UC Veterinary Medical Center, San Diego

Companion Animal Hemodialysis Information for Clients

What is dialysis? What is hemodialysis?

Strictly speaking, dialysis is the diffusion of water and dissolved molecules called solutes across a semi- permeable membrane. In medicine, we do this with the intent of removing waste products from an animal̢۪s or person̢۪s body when their own kidneys fail. In hemodialysis, aspecial machine pumps blood from the patient through an artificial kidney, which removes accumulated wastes (urea, creatinine, phosphate and many others) that the patient̢۪s own kidneys normally would filter from the blood and excrete from the body. The artificial kidney contains many small, hollow fibers (picture a bundle of tiny soda straws) through which the blood passes. The fibers are made of a semi-permeable, synthetic material, which allows passage of water and some small molecules. The fiber bundle is encased in a cylindrical shell through which the dialysate solution flows. Dialysate is a balanced electrolyte, sugar, salt, and water solution that bathes the blood-filled fibers. Wastes move from the blood (the area of high concentration) through the membranes into the dialysate (the area of low concentration), and the used dialysate is discarded. Solute diffusion in hemodialysis is similar to that in the process of brewing tea. Think of the dry tea as the blood with waste products, the tea bagas the dialysis membrane, and the hot water as the dialysate.

In addition to removing solute wastes, the kidneys also maintain normal electrolyte, acid-base, and water balance. We can use dialysis to correct imbalances in any of these parameters by prescribing more or less of certain substances in the dialysate. If a pet is over-hydrated, we can remove water from the blood by a process called ultrafiltration. During ultrafiltration, pressure across the dialysis membranes draws specificallyprogrammed volumes of water from the blood at a precisely controlled rate. The extra fluid is then discarded with the contaminated dialysate. Conversely, we can also easily administer fluids to a dehydrated pet during a dialysis session. Monitoring equipment helps us ascertain that fluid is administered or removed at a saferate for the pet.

When is dialysis used in veterinary medicine?

Most human dialysis patients have chronic (long-term, irreversible) renal (kidney) failure; they rely on dialysis treatments 2-3 times per week for their entire lives, unless they receive kidney transplants. In contrast, most veterinary dialysis patients have acute (recent onset) renal injury, which means that something happened to cause sudden failure of previously adequately-functioning kidneys. Such an injury is often partiallyor fullyreversible. It is important to understand that dialysis does not treat or repair the kidneys themselves. Instead, it serves as a bridging measure by re-establishing and maintaining metabolic balance, in order to give damaged kidneys the opportunity to repair themselves and to recover function. Without the extratime dialysis provides, most patients with severeacute renal failure will die before their kidneys can recover enough function to sustain life.

Most canine dialysis patients have damaged kidneys from antifreeze poisoning, kidney infections (like leptospirosis or pyelonephritis), grape/raisin toxicity or complications of other systemic disease. Cats, like dogs, may suffer from antifreeze poisoning or kidneyinfection. Lilies, especially Easter lilies, are potent kidney toxins for cats, also. Ureteral obstruction (blockage of the tubes connecting the kidneys to the bladder) is the most common reason for a cat to need dialysis. Dialysis can stabilize severely ill cats with ureteral obstructions to give the obstruction a chance to resolve and/or to stabilize the cats for surgical correction of the blockage(s). Dialysis treatments two or three times weekly can also maintain pets with chronic renal failure, when medical management alone can no longer provide a good quality of life. Some of these pets, especially cats, may be candidates for kidney transplantation, and dialysis is often needed before and/or after transplantation for stabilization and support.

What happens to my pet during a dialysis session?

Atthe beginning of a session, your pet is greeted (most pets like coming to dialysis) and given a thorough physical examination, including measurement of weight, temperature, heart rate, and blood pressure. Dogs lie on a soft pad, and cats lie on a fleece pad inside half of a pet carrier (cats feel more secure if they are a bit “hidden”). All pets wear a special harness (like a nylon walking harness you’d attach to a leash), which is clipped to leads on three sides of the padded treatment table. This restraint system keeps your pet safely on the table, but lets her or him move and change positions at will. A dialysis team member then unwraps, closely examines, and meticulously cleans the dialysis catheter. These catheters are the lifelines of our patients! We take a small sample of blood from the catheter to measure red cell volume, clotting time, kidney values, and any other parameters the doctor requests for that day. Because your pet has a dialysis catheter in place, we do not need to use a needle to take blood. In fact, for most patients, the only unpleasant part of a dialysis session is having a temperature taken.

When the dialysis catheter, dialysis prescription and patient are ready, we attach the dialysis machine̢۪s blood lines to the patient̢۪s two catheter lines and begin the dialysis treatment. Initially, the machine draws blood from your pet, through the lines to fill the extracorporeal (outside the body) circuit, and fluids flow from the circuit back to your pet to help make up for the blood being withdrawn. In a cat, about a quarter-cup of blood (60 ml or 2 ounces) is outside the body at any given time. In a dog, filling the extracorporeal circuit requires between a quarter and a full cup (60-240 ml or 2-8 ounces) of blood (we vary the circuit size to fit the pet̢۪s size). After this initial equilibration period, blood simultaneously and cyclically leaves and returns to a large blood vessel near the heart, so your pet should not feel any shifts of volume through the course of a dialysis treatment. After acclimating during one or two treatments, most pets spend their time on dialysis comfortably napping.

During a dialysis session, blood pressure, heart rate, clotting time, and machine parameters are recorded at least every 30 minutes. Temperature, ECG and other parameters can be measured if needed. Patient attitude and well-being, blood volume and blood oxygenation aremonitored continuously. Pets may eat or drink during dialysis if they choose to. At the end of the session, the blood in the extracorporeal circuit is returned to your pet in a process called rinseback. The catheter access lines are carefully cleaned again, locked with heparin to prevent clot formation, sealed, and bandaged with a neck wrap. After we re-assess physical parameters and feel comfortable that your pet is stable following treatment, she or he may leave the dialysis unit. Most pets feel great after dialysis and many pets are outpatients, living at home and coming to the clinic on dialysis days for 6-8 hours.

Why do treatments take so long?

A standard hemodialysis session lasts about 4 hours in a cat and 4-6 hours in a dog; stable patients are treated 2-3 times per week. This process is extremely efficient, but a single dialysis session must accomplish in 3-5 hours 2-3 times a week what kidneys do 24 hours a day, every day. In addition to the actual dialysis time, patient examination and catheter preparation require 60 minutes or more, prior to and following treatment. Longer treatments are more physiologic, and in some cases wemay need to extend a treatment for 8 hours or more for the health and safety of your pet. Each session̢۪s prescription (which includes length of treatment), is created at the time we evaluate your pet̢۪s status, and is designed to optimize his or her benefit from a given treatment. Dialysis prescriptions can and do change significantly from session to session.

Who are the members of the dialysis team?

The doctors at UCVMC-SD who managedialysis patients areboard certified in veterinary internal medicine and have elected to focus their professional activities on nephrology/urology and hemodialysis. The veterinary nurseswho treat and carefor dialysis patients arespecifically trained to handle the dialysis catheters and machines, and to detect subtle changes in patients that might herald problems. They are skilled in critical care, and their technical expertise is indispensable for safe and successful patient management. The core dialysis team at UCVMC-SD is

If you ever have questions or concerns regarding your pet̢۪s treatment, disease, or general well-being, never hesitate to ask a dialysis team member. If your pet has a medical emergency related to anyaspect of dialysis, a dialysis team member is available to you. Call