip vacuum sheath combined with a 7.5F single-use digital ureteroscope in the treatment of upper urinary tract stones.

Parameters	Values (n=74)†
Operative time (min)	105.95±56.06 [30–265]
Postoperative hospital time (days)	1.69±1.40 [0–7]
Basket usage	27 (36.49)
SFR
Grade A (absolute stone free)	56 (75.68)
Grade B (≤2 mm fragments)	2 (2.70)
Grade C (2.1–4 mm)	12 (16.21)
Grade D (>4 mm)	4 (5.41)
Major complications
Fever (<38.5 ℃)	2 (2.70)

^†, a total of 74 patients, including 6 cases have bilateral stones.Data are presented as n (%) or mean ± standard deviation [range]. SFR, stone-free rate.

The postoperative complication rate was 2.7%. Two patients developed transient low-grade fever (37.5 ℃), which resolved with observation and symptomatic management (Clavien-Dindo Grade I). No high-grade complications (e.g., transfusion, sepsis, or ureteral injury) were observed, and no patient had a body temperature exceeding 38.5 ℃.

Discussion

This study evaluates the efficacy of a novel approach combining a 7.5F disposable digital ureteroscope with a terminally curved negative-pressure sheath for treating upper urinary tract stones. Our retrospective analysis of 74 patients demonstrates favorable stone clearance rates and a low incidence of postoperative complications, contributing to the existing literature and informing future clinical practice.

The demographic profile of our cohort, with a male predominance, aligns with previous studies suggesting that sex-related anatomical and hormonal factors may influence stone characteristics and treatment outcomes (1). The mean stone size of 24.78 mm in our series is associated with higher complexity, reinforcing the need for tailored surgical strategies to optimize SFR and minimize risks (6,7).

Standardizing the use of a 7.5F disposable digital ureteroscope with an 11/13F flexible negative-pressure sheath likely enhanced procedural efficiency and safety. The mean operative time of 105.95 minutes is consistent with reports for complex cases, where longer duration may correlate with increased complications (8,9). The negative-pressure sheath facilitated stone clearance by maintaining a stable operative field and improving visibility, potentially reducing complications such as hemorrhage or perforation (10). These findings underscore the value of integrating innovative tools to improve endourological outcomes.

The stone clearance rates in this study are commendable, with a total SFR (Grades A+B) of 78.4% at one month. This aligns with contemporary studies using advanced lithotripsy techniques (10,11). For complex stones or lower pole calculi, SFRs with conventional non-suction sheaths or reusable scopes often range from 70% to 85% (3,4). Our results align more closely with recent studies evaluating suctioning ureteral access sheaths (UAS). For instance, a systematic review by Wang et al. concluded that flexible negative-pressure sheaths could achieve SFRs exceeding 90% (10). Similarly, a propensity score-matched study by Lei et al. reported comparable high SFRs when using a navigable suction sheath versus a non-suction UAS (11). The high clearance rate in our series may be attributed to the synergistic effect of the active, continuous fragment evacuation provided by the vacuum sheath and the consistent optical/mechanical performance of the single-use ureteroscope, which mitigates the performance degradation sometimes associated with reusable devices. Besides, the high SFR may also be attributed to effective laser fragmentation and the anatomical advantages offered by the flexible sheath, which enhances access and permits active fragment evacuation (12). Furthermore, the use of a UAS may reduce mucosal trauma, potentially preserving long-term renal function (13).

The low complication rate (2.7%) observed in this cohort highlights the safety of this approach. The absence of severe complications, such as transfusion or sepsis, suggests that this technique mitigates risks commonly associated with ureteroscopy (14). Procedural standardization and advanced equipment, such as the negative-pressure sheath, likely contribute to this favorable safety profile by improving fluid management and reducing stone migration or ureteral injury (15,16).

The mean operative time of approximately 106 minutes is consistent with durations reported for complex stone cases using advanced lithotripsy systems (8,9). A significant efficiency indicator in our study was the reduced reliance on stone retrieval baskets, used in only 36.5% of cases—primarily for displacement rather than extraction. This contrasts with many conventional Retrograde Intrarenal Surgery (RIRS) series, where basket usage rates can exceed 50–60%. This reduction can be directly attributed to the effective clearance mechanism of the vacuum sheath, minimizing the need for ancillary instrumentation, which may streamline the procedure and potentially lower costs (17-19). Our results suggest that the combination of an efficient lithotripsy system and active fragment clearance can minimize the need for basket manipulation, aligning with trends toward streamlined endourological procedures (19,20).

There are several limitations in this study. First, the sample size of 74 patients is relatively small, which may limit the statistical power and generalizability of our findings. Second, the retrospective design introduces potential selection bias. Third, all procedures were performed by a single senior surgeon. While this ensured technical consistency and standardized the application of the novel technique, it may introduce a “single-surgeon bias”. The favorable outcomes regarding operative time, complication rates, and basket usage might not be fully generalizable to broader clinical settings involving surgeons with varying levels of experience. The expertise of a high-volume surgeon could positively influence the efficiency and safety profile, potentially overestimating the effectiveness achievable in routine practice. Finally, the lack of long-term follow-up data restricts our ability to assess the durability of treatment outcomes and the long-term safety of this technique.

Conclusions

For upper urinary tract calculi—particularly those in the inferior renal calyx—the combination of a distally deflectable negative-pressure sheath and a 7.5F disposable digital ureteroscope represents an efficient and safe treatment strategy. This approach achieves excellent SFRs, minimizes complications, and significantly reduces the need for stone retrieval baskets through active fragment clearance. Future prospective randomized controlled trials are warranted to validate these advantages.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Peking University People’s Hospital (No. 2024PHB170-001) and informed consent was taken from all the patients.

Data Sharing Statement

Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-aw-814/dss

tau-15-02-56-dss.pdf ^{(75.4KB, pdf)}

DOI: 10.21037/tau-2025-aw-814