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Author Interview: Timothy W.I. Clark, M.D.

University of Pennsylvania School of Medicine, Penn Presbyterian Medical Center, 39th and Market Street, Philadelphia, PA 19104

Publication:

Computational Flow Dynamics and Preclinical Assessment of a Novel Hemodialysis Catheter.

Clark, T. W., Van Canneyt, K. and Verdonck, P. (2012), Computational Flow Dynamics and Preclinical Assessment of a Novel Hemodialysis Catheter. Seminars in Dialysis.
doi: 10.1111/j.1525-139X.2012.01052.x

Computational Flow Dynamics and Preclinical Assessment of a Novel Hemodialysis Catheter.
What are the main findings of the study?

Nephrologists are very aware of the need for dialysis catheters to deliver adequate levels of blood flow, and that catheter recirculation compromises solute clearance. Certain parameters have been less well examined in assessing catheter performance, namely that of physical stress on blood cells (erythrocytes, white blood cells and platelets) entering and leaving the catheter, the duration of time that blood resides in the catheter tip (the residence time) and flow characteristics which may cause platelet activation (and therefore potentially thrombus formation).

We examined these characteristics in a hemodialysis catheter with a novel tip design, designated the VectorFlow catheter. This catheter has helically contoured distal lumens to produce three-dimensional deflection of blood entering and leaving the catheter. We compared catheter recirculation between the VectorFlow catheter and the Palindrome (Covidien, Mansfield, MA) catheter, and also compared this to simulated catheters of a variety of tip designs similar to current commercially available dialysis catheters.

We also measured mean shear stress, blood cell residence time and platelet lysis index. The VectorFlow catheter was associated with an 18% reduction in mean shear stress compared to the Palindrome catheter. The VectorFlow and the Palindrome catheter had low levels of platelet lysis index; the residence times were also similar.

However, significant differences in calculated recirculation were seen. The VectorFlow catheter, because of three-dimensional deflection of blood at the catheter tip, resulted in a 99.7% decrease in recirculation compared to the Palindrome catheter within the computational flow dynamics model. Similar patterns in reduced recirculation were observed in the bench and animal models.

Were any of the findings unexpected?

We expected to find a low level of recirculation with the novel catheter design because of the three dimensional deflection of blood flow vectors.

Since all current dialysis catheters have some level of recirculation, we did not expect that this design would be completely absent of any detectable recirculation in the computational flow dynamics model, the bench model or the animal model.

We also found that the catheter was associated with favorable flow dynamics with respect to shear stress, blood cell residence time and platelet lysis index.

What should clinicians and patients take away from this study?

Catheter tip design is the single biggest feature distinguishing currently available dialysis catheters. Differences in catheter tip design can result in significant differences in recirculation and flow dynamics. Further work is needed to determine how favorable flow dynamics translate into a significant clinical benefit such as reduced catheter thrombosis. However, these results are encouraging preclinical data.

What recommendations do you have for future studies as a result of your study?

Although they are the least desirable form of vascular access, a significant number of patients receive dialysis through catheters while awaiting maturation of a fistula or creation of a new permanent access.

Not all dialysis catheters are alike. Catheter flow rates are important however to achieve optimal dialysis adequacy the level of catheter recirculation needs to be as low as possible. Emerging data suggests that flow dynamics as blood enters and leaves the catheter are additional critical parameters.

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