Since the first description in 1974 of the ureteral access sheaths (UAS), its use during retrograde intrarenal surgery (RIRS) has showed multiple benefits. In addition, due to minimizing intra renal pressure (IRP), it could decrease the incidence of infectious complications after ureteroscopy, that have an overall incidence of 10% after RIRS. Nonetheless, there is still discordant data about the role of UAS in decreasing the risk of UTI and sepsis, and the use of UAS may cause lesions to the ureter by direct trauma during sheath insertion or affecting blood flow during its usage. During the last 10 years, suction access sheaths for mini-PCNL and RIRS have sparked interest among endourologists as they may achieve higher stone-free rates (SFR) and lower complication rates. In this paper, we perform a narrative review, covering the current evidence regarding flexible and navigable ureteral access sheath for RIRS.

Keywords

Ureteroscopy, suction, UAS, RIRS, stone

Since the first description in 1974 of the ureteral access sheaths (UAS) [1], its use during retrograde intrarenal surgery (RIRS) has showed multiple benefits, such as facilitating multiple entries into the kidney during the procedure and achieving better vision due to improved irrigation and outflow, washing out small stone particles created during lithotripsy, a feature that may improve stone clearance [2]. In addition, due to minimizing intra renal pressure (IRP), it could decrease the incidence of infectious complications after ureteroscopy [3]. Urinary tract infections (UTI) and sepsis still represent a major issue, with an overall incidence of 10% after RIRS [4]. Nonetheless, there is still discordant data about the role of UAS in decreasing the risk of UTI and sepsis [5], and the use of UAS may cause lesions to the ureter by direct trauma during sheath insertion or affecting blood flow during its usage [6, 7].
The study of IRP has been more frequently debated, since a prolonged increase in IRP can lead to complications, especially related to pyelorenal backflow, leading to potential severe complications [8]. During the last 10 years, suction access sheaths for mini-PCNL and RIRS have sparked interest among endourologists as they may achieve higher stone-free rates (SFR) and lower complication rates [9-12]. In this paper, we perform a narrative review, covering the current evidence regarding flexible and navigable ureteral access sheath for RIRS.

We performed a comprehensive English literature research for original and review articles through December 2024 and January 2025, using Pubmed and Embase databases, as well as a comprehensive review of The American Urological Association (AUA) guidelines and European Association of Urology (EAU) Guidelines. We searched for the following terms: "ureteral access sheath", "flexible navigable ureteral access sheath", "flexible navigable suction ureteral access sheath". and "(("Ureteral Access Sheath" OR "ureteral access sheath" OR "UAS") AND ("Aspiration" OR "Suction") AND ("Retrograde Intrarenal Surgery" OR "RIRS" OR "Flexible Ureteroscopy") AND ("Kidney Calculi"[Mesh] OR "renal stones" OR "nephrolithiasis" OR "urolithiasis")).
The combination of terms found 794 related articles; articles that were not in English, case reports, editorials, duplicated papers and papers without available abstract were not considered for this review. After the initial screening, 43 full-text studies were left for evaluating eligibility. Finally, 21 papers were considered eligible and included in this review (Figure 1).

The European Association of Urology (EAU) accepts the use of UAS as part of routine practice in RIRS, being safe and useful for large and multiple renal stones, or if a long procedural time is expected [13, 14]. The American Urological Association (AUA) guidelines also discusses their positive role, but there is no specific recommendation for patient selection for UAS selection [14, 15]. Currently, there is insufficient evidence to create consensus on suction access sheaths. The European Association of Urology (EAU) guidelines do not mention ureteral FANS, but they remark that there is some evidence regarding suction access sheaths for mini-PCNL in order to reduce IRP and increase SFR [13, 16]. The American Urological Association (AUA) does not mention any recommendations regarding these devices [15].

FANS-UAS stone-free rate

Of the 21 studies analyzed, 20 reported stone-free rate (SFR) in their results (Table 1), defining it as the sum of SFR-A (no residual fragments) and SFR-B (one residual fragment smaller than 2 mm) within the first 30 days. Additionally, SFR-A is also referred to as the Zero-Fragment Rate (ZFR). Two studies in the pediatric population reported a high SFR with FANS-UAS [17, 18]. Seven studies [17, 19-24] compared the performance of FANS-UAS with conventional UAS (CUAS), finding that the initial and final SFR was statistically higher for FANS-UAS. However, the final SFR showed no statistically significant differences in pediatric population [17]. In the adult population, the overall SFR with FANS-UAS was greater than 90%. Two studies [25, 26] stratified their results based on the caliber of the ureteral access sheath. Kwok et al. [25] reported a significantly higher ZFR in the smaller-diameter group (67.5% vs. 52.9%, P = 0.02), but they were not able to find statistically significant differences between smaller and larger diameters for SFR (SFR smaller group: 95.9%; SFR larger group: 95.3%; P > 0.99). In contrast, Gauhar et al. [26] reported better outcomes with larger sheath diameters (SFR 10 Ch: 68.8%; SFR 12 Ch: 94.7%; P < 0.01). However, although Castellani et al. [27] subdivided their cohort into 2 groups according to the source of energy source used for lithotripsy (Thulium-fiber laser (TFL) and Pulsed-Thulium:YAG Laser), the group with the higher stone-free rate (Pulsed-Thulium:YAG laser) also had a greater proportion of cases treated with smaller caliber sheaths (10-12 Ch) than the other group (TFL 12.5%; Pulsed-Thulium:YAG Laser 98.4%, P < 0.001).

