Description

The kidneysí function is to maintain the balance of certain chemicals in your dogís blood while filtering out the bodyís wastes as urine. The kidneys also help regulate blood pressure, assist with the regulation of the production of calcium and phosphorus metabolism, and produce a hormone that stimulates red-blood-cell production called erythropoiten.

Failing kidneys cannot remove certain toxins from the blood. The toxins include urea (a nitrogen-containing byproduct of protein metabolism) and creatinine (a chemical byproduct of muscle exertion). Therefore, when the kidneys fail, there are exceptionally high levels of these wastes products. Other blood components usually regulated by the kidneys - such as phosphorus, calcium, sodium, potassium, and chloride - may also rise or fall abnormally. Failing kidneys may also produce extremely dilute urine or urine that contains too much protein. Healthy kidneys produce concentrated urine that is relatively protein-free.

Chronic renal disease may not have a readily identifiable cause, but is generally related to aging. It is a common condition in old dogs. It occurs when there is deterioration and loss of the functional nephrons to the point where the kidneys cannot perform their function. Normal wastes are no longer removed from the bloodstream, so toxic levels of the wastes develop within the body. The kidneys can no longer conserve water, so abnormally large amounts of urine are produced, and water is lost from the body. Chronic kidney failure is an irreversible loss of function that occurs gradually over months or years.

Cavaliers who have developed Mitral Valve Disease which progresses to congestive heart failure are susceptible to chronic renal failure. This is due to reduced blood flow to the kidneys.

Clinical Signs

The signs of chronic renal disease develop slowly over time. Since the kidneys can no longer conserve water, there is an increase in the frequency and volume of urination. In an effort to compensate and keep the body hydrated, the dog will consume larger quantities of water. Occasional vomiting can also occur as an early sign.

In addition to uremia (an increase of urea in the blood), ulcers may develop, as well as weight loss, muscle wasting, poor appetite, depression, bleeding or ulcerous gums, 'ammonia' or otherwise very strong rancid bad breath, and possible seizures. The dog may demonstrate only one or two of these signs, which can easily be mistaken for something less dramatic, like gastritis.

Diagnosis

In the early stages of the disease, the nitrogen levels may or may not be elevated in the bloodstream. The diagnosis is confirmed by testing urine for protein loss and specific gravity, and blood for blood urea levels. Kidneys can lose over 75% of their function before they can no longer detoxify the body. Blood tests may also reveal a decreased production of red blood cells, which causes anemia. Other exams that may be performed include X-ray, ultrasound examination, and kidney biopsy. Many veterinarians recommend routinely screening for signs of kidney failure once a dog reaches 7 or 8 years of age. This is especially important to do if the dog is already known to have Mitral Valve Disease, with the potential of going into congestive heart failure as well.

Therapy

Most cases of chronic renal failure are not reversible. Treatment is geared to getting the most function out of any remaining kidney tissue. Low protein diets which are otherwise rich in energy may help reduce the nitrogen intake, therefore reducing the workload of the kidneys. Renal failure can also cause high blood pressure, so sodium restriction is an important step in the management of this disease. Special prescription diets for canned and dry food can be purchased at the veterinariansí. Water must be available at all times. Rest is important, and stress should be avoided.

Kidney failure can affect many other organs due to the increased toxins not effectively being eliminated by the kidney. One major organ is the stomach. The stomach lining becomes inflamed and ulcerated due to the increase in urea nitrogen in the blood stream. H2 blockers, such as cimetidine, assist in reducing the stomach irritation. To help keep levels of phosphorus under control, phosphate binders are given orally. These include aluminum hydroxide, aluminum carbonate, calcium carbonate, and calcium acetate.

There are some treatments which can be tried to manage the toxic effects of kidney failure:

• Intravenous fluid therapy. This is a short-term measure which can be used to correct dehydration, replace lost electrolytes and reduce the toxic levels of harmful waste products and chemicals in the blood.
• Medication to stop vomiting and stimulate appetite.
• Benazapril (Fortekor) - for the management of congestive heart failure in dogs may be a little easier on the kidneys than enalapril (Enacard, Vasotec).
• Drugs to stimulate red cell production to combat anemia.
• Calcitriol is a substance which helps regulate the levels of calcium and phosphorus. Some urologists are now recommending treating with calcitriol as soon as kidney disease is diagnosed. The dose is 2.5ug/kg every day. If phosphorus levels are above 6, this drug should not be administered.

If your dog has already experienced an episode of congestive heart failure, you will need to work closely with your veterinarian to balance the medical management for the congestive heart failure with the medical management for any chronic renal failure which may be developing as well. It is very important to report any changes in your dogís eating, drinking, and elimination habits to your veterinarian. These changes may alert your veterinarian to investigate for kidney disease - or help to adjust treatment if therapy has already begun.

References

The Urinary System, The Health of Your Dog, John Bower & David Youngs, Alpine Publications Inc., 1989, p. 176-177.

Chronic Renal Failure, The Merck Veterinary Manual, Seventh Edition, Merck & Co., 1991, p. 877-878.

Additional Reading

Websites

http://www.netcomuk.co.uk/~pdownes/scraps/alwaysloved.html

http://www.cah.com/library/caninekidney.html

http://www.marvistavet.com/html/chronic_renal_failure.html