Two needles are inserted into a blood vessel (called an arteriovenous fistula or AV fistula) or arteriovenous graft (or AV graft), usually in your arm. Each needle is attached to a tube. One tube carries your blood into the dialyzer, where it's cleaned. Clean blood returns to your body through a second tube and needle. If the AV fistula or graft has been placed but it's not ready to use, or if choices for permanent access aren't appropriate, you may have a dialysis catheter placed in a large blood vessel. The catheter is usually for temporary access. But if there is no other choice, it may be used long-term (permanently). This catheter helps carry blood to and from the dialysis machine.