A modeling study of position and orientation of hemodialysis needles and the impact on vascular access

Abstract

Abstract Patients with chronic kidney disease (CKD) need renal replacement therapy (RRT) and the favored method is hemodialysis (HD). An arteriovenous fistula is the preferred choice of vascular access, with two metal needles used to transfer the blood with waste to the dialysis machine and return the blood without waste from the dialysis machine to the patient’s body. However, wounds on the veins can cause blood clots which if left untreated could be life threatening. The hemodialysis needles can cause vascular wall abnormalities. The position and orientation of these needles might cause intimal hyperplasia (IH) and finally lead to blood clots. This study aims to analyze the hemodynamic effects on the vascular endothelium in AVF vascular access. A 15G needle was placed inside a vein at angles of 20°, 40°, and 90° with normal insertion and flipped needle in an idealized cephalic vein with the bore of the needle centrally located, conforming to standard cannulation practice. The 3D model created by SolidWorks consists of shaft, back eye, bevel, and vein only; the vein and 15G needle were assembled together. The mathematical model of blood rheology in this paper used Carreau’s law in the fluid domain. It was imported into Ansys CFX for calculation, a finite volume based software, which was implemented to solve the governing equations of the blood flow. The result showed that if the venous needle was not towards the venous return, a vortex appeared at the vein both upstream and downstream due to the venous needle, resulting in wall shear stress at the vein increasing significantly, and the flipped bevel seems to cause higher wall shear stress. For antegrade positioning of the vein vascular access return in the model when normally inserted, it was found that only 1% of the flow out of the back eye and vortex occurred downstream of the vein. Needles placed at a higher angle can increase wall shear stress and pressure on the vein. The flipped bevel is not significant in terms of either pressure or wall shear stress. However, when the needle is placed at a greater angle, wall shear stress and pressure on the vein were also increased. The flipped bevel caused higher wall shear stress and pressure when increasing the needle angle. Jetting from the venous needle causing intimal hyperplasia (IH) leads to blood clots, pain on the vein, and ultimately arm pain. Thus, the best cannulation procedure is for the venous needle to be toward the venous return, at a lower angle, and with the tip of the needle on the middle of the vein. Furthermore, the back eye should not be used for the venous needle but should be used for the arterial needle.