The most important function of the kidneys is to filter nitrogen and other waste products out of the blood. When the kidneys aren't working properly, toxic wastes can build up to dangerous levels. This is called "azotemia." Many things can damage the kidneys – some happen suddenly, while others develop gradually over time. Acute or sudden-onset renal failure (ARF) is the less common of the two types of kidney failure in dogs. ARF is a clinical condition characterized by some severe and unexpected insult to the kidneys, usually to both of them. Uremic toxins, which normally would be filtered by functional kidneys and excreted in the urine, quickly accumulate in the bloodstream, causing serious imbalances in the electrolyte composition of blood and other bodily fluids. Acute renal failure may be reversible if it is caught quickly and treated aggressively, although more often than not it ultimately is fatal. Chronic renal failure, which is the more common, slowly-progressive form of the disease, is almost always irreversible. With either acute or chronic renal failure, the primary waste product that builds up in circulation is blood urea nitrogen, known as "BUN" in medical circles.
Causes of Acute Renal Failure
Domestic dogs can develop acute renal failure (ARF) for a number of different reasons, the most common of which is ingestion of some sort of toxic chemicals. Other causes include: shock, trauma, hypoadrenocorticism (Addison's Disease), blood clotting/coagulation disorders, adverse reactions to medication (non-steroidal anti-inflammatory drugs (NSAID); others), prolonged exposure to general anesthesia, prolonged exposure to temperature extremes (hyperthermia; heatstroke; hypothermia), high blood pressure (hypertension), insufficient blood flow to the kidneys, adrenal gland insufficiency, congestive heart failure, urinary tract obstruction (from uroliths (stones), blood clots or inflammatory debris), rupture of the urinary bladder or urethra, ingestion of poisons (especially ethylene glycol antifreeze), administration of chemotherapeutic drugs, heavy metal intoxication, venom from insect or snake bites, ingestion of toxic foods (chocolate, grapes, raisins, etc.), ingestion of toxic plants (Easter lilies; others), Leptospirosis, Lyme Disease, Rocky Mountain Spotted Fever, pancreatitis, septicemia, adverse reaction to blood transfusion products, hypervitaminosis D (toxicity due to ingestion of cholecalciferol-containing rodent bait or certain pharmaceuticals), lymphosarcoma, glomerulonephritis, disseminated intravascular coagulation (DIC) and liver failure.
Prevention of Acute Renal Failure
Companion dogs – especially those over 7 years of age - should receive an annual veterinary check-up with blood and urine screening to monitor their kidney function and the health of other vital organs. It is good to establish a geriatric baseline of key components of the blood and urine, so that any dramatic changes in those levels can be investigated. Kidney failure should be high on the list of differentials in older dogs that develop systemic illness, blood clotting problems, blood pressure instability or liver, heart or multiple organ failure. Dogs receiving nephrotoxic drugs (those that are known to be toxic to the kidneys) should have their blood urea nitrogen levels monitored on a regular basis. Of course, antifreeze, household cleaners and other chemicals should always be stored well away from pets.
The prognosis for dogs with ARF is highly variable and difficult to predict, although this is a less common and usually less discouraging disorder than chronic renal failure. Life expectancy can range from days to years after diagnosis. Once a dog is in acute renal failure, a veterinarian is in the best position to discuss the course of disease and potential management options with the owner. If leptospirosis infection is the cause of acute renal failure, the owner should be advised to handle urine extremely carefully, as the causative microorganism is zoonotic – which means that it can infect humans.
Effects of Acute Renal Failure on Dogs
Dogs suffering from acute renal failure (ARF) usually become very sick, very quickly. Unfortunately, the symptoms of ARF typically aren't noticed by owners until more than 75% of their dog's functional kidney tissue has been damaged and the dog is really quite ill.
