The Vortex Effect in Minimally Invasive Percutaneous Nephrolithotomy

Introduction: Minimally invasive percutaneous (MIP) nephrolithotomy was initially discredited with assumptions of difficult stone fragment retrieval because of the equipment's smaller size. However, in 2008 Nagele et al. described a hydrodynamic phenomenon that allowed stone retrieval without the aid of endoscopic tools.1–3 This study aims to describe the physical principles of the “vortex effect” to better understand its applicability in MIP procedures. Methods: Two acrylic phantom models were built based on the cross-sectional area (CSA) ratio of an MIP nephroscope and access sheaths (15/16F and 21/22F MIP-M™, Karl Storz®). The nephroscope–phantom was 10 mm in diameter. The access sheaths had diameters of 14 mm (CSA ratio: 0.69) and 20 mm (CSA ratio: 0.30). The models were adapted to generate hydrolysis, and hydrogen bubbles enhanced flow observation on a green laser background. After calibration, the experimental flow rate was set to 12.0 mL/sec. Three 30-second trials assessing the flow were performed with each model. Computational fluid dynamic simulations were completed to determine the speed and pressure profiles. Results: In both models, as the incoming fluid from the nephroscope–phantom attempted to move toward the collecting system, a stagnation point (SP) was demonstrated. No fluid entered the collecting system phantom. Utilizing the 14 mm sheath, we observed a random generation of several vortices and a pressure gradient (PG) of 114.4 Pa between the nephroscope's tip and SP. When the 20 mm sheath was examined, a significantly smaller PG (19.4 Pa) and no noticeable vortices were noted. Conclusions: The speed of the fluid and equipment geometry regulate the PG and the vortices field, which are responsible for the production of the vortex effect. Considering the same flow rate, a higher ratio between the CSA of the nephroscope and access sheath results in improved efficacy of the vortex. Patient Consent Statement: This is a bench study. No patients were involved in this study. Consent statements are not applicable to this type of study. W.R.M. reports a relationship with Olympus Surgical Technologies America that includes consulting or advisory, funding grants, and speaking and lecture fees. W.R.M. reports a relationship with Boston Scientific Corp that includes consulting or advisory, funding grants, and speaking and lecture fees. W.R.M. reports a relationship with Fortec that includes consulting or advisory, funding grants, and speaking and lecture fees. W.R.M. reports a relationship with IPG that includes consulting or advisory, funding grants, and speaking and lecture fees. D.A.N. reports a relationship with Boston Scientific Corp that includes consulting or advisory, funding grants, and speaking and lecture fees. D.A.D. reports a relationship with Lumenis Inc Americas that includes consulting or advisory, funding grants, and speaking and lecture fees. All other authors have no disclosures to inform. Runtime of video: 8 mins 00 secs This video article was presented at the AUA 2023 in Chicago.