heparin to close catheter

I believe that hemodialysis units differ widely in how heparin is added to close the line at the end of dialysis. We fill the volume of the catheter with heparin 10,000 u/ml. Many units use a combination of heparin and saline. Our method may be dangerous because:

1. the RN is not always able to remove the heparin prior to the next dialysis treatment

2. the volumes of some of the new ash-split catheters are almost double that of permcaths

Does anyone have any information on whether there are guidelines for this? What do you do?