The dialysis unit (out-pt, mostly) sends problem HD cath pts (LOW flow during dialysis) to our Interventional Radiologist, who performs a cathogram (injects iodine contrast into each port, imaging the injection under fluoro) first. He then orders a two-hour infusion of 3 - 5 mg tPA per port. Usually this corrects the prob. I know urokinase is back on the market, appreciated sunnygirl's post w/the uro dose info. So far our Rads are more comfortable w/tPA.
If the tPA is unsuccessful (dialysis still gets LOW flows), the Radiologist performs a fibrin sheath stripping. Special catheter is introduced from the groin, threaded up to where the HD cath sits in the SVC, and a snare (looks like a wire lasso, Radiologist "steers" and "loops" it from near the hub) is positioned around each port, tightened, and then slid over the catheter to literally strip the fibrin sheath off. Some people build more fibrin, faster, than others, and a lot of buildup can hamper flow thru the dialysis ports.
Last-ditch "cure" for continued low flows: Replace HD cath.