Impact of side-hole geometry on the performance of hemodialysis catheter tips: A computational fluid dynamics assessment

Abstract

Hemodialysis catheters are used to support blood filtration, yet there are multiple fundamentally different approaches to catheter tip design with no clear optimal solution. Side-holes have been shown to increase flow rates and decrease recirculation but have been associated with clotting/increased infection rates. This study investigates the impact of changing the shape, size and number of side-holes on a simple symmetric tip catheter by evaluating the velocity, shear stress and shear rate of inflowing blood. A platelet model is used to examine the residence time and shear history of inflowing platelets. The results show that sideholes improve the theoretical performance of the catheters, reducing the maximum velocity and shear stress occurring at the tip compared to non-side-hole catheters. Increasing the side-hole area improved performance up to a point, past which not all inflow through the hole was captured, and instead a small fraction slowly 'washed-out' through the remainder of the tip resulting in greater residence times and increasing the likelihood of platelet adhesion. An oval shaped hole presents a lower chance of external fibrin formation compared to a circular hole, although this would also be influenced by the catheter material surface topology which is dependent on the manufacturing process. Overall, whilst side-holes may be associated with increased clotting and infection, this can be reduced when side-hole geometry is correctly implemented though; a sufficient area for body diameter (minimising residence time) and utilising angle-cut, oval shaped holes (reducing shear stress and chances of fibrin formation partially occluding holes).

Computational fluid dynamics of the right atrium: Assessment of modelling criteria for the evaluation of dialysis catheters

“…Given the importance of using non-Newtonian models for the study of local haemodynamics [ 30 ], and similarly to the recent paper by Owen et al (2020) [ 31 ], blood was considered a Non-Newtonian fluid [ 32 ] and modelled using the Bird-Carreau model: where μ is the blood viscosity, μ ∞ is the high shear viscosity, μ 0 is the low shear viscosity, λ is the time constant, is the shear rate and n is the Power law index [ 33 ]. As per previous studies, the following values were used: λ = 3.313 s, n = 0.3568, μ 0 = 0.056 Pa s and μ ∞ = 0.00345 Pa s [ 33 , 34 ] and a blood density of 1060 kg/m 3 .…”

“…Given the importance of using non-Newtonian models for the study of local haemodynamics [30], and similarly to the recent paper by Owen et al (2020) [31], blood was considered a Non-Newtonian fluid [32] and modelled using the Bird-Carreau model:…”

Staphylococcus aureus accumulation at the tip of hemodialysis catheters with or without tip side holes in catheter related bloodstream infection in a large animal

“…15 However, side holes in a catheter may have mechanistic and physiological disadvantages. 16 In presence of side holes, blood flow around and through the tip of the catheter almost instantly removes anticoagulant lock solutions, thus practically favoring clot formation at the tip. [17][18][19][20] In a computational fluid dynamics analysis, distal side holes present clotting risk at the catheter tip due to the creation of a low flow zone.…”

Numerical modelling of blood rheology and platelet activation through a stenosed left coronary artery bifurcation

“…Evaluating the behaviour of platelets and their association with thrombus/clot formation is relevant for vascular pathologies [ 14 , 73 ] (e.g. stenosis/aneurysms) but also the function of medical devices [ 36 , 74 ] (e.g. catheters/stents).…”

“…This study examines four different rheological models, consisting of two single-phase models (which consider blood a single homogenous fluid), and two multiphase models (which consider blood as a dilute suspension of RBC within a plasma continuum). Of the two single-phase models, one assumes blood to be Newtonian [ 35 ] with constant viscosity (Single Newtonian, SN), and the other uses a shear dependant Carreau [ 36 ] viscosity definition (Single Carreau, SC). Similarly for the two multiphase models, one uses a Newtonian approach, where the viscosity of each phase is constant (Multi Newtonian, MN) and the other uses a modified Krieger model with 5 parameters [ 26 ] (MKM5) which allows RBC viscosity to vary with both shear forces and hematocrit.…”