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Mammals are born with between three and four times as much kidney tissue as they need to survive. Thus an animal must lose 60-75% of its functioning kidney mass before exhibiting signs of illness.
Role of the Kidneys:
The kidneys are responsible for filtering waste products from the blood and excreting them in the urine. The kidney has tow essential functional areas. The filtering apparatus, or glomeruli, filter the blood allowing small blood components such as waste products and electrolytes to enter the kidney. The second area is a series of tubules in which a complex series of steps occurs the end result of which is the return to the body of most of the water and electrolytes that have entered the kidneys.
Signs of Chronic Kidney Disease:
Mammals are born with between three and four times as much kidney tissue as they need to survive. Thus an animal must lose 60-75% of its functioning kidney mass before exhibiting signs of illness. The early signs of chronic kidney disease are usually polyuria and polydipsia- the increase in urine volume and water consumption. This occurs because the kidney loses its ability to reabsorb water in the tubules resulting in increased fluid loss and subsequent increased water consumption to maintain adequate hydration. This stage can goes on for many months or years prior to the development of additional symptoms. As the disease progresses, weight loss, loss of appetite, anemia and vomiting will develop. Animals also develop a characteristic uremic odor to their breath. Occasionally in case of acute renal failure, there may be a complete cessation of urine production, but this is far less common than the polyuric form of renal failure.
Diagnosis of Chronic Kidney Disease:
Chronic renal failure is difficult to detect in its early phases. Because of the vast reserves f the kidney, the blood test measuring creatinine and blood urea nitrogen (BUN) used to check for kidney disease are normal until at least 70% of the kidney is non-functional. Urinalysis is often normal with the exception of the urine being poorly concentrated. This in itself is often a normal finding in a well-hydrated animal. Physical examination may reveal abnormalities in the size of the kidneys as may radiographs. He use of ultrasound to image the kidneys can give information suggestive of kidney disease. Ultimately kidney biopsy is the best way to define kidney disease, but this is rarely performed due to expense, risk and the fact that it rarely yields information that will radically alter treatment of the patient. In most instances, older animals with a history of polyuria and polydipsia with small kidneys on physical examination, radiographs and or ultrasonographic evaluation are deemed likely to have chronic renal failure.
Treatment of Chronic Kidney Disease:
The treatment for chronic renal disease varies depending on the stage at which it is identified. Most pets with early chronic renal failure ( normal to slightly elevated BUN and Creatinine, history of polyuria/polydipsia, normal appetite, no weight loss and normal blood count) are treated with special diets containing low levels of high quality protein, and low phosphorous content. These animals should also be evaluated for hypertension which is a common sequela to chronic renal disease.
Animals with clinical symptoms such as weight loss, anorexia and anemia should be treated more aggressively. An initial 2-3 day period of hospitalization and aggressive fluid therapy is indicated to try to lower BUN and creatinine levels and restore appetite.. Supplemental treatments such as administration of phosphate binders to lower blood phosphorous levels and vitamins and bone marrow stimulants to ffightanemia may be indicated for certain cases. BUN and creatinine levels should be rechecked at the end of this period to evaluate response to therapy. Significant decreases in BUN and creatinine levels bode well for long term ssuccess whereas a worsening of the values or a failure to improve in the face of aggressive fluid therapy indicates a much more guarded prognosis for the pet.
Long term care for animals with moderate chronic renal failure involves the use of prescription low protein diets, and if possible the administration of subcutaneous fluids 2-3 times weekly by the owner. This in itself is probably the single most beneficial treatment for these patients in terms of maintaining the quality of life.
One of the most important things to realize about pets with managed chronic renal disease is that they are NOT normal! It is essential that they be closely monitored by the owner, and if anything out of the ordinary appears they should be rechecked by the veterinarian immediately. These animals walk a fine line between having enough kidney function to maintain themselves and going into full blown kidney shutdown. The most common things that tip them off the scale are events that lead to dehydration. Thus episodes of anorexia, vomiting or even lethargy where the animal is not getting up to drink adequately are cause for real concern. If these are not recognized promptly and addressed medically, it can result in the death of the pet.
Early diagnosis, appropriate treatment and identification of sequelae such as hypertension are critical in giving the best outcome for these pets. Done properly, treatment can add up to 3-4 years to the life of a pet.
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