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Ureteral Access Sheath (UAS)

Coaxial tube-and-dilator system placed retrograde over a guidewire into the ureter to serve as a working conduit for repeated passage of a flexible ureteroscope during retrograde intrarenal surgery (RIRS). Improves irrigation flow, substantially reduces intrarenal pressure (IRP), and enables efficient stone-fragment / tumor-biopsy retrieval — at the cost of measurable ureteral-wall injury during placement. For the reconstructive surgeon, the UAS is encountered during diagnostic / therapeutic flexible ureteroscopy for UTUC, stricture, iatrogenic ureteral injury workup, and post-reconstruction surveillance — the procedural settings detailed on the flexible ureteroscope page.[1][2]

Design​

  • Two components — inner tapered dilator (advanced over a 0.035-inch guidewire to dilate the ureter) and outer sheath (left in place as working conduit).[1][3]
  • Hydrophilic outer coating to reduce friction during insertion.
  • Radiopaque markers for fluoroscopic positioning.
  • Wall rigidity sufficient to resist kinking; flexibility sufficient to navigate ureteral curves.
  • Dual-wire (classic) vs single-wire configurations; single-wire has lower buckling force but higher dilator-removal force.

Bench data (De 2015) comparing four commercial sheaths: Navigator HD most lubricious and rigid; Cook Flexor (Parallel and Regular) least traumatic to tissue; Re-Trace longest, most flexible tip (51 mm).[3]

Sizes​

UAS sizes are designated by inner / outer French; lengths 13–55 cm (shorter for females, longer for males / proximal-ureteral access).

Size (in/out Fr)Typical use
9.5/11.5Small or pediatric ureter; smallest profile
10/12Standard RIRS with thin scope; multiple brands
11/13Common default
12/14Most-studied size; balance of access and safety
14/16Large stone burden, infectious stones; improved irrigation outflow, lower infectious complications vs 12/14[4]
16/18Rarely used; generally requires pre-stenting

Intrarenal Pressure (IRP) — The Principal Physiological Benefit​

Without a UAS, mean IRP during fURS reaches 47.6–64 mmHg — above the safety threshold of 30–40 cmH₂O that triggers pyelovenous and pyelolymphatic backflow and infectious-complication risk.[5][6]

UAS placement creates a low-resistance outflow pathway around the scope, dropping IRP into the safe range:[6][7][8]

ConditionMean IRP
Scope alone64 mmHg
11/13 UAS51 mmHg
12/14 or 13/15 UAS39–40 mmHg
UAS tip in renal pelvis24 mmHg
UAS tip at UPJ61 mmHg

The scope-to-sheath ratio matters — a 12/14 UAS with a 2.8 mm scope maintains safe IRP at irrigation up to ~ 80 cc/min.[7]

Suction Sheaths — Vacuum-Assisted UAS / FANS​

Vacuum-assisted UAS (vaUAS) and Flexible and Navigable Suction (FANS) sheaths add active suction through the sheath, dramatically lowering IRP and adding active dust evacuation:[9][10]

  • Conventional UAS at 60–70 cc/min irrigation → IRP ~ 30 mmHg.
  • vaUAS (vent closed) → IRP < 5 mmHg.
  • FANS sheath has a bendable tip that can be navigated into individual calyces.

RCT data on FANS vs traditional UAS:

StudyOutcome
Xie 2025 SR / meta[11]FANS — immediate SFR 79.1% vs 56.5%; total complications 7.2% vs 19.0%; postop fever 3.3% vs 10.4%
Arikan 2025 multicenter RCT[12]FANS — shorter OR time, higher early SFR, particular benefit in hydronephrosis

Ureteral Injury — PULS Classification and Risk Factors​

The principal complication of UAS placement is ureteral-wall injury. The Traxer / Thomas Post-Ureteroscopic Lesion Scale (PULS):[13]

GradeInjury
0No lesion
1Mucosal erosion only
2Mucosal + submucosal (perforation without muscle injury)
3Smooth-muscle injury
4Complete wall perforation, periureteral fat visible

In the original 359-patient series: 46.5% had some injury, 13.3% severe (≥ grade 3).[13] Predictors:

  • No preoperative DJ stenting → severe-injury risk × 7 (pre-stenting markedly protective).[14]
  • Sheath size: 12/14 vs 9.5/11.5 → high-grade injury 11.9% vs 5% (p = 0.013); stricture rate not significantly different (2.5% vs 0.6%).[4]
  • Force-guided insertion (Ali 2026): ≤ 6 N threshold permitted safe passage in 58%, with zero PULS-3 injuries; both high-grade injuries occurred at ≥ 8 N. Pre-stenting OR 3.05 for safe passage.[15]
  • Subjective difficult placement and longer insertion time correlate with high-grade injury (Loftus 2020).[16]

Long-Term — Clinical Stricture Risk​

Despite the high incidence of endoscopic injury, clinically significant strictures are rare:

  • Stern 2019 — 56 patients with high-grade UAS injuries: 1 de-novo stricture (1.8%) at median 35.8-mo FU; comparable to no-injury rate.[17]
  • Cooper 2020 — 1,332 ureteroscopies: stricture rate 1.0%; UAS use not associated with postop hydronephrosis.[18]

That said, the broader stricture-risk picture from population data (Sunaryo 2022, see semi-rigid ureteroscope page) shows UAS use as one of several risk factors (OR 4.6 in that analysis) and PULS-3 transmural injury carries up to 13.3% stricture rate.

