Flexible and navigable suction access sheaths: what size stone particles can be cleared?

OBJECTIVES

To perform benchtop experiments on flexible and navigable suction (FANS) ureteric access sheaths (UASs) to determine the clearance capabilities for various stone sizes when paired with different-sized ureteroscopes.

METHODS

Quartz stones were used as a surrogate for renal stones. Stone samples were created to simulate the range of particle sizes produced by 'dusting' a 1-cm calcium oxalate monohydrate stone. The stone mixture was introduced into an open vial at a 30° angle in aliquots every 3 min over the course of 30 min, mimicking their gradual production by lasertripsy. This benchtop model focused on the effects of geometry (between FANS access sheath and ureteroscope) and suction, excluding complex fluid flow. An 11/13-F ClearPetra® FANS UAS with an indwelling ureteroscope was free to move in the vial and targeted visible stones. The vial was intermittently filled to 40 mL with water and emptied using 200-mmHg suction. The experiment had two arms: (1) a permanently indwelling ureteroscope in the FANS UAS to mimic continuous lasering with aspiration and (2) intermittent withdrawal of the ureteroscope to mimic pausing lasering to clear larger fragments through the empty FANS sheath lumen. Three ureteroscope sizes were used: 9.5-F (Lithovue™), 7.5 F (PUSEN) and 6.3 F (Hugemed). The experiment was performed three times for each ureteroscope.

RESULTS

With a permanently indwelling 9.5-F ureteroscope, the FANS UAS cleared 64% of the overall stone mass but became blocked after an average of 21 min. Intermittent withdrawal of the ureteroscope cleared all stones. With indwelling 7.5-F and 6.3-F ureteroscopes, the FANS UAS did not become blocked and completely cleared stones of up to 500 μm and 2 mm, respectively.

CONCLUSIONS

Without withdrawing the ureteroscope (potentially allowing continuous lasertripsy), it is possible to continuously aspirate small fragments alongside a 7.5-F and a 6.3-F ureteroscope in an 11/13-F FANS UAS. Intermittent withdrawal of either of the ureteroscope from the FANS UAS allows complete stone clearance.