Chronic access system for extracorporeal treatment of blood including a continuously wearable hemodialyzer

A method for obtaining access to a patient's arteriovenous pressure differential for extracorporeal blood flow comprising the steps of:

• (a) selecting a venous segment in the patient's forearm and transecting and occluding the distal end thereof;
• (b) anastomosing a remaining end portion of the transected vein to a selected artery in the patient's forearm, creating a fistula;
• (c) debranching the selected venous segment;
• (d) inserting a first needle cannula percutaneously into the debranched vein segment for accessing AV pressure differential and extracorporeal blood flow and inserting a second needle cannula percutaneously into the debranched vein for return of the extracorporeal blood flow to the patient's circulation;
• and
• (e) sequentially applying and removing compression to the forearm between the first and second needle cannulae sufficient to substantially occlude blood flow through the debranched vein segment during the compression and thereby establishing the pressure differential in that when the compression is being applied, the first needle cannula is exposed to arterial pressure and when released, the first and second needle cannulae are exposed to venous pressure.