Complications at Hemodialysis: Access Issues

In order to perform hemodialysis on a patient, one prerequisite is a means to get blood from the patient to the dialysis machine. This is called an "access." You might have heard of terms like grafts, fistulas, and catheters.  All these are different kinds of dialysis accesses that might be used to dialyze a patient.  The details about these various dialysis accesses are covered here. This article will exclusively talk about complications that might be related to the access' function in a dialysis patient. This is part of a series of articles covering the complications of dialysis (other articles here and here).

The term stenosis implies narrowing. Both grafts and fistulas can develop narrowing of their lumen for various reasons (which can range from surgical causes at the time of placement, to the way that access is stuck at dialysis). Dialysis staff will typically examine the graft/fistula before every treatment and look for telltale signs of stenosis:

• Depending on the location of the stenosis, an access could be hyper-pulsatile, or even have poor flow of blood.
• Swelling or tingling in the arm where the access is present may be noticed.
• Pressure in the access might change and will be reflected on the dialysis machine alarms.
• Increased bleeding time after cessation of treatment is a common sign as well.  
• You might see that the efficiency of dialysis could go down because of access "recirculation". Recirculation happens in the access when treated blood being returned from the dialysis machine to the patient, mixes in with the blood that is on the way from the patient to the machine, thus creating an inefficiency in treatment.  This will usually lead to inadequate measures of dialysis dose and adequacy.  
• If the stenosis is allowed to persist for too long a time, it'll often lead to blood clot formation at that site or proximal to it, which is called a "thrombus".

The term thrombosis refers to a blood clot.  It can develop inside dialysis grafts, fistulas, or catheters for various reasons, but a common reason for a thrombus to form is stenosis. Once a thrombus has formed in a dialysis access, further meaningful dialysis is often impossible until the problem is addressed. All of the above signs are possible in a situation of access thrombosis. 

Once clinical suspicion is raised about these complications based on the features noted above, your nephrologist might refer you to a vascular surgeon or an imaging center. Certain studies can help confirm the diagnosis:

• An ultrasound of the access might show signs of stenosis/thrombosis
• The diagnosis however is often confirmed by injecting a special dye into the access with pictures being taken, just like an x-ray. The procedure is called a fistulogram and this will indicate the site of the stenosis or thrombosis pretty well

Treatment is handled by either interventional nephrologists or vascular surgeons.  The interventionalist will insert a catheter into the access, and try to widen the narrowed segment, a procedure called percutaneous transluminal angioplasty.  If a blood clot is found, it can be removed by medications or mechanically, a procedure called thrombectomy.  If it looks like this minimally invasive approach will not work, surgical correction might be necessary.

Dialysis catheters are the least preferred way of doing hemodialysis for good reasons. They carry the highest risk of infection, and unless there is a good reason not to (or if it is an emergency), no patient should be starting dialysis via a catheter.

Once inserted, catheters might not work right from the get-go, something called early catheter malfunction, and that is usually because of malpositioning of the catheter in a vein. The catheter in this situation can sometimes be manipulated and repositioned to make it work, or it needs to be exchanged.

In some instances, a catheter that has been functioning well for weeks to months can stop working, and this could be indicative of blood clot formation inside or around the catheter. This thrombus will require treatment, either using "clot-busting" thrombolytic medications, or the catheter needs to be changed.  It is because of this risk that dialysis catheters are "locked" with anticoagulant medications after use to prevent blood clot formation.