The incidence of kidney stone disease has been rising globally, leading to greater clinical and economic burden. Ureteroscopy (URS) has emerged as the primary surgical treatment modality for urolithiasis, with various technological advancements significantly enhancing URS safety and efficacy.¹ Thulium fiber and Ho:YAG lasers with pulse modulation allow dusting of stones into finer fragments with lower retropulsion compared with traditional Ho:YAG lasers. The introduction of ureteral access sheaths (UASs) with suction helps reduce intrarenal pressure (IRP), improves stone fragment clearance and visibility, and facilitates instrument exchanges.^2,3

Conventional rigid UASs are limited by their inability to navigate through the ureteropelvic junction or access anatomically challenging calyces. Flexible and navigable suction ureteral access sheaths (FANSs) offer the ability to cross this barrier by deflecting in concert with the flexible ureteroscope to access stones in challenging locations, thus improving stone-free rates and reducing IRP by delivering suction in close proximity to where lithotripsy is occurring.⁴

Notably, FANSs allow the administration of highly pressurized irrigation inflow (200-250 mm Hg) and high continuous suction (200 mm Hg), providing high throughput in the renal collecting system and ideally maintaining the IRP at < 30 mm Hg to avoid complications.^5,6 This not only improves visibility and stone-free rates but minimizes IRP and its potential complications, including patient discomfort/pain, fluid absorption, pyelorenal backflow, forniceal rupture, and urosepsis.⁵ The high throughput within the renal collecting system also leads to a theoretical risk reduction of thermal injury associated with prolonged laser use.⁷

An international, multicenter, randomized controlled trial recently compared safety and efficacy between FANSs and traditional UASs in URS for upper urinary tract stones ≤ 30 mm.⁸ Patients treated with FANSs for renal stones demonstrated higher stone-free rates immediately (on kidney-ureter-bladder x-ray and ultrasonography) and 3 months postoperatively (on low-dose CT), lower overall operative complication rates and postoperative fever rates, lower intraoperative use of stone baskets, and better improvements in quality of life scores, even when adjusted for stone diameter. There were no significant differences in terms of operative time, hospitalization lengths, or retreatment rates. These results highlight the clinical superiority of FANSs over traditional UASs and how they should be incorporated routinely in current endourologic practice to optimize patient outcomes.

We recently conducted a clinical study where IRP was monitored in real time using FANSs during flexible URS for renal stones.³ IRP was automatically measured throughout the intervention using a ureteroscope with pressure-sensing capability, and FANSs allowed continuous high throughput within the renal collecting system.⁹ This allowed for real-time adjustment of suction pressure based on the IRP readings. The median IRP for all cases was 22.0 mm Hg, with a median procedure time of 35.9 minutes. The IRP remained < 40 mm Hg in 76.2% of the total time in all interventions and < 60 mm Hg in 94.1% of the total time. These results demonstrate that FANSs allow for low intrarenal pressures to be maintained despite using high irrigation pressures, providing an optimal balance between mitigating IRP-related complications and achieving higher stone-free rates and enhanced visibility.

This technology has altered the parameters of what is readily achievable using ureteroscopy and laser lithotripsy. Stones > 2 cm have traditionally been treated using percutaneous nephrolithotomy due to its ability to fragment stones and remove large pieces through percutaneous sheaths. Without suction, comminution of larger stones portended a risk of steinstrasse as all the dust and fragments attempted to clear through the ureter. Now with active suction, larger stones can be tackled ureteroscopically with no fear of steinstrasse, as demonstrated in a recent international, multicenter, randomized noninferiority trial comparing flexible URSs with FANSs vs mini–percutaneous nephrolithotomy in treatment of 2- to 3-cm renal stones.¹⁰

Our study also underlined the importance of FANS size on IRP. The ratio of endoscope-sheath diameter (RESD) is the ratio between the outer diameter of the ureteroscope and the inner diameter of the access sheath. Studies have shown that an RESD < 0.85 allows for acceptable flow and low IRP.¹¹ In our standard practice, we generally opt for a UAS size of 2F to 2.5F above the scope size. In our study, median IRP was 29.0 mm Hg for the 11F/13F sheaths (RESD of 0.86) and 14.0 mm Hg for the 12F/14F sheaths. This suggests that the incorporation of suction and high-flow capacity with FANSs allows for lower IRP to be maintained, even when using smaller sheath sizes, which is sometimes necessary to reduce trauma and navigate tighter or more tortuous ureters.

Although FANSs show a promising impact on reducing IRP, caution is still warranted, especially in certain situations. For instance, when working in a calyceal diverticulum or a small renal calyx with a narrow infundibulum, IRP can increase rapidly despite high throughput in the renal collecting system. Additionally, with heavy dusting, stone dust can build up between the scope and the sheath, leading to impaired outflow and increased IRP. In these scenarios, periodic withdrawal of the scope from the FANS may be necessary to minimize the risk of complications, and real-time monitoring of IRP could be useful.¹²

In conclusion, FANS offers promising outcomes in higher stone-free rates, improvements in quality-of-life outcomes, and intraoperative visibility while reducing IRP and its potential operative complications despite the use of high irrigation inflow. The future of stone suction removal is now—with safer, more efficient management of patients with renal stones.