Clinical efficacy analysis of tip‑flexible suctioning ureteral access sheath combined with disposable flexible ureteroscope to treat 2–4 cm renal stones

Kidney stones are among the most common urological diseases, with a significantly rising prevalence globally [1]. Treatment has evolved from traditional open nephrolithotomy to minimally invasive techniques. For stones ≤ 2 cm, the European Association of Urology recommends retrograde intrarenal surgery (RIRS) as the preferred treatment [2‐4]. For stones > 2 cm, choices vary between centers, mainly between RIRS and percutaneous nephrolithotomy (PCNL) [5, 6]. However, PCNL requires establishing a tract through the renal parenchyma, which is especially demanding for patients without significant hydronephrosis, as it requires considerable surgical skill and experience due to the dense parenchyma filled with stones. Such cases are prone to complications like severe bleeding and infections, and have longer recovery times [7, 8].

Recent advances in endourology have explored the application of RIRS in treating stones larger than 2 cm. Yet, due to limited stone clearance rates in large burden kidney stones, multiple surgeries might be necessary, increasing the risk of intrarenal pressure and potential complications like renal rupture and severe infections [2, 9, 10]. The advent of a TFS-UAS has expanded the indications for ureteroscopic procedures. Its tip can passively flex with the ureteroscope to reach all calyces, allowing for effective stone fragmentation and direct suction of the irrigation fluid and fragments, achieving better outcomes than T-UAS [11].

Currently, the combination of the TFS-UAS and a DFU is primarily used to treat kidney stones smaller than 2 cm, demonstrating good clinical efficacy [11‐13]. Research on using this technology to treat stones with a diameter of 2–4 cm has been relatively limited. Since 2017, Ganzhou People’s Hospital has been implementing RIRS technology and, since 2019, has used the TFS-UAS in combination with DFU for stone fragmentation and clearance, successfully treating renal stones of 2–4 cm with favorable results.

In China, the prevalence of kidney stones is approximately 6%, with a higher incidence rate in the southern region compared to the northern region [15]. Kidney stones can cause recurring symptoms such as pain, hematuria, and urinary frequency/urgency. Large stone burdens may result in severe complications, including uremic syndrome, chronic kidney disease, urinary perforations, and renal effusion [16, 17]. Recent advancements in flexible ureteroscope manufacturing, endoscopic surgical techniques, and stone fragmentation tools like holmium lasers have made RIRS the preferred technique for managing small-burden renal stones. T-UAS plays a crucial role in RIRS, although it is associated with high rates of residual stone fragments [18, 19]. Studies indicate that residual fragment rates for sizes smaller than 3 mm, 2 mm, and 1 mm are 16.7%, 48.5%, and 77.8%, respectively [20]. Moreover, prolonged use of T-UAS in lithotripsy, lacking negative pressure suction or pressure control, can increase the risk of complications like bleeding and infections. Research has shown that the single-session stone clearance rate for ureteroscopic lithotripsy exceeds 90% for renal or upper ureteral stones smaller than 2 cm [21]. Conventional ureteroscopy often does not achieve complete stone removal in a single session for large stones (> 2 cm) and may lead to the formation of steinstrasse within the ureter, necessitating multiple surgeries [22]. Furthermore, studies reveal that the single-session stone clearance rate decreases with increasing stone size, dropping to as low as 62% [23]. In addition, prolonged operative times are linked to an increased risk of complications such as bleeding and infection [24‐27].

To minimize surgical complications, some studies have utilized modified ureteroscopes with suction sheaths. However, the distal end of these sheaths reaches only the pelviureteric junction and cannot extend into the renal pelvis or calyces, resulting in low stone retrieval efficiency [25]. In addition, the UAS opening is prone to obstruction, which elevates renal pelvis pressure and causes reflux, increasing the risk of bleeding and infection [28]. Previous studies have shown that TFS-UAS reduces intrarenal pressure (IRP), increases SFR, shortens operative times, and lowers complication rates [29, 30]. TFS-UAS negative pressure suction sheaths, compared to T-UAS, provide flexible access to calyceal stones. They allow the sheath’s front end to be positioned precisely within a calyx for effective stone fragmentation and retrieval, aiming to reduce residual stones and recurrence [25, 31]. The simultaneous suction feature aids in stone aspiration and importantly, facilitates the rapid removal of irrigation fluids during surgery. This maintains a low-pressure environment in the renal pelvis, helping to prevent severe intraoperative and postoperative infections [27].

