Thomas P. Nifong, MD and Timothy J. McDevitt, PhD. CHEST July 2011 vol. 140 no. 1 48-53
Abstract
Background: Catheter-related thrombosis is a common complication in all anatomic sites, especially when smaller veins of the upper extremity are considered. It is presumed that the presence of a catheter within the lumen of a vein will decrease flow and potentially create stasis, and clinical data suggest that the size of the catheter impacts thrombosis rates. We sought to determine, both mathematically and experimentally, the impact of catheters on fluid flow rates.
Methods: We used fluid mechanics to calculate relative flow rates as a function of the ratio of the catheter to vein diameters. We also measured the flow rate of a blood analyte solution in an annular flow model using diameters that simulate the size of upper extremity veins and commonly used peripherally inserted central catheters (PICCs).
Results: We compared each of the derived relative flow rates to the experimentally determined ones for three cylinder sizes and found a correlation of r2 = 0.90. We also confirmed that the decrease in fluid flow rate with each successive catheter size is statistically significant (P < .0001).
Conclusions: Our results demonstrate that fluid flow is dramatically decreased by the insertion of a centrally located obstruction. Assuming that blood flow in veins behaves in a similar manner to our models, PICCs, in particular, may substantially decrease venous flow rates by as much as 93%.
The Bottom Line
How does this work advance the field?
Clinical data already show that the risk of catheter-related thrombosis increases with the size of the catheter, but it does not truly determine how the increased catheter size may cause thrombosis. The modeling described combines both catheter and vein size and quantifies the impact of this relationship on fluid flow. The model suggests that flow rates are highly dependent upon this relationship.
What are the clinical implications?
Clinicians are faced with balancing risks and benefits, and larger multilumen catheters cannot be entirely avoided. By further exploring the catheter to vein size ratio in a clinical model, a threshold could be determined that shifts the risk-benefit ratio. This study begins to explore such a threshold.
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