Symptoms of Acute Renal Failure
The symptoms of acute renal failure typically come on suddenly, as its body tries to compensate for the kidneys' inability to filter and flush toxins out in the urine. Among the first signs noticed by most owners are increased thirst and water intake (called "polydipsia") and passage of unusually large amounts of urine (called "polyuria"). Sometimes, housetraining accidents start to happen. Occasionally, owners will notice a smaller urine output than normal, especially in late-stage disease; this is called "oliguiria". Other things that owners may see include one or more of the following:
Abdominal discomfort and pain (from enlarged, firm, sore kidneys)
Lack of appetite (anorexia; inappetence; typically happens suddenly)
Lethargy; apathy; listlessness
Vomiting (+/- blood in vomitus)
Diarrhea (+/- blood in stool)
Bloody, normally-formed stool
Bad breath (halitosis; strong ammonia-like odor from build-up of blood urea nitrogen in circulate)
Brownish discoloration of the surface of the tongue
Bleeding problems (abnormal blood clotting; prolonged coagulation times)
Changes in cognition or mental state; disorientation
Dehydration (can become severe)
Poor body condition (loss of muscle tone; dull, dry coat)
Pale gums and other mucous membranes (pallor)
Acute onset of blindness (from hypertension)
Ataxia (lack of coordination)
Seizures, tremors, shivering, shaking (neurological signs; with severe disease)
Polyuria and polydipsia (shortened to "PU/PD") are very commonly associated with a number of different disorders and, without more, are not diagnostic of acute renal failure. However, excessive water intake and urine output almost always do accompany renal failure, when it is present. The bad breath and oral ulcers are caused by the accumulation of toxins in the blood. In severe cases, dogs with ARF may develop high blood pressure (hypertension), with the adverse effects associated with that condition.
Dogs at Increased Risk
Acute renal failure (ARF) tends to be more common in the fall and winter months, when dogs are more likely to get into antifreeze containing ethylene glycol, which is one of the most common causes of ARF. Also, cold, damp weather is more supportive of the infectious leptospirosis microorganisms. Frequently, dogs with acute renal failure are younger than those with chronic renal failure. Large breed, free-roaming dogs seem to be predisposed to ARF, probably due to their increased access to poisonous plants, chemicals, snakes and insects, microorganisms and other nephrotoxins (things that damage the kidneys). Dogs with recurrent bouts of mild acute renal failure are more likely to develop chronic renal failure over time, as are dogs that have suffered from kidney stones (nephroliths; uroliths) or other types of kidney disease.
Systemic illness, dehydration, low blood pressure (hypotension), advanced age and administration of certain pharmaceuticals (including sulfonamides, amphotericin B, aminoglycosides, cisplatin, tetracyclines, radiocontrast agents and non-steroidal anti-inflammatory drugs [NSAIDs]) seem to put dogs at increased risk of going into acute renal failure.
Acute renal failure (ARF) can be tricky to diagnose, because many of the signs of this disease mimic those caused by other ailments. However, given time and a willing owner, veterinarians have the skills and the tools to arrive at a definitive diagnosis. Dogs with ARF that is severe enough to cause noticeable signs usually arrive at the veterinary clinic with a normal hair coat and in good body condition. Their owners bring them in because their pets suddenly have become weak, listless, lethargic, depressed and dehydrated, despite drinking a lot more water than usual and urinating frequently in high volumes. They also may have developed abnormally bad breath.
The attending veterinarian will take a thorough history from the owner, not only about the dog's historical health and vaccination status but also about what potential toxins it may have had access to in the past few weeks. Exposure to antifreeze will be at the top of that list. She will examine the dog physically from nose tip to tail. The initial database undoubtedly will include a complete blood count, a serum biochemistry profile and a urinalysis, all of which are routine, easy to conduct and relatively inexpensive, especially when considering the vast amount of useful diagnostic information they can provide about kidney and other organ function. The results of these tests in dogs with acute renal failure will reveal elevated blood urea nitrogen (BUN), elevated blood creatinine and phosphorus levels, abnormally low urine specific gravity and/or evidence of a urinary tract infection or obstruction. The high levels of circulating BUN, creatinine and phosphorus are caused by the kidneys' inability to properly filter waste and other products from the blood; the low urine specific gravity reflects the kidneys' failure to concentrate the urine normally, which makes it overly dilute. This is what contributes to the dog's dehydration, despite a high water intake. The blood work from dogs with ARF typically does not show that they are anemic, unlike that from dogs with chronic renal failure. More specific blood tests can be conducted to rule in or out the presence of ethylene glycol (antifreeze) and to detect leptosiprosis infection. Direct or indirect blood pressure tests will identify low or high blood pressure, and abdominal ultrasounds or radiographs (X-rays) can reveal abnormal kidney size, tissue or structure, cysts, tumors, urinary tract obstructions or other disorders, although these are more commonly found in dogs suffering from chronic rather than acute renal disease.
If the initial diagnostic procedures point to acute renal failure, a urinary catheter may be placed so that the medical team can accurately monitor the dog's urine output. The dog probably will be put on intravenous fluids to correct rehydration and try to flush toxins into the urine. Fine needle aspirate samples of kidney tissues may be taken, with or without ultrasound guidance, so that the veterinarian can evaluate the cellular structure under a magnification. This is especially useful for determining whether lymphosarcoma is responsible for the kidney enlargement. Renal tissue biopsies can also be taken and submitted to a laboratory for assessment.
