In vitro studies with four flexible deflectable ureterorenoscopes were conducted for flow, pressure, and deflection characteristics. Various modes of irrigation were implemented including gravity, hand (syringe), and roller pump (Uromat). The addition of a 3.0F instrument in the working port of a 3.6F flexible ureterorenoscope resulted in a hydraulic resistance 1300 times greater than baseline (no instrument present). The same 3.0F instrument in a 4.0F channel increased resistance to 264 times control. The resistance to flow was significantly reduced if a 2.5F or 2.0F instrument or a 0.7F laser fiber was placed in the working port. Mechanical irrigation (either by hand or with the roller pump) was required to overcome these high resistances and provide an adequate flow of irrigation fluid. We found the combination of a 4.0F working port, smaller inserted instruments (2.0F-2.5F), and the addition of a mechanical form of irrigation to be optimal in terms of irrigant flow and visibility during flexible ureterorenoscopy.
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