Fluid mechanics and clinical success of central venous catheters for dialysis--answers to simple but persisting problems.

Over 60% of patients initiating chronic hemodialysis in the United States have a chronic central venous catheter (CVC) as their first blood access device. Although it would be better if these patients started dialysis with fistulas, the CVC is used because it is a reliable and relatively safe method for obtaining blood access over a period of months. Drawing blood from a vein at 300-400 ml/minute is a relatively delicate and somewhat unpredictable process, and there is always a tendency for the vein wall to draw over the arterial tip and obstruct flow. Several methods have been employed to minimize this problem and maximize blood flow, and differing catheter designs have resulted. With all of the different catheter designs now on the market, it is natural to ask what is the logic of different designs. Moreover, in the absence of many direct comparative studies it is natural to ask whether one design is really better than another. There is some misinformation regarding catheter design and function. The following is a list of 10 frequently asked questions In this review, the hydraulic features of CVC are discussed and explained, and logical answers are provided for the following questions: 1. Why do ''D'' catheters flow better than concentric or side by side catheters? 2. Why are all catheters about the same diameter? Does making them bigger really decrease the resistance to flow? 3. Why might a split tip catheter flow better than a solid body catheter? 4. What happens to injections of lock solution at catheter volume? 5. What's better-numerous side holes or none? 6. Why does blood rise into some internal jugular catheters over time, displacing the lock solution? 7. How can a little kink (or stenosis) decrease flow so much? 8. Where should the tips be placed-superior vena cava or right atrium? 9. Which is really better, splitsheath or over-the-wire placement? 10. Which dialysis access has a lower complication rate--CVC or arteriovenous (AV) graft? There remain important problems with CVC for dialysis. With a few more improvements, chronic CVC for dialysis could become a painless, effective and safe long-term access for the majority of dialysis patients and acceptable as an alternative to AV grafts.