Vascaths are for short-term access (72 hours is pushing the recommended maximum time) - ARF, newly-diagnosed renal failure without warning, failure of long-term dialysis access etc. They can be inserted by residents/registrars (at least in my hospital) on the ward, and removed by nurses.
Permacaths are for longer periods, and are occasionally even used as the permanent mode of access (though I have not seen that myself). We usually use them while waiting for a fistula to mature etc. They are inserted in theatre, and removed in theatre (they have an internal Dacron cuff, which encourages tissue permeation, thus reducing the risk of infection).
Unlike other uses for vascaths (long-term drug administration etc), flow rate is vital - you need to be able to pull through a minimum of 250ml/min (200 in a real push) for effective haemodialysis. Because vascath/permacath patency is literally a life-and-death matter, they are locked with high-dose heparin after use, and never used for medication administration or blood collection (the
only exception would be in a code, with no other access possible).
Hope this helps