Renal Failure in Dogs and Cats
By Dr. Malize Hattingh
Like all mammals, cats and dogs have 2 bean-shaped kidneys located in the abdomen just below the lumbar spinal region. The important functions of the kidneys include:
• Removal of waste products from the blood to produce urine.
• Conservation of water. • Preserving normal electrolyte (like sodium and potassium) levels in the blood.
• Release of the hormone erythropoietin that stimulates red blood cell production.
• Maintenance of normal blood volume and blood pressure.
WHAT IS THE DIFFERENCE BETWEEN KIDNEY DISEASE AND KIDNEY FAILURE?
Kidney disease: the presence of morphological or functional lesions in 1 or both kidneys. This is not synonymous to renal failure unless generalized renal disease exists. Renal disease may escape detection until it becomes generalized with clinical signs as a result of serious impairment of function. Kidney failure: When 2/3 to ¾ of both kidneys are not functioning normally it causes the retention of wastes products in the body, because the kidneys are unable to eliminate it effectively.
CAUSES OF ACUTE AND CHRONIC RENAL FAILURE:
Acute kidney failure means that the problem developed over a few days and is potentially reversible. Many different things can cause acute kidney failure.
Certain poisons like antifreeze (radiator fluid, ethylene glycol) and certain drugs (like pain medication and certain antibiotics) are well known for their ability to damage the kidney.
Severe infections in the kidney from bacteria can cause sudden kidney failure.
Anything that decreases blood flow through the kidney. For example dehydration from severe vomiting and diarrhoea, heatstroke or other disorders causing massive damage to blood vessels, such as bee stings or snakebites.
Persistent obstruction to urine flow (for example bladder stones, severe bladder infection or inflammation etc.) or rupture of the excretory pathway (bladder, urethra, ureters) can cause irreversible renal damage. This is a very important cause in cats and can occur at any age.
In contrast to acute renal damage, chronic kidney disease has been present for months to years and is irreversible. Dogs and cats with chronic kidney disease cannot be cured, but their symptoms can often be managed successfully.
Because chronic kidney disease is completely advanced when it is diagnosed, it is often impossible to determine the original cause for the kidney damage. Although it is most commonly diagnosed in older dogs and cats, chronic kidney failure is not simply a result of ageing. CRF may be congenital / familial or acquired in origin. The former is suspected on the basis of breed, family history and age of onset of renal disease. Acquired renal failure may result from any disease process that injures the kidneys and cause sufficient irreversible loss of functional nephrons to result in renal failure like tumours, chronic infections, and bladder stones causing persistent obstruction to urine flow.
Dogs and cats with mild kidney disease may appear healthy.
However, dogs and cats with marked loss of kidney function can become very ill. The earliest symptoms of chronic kidney are increased thirst and increased urine volume. These symptoms result from impairment of the kidneys' ability to produce concentrated urine. Other common problems include weight loss, poor hair coat and increasingly selective appetite.
Further decline in kidney function results in progressive inability to eliminate waste products, leading to retention of toxic wastes in the body. Prominent symptoms of this include: loss of appetite, vomiting, ulcers in the mouth, (foul ammonia-smelling) breath, weakness and lethargy • Other important effects of declining kidney function include anaemia and high blood pressure (hypertension). High blood pressure may cause sudden blindness, stroke-like signs, or injury to the kidneys and heart.
Blood and urine tests are used to determine if kidney failure is present, and if it is, how severe it is.
Urinalysis can help determine whether the kidneys can form concentrated urine and provide evidence of other urinary tract problems such as urinary tract infection.
Blood tests used to evaluate kidney function include the blood urea nitrogen and creatinine concentrations. Because only the kidneys eliminate creatinine from the body, increased urea and creatinine concentrations indicate decreased kidney function.
Other tests, such as x-rays, ultrasound and special blood tests are usually necessary to tell what caused the kidney failure. Sometimes a biopsy of the kidney is recommended. The cause of kidney failure is not always easily discernible.
The initial treatment for acute kidney failure is usually intravenous fluids (IV). These fluids are used to restore good hydration and to flush out the substances that the kidneys are supposed to be removing from the bloodstream. Fortunately, most dogs and cats with chronic kidney disease can be treated, providing a good quality of life for months or years.
Treatment is tailored to the unique requirements of each pet but may include a “kidney-friendly” diet; hydration therapy; and medications designed to control symptoms (such as vomiting or poor appetite), acid-base and electrolyte complications, anemia, proteinuria, and hypertension.
Animals with renal failure require dietary modifications, due to the fact that their kidneys are unable to cope with their previous normal work load. Readymade commercial food is easily available for this reason.
These foods have the following in common: reduced phosphorous, higher quality and reduced quantity protein, non-protein calories, increased fibre, increased B vitamins, added anti- oxidants and supplemented omega-3 fatty acids. All of this will helps to slow down the progression of kidney disease.
• An important goal of managing patients with chronic kidney disease is to recognize the condition while it is still mild and attempt to slow or stop progression to more severe disease.
• Water should never be withheld from dogs and cats with chronic kidney disease.
THE IMPORTANCE OF REGULAR CHECK-UPS:
Kidneys are composed of many small functional units called nephrons. Dogs, cats, and humans are normally born with such an abundance of nephrons that loss of more than two thirds of these nephrons can occur before symptoms of kidney disease become apparent. On the other hand, surplus nephrons make it difficult to diagnose kidney disease before substantial numbers of nephrons have been lost. As a consequence, kidney disease can be an insidious condition that remains unrecognized either until blood and urine tests are performed or the patient becomes ill.
This is why regular follow-up examinations are important not only for the successful treatment of dogs and cats with chronic kidney disease, but also the early diagnosis of cases. Most pets should be examined on a regular schedule to evaluate for changes in kidney function and treatment needs. The frequency of these visits depends on the severity and type of kidney disease and the medications being used. It is advisable to have any cat and small bread dog over 8 years of age screened every 6 months for possible renal problems and large breed dogs even earlier.