A Comparative Study Between the Usage of Flexible and Navigable Suction Ureteral Access Sheath Versus Traditional Access Sheath in Retrograde Intrarenal Surgeries

Urinary calculus is a worldwide urological disease, with a prevalence ranging from 1% to 13% in different regions . Currently, the main therapeutic methods beyond conservative treatment for renal calculi include extracorporeal shock wave lithotripsy (ESWL) and minimally invasive endoscopic surgical methods, including percutaneous nephrolithotomy (PCNL) and retrograde intrarenal surgery (RIRS). Treatment plans depend on the characteristics of calculi, patient factors, surgeon experience and the condition of medical centers .

Technological advancements in RIRS have been numerous in recent years, with the introduction of single-use flexible ureteroscopes and higher-power lasers being the most notable. High intrarenal pressure (IRP) can lead to pyelovenous backflow and infection from transient bacteraemia, particularly during laser lithotripsy. Another major concern is the retention of residual fragments (RFs), which are pieces that are hidden from view because of the snow-globe effect .

Therefore, in order to facilitate the clearance of RF and enhance the overall performance of RIRS, a variety of adjuncts have been developed, including pressure sensors to regulate IRP, a direct in-scope vacuum technique to aspirate dust, and stone retrieval devices that utilize suction technologies .

These objectives are all designed to achieve the triumvirate of successful RIRS: a high stone-free rate (SFR), minimal ancillary interventions, and minimal complications-the ultimate goal of all RIRS surgeons .

The ureteral access sheath (UAS) has been used in RIRS to reduce IRP and hence infectious complications, as well as to improve drainage, stone clearance, and intraoperative vision, thus shortening operative time. However, there still remains some debate over the ideal UAS size - too large risks injuring the ureteral mucosa and causing ischaemia, while too small defeats its purpose of improving drainage .

The addition of suction to a traditional UAS resulted in the conception of suction ureteral access sheath (SUAS). As demonstrated in clinical studies, the SUAS has the potential to reduce intrarenal temperature and pressure, thus reducing infectious complications and improving SFR .

Nevertheless, the SUAS continues to exhibit certain constraints . If it is positioned below the uretero-pelvic junction (UPJ), as is the case with the traditional UAS, the application of suction results in the collapse of the proximal ureteral mucosa. This reduces the calibre of the narrow UPJ and impedes the aspiration of RF by acting as a functional valve to block the opening of the UAS. Despite being positioned across the UPJ, it is incapable of overcoming acute angles or reaching distant calyces to facilitate the complete aspiration of particulate that has settled in dependent calyces .

A flexible-tip SUAS, also known as the flexible and navigable suction UAS (FANS), was developed as a natural evolution. This SUAS could be navigated using the flexible scope. FANS can be securely maneuvered into individual calyces under fluoroscopic guidance to remove fragments and dust more thoroughly and targeted through suctioning .