In this study, we used TFS-UAS combined with DFU to manage large renal calculi with diameters ranging from 2 to 4 cm, achieving relatively positive outcomes. This study observed that the SFR on the first and thirtieth postoperative days using TFS-UAS were 87.20% and 95.20%, respectively, significantly higher than the control group’s rates of 73.45% and 85.84%. The observation group experienced complications including one case of postoperative fever and another of mucosal damage in the renal pelvis during sheath placement, with an overall complication rate of only 1.6%, which was lower than the control group’s rate of 14.15%.

First, the TFS-UAS features a wide range of bending angles, allowing access to the renal pelvis, upper-middle, and most lower calyces, while preserving the ureteroscope’s bending and steering flexibility. Consequently, flexible control of the aspiration sheath during surgery leads to high stone clearance rates and reduced complications. Second, the technique uses low negative pressure aspiration to maintain a low-pressure state in the renal pelvis, drawing perfusion fluid into the aspiration bottle while keeping the renal pelvis or calyces adequately filled. The combination of these factors facilitates flexible movement of the ureteroscope within the renal pelvis and calyces. This approach allows for the effective removal of stone debris via efficient irrigation fluid circulation, maintains clear visibility, and prevents laser energy-induced damage to the renal pelvis and calyceal mucosa. In patients with infectious stones, the renal pelvic mucosa becomes more fragile from prolonged infection and stone irritation, elevating the risk of bleeding. In such cases, stones are fragmented before retrieval without aspiration during the fragmentation process to mitigate this risk. Stone aspiration uses lower suction levels to avoid mucosal damage from excessive aspiration force, thus preventing renal pelvic mucosal bleeding during surgery. However, clearing kidney stones from lower calyces with challenging angles continues to be difficult. To address these stones, the study positions the sheath opening as close to the calyceal neck as possible when the IPA is too acute for direct access. The ureteroscope is inserted into the calyx, and the assistant is instructed to apply pressure on the affected renal area to minimize angles and facilitate stone location. Irrigation flow is moderately increased, using high-pressure irrigant to help flush out fragmented stones.

Unlike other studies [12, 13], the average operative time for the observation group in this study was notably longer compared to the control group. In the observation group, the flexible ends of the ureteroscopic sheaths could reach all renal calyces, allowing for the effective use of this flexibility during surgery to extract shattered stones via vacuum suction. However, larger stone fragments (approximately 2–3 mm in diameter) were challenging to remove within the confined space of the sheath, necessitating the withdrawal of the ureteroscope to facilitate stone extraction. To maximize the stone-free rate in a single procedure, frequent scope withdrawals for stone clearance were required, consuming additional surgical time. In contrast, the control group employed a method aimed at pulverizing stones, as their sheaths could not reach the renal calyces, leaving more fragments to be expelled postoperatively via a double-J stent. Consequently, the average surgical time for the observation group was (101.17 ± 25.64) minutes, longer than that for the control group (86.23 ± 20.35) minutes. However, the observation group, equipped with vacuum suction control, maintained a clear surgical field and safe intrapelvic pressures, hence not increasing the complication rate with extended surgery time unlike traditional ureteroscopic sheaths. Initially, using flexible sheaths, the technique of simultaneous fragmentation and suction occasionally caused larger particles to lodge in the sheath gap, potentially damaging the sheath’s plastic surface upon forced removal, yet not impairing its visibility or flexibility. With advancements and improvements in surgical techniques, especially using pulverization to reduce stone size followed by collective suction, the likelihood of ureteroscope damage significantly decreased.

This study has certain limitations; primarily, it utilized a retrospective research methodology and involved a small sample size, which may affect the accuracy of the conclusions. Initially, standard ureteroscopic sheaths were used for stone removal, while later stages predominantly used flexible-tip suction sheaths, and the chronological variation might also influence the outcomes. Therefore, a larger-scale prospective comparative study is required to validate our hypotheses.

In conclusion, the use of TFS-UAS combined with DFU for treating renal stones of 2–4 cm in diameter demonstrates a high stone clearance rate and good safety profile, indicating substantial clinical value.