-----Chronic Renal Failure
River Road Veterinary Clinic
Box 309
Norwich, Vermont 05055
Phone: 802-649-3877 Fax: 802-649-1345
email: RRVC@Valley.net.com
www.rrvetclinic.com
Dr. Christine Pinello - Dr. JoAnne Giel - Dr. Kathy Ling Newcomb
Chronic Renal Failure
Article by: David J. Polzin
Renal failure (kidney failure) occurs when kidney function has deteriorated
to such a degree that the kidneys can no longer perform their normal
functions of excreting wastes, maintaining water and electrolyte balance,
and producing hormones. Renal failure occurs in acute or chronic forms.
Acute renal failure is of recent onset and is potentially reversible.
In contrast, chronic renal failure has been present for months to years
at the time of diagnosis and is irreversible. Dogs and cats with chronic
renal failure cannot be cured, but their clinical signs can often be
managed successfully.
Kidneys are composed of many small functional units called nephrons
(approximately 190,000 in cats and approximately 400,000 in dogs). Dogs,
cats, and humans are normally born with such an abundance of nephrons
that signs of kidney failure do not become apparent until more than
two thirds of the nephrons have been damaged. Because of this redundant
kidney tissue, it is possible to donate a kidney for transplantation
and survive. On the other hand, surplus nephrons make it difficult to
detect chronic kidney diseases until they are well advanced. As a consequence,
chronic kidney failure is often an insidious condition that remains
unrecognized until it is severe. Because kidney disease is often quite
advanced at the time of initial diagnosis, the initiating cause of chronic
renal failure can rarely be established. Although chronic renal failure
occurs most often in older dogs and cats, renal failure is not simply
a result of aging.
The earliest signs of renal failure are typically thirst (polydipsia)
and increased urine volume (polyuria). These signs result from inability
of the diseased kidneys to form concentrated urine. Other common early
signs include weight loss, poor haircoat, and an increasingly selective
appetite. Further decline in kidney function result in progressive inability
to excrete waste products, leading to retention of toxic wastes in blood
and tissues in the body. This is called uremia (literally, urine in
the blood). Prominent clinical signs of uremia include loss of appetite,
vomiting, ulcers in the mouth, "uremic" (foul ammonia smelling)
breath, weakness, and lethargy. Other important effects of renal failure
include anemia (caused by inability of failing kidneys to produce erythropoietin,
the hormone responsible for making red blood cells) and high blood pressure.
Anemia worsens the weakness, lethargy, and loss of appetite of dogs
and cats with chronic renal failure, and high blood pressure may cause
sudden blindness, strokelike signs (such as mental dullness, sudden
behavioral changes, coma, or seizures), or injury to the kidneys and
heart.
Diagnosis of chronic renal failure is confirmed by laboratory evaluation
of your pet's blood and urine. A urine test can help determine whether
the kidneys can form concentrated urine and provide evidence of other
urinary tract problems such as urinary tract infections. Blood tests
used to evaluate kidney function include blood urea nitrogen (BUN) and
serum creatinine concentrations. Because the kidneys excrete urea and
creatinine, increases in urine and creatinine concentrations in blood
indicate decreased kidney function. These tests are usually done together
because they provide different information. The serum creatinine concentration
is the more specific test for kidney function, and treatment and other
factors may influence the BUN. In addition to evaluating kidney function,
other tests may be used to evaluate your pet for anemia, electrolyte
and acid-base abnormalities, nutrition, and hypertension. Ultrasound
examination and x-rays may also be used to evaluate kidney disease.
Fortunately, most dogs and cats can be treated, providing a good quality
of life for months or years. Treatment for chronic renal failure is
tailored to the unique clinical requirements of each pet but may include
a special diet (e.g., limiting protein, phosphorus, and salt intake);
hydration therapy; and medications designed to control clinical signs
(such as poor appetite, nausea and vomiting), acid-base and electrolyte
disturbances, anemia, and hypertension. Consumption of excess protein
may make some pets ill because the waste products of protein metabolism
are excreted by the kidneys and are retained in renal failure. Dehydration
(abnormal depletion of body fluids) is a special threat to pets with
renal failure, and they may deteriorate if episodes of vomiting, diarrhea,
or inadequate water intake are not dealt with promptly. Water should
never be withheld from dogs and cats with renal failure.
In humans, renal failure is most often managed by dialysis (hemodialysis
or peritoneal dialysis) or renal transplantation. Chronic hemodialysis
and peritoneal dialysis have thus far not proved to be satisfactory
options for dogs and cats with chronic renal failure because they are
expensive and fail to provide an acceptable quality of life. Renal transplantation
is an expensive but potentially useful option for selected cats but
has not met with similar success in dogs. Renal transplantation is best
reserved for cats that can no longer be managed by standard medical
therapy.