Stone-Free Rate — Debated​

  • CROES (Traxer 2015, n = 2,239) — UAS vs no UAS: unadjusted 75.3% vs 50.4%, not significant after propensity adjustment (p = 0.604); UAS reduced infectious complications.[19]
  • Huang 2018 meta (8 trials, n = 3,099) — no SFR difference (OR 0.83, p = 0.45).[20]
  • Bakayoko 2025 multicenter real-world — comparable SFR; UAS associated with longer OR time and higher post-op stenting rates.[21]
  • Tracy 2018 — 14/16 UAS treated 30% more stone burden per minute than 12/14 at equivalent SFR and complication rates.[22]

Infectious Complications — UAS Protects​

  • Villa 2023 (tertiary center) — URS without UAS carried OR 14.6 (95% CI 1.08–197.1) for septic shock (no significant effect on fever / sepsis alone).[23]
  • Chen 2018 — 14/16 vs 12/14 UAS — infectious complications 1.6% vs 6.4%; in stones > 2 cm or infectious stones, 3.1% vs 15.0%.[4]
  • CROES — reduced postop infectious complications with UAS.[19]

Ureteroscope-Protection Effect — Inconclusive​

Theoretical advantage; Özman 2024 found ureteroscope lifespan not correlated with rate of sheathless cases, but strongly correlated with frequency of lower-calyx procedures.[24]

Strategies to Facilitate UAS Placement​

  • Pre-stenting for ≥ 1 week — single most effective; × 7 reduction in severe injury and increased successful passage of larger sheaths.[13][15]
  • Force-guided insertion ≤ 6 N — eliminates high-grade injury in bench / clinical-force data.[15]
  • Downsize on resistance — switch to a smaller sheath rather than force.[16]
  • Tamsulosin — evidence unclear; one force-sensor study showed no benefit.[15]

Evolving Position — When Is UAS Still Essential?​

Three contemporary developments may reduce routine UAS need:[25]

  1. Thulium fiber laser — finer dust, less retrieval burden.
  2. Smaller single-use digital ureteroscopes (7.5 Fr) — safe IRP up to 120 cc/min irrigation without a UAS.[8]
  3. Integrated pressure-measuring and aspiration platforms — active IRP monitoring and pressure control.

UAS remains valuable for large stone burden, infectious stones, planned repeated scope passes, planned UTUC biopsy / ablation, and any setting where sustained low IRP is the priority.

Reconstructive-Urology Positioning​

In WARWIKI scope, the UAS is encountered when fURS is required for:

  • UTUC diagnostic biopsy and laser ablation (kidney-sparing endoscopic management).
  • Iatrogenic ureteral injury workup proximal to the UPJ.
  • Stricture mapping at the proximal ureter / pelvis / calyces.
  • Post-reconstruction surveillance of pyeloplasty / ureteral-reimplantation / ileal-ureter anastomoses.

Pre-stenting is especially important in the previously instrumented / radiation-bed / post-pelvic-surgery ureter — the cost of UAS-related injury here is much higher because the next operation may be open reconstructive repair.

See also: Flexible Ureteroscope, Semi-Rigid Ureteroscope, Guidewires, Open-Ended Ureteral Catheters, Double-J Stent, Nephrostomy Tube.

References​

1. Kaplan AG, Lipkin ME, Scales CD, Preminger GM. "Use of ureteral access sheaths in ureteroscopy." Nat Rev Urol. 2016;13(3):135–40. doi:10.1038/nrurol.2015.271

2. De Coninck V, Keller EX, Rodríguez-Monsalve M, et al. "Systematic review of ureteral access sheaths: facts and myths." BJU Int. 2018;122(6):959–69. doi:10.1111/bju.14389

3. De S, Sarkissian C, Torricelli FC, Brown R, Monga M. "New ureteral access sheaths: a double standard." Urology. 2015;85(4):757–63. doi:10.1016/j.urology.2014.07.009

4. Chen Y, Liao B, Feng S, et al. "Comparison of safety and efficacy in preventing postoperative infectious complications of a 14/16 F ureteral access sheath with a 12/14 F ureteral access sheath in flexible ureteroscopic lithotripsy." J Endourol. 2018;32(10):923–7. doi:10.1089/end.2018.0222

5. Croghan SM, Skolarikos A, Jack GS, et al. "Upper urinary tract pressures in endourology: a systematic review of range, variables and implications." BJU Int. 2023;131(3):267–79. doi:10.1111/bju.15764

6. Chew BH, Shalabi N, Herout R, et al. "Intrarenal pressure measured using a novel flexible ureteroscope with pressure-sensing capabilities: a study of the effects of ureteral access sheath, irrigation, and working channel accessories." J Endourol. 2023;37(11):1200–8. doi:10.1089/end.2022.0841

