Kidney Failure in Dogs and Cats
How common is kidney failure?
Kidney failure is very common in older dogs and cats, affecting as many as one third of pets over ten years of age. Early diagnosis and treatment of allows successful long term management in many cases.
Anatomy of the kidneys
What are the kidneys?
The kidneys are a pair of organs located just behind the liver and under the spine in normal dogs and cats. They can usually be felt (or palpated) by a veterinarian just behind the ribcage in the upper part of the abdomen, although this may be more difficult in very large or obese pets. They are usually described as being bean-shaped, and have a firm, smooth capsule. The kidneys are vital for a large range of essential functions in the body, and kidney failure in both cats and dogs can therefore lead to disruption of many bodily functions.
What do the kidneys do?
The kidneys perform many homeostatic functions (i.e. they maintain a healthy environment in the body). These functions include:
- excretion of waste products
- excretion of drugs
- maintaining blood pH by excreting acid and reabsorbing bicarbonate
- regulation of blood pressure
- maintaining blood volume
- activation of vitamin D
- producing erythropoeitin(EPO) to prevent anemia
Normal kidney function in the dog and cat
The kidney is a wonderfully complex organ, and the mechanisms by which it performs its many functions are varied and complex. However, many of the most important functions can be summarised through the processes of filtration, secretion, and reabsorption.
The renal artery is responsible for delivering 20-25% of the blood volume from each heart beat to the kidney. This is a staggering volume of blood to be supplied to a single pair of organs. The kidney is divided into many thousands of nephrons, which are all independent units performing similar tasks. Blood is filtered through the sieve-like glomerulus in each nephron to produce the filtrate. Large molecules cannot pass through the glomerulus, and so important blood components such as proteins are retained in the circulation. Smaller molecules may be lost into the filtrate produced, but can be reabsorbed at a later stage if needed.
Many drugs and toxic products may be secreted by the cells of the renal tubule into the filtrate. These cells are also capable of reabsorbing vital small molecules from the filtrate. Glucose and smaller proteins, as well as bicarbonate, are some of the substances recovered in this way.
Through these actions as well as sequential dilution and concentration of the filtrate, the nephron eventually produces urine, which passes from the collection duct through the ureters and into the bladder, from whence it can be voided.
Function of the nephron- video tutorial
Acute kidney failure
A sudden, abrupt decrease in function of the kidneys results in the syndrome of acute kidney failure. Common causes of acute kidney failure in dogs and cats include:
- toxins (e.g. ethylene glycol, lily plants, raisins/grapes)
- drugs (nonsteroidal anti-inflammatories, aminoglycoside antibiotics, doxorubicin)
- kidney infection
- clot formation preventing blood flow to kidneys
- shock or congestive heart failure
- urinary tract obstruction
Did you know that as few as 10 raisins could cause acute kidney failure in a small breed dog such as a terrier?
Signs of acute kidney failure
Pets suffering from acute renal failure usually present to veterinarians as being quite suddenly unwell. Signs such as vomiting, lethargy, weakness and collapse usually predominate. Your pet will very often not be drinking an adequate amount, and a dry mouth with other signs of dehydration like sunken eyes and a prolonged skin tent will be present.
Typically, in acute kidney disease, your veterinarian will find the kidneys to be enlarged and painful. This is distinct from chronic disease, where the kidneys are usually small and may be irregularly-shaped. Another distinction between the two conditions is that animals with acute illness are usually in good condition, whereas those with chronic renal failure are usually underweight due to prolonged illness.
How to tell if your pet is dehydrated
Treatment of acute kidney failure
Many pets with this disease will be very unwell, and may require emergency treatment for the effects of shock or severe electrolyte imbalances such as hyperkalemia or acidosis. Your veterinarian will need to run a battery of blood and urine tests in order to try to identify an underlying cause such as intoxication. These animals require intensive management, especially during the first few days of illness, and will need to be hospitalised for a period of time.
Intravenous fluid therapy is the most important treatment for kidney disease. However, it is not a simple matter to provide fluids to an animal with non-functioning kidneys. Many of these patients are unable to produce adequate amounts of urine, and overhydration of the animal is a very real risk, which can lead to potentially fatal consequences such as pulmonary oedema (flooding the lungs). Your veterinary team will need to monitor your pet carefully, particularly his respiratory rate, blood pressure, body weight, and urine output in order to prevent overinfusing him.