Urinary tract infections (UTIs) are common in dogs with kidney disease. Resolving those infections may help improve kidney function and alleviate discomfort in some dogs.
Acute renal failure (ARF) shows up suddenly as the result of some severe insult to the kidneys. The goals of treating this condition are to alleviate the symptoms of uremia, correct life-threatening electrolyte abnormalities and dehydration, restore proper urine production and concentration, delay progression of disease if possible and improve the dog's overall comfort.
It is critical to flush circulating toxins and waste products from the blood of a dog in acute renal failure. Most decompensated animals will not tolerate oral fluids or medications. Dogs that are dehydrated, anorexic and vomiting are already showing signs of uremia and usually need to be hospitalized. In the clinic, veterinarians and technicians can start immediate, aggressive intravenous fluid and electrolyte replacement therapy, to try and force accumulating toxins into the urine. After fluid and electrolyte balances have been corrected, fluids can be given under the skin, rather than directly into a vein. Many owners can do this at home. If an ingested toxin is suspected as the cause of the kidney crisis, activated charcoal, cathartics and/or specific antidotes can be administered to bind the toxic material until it can be eliminated from the body through one end (vomiting) or the other (in urine or stool). Blood pressure will be monitored regularly. If persistent high blood pressure is present, it may be managed with medication.
Dietary changes can be helpful when they are customized to the individual dog with acute renal failure. Dogs that are vomiting may be kept off food until their vomiting resolves. They may need to get their calories through force-feeding or use of feeding tubes. Protein is usually poorly metabolized by dogs in renal failure, and phosphorus and sodium tend to accumulate in their blood. Most renal diets have much lower protein, phosphorus and sodium levels than regular maintenance diets.
Some veterinarians recommend supplementing the diet with omega-3 fatty acids, on a case-by-case basis. Like people, dogs may resist sudden dietary changes, especially when they aren't feeling well. It may quickly become more important for a dog with ARF to receive adequate calories than it is for him to eat a perfectly balanced diet. When a sick dog refuses to eat and starts dropping weight, it becomes increasingly difficult for his body to fight the disease. A tasty, calorie-packed diet may be the best choice for dogs with acute renal failure, at least in the short term, unless and until the effects of the disease can be controlled.
While free access to fresh water is always important, it is essential for dogs in renal failure. They must be able to drink enough water to compensate for their increased urine output, or they may develop severe, debilitating and life-threatening dehydration. As mentioned above, sometimes even free access to fresh water is not sufficient, and intravenous or subcutaneous fluids must be administered.
If vomiting and oral or gastric ulcers are involved, a number of prescription and over-the-counter medications are available to decrease stomach acidity, reduce nausea and vomiting and soothe the gums and stomach lining. The dog's veterinarian can also prescribe drugs to help manage blood pressure, if necessary. Some drugs are metabolized by the kidneys or are known to cause renal damage. Obviously, these should not be used in patients with renal failure. When a dog is suspected (or confirmed) to have ingested antifreeze, specific treatments can reverse the toxicity, if they are administered within a day or two after the incident. If leptospirosis is the cause of acute kidney failure, intravenous and oral medications are available to resolve the infection.
Kidney transplants are available at a handful of veterinary teaching and referral hospitals and are gradually becoming more common, especially for dogs with chronic rather than acute renal failure. Kidney dialysis is another potential therapy. It also is only available at a limited number of highly specialized teaching and private referral centers. Dialysis involves routing the dog's blood through special catheters into a machine that is designed to perform the filtering functions of normal kidneys. The procedure lasts 3 to 4 hours and must be done several times a week. Dialysis is extremely expensive and is rarely used in veterinary medicine. However, it too is slowly becoming more available, especially for short-term management of dogs with acute renal failure, to allow for return of renal function, regeneration and repair. If treatment and management attempts do not improve kidney function and relieve the animal's discomfort, euthanasia may be the only humane option.
The prognosis for dogs with acute renal failure is difficult to predict. A veterinarian is the best one to discuss the course of the disease and treatment options with the owner. Dogs with infectious and obstructive causes of ARF tend to have a slightly better prognosis than those with toxic causes. Unfortunately, the prognosis for any dog with acute renal failure is unfavorable. Owners should expect their dogs to be hospitalized for days to weeks, at a minimum.