Convectively Dominated Heparin Leakage From Multiple Catheter Designs: An In Vitro Experimental Study

Central venous catheters (CVCs) are routinely filled with a heparin lock while not in use to avoid thrombus formation near the tip. However, heparin leakage is known to occur, and the lock effectiveness remains in question. It was recently shown that convective fluxes from the blood flow in the host vein transport the majority of locking solution away from the tip of hemodialysis catheters immediately after instillation. Combined with the low diffusivity of heparin, this results in concentrations of heparin at the catheter tip that are orders of magnitude lower than at instillation for the majority of the interdialytic phase, diminishing the antithrombotic effectiveness of the lock. In this study, heparin losses from three different CVCs with different tip designs are measured in a pulsatile flow loop. Planar laser-induced fluorescence and particle image velocimetry measurements of heparin concentration and fluid velocity are recorded downstream of the catheters and combined to evaluate heparin losses from each of the different catheter designs. Additionally, locking solution losses are measured from one catheter (Hickman) subjected to three different flow conditions. Heparin losses are shown to depend weakly on flow condition but be highly dependent on catheter design. Convective losses from the Hickman catheter, with no side holes, are minimal (1-2%), although losses from the other two catheter types, both with a number of side holes, are significantly higher (7%). These results indicate the potential to maintain a high concentration of locking solution during the interdialytic phase with proper catheter design, particularly focusing on side hole distribution and shape.