Editorial Comment on: Fluid Dynamic Analysis of Hand-Pump Infuser and UROMAT Endoscopic Automatic System for Irrigation Through a Flexible Ureteroscope by Lama et al.

In the flexible ureteroscope surgery, the superior “flow rate” with the irrigation is definitely important, because better surgical performance could be achieved by clear vision of the operation field. One research regarding this point has been published in the Journal of Endourology (Daniel Lama, et al. In J Endourol. 2018/01/24 Apr 5). In their article, the authors presented the important information about the irrigation “flow rate” characteristics in a flexible ureteroscope, which was produced by a manual and automated-pump irrigation system. With their relatively simple research, the authors clearly showed that the E.A.S.I.^® pump provided more stable “flow rate” and “irrigation pressure” than the hand-pump infuser.

With concerning about efficacy “flow rate” of the irrigation in the ureteroscope, understanding of the physics, in other word hydrodynamics, is very helpful. As the authors mentioned in their article, the principle of hydrodynamics is that “flow rate” impacts “irrigation pressure” and “resistance” also impacts “irrigation pressure.” In another words, “flow rate” occurs as a result of the relationship between “irrigation pressure” and “resistance.” The relationship is expressed by the following equation: “Flow rate” = “irrigation pressure”/“resistance.” ^1,2 To achieve the effective “flow rate,” it is required to increase the “irrigation pressure” at the working channel or to decrease the resistance that was settled at the working channel of the ureteroscope. In this research, the four “resistance” statuses at the working channel, such as none, 200 μm holmium laser, 1.7F nitinol basket, or 2.67F guidewire, were examined. This result clearly shows that difference of the “flow rate” according to the diameter of the four different occupied equipment (Fig. 2 in Daniel Lama et al.). This study reminds us this important physics is working even with using the latest model of the flexible ureteroscope.

Their results also help us to further understand how to lower the intrarenal pressure during ureteroscopic operation. The same hydrodynamics formula works on it; it can be shown that “Intrarenal pressure” = “Drainage resistance” × “flow rate at the tip of the ureteroscope.” The ureteral access sheath and the smaller shaft ureteroscope can decrease “intrarenal pressure” by decreasing the “drainage resistance.” This knowledge provides us the important information about the methodology of how to achieve the clear operation field with lower intrarenal pressure.