Abstract
The morphology and function of blood access, no matter how created, are strongly influenced by the following factors: 1. Condition of vessels before surgery: AV-fistulas must be abandoned in patients with severe arteriosclerosis and accompanied by narrowing of the lumen.
Phlebosclerosis and various degrees of thrombosis may be found in veins previously subjected to multiple venipuncture. Stenosis or thrombosis of veins proximal to the AV-fistula results in various long-term complications.
2. Local changes after the AV-fistula creation: Once the arterio-venous anastomosis is created, the arterialized vein is exposed to continuous pressure loading, depending upon its diameter, and this inevitably results in intimal venous hyperplasia. This morphological change is most prominent in the vein close to the anastomosed site where local hemodynamic changes, i.e., the eddy and jet current of inflowing blood cause irregular hyperplasia of the venous intima and narrowing.
Subsequent poor blood flow results in thrombosis and obstruction of the arterialized venous lumen.
The vein at the puncture site is damaged by frequent physical injury and as a result, the venous wall loses its basic structure and is ultimately replaced by connective tissue fibrosis. The inner surface of the vein becomes unevenly irregular, and this in turn becomes the cause of stenosis, poor blood flow and thrombus formation. Marked thinning of the venous wall by multiple venipuncture results in pseudoaneurysm, where mural thrombosis develops and the proximal venous limb is subjected to the eddy and jet current, and this is another cause of venous intimal hyperplasia. The punctured veins exhibit the basic changes described above, and these are also modified by infection which is rather common and difficult to treat in artificial grafts. 3. Superficialized artery back-up access is at times accompanied by pseudoaneurysm, which is due to extravasation of blood after dialysis needles have been removed, and hemorrhage.
4. Influence of metabolic and circulatory status upon the vessels: Calcification occurs predominantly in the artery, at the anastomosed site as well as in pseudoaneurysmal veins, and may be attributable to a stenosed lumen and poor blood flow. Abnormal lipid metabolism and hypertension accelerate arteriosclerosis.
Severe hypotension, persistent or transient, may cause the formation of thrombus. Thus, artificial AV-fistulas are constantly exposed to inevitable damage.
