Hemodialysis fistulas or ports for dialysis are surgically created communications between the native artery and vein in an extremity. Direct communications between artery and vein are called native arteriovenous fistulas (AVFs). Polytetrafluoroethylene (PTFE) and other materials (Dacron, polyurethane) are used or have been used as a communication medium between the artery and the vein and are termed prosthetic hemodialysis access arteriovenous grafts (AVGs). The patency rates for AVFs are about four times greater than for AVGs. The access that is created is routinely used for hemodialysis two to five times per week. Preservation of a patent well-functioning dialysis fistula is one of the most challenging issues for the dialysis patient. As many as 25% of hospital admissions in the dialysis population have been attributed to vascular access problems, including fistula malfunction and thrombosis.

In fact, only 15% of dialysis fistulas remain patent and can function without problems during the entire period of a patient’s dependence on hemodialysis. The majority of patients who have native fistulas placed will be problem free with their fistulas for a mean of 3 years after creation, whereas prosthetic PTFE grafts usually last only about a year before indications of failure or thrombosis are noted.

Long-term secondary patency rates are reportedly 7 years in the forearm, 3 to 5 years in the upper arm for native fistulas, and about 1 year for prosthetic grafts after multiple interventions to treat the underlying stenosis and thrombosis.

The underlying cause of AVF failure in the nonacute setting or outpatient setting is invariably thrombosis due to venous anastomosis in prosthetic grafts or anastomosis of the outflow vein in native fistulas (Table 29.2). The pathophysiology behind this failure is the eventual intimal hyperplasia at the anastomosis site. Future therapy is directed at halting the intimal growth of anastomotic vessels, using technology similar to that employed with drug-eluting cardiac stents.

The main cause of AVF thrombosis in the acute care setting, particularly the perioperative period, is almost always low flow, usually caused by hypotension and/or poor cardiac output. A sudden decrease in blood pressure can lead to platelet aggregation, sledging, and eventual thrombosis. An important secondary cause for the loss of a patent fistula is excessive external pressure on the AVF, usually as a result of monitoring or positioning. Remember also that surgical patients are in a hypercoagulable state—this may also predispose to thrombotic events.