Presented by: Bingyuan Yang MB BChir
University of Oxford

Introduction

Residual stone dust and fragments following ureteroscopy are a problem for clinicians and patients. They are thought to contribute to lower stone-free rates and higher rates of recurrence. There is little evidence on the effectiveness of intraoperative irrigation in removing these fragments. Furthermore, opinion is divided as to whether all stone fragments should be extracted surgically, or whether fine particles may be left to wash out of the kidney naturally. We present an in vitro model using canine urinary stone investigating the effectiveness of ureteroscopic irrigation at evacuating stone fragments of known size.

Materials

Stone dust was produced from canine struvite stone using a Ho:YAG laser at 2J 30Hz. This dust was then wet sieved into fractions consisting of particles of <63um, 63-125um, 125-250um, 250-500um, 500-1000um and 1000-2000um. Equal dry masses of each fraction were combined to form 0.5g of dry uniform stone dust mix.

The uniform stone dust was introduced into the mid-pole calyx of an anatomical kidney and ureter model (Pulse Medical Demonstration Models, USA). The model was filled with water and placed supine, and a single-use digital flexible ureteroscope (LithoVue, Boston Scientific Corp, USA) introduced to the kidney and aimed towards the dust. The dust was irrigated via the scope for 30 minutes at 15 ml/min using a pump, after which the model was brought into a vertical position. All remaining particles in the model after this final manoeuvre were deemed to be residual. These residual particles were collected and wet sieved to categorise them by size.

Results

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Particles of size >250um predominantly remained in the kidney, with 83-88% of these particles remaining after irrigation. Particles <250um washed out more effectively but 40-48% of these particles still remained after irrigation.

Conclusion

The size of particles has a major impact on the effectiveness of irrigation, with a sharp contrast above and below 250um. Despite 30 minutes of targeted irrigation at clinically representative rates, over 83% of particles >250um remained in the kidney. The size and large number of these particles would make them both technically challenging and extremely time-consuming to extract clinically using a stone basket. Further work will be done to investigate the effect of irrigation rate and duration on particle washout.

Disclaimer: Bench test results may not necessarily be indicative of clinical performance.

Funding

Boston Scientific Corporation: research grant

Co-Authors

Aditi Ray, PhD
Boston Scientific Corporation

James Zhang, PhD
Boston Scientific Corporation

Ben Turney, FRCS DPhil
University of Oxford