Haemodialysis Catheter Placement and AV Fistula
Haemodialysis is a method for removing toxins such as creatinine and urea, as well as free water from the blood when the kidneys have failed. Blood is passed over membrane filters in a dialysis machine and returned to the body.
Haemodialysis can be performed as an outpatient or inpatient procedure.
In haemodialysis, three primary methods are used to gain access to the blood: an intravenous catheter, an arteriovenous fistula (AV) and a synthetic graft. The type of access is influenced by factors such as the expected time course of a patient's renal failure and the condition of his or her vasculature. Patients may have multiple accesses, usually because an AV fistula or graft is maturing and a catheter is still being used. The creation of these types of vascular accesses requires surgery
Catheter access consists of a plastic catheter with two channels which is inserted into a large vein to allow blood to be withdrawn from one lumen, to enter the dialysis machine and to be returned via the other lumen
Catheters are usually found in two general varieties, tunnelled and non-tunnelled.
Non-tunneled catheter access is for short-term access (up to about 10 days) and the catheter emerges from the skin at the site of entry into the vein.
Tunneled catheter access involves a longer catheter, which is tunneled under the skin from the point of insertion in the vein to an exit site some distance away. It is usually placed in the internal jugular vein in the neck and the exit site is usually on the chest wall. The tunnel acts as a barrier to invading bacteria and as such, tunneled catheters are designed for short- to medium-term access (weeks to months only), because infection is still a frequent problem.
Other complications include venous stenosis (narrowing) due to scar tissue formation. Patients on long-term haemodialysis can literally 'run out' of access, so this can be a fatal problem.
Catheter access is usually used for rapid access for immediate dialysis, for tunneled access in patients who are deemed likely to recover from acute renal failure, and for patients with end-stage renal failure who are either waiting for alternative access to mature or who are unable to have alternative access.
Catheter access is often popular with patients, because attachment to the dialysis machine doesn't require needles. However, the serious risks of catheter access noted above mean that such access should be contemplated only as a long-term solution in the most desperate access situation.
AV (arteriovenous) fistulas are recognized as the preferred access method. To create a fistula, a surgeon joins an artery and a vein together. This forms a "shortcut" and blood preferentially flows through the fistula.
Fistulas are usually created in the nondominant arm and may be situated on the hand, the forearm or the elbow. A fistula takes a number of weeks to mature. During treatment, two needles are inserted into the fistula, one to draw blood and one to return it.
The advantages of the AV fistulae over catheters are lower infection rates, because no foreign material is involved in their formation, higher blood flow rates (which translates to more effective dialysis), and a lower incidence of clotting.
An arteriovenous graft
Arteriovenous grafts are much like fistulas except that an artificial vessel is used to join the artery and vein. The graft usually is made of a synthetic material, often PTFE, but sometimes chemically treated, sterilized veins from animals are used. Grafts are inserted when the patient's native vasculature does not permit a fistula. They mature faster than fistulas, and may be ready for use several weeks after surgery. AV grafts are at high risk to develop narrowing, especially in the vein just downstream from where the graft has been sewn to the vein. Narrowing often leads to clotting. As foreign material is used there is a significant greater risk for infection.