Veterinary Task Force for Dialysis

What does dialysis mean?
Extracorporeal blood purification (commonly called dialysis or haemodialysis) is a process that allows the removal of toxic substances through the passage of blood into an "artificial kidney". Dialysis can be performed in both dogs and cats. Dialysis involves the passage of blood through an extracorporeal circuit (extracorporeal circulation) and through a filter composed of many membranes. The passage through the filter allows the removal of toxic chemicals; the blood, once purified, returns to the patient. In dogs and cats, dialysis treatments are primarily used in acute renal failure, but are also used as life-saving therapies in case of poisoning, overdose of drugs and severe electrolyte imbalances. The basic principles are the same in the different scenarios, but what changes are the techniques used. To date, animals of any weight, from under 1.5 kg to over 100 kg, can be safely treated.

What are the dialysis techniques in dogs and cats?
Dialysis can take place in different ways and the techniques differ on the basis of what happens inside the filter; each technique has specific therapeutic indications. In our veterinary clinic for dogs and cats, we use the haemofiltration system; this process uses a convective force to remove low and medium molecular weight toxins as well as excess fluids. The dialytic treatment can be intermittent or continuous; the first one is of short duration (4-6 hours) and uses high blood flows while the second one is of longer duration (24-48 hours) and uses low blood flows. There are also mixed dialytic treatments; the type used depends mainly on the clinical conditions of the dog or cat.

When is dialysis indicated in dogs and cats?
Dialysis is the treatment of choice in cases of severe, acute renal failure that is refractory to standard medical therapy. Specifically, the following conditions are indicated for dialysis: anuria and severe oliguria (respectively, the complete or partial inability to produce urine), severe electrolyte and acid-base alterations, the presence of generalised oedema and severe renal insufficiency that does not respond to standard treatments. Dialysis treatment leads to a more favourable prognosis if performed promptly; therefore, a dog or cat becomes a candidate for dialysis if, after 24 to 48 hours, standard medical therapy is not effective. In the case of intoxicated dogs and cats, the timeliness of dialytic treatment acquires an even more fundamental importance. The promptness in the execution of the treatment makes it possible to maximise the removal of the toxic substance from the blood and to limit its damage.

How many dialysis treatments should be performed in dogs and cats?
It is important to emphasise that dialysis does not in itself repair renal damage, but rather replaces the kidney in many of its functions. The dialysis proccess improves the quality of life of dogs and cats in their most critical moments. Unfortunately, in most cases, it is not possible to predict a priori the number of dialysis sessions necessary to obtain a functional recovery of the kidney. Often dialysis sessions have to be repeated every 2-4 weeks; only a small number of dogs and cats achieve a faster recovery. Some patients need months to gain adequate kidney function and unfortunately, others end up with irreversible kidney damage.

What is the prognosis in dogs and cats treated with dialysis?
The prognosis and duration of dialysis vary greatly from one patient to another; the most important prognostic factors are represented by the cause and severity of the renal damage, the patient's clinical condition and by the potential presence of other concurrent diseases. The survival rate of dogs and cats undergoing dialysis is 40-50%. The prognosis is better if acute renal failure is due to infectious diseases (such as leptospirosis in dogs), with a survival of 60-100%; if acute renal failure is hemodynamic (such as heart failure) or metabolic (such as hypoadrenocorticism) survival is reduced to 40-70%. Unfortunately, the prognosis is guarded in cases of acute intoxications, with a survival of 20-40%; in cases of ethylene glycol intoxication prognosis is poor. Among patients treated with dialysis who survived from acute renal failure, only half usually return to normal renal function. The above percentages will hopefully improve in the coming years due to the more frequent use of dialysis.

Are there other blood purification techniques in dogs and cats?
Plasmapheresis purifies the blood from molecules that are bound to circulating proteins or from very large circulating proteins (e.g., antibodies). Plasmapheresis exploits specific filters that separate the liquid component of blood (i.e., plasma) from the corpusculated component (i.e., red and white blood cells). The plasma consequently obtained can be eliminated and replaced with plasma from a healthy animal donor. Plasmapheresis has been used successfully in dogs with immune-mediated haemolytic anaemia, myasthenia gravis and other autoimmune diseases, as well as in dogs with hyperviscosity syndrome. Plasmapheresis is not indicated for the treatment of acute renal failure.

Conclusions
Dialysis is increasingly common in dogs and cats. For several diseases, in particular for acute renal failure, dialysis is often the only reasonable therapeutic choice to avoid a fatal outcome.

To receive information regarding the Veterinary Task Force for Dialysis and for questions about clinical cases, those who are interested may contact Dr. Corinne Amram and Dr. Filippo Ferri at the following email address: nefrologia@istitutoveterinarionovara.it

Contacts

Veterinary Task Force for Dialysis