Blood flow in hemodialysis catheters: a numerical simulation and microscopic analysis of in vivo-formed fibrin.

Although catheters with side holes allow high flow rate during hemodialysis, they also induce flow disturbances and create a critical hemodynamic environment that can favor fibrin deposition and thrombus formation. This study compared the blood flow and analyzed the influence of shear stress and shear rate in fibrin deposition and thrombus formation in nontunneled hemodialysis catheters with unobstructed side holes (unobstructed device) or with some side holes obstructed by blood thrombi (obstructed device). Computational fluid dynamics (CFD) was performed to simulate realistic blood flow under laminar and turbulent conditions. The results from the numerical simulations were compared with the fibrin distribution and thrombus architecture data obtained from scanning electron microscopy (SEM) and two photons laser scanning microscopy (TPLSM) on human thrombus formed in catheters removed from patients. CFD showed that regions of flow eddies and separation were mainly found in the venous holes region. TPLSM characterization of thrombi and fibrin structure in patient samples showed fibrin formations in accordance with simulated flux dynamics. Under laminar flow conditions, the wall shear stress close to border holes increased from 87.3±0.2 Pa in the unobstructed device to 176.2±0.5 Pa in the obstructed one. Under turbulent flow conditions, the shear stress increased by 47% when comparing the obstructed to the unobstructed catheter. The shear rates were generally higher than 5000/s and therefore sufficient to induce fibrin deposition. This findings were supported by SEM data documenting a preferential fibrin arrangement on side hole walls.