Why do catheters stop working anyways? The most common answer: fibrin sheaths. The above pictures shows a tunneled dialysis catheter which was removed secondary to poor flows, taken from an article by Peel and Turney from a 2003 NDT issue, which was found to have an extensive fibrin sheath covering the ports on the line and presumably responsible for decreasing flow. There are various options to help treat this: while we frequently reach for TPA, I would imagine that thrombolysis likely work best when there is a thrombus at the catheter tip--and not so much for fibrin sheaths. Pulling back the catheter a few cm (a common maneuver for temporary dialysis lines) may help initially, but the fibrin sheath is still present and may still limit flow. The interventional radiologist has access to tools which allow sheath stripping by the introduction of snares via a 2nd venous access site and passed over the line.
Another question I have is this: what happens to the sheath after you remove the catheter? Presumably it is gradually resorbed with time much like a DVT. Still, you have to wonder if persistent sheaths have the ability to cause complications such as emboli or clot.