Novel small fragment removal system may improve extraction of renal calculi: an in vitro study

Objective: To describe a novel Small Fragment Removal System (SFRS) which is hypothesized to improve stone fragment removal during flexible ureteroscopy in patients with urolithiasis. The SFRS consists of three parts: a Syphon Ureteric Access Sheath (SUAS), a Dual Action Pump (DAP) and an Agitator. This bench assessment aims to assess the SFRS's impact on intra-renal pressure (IRP), irrigant flow rate and stone fragment removal compared to a traditional UAS.

Materials and methods: A validated phantom kidney and fibre optic pressure sensor was used to assess IRP. Standardized irrigation via a flexible ureterorenoscope was instilled through a traditional UAS and compared to the novel SFRS. Both were 11/13Fr in size. Measured minute volume, IRP and percentage of stone fragments removed were compared.

Results: The mean IRP using a traditional UAS and SFRS was 24,3mmHg and 9,4mmHg respectively. The flow rate of the traditional UAS was 25mL/min, compared to 31mL/min with the SFRS attached. During bolus fluid administration using the traditional UAS the maximum IRP increased to 41mmHg, compared to 9,3mmHg with the SFRS attached. A mean of 42,7% (0,103 g of 0,305 g) of weighed dry stones were removed with the traditional UAS compared to 77,6% (0,233 g of 0,299 g) with the SFRS attached, p = 0,017.

Conclusions: The described Small Fragment Removal System (SFRS) is different from traditional UASs by incorporating a syphoning mechanism. In addition, it has a Dual Action Pump which both boluses and augments the aspiration of irrigant by the Syphon. It further includes a deflectable Agitator to flush out stone fragments.