Other treatments will depend on the underlying cause of the disease and the findings on blood tests. Renal replacement therapy(dialysis) may be necessary in very severe cases, but is only available in relatively few institutions (click here to see an up to date list).
Unfortunately, the mortality rate in veterinary patients with acute renal failure is very high, and many of those animals that do survive may be left with some degree of chronic kidney disease.
Staging chronic kidney disease
The International Renal Interest Society exists to help guide and educate veterinarians in the diagnosis and treatment of kidney disease. All animals with any degree of renal impairment should ideally be staged according to their guidelines.
Chronic kidney failure in dogs and cats
Chronic renal disease refers to an irreversible, long-standing loss of kidney function. The causes include:
- incomplete recovery from acute renal failure
- low grade bacterial infection
- immune disease such as glomerulonephritis
- high blood pressure
- congenital or hereditary defects (eg polycystic kidney disease)
Except in the case of incomplete recovery from acute renal failure, the onset of illness usually goes unobserved by the owner, and most animals with chronic kidney failure have irreversibly lost up to 75% of their kidney function by the time they are seen by their veterinarian. In many cases of chronic renal disease it will not be possible for your veterinary surgeon to determine what originally caused the disease, as there may not be any remaining evidence of the initial 'insult' many months after it occurred.
Signs of chronic kidney disease
Because most pets develop chronic renal failure slowly and over a long period of time, the signs of illness may be subtle and can be overlooked. It is worth bearing in mind that a recent study found that one in three cats over 12 years old have chronic renal disease. Many of these older cats would have been considered by their owners to be in good health.
Signs observed by owners and veterinarians include:
- weight loss
- halitosis (bad breath), possibly smelling of urine
- increased thirst
- poor appetite
- mouth ulcers
- small, irregular, non-painful kidneys
Blood tests may help your veterinarian in making the diagnosis, although amazingly these may produce normal results unless around two thirds of kidney function has already been lost. Urine analysis is the key step in diagnosis, as a loss in concentrating ability is the hallmark of chronic renal failure. Other abnormalities may also be detected depending on any underlying cause. Bacterial culture should be performed on the urine of all newly-diagnosed patients as there is a high incidence of occult (difficult to detect) infection in these animals.
Treatment of pets with chronic renal disease
When first diagnosed by your veterinarian, your pet may require treatment with any or all of antibiotics, intravenous fluids, or corticosteroids. The specifics will vary depending on each individual's main presenting problems. The aim of this initial treatment period will be to stabilise your pet before instituting long term management, which is what we will focus on below.
Dietary modification has an enormous impact on the quality of life and survival time in chronic kidney patients. Included as a nutrient under this heading is water- encourage your pet to drink as much as possible by providing multiple drinking bowls around the house. Sometimes offering rainwater or bottled water as opposed to tap water may increase water intake. Some of the strategies employed by commercial pet food companies in producing their kidney diets include:
- reduced phosphorus
- restricted protein levels
- omega 3 fatty acid supplementation
- increased potassium levels
- alkalinising agents
Maintaining blood phosphate levels within the recommended range is a key aim for veterinarians, and if dietary restriction of phosphorus is not adequate to accomplish this your veterinarian may prescribe an intestinal phosphate binder such as aluminium hydroxide.
Pets that are losing significant amounts of protein in their urine have been shown to have a 50% reduced survival time to those that are not proteinuric, and they may benefit from an angiotensin converting enzyme inhibitor(ACEi) such as enalapril or benazepril.
Around one third of cats and a significant number of dogs in chronic renal failure will suffer from high blood pressure or hypertension and although an ACEi may reduce blood pressure by a small amount, another agent such as a calcium channel blocker is usually required to reduce arterial blood pressure to within the normal range in these cases.
Calcitriol may be useful in some animals with renal secondary hyperparathyroidism (a condition which arises during renal failure and can cause one pain), but is a treatment which carries the risk of causing serious problems to the patient and requires very careful management and monitoring.
Food for pets with chronic renal disease
Anemia of chronc renal disease
Severe anemia (low levels of red blood cells) can develop for a number of reasons such as gastrointestinal ulceration and lack of erythropoetin in chronic renal disease. Treatment may be attempted by using human erythrocyte stimulating agents such as epoetin and darbepoetin with iron dextran supplementation. If successful, this can greatly improve your pet's quality of life. However, around a third of patients will fail to respond, and of those that do initially improve, around a quarter may later develop a more severe form of anemia refractory to further treatment.