7. Guan W, Liang J, Wang D, et al. "The effect of irrigation rate on intrarenal pressure in an ex vivo porcine kidney model — preliminary study with different flexible ureteroscopes and ureteral access sheaths." World J Urol. 2023;41(3):865–72. doi:10.1007/s00345-023-04295-1

8. Han Z, Wang B, Liu X, et al. "Intrarenal pressure study using 7.5 French flexible ureteroscope with or without ureteral access sheath in an ex-vivo porcine kidney model." World J Urol. 2023;41(11):3129–34. doi:10.1007/s00345-023-04598-3

9. Gadzhiev N, Aloyan A, Yuen SKK, et al. "Intrarenal pressure variations during flexible ureteroscopy in a porcine kidney model: impact of ureteral access sheath types and irrigation methods." World J Urol. 2025;43(1):501. doi:10.1007/s00345-025-05857-1

10. Wang D, Han Z, Bi Y, et al. "Comparison of intrarenal pressure between conventional and vacuum-assisted ureteral access sheath using an ex vivo porcine kidney model." World J Urol. 2022;40(12):3055–60. doi:10.1007/s00345-022-04149-2

11. Xie Y, Gong H, Zheng Q, et al. "Efficacy and safety of flexible and navigable suction access sheaths versus traditional access sheath in flexible ureteroscopic lithotripsy: a systematic review and meta-analysis." World J Urol. 2025;43(1):487. doi:10.1007/s00345-025-05856-2

12. Arikan O, Erdogan E, Aydin ME, et al. "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." J Endourol. 2025;39(7):646–51. doi:10.1089/end.2024.0921

13. Traxer O, Thomas A. "Prospective evaluation and classification of ureteral wall injuries resulting from insertion of a ureteral access sheath during retrograde intrarenal surgery." J Urol. 2013;189(2):580–4. doi:10.1016/j.juro.2012.08.197

14. Fulla J, Prasanchaimontri P, Rizk A, et al. "Ureteral diameter as predictor of ureteral injury during ureteral access sheath placement." J Urol. 2021;205(1):159–64. doi:10.1097/JU.0000000000001299

15. Ali SN, McCormac A, Saadat S, et al. "Ureteral access sheath deployment: understanding the force tolerance of the human ureter and the development of ureteral injury during endoscopic surgery." J Endourol. 2026;40(3):296–302. doi:10.1177/08927790251400350

16. Loftus CJ, Ganesan V, Traxer O, et al. "Ureteral wall injury with ureteral access sheaths: a randomized prospective trial." J Endourol. 2020;34(9):932–6. doi:10.1089/end.2018.0603

17. Stern KL, Loftus CJ, Doizi S, Traxer O, Monga M. "A prospective study analyzing the association between high-grade ureteral access sheath injuries and the formation of ureteral strictures." Urology. 2019;128:38–41. doi:10.1016/j.urology.2019.02.032

18. Cooper JL, François N, Sourial MW, et al. "The impact of ureteral access sheath use on the development of abnormal postoperative upper tract imaging after ureteroscopy." J Urol. 2020;204(5):976–81. doi:10.1097/JU.0000000000001147

19. Traxer O, Wendt-Nordahl G, Sodha H, et al. "Differences in renal stone treatment and outcomes for patients treated either with or without the support of a ureteral access sheath: the CROES ureteroscopy global study." World J Urol. 2015;33(12):2137–44. doi:10.1007/s00345-015-1582-8

20. Huang J, Zhao Z, AlSmadi JK, et al. "Use of the ureteral access sheath during ureteroscopy: a systematic review and meta-analysis." PLoS One. 2018;13(2):e0193600. doi:10.1371/journal.pone.0193600

21. Bakayoko A, Mardelli C, Dupuis H, et al. "Does the use of a ureteral access sheath improve perioperative outcomes in ureteroscopy? A real-world multi-institutional study." Urolithiasis. 2025;53(1):182. doi:10.1007/s00240-025-01865-3

22. Tracy CR, Ghareeb GM, Paul CJ, Brooks NA. "Increasing the size of ureteral access sheath during retrograde intrarenal surgery improves surgical efficiency without increasing complications." World J Urol. 2018;36(6):971–8. doi:10.1007/s00345-018-2204-z

23. Villa L, Dioni P, Candela L, et al. "Understanding the role of ureteral access sheath in preventing postoperative infectious complications in stone patients treated with ureteroscopy and Ho:YAG laser lithotripsy: results from a tertiary care referral center." J Clin Med. 2023;12(4):1457. doi:10.3390/jcm12041457

24. Özman O, Başataç C, Akgül M, et al. "The effect of ureteral access sheath use / caliber change on outcomes of retrograde intrarenal surgery, short-term kidney functions, radiation exposure, ureteroscope lifetime, and factors predicting insertion failure: a RIRSearch study." J Laparoendosc Adv Surg Tech A. 2024;34(1):33–8. doi:10.1089/lap.2023.0358

25. De Coninck V, Somani B, Sener ET, et al. "Ureteral access sheaths and its use in the future: a comprehensive update based on a literature review." J Clin Med. 2022;11(17):5128. doi:10.3390/jcm11175128