A Study Of The Effects Of Side Holes In Indwelling Needles For Hemodialysis On Actual Blood Flow Rate Using Computational Fluid Dynamics Analysis

Abstract

In indwelling needles, use of thinner needles leads to a greater discrepancy between set blood flow rate and actual blood flow rate. Providing side holes in the indwelling needle is an effective means for increasing the actual blood flow rate without changing the diameter of the indwelling needle. Given this situation, we are seeking theoretical optimization of side holes using computational fluid dynamics (CFD) analysis. The blood removal pressure obtained at each prescribed blood flow rate was determined at the blood removal end. In addition, I defined fluid resistance in order to reconcile the results of the analysis with the experimental results. The results showed that the blood removal flow rate obtained from the CFD analysis conducted on indwelling needles with side holes was largely consistent with the actual blood flow rate obtained from the experiment. Thus, we were able to explore the optimization of side holes from a theoretical standpoint using CFD analysis. 1. Background In recent years, with improvements in the physical constitution of blood dialysis patients and the spread of on-line hemodiafiltration in Japan, attempts are being made to carry out hemodialysis with a higher flow rate setting for blood removal than the conventional setting. However, a larger set blood flow rate corresponds to a larger discrepancy between the set and actual blood flow rates at which blood can be removed. To compensate for this discrepancy, indwelling needles tend to have larger aperture diameters. Along with this increase in diameter, patients are suffering greater pain on puncture, and indwelling needles with a small aperture diameter are needed to reduce puncture pain while at the same time offering a smaller discrepancy between the set and actual blood flow rates. Providing side holes in the indwelling needle is an effective means for increasing the actual blood flow rate without changing the diameter of the indwelling needle. Reports have indicated, however, that when side holes are provided, resistance actually increases during blood removal, and discussion of the number and shapes of side holes, as well as the locations at which side holes are provided, has remained inadequate. Given this situation, we are seeking theoretical optimization of side holes using computational fluid dynamics (CFD) analysis. 2. Method We created a model for analysis in which a 17-G indwelling needle with an effective length of 30 mm and no side holes was positioned in a blood vessel with an inner diameter of 12 mm(Fig.1).For the fluid flowing through the blood vessel, we used water. Flow rate at the inflow entrance of the blood vessel was defined as 700 ml/min, and pressure at the outflow exit was defined as 0 Pa. We also prepared an experimental model with the same conditions as the analysis model. Using a manometer, we measured blood removal pressure at the blood removal exit of the indwelling needle in relation to the blood flow rate set for the roller pump, and the resulting blood removal pressure was set for the blood removal exit of the analysis model. Next, we created an analysis model of an indwelling needle with one side hole that was round, with a diameter of 0.5 mm, located 3.3 mm from the tip of the indwelling needle. We also created models with two and three side holes, and conducted CFD analysis to assess the impact of the number and locations of side holes on the actual blood flow rate. Fig.1 Analysis model (17-G 30mm no side holes) 3. Results and Discussion Looking at the results of CFD analysis for the 17-G indwelling needle with no side holes, even though the blood removal pressure obtained through measurement was defined as the blood removal pressure for the analysis model, the blood removal flow rate obtained from the analysis was considerably higher than the actual blood flow rate obtained from the experiment (Fig.2). Therefore, in order to achieve consistency between analysis results and experimental results, we defined a resistance force for the blood removal exit of the indwelling needle, based on the pressure loss coefficient and flow velocity. Looking at changes in the pressure loss coefficient in relation to the set blood flow rate, the pressure loss coefficient was largely constant when the set blood flow rate exceeded 200 ml/min. Because the pressure loss coefficient is determined on the basis of the shape of the indwelling needle, the results suggest that for the 17-G indwelling needle used in our study, the impact of side holes can be theoretically investigated using the pressure loss coefficient (Fig.3). We therefore performed CFD analysis on the models in which the number of side holes had been increased from one to three, using the pressure loss coefficient. The results showed that the blood removal flow rate obtained from the CFD analysis conducted on indwelling needles with side holes was largely consistent with the actual blood flow rate obtained from the experiment. Thus, we were able to explore the optimization of side holes from a theoretical standpoint using CFD analysis. Fig.2 Acutual blood flow rate (17-G 30mm no side holes) Fig.3 Defined a resistance force (17-G 30mm no side holes)