Intraoperative IRP and perioperative complications

There were only two papers that described intraoperative IRP measurements during surgery among their results. Chen et al. [8] described and stratified IRP during RIRS with FANS-RIRS according to different variables. IRP was measured using LithoVue Elite™ ureteroscope (Boston Scientific Corp., Marlborough, MA, USA) with pressure sensing capability. The IRP remained below 40 mmHg in 76.2% of the total time in all procedures, but the overall amount of procedure time spent at pressures between 60-80 mmHg and > 80 mmHg was 3.6% and 1.8% respectively. Median IRP was 29.0 mmHg for the 11/13 Ch diameter and 14.0 mmHg for the 12/14 Ch diameter (P = 0.008). Pre-stenting also significantly decreased IRPs (pre-stented 14.5 mmHg; non-prestented patients 29.0 mmHg (P < 0.001)). Other variables significantly associated with lower IRP were the use of preoperative alpha-blocker and having a prior endourological intervention (any ipsilateral URS or ureteral stenting within the last 5 years). Bai et al. [30] measured IRP in 30 patients with a computed numerical control system based on sheath-side fiber optic pressure sensor monitoring, where the fiber optic pressure sensor enters the renal pelvis through a side channel to monitor renal pelvis pressure. During lithotripsy, pressure variated across calyxes and upper ureter, with statistically significant differences (Upper calyx 19.82 ± 0.57; Middle calyx 18.07 ± 0.85; Lower calyx 20.32 ± 0.72; Upper ureter 21.59 ± 1.14; P < 0.001). All values are below the cut-off value of 35–40 mmHg when the pyelotubular back-flow usually occurs [39-41], hence increasing the risk of infectious complications and postoperative pain.
All papers describe an overall complication rate lesser than 20% with the use of FANS (Table 2), including intra and postoperative ones. Most of the complications are Clavien-Dindo grades 1 or 2. The infectious complication rate was rather low. Regarding urosepsis, defined as sepsis (life-threatening organ dysfunction caused by a dysregulated host response to infection) caused by a urogenital tract infection, has an incidence between 0.1 and 4.3% after ureteroscopy [4]. All but one of the papers cited in this article had 0% rate of urosepsis. Giulioni et al. [34] analyzed different suction modalities (via Access Sheath, via Scope and via catheter), with an overall low complication rate for all of them.

Postoperative pain was measured at day 1 after surgery using a 10-point visual analogue score (1-4: mild pain; 5-8: moderate pain; 9-10: severe pain). Eleven papers describe postoperative pain [18, 21, 25, 27-31, 35, 37, 38], reporting low rates of discomfort after surgery.

Surgical times (ST)

We only considered for this section those papers that compared ST according to different features, such as UAS diameter, stone location, suction. energy used for lithotripsy and anesthesiology ventilation modality during surgery (Table 3), including thirteen articles. ST were measured in minutes and divided into three categories: Operative time, ureteroscopy time and laser time.

Turedi et al. [17] , Rico et al. [20] and Kwok et al. [25] found a statistically significant difference in operative time (OT) in favor of the suction UAS and the larger UAS. Regarding ureteroscopy time, only Kwok et al. [25] were able to describe a statistically significant difference for larger UAS. Finally, Castellani et al. [27] and Lim et al. [38] described statistically significant shorter laser times for Pulsed Thulium:YAG laser and Gated ventilation. The rest of the papers did not find differences in ST. In addition, Giulioni et al. [34] described shorter operative times in the different analyzed suction modalities.

Intraoperative ergonomy

Nine papers evaluated subjectively different ergonomics [18, 23, 25, 26, 28, 29, 31, 37, 38] (Table 4). Except for Gauhar et al. [22] that did not use a numeric-scale, and Geavlete et al. [23] that used an ascending scale from 0 to 10, from worst to best, the rest of the articles used a Likert-scale between 1 (excellent) and 5 (difficult) to assess either subjective maneuverability, visibility, manipulation of the sheath and ease of suction. Overall results were between excellent or very good in all sections. Kwok et al. [25] found statistically significant differences in visibility and ease of suction depending on the diameter (better visibility with larger sheaths and easier suction with smaller sheaths). In addition, Gauhar et al. [37] described significant differences in visibility and manipulation depending on the source of energy (results were better in the TFL group compared to the HPHL group).

Study limitations

Our study has some limitations. The nature of its design (narrative review) is not exempt from bias. The included stud¬ies differ significantly in terms of study design and methodologies, patient demo¬graphics, and outcome measures. For instance, many of the studies did not compare FANS-UAS against CUAS. Many of these studies were performed by high-volume experienced centers/surgeons, being difficult to extrapolate these results to less experienced centers.

Current evidence on the safety profile and stone-free rates (SFR) of suction ureteral access sheaths (UAS) demonstrates superior outcomes compared to standard UAS, supporting their recommendation and adoption in routine clinical practice.

Authors contributions

“Conceptualization”, L.E.O.P.; methodology, L.E.O.P.; J.G.R.; validation, L.E.O.P.; J.G.R.; formal analysis, L.E.O.P., E.J.G.R.; investigation, L.E.O.P., E.J.G.R., A.S.P., G.F.J.B.H.; data curation, L.E.O.P.,; writing—original draft preparation, L.E.O.P., E.J.G.R., A.S.P., G.F.J.B.H.; writing—review and editing, L.E.O.P., E.J.G.R., A.S.P., G.F.J.B.H.; supervision, L.E.O.P., A.S.P., E.J.G.R., M.A.R.L., A.S.P., G.F.J.B.H., A.S.B., L.I.V., P.M.D., I.G.R., J.G.R., S.A.G., J.M.S.; All authors have read and agreed to the published version of the manuscript.

Availability of data and materials

Not applicable.

Financial support and sponsorship

None.

Conflicts of interest

All authors declared that there are no conflicts of interest.

Ethical approval and informed consent

Not applicable.

Consent for publication

Not applicable.

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