Answer: “Clotting” of the dialysis access is a common problem for the hemodialysis patient. Also known as thrombosis, clotting is actually the conversion of the liquid blood into a solid plug in the dialysis access. This plug stops the blood from moving freely through the access. Although clotting of blood when it is outside the body is normal and protects us from excessive bleeding when we are injured, clotting of blood inside a blood vessel is abnormal and is usually the result of sluggish blood flow through the vessel. There are a number of things that can cause sluggish access blood flow including poor blood flow into the access, narrowing in the outflow of the access, compression of the access and blood pressure drops.

Poor flow into the access is sometimes a technical problem with the original connection of the artery to the vein (on a fistula) or of the artery to the graft material (on an AV graft) at the time of surgery. Sometimes the blood flow into the access is poor because of diseased arteries due to diabetes, high blood pressure, older age or history of smoking.  Narrowing of the outflow of the access occurs when scar tissue forms at the connection of the graft material and the vein. Sometimes the narrowing may already be present in the deeper veins at the time of the surgical placement of the dialysis access, especially if a patient previously had a dialysis catheter in the deeper vein, such as a subclavian vein. 

Compression of the access may be accidental if, for example, a patient sleeps on the arm with the access or the patient is under anesthesia for a surgical procedure and the arm with the access is not positioned properly or if a blood pressure is taken in the dialysis access arm. Compression of the access may be intentional in an effort to stop prolonged bleeding from the access site after the needles are withdrawn following a dialysis procedure. In that setting, care must be taken to avoid excessive or prolonged pressure, especially if a mechanical compression device is used.

Blood pressure drops occur when too much fluid is removed during dialysis. This may happen if a person gains muscle or fat weight and needs a dry weight increase. These blood pressure drops may also occur when a large volume of fluid is removed at a single dialysis treatment. If the blood pressure falls while the patient is still on dialysis, lying back helps to preserve flow through the access and administration of fluid will help raise blood pressure back to normal. Sometimes, patients experience blood pressure drops after the dialysis treatment is finished and they have already gone home. If this occurs, the patient should also lie back to help preserve flow through the access and take fluids by mouth to help raise the blood pressure to normal.

There are several things that a patient can do to help prevent clotting of the dialysis access. First, patients should attend all dialysis treatments and undergo routine monitoring of the blood flow through the dialysis access. If the flow decreases, a test should be performed to determine the cause of the problem. Problems with the inflow to the fistula or graft can be referred to the surgeon for surgical repair. Problems with the outflow of the access may be able to be corrected in the radiology department with “ballooning” or angioplasty of the narrowed section of the vein.

In addition, patients should be careful of the amount of fluid consumed and weight gained between dialysis treatments. Controlling the dietary salt intake can help to decrease thirst and prevent large fluid gains. Patients should also be aware of blood pressure decreases on dialysis and report them to their nephrologist. The nephrologist may increase the dry weight or re-adjust blood pressure medications to help to prevent future blood pressure drops.

As every hemodialysis patient knows, their vascular access it literally their “lifeline” which must be treated with the utmost care to keep it functioning properly. Clotting of a fistula or graft is usually due to an identifiable reason, and treatment of a clotted access should include, in addition to removing the clot, an investigation and correction of that reason, if possible, so that the access does not soon clot again. Unfortunately, some clotted accesses cannot be fixed, but in such cases the nephrology practitioner, surgeon and patient should try to learn the causes of the clotted access before planning any new access. 

Answer provided by Jay Wish, MD and Kelly Weigel, MSN, CNP.

Dr. Wish is a Professor of Medicine in the Division of Nephrology at the University Hospital in Cleveland, Ohio. Dr. Wish is also a member of the AAKP Medical Advisory Board.

Ms. Weigel has been a nephrology nurse for 19 years and an acute care nurse practitioner specializing in nephrology and hemodialysis vascular access since 1997. She currently is an Instructor of Medicine at Case Western Reserve University School of Medicine.

The Dear Doctor column provides readers with an opportunity to submit renal related health questions to healthcare professionals who specialize in the area of concern. The answers are not to be construed as a diagnosis and therefore, altercations in current healthcare should not occur until the patient's physician is consulted.

This article originally appeared in aakpRENALIFE, July 2004, Vol. 20 No. 1. 

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