Working tools in flexible ureterorenoscopy - Influence on flow and deflection: What does matter?

Introduction: Flexible renoscopes offer access to almost all points within the collecting system. For stone workup, excellent visualization is mandatory. Therefore, irrigation flow is of critical importance. The aim of this study was to evaluate the effect of tools and probes on deflection angle and irrigation flow volume in the latest generation of flexible renoscopes. Methods: Five flexible renoscopes [Wolf (Viper), Storz (FlexX(2)), ACMI (DUR-8 Elite, DUR-D), Olympus (URF-P5)] were tested. Deflection angle, lowest diameter of the bent tip, and flow rates were measured. Recorded parameters were deflection angle and flow rate of the empty and loaded scopes. A laser probe (273 mu m), biopsy forceps (2.4-3.0 French), and tipless nitinol baskets (1.5-2.4 French) were tested. Results: Deflection has no influence on flow rate. The size of the basket has no influence on the maximum angle of deflection. Introducing the laser fiber or the biopsy forceps leads to relevant loss of deflection (laser fiber: 4.44%-10.21%; biopsy forceps: 30.7%-57.8%). The inner diameter of the bent tip increases with introduction of a laser fiber (+1 to 3 mm) or the biopsy forceps (+13 to 34 mm). Flow rates are dependent on the size of the tool used. Loss of irrigation volume varies from 62.24% (1.5 French) to 99.1% (3.0 French). The use of a laser fiber leads to a decrease in irrigation volume of 53.7%. Conclusion: Irrigation flow, loss of deflection, and intraoperative visualization are dependent on the working tool used. The provided data, in awareness of the patient's anatomy, help to select scopes, probes, and tools correctly for successful ureterorenoscopy.