Three years' experience with bypass cannulae for chronic hemodialysis.

In 14 patients over the past three years, "bypass" cannulae have been inserted to relieve obstruction in cannulae used for chronic hemodialyses. Experience with these patients has prompted changes resulting in improved technique.Clotting was the major cause of cannulae failure and infection was the second most important cause. Other causes of failure included: venous atheroma, cannulae extrusion, aneurysms of the vessel at the cannulae tips, obstructive vegetation on the vessel wall, calcium deposits on the vessel wall, and thrombi on the vein walls.The mean survival time was improved from 1.9 months in 1963-1964 to over 9.0 months in 1965-1966. The longest surviving cannula set was two years and the shortest one week.It is considered that the most important factors contributing to increased cannula survival are improved cannula care by patients and staff, the use of angiography for accurate diagnosis, and prompt anticoagulation if atheromatous stenosis of the venous component is encountered.