Definition of Acute Renal Failure
Kidney failure, also called renal failure, is the inability of the kidneys to filter waste products out of the blood. Normal kidneys remove nitrogen and other wastes from circulation so that they can be excreted in urine. When the kidneys don’t work properly, toxic wastes build up in the dog’s blood. Acute renal failure (ARF) happens when there is some sudden and severe insult to the kidneys. Toxins which normally are filtered out of the dog’s system by its functional kidneys accumulate in the bloodstream, causing imbalances in bodily fluids. The main waste product that builds up in dogs with ARF is blood urea nitrogen (BUN). A dog’s kidneys are especially vulnerable to being damaged by toxins, because about 25% of its blood passes through the kidneys with each heartbeat, and the kidneys are highly sensitized to circulating toxins.
Causes of Acute Renal Failure
A number of things can cause domestic dogs to develop acute renal failure (ARF). The most common of these is eating or ingesting some solid, liquid or other substance that is poisonous to the kidneys; this is called “nephrotoxicity.” The nephron is the structural and functional unit of the kidneys. Each kidney contains many nephrons, and each of those is a complex system of highly regulated tubules and membranes. Nephrons are designed to remove certain end-products of metabolism from the blood, including urea, uric acid and creatinine. They also regulate circulating levels of sodium, chloride and potassium, and other things. The kidneys are especially vulnerable to being damaged by nephrotoxins because about 25% of a dog’s blood passes through its kidneys with each heartbeat, and the kidneys are highly sensitized to circulating toxins.
Some of the materials known to be nephrotoxic to dogs include:
- Antifreeze (especially ethylene glycol antifreeze)
- Administration of certain drugs including chemotherapeutic agents, aminoclycosides, sulfonamides, tetracyclines, cyclosporine, cisplatin, ACE inhibitors, radiocontrast agents, amphotericin B, non-steroidal anti-inflammatory drugs (NSAIDs), methoxyflurane, others
- Heavy metal intoxication including arsenic, copper, iron, lead, mercury, silver, zinc
- Venom from insect or snake bites
- Ingestion of toxic foods such as chocolate, grapes, raisins
- Ingestion of toxic plants
- Ingestion of cholecalciferol-containing rodenticides (rat/mouse bait) or human medications that contain vitamin D
- Hypercalcemia
Other possible causes of acute renal failure in dogs include:
- Anaphylactic shock
- Physical trauma to one or both kidneys
- Hypoadrenocorticism (Addison’s Disease)
- Blood clots and coagulation disorders
- Prolonged exposure to general anesthesia
- Prolonged exposure to temperature extremes
- High blood pressure (hypertension)
- Low blood pressure (hypotension)
- Congestive heart failure
- Urinary tract obstruction (stones, blood clots, bacterial build-up, inflammatory debris)
- Rupture of the urinary bladder or urethra
- Leptospirosis
- Lyme Disease
- Rocky Mountain Spotted Fever
- Pancreatitis
- Septicemia
- Adverse reaction to blood transfusion products
- Lymphosarcoma/lymphoma
- Glomerulonephritis
- Disseminated intravascular coagulation (DIC)
- Liver failure
Prevention of Acute Renal Failure
Companion dogs, especially older ones, should receive an annual veterinary check-up with blood and urine screening to monitor their kidney function and the health of other vital organs. Establishing a geriatric baseline of key components of the blood and urine makes identifying any later changes in those levels much easier. Acute renal failure is more common in younger dogs and those that are allowed to range freely. Dogs receiving nephrotoxic drugs should have their blood urea nitrogen levels monitored regularly and should always have free access to abundant fresh water to keep them well-hydrated. Antifreeze, household cleaners and other dangerous chemicals should be stored well away from pets.
Special Notes
Once a dog has developed acute renal failure, a veterinarian who is experienced in internal medicine should be consulted to discuss the course of disease and potential management options with the owner. If leptospirosis may be the cause of ARF, the owner should handle urine extremely carefully, because the causative microorganism is zoonotic – which means that it can infect humans as well as dogs.
Initial Evaluation
Acute renal failure (ARF) in dogs can be tricky to diagnose because many of its signs mimic those of other ailments. However, given time and a willing owner, veterinarians have the skills and tools necessary to arrive at a definitive diagnosis. A dog with ARF that is severe enough to cause noticeable signs usually arrives at the veterinary clinic with a fairly normal hair coat and in good body condition. The owner typically brings his dog in because it has become weak, listless, lethargic, depressed and often dehydrated, despite drinking lots of water and urinating more frequently and in higher amounts than usual. The dog may have also developed strange or very bad breath.
Diagnostic Procedures
The veterinarian will take a thorough history from the owner about his dog’s general health, vaccination status and symptoms, and also about its potential access to toxic substances including antifreeze over the past few weeks. The vet will examine the dog from nose to tail tip. She may detect an elevated heart rate (tachycardia) or respiratory rate (tachypnea). The initial database usually includes taking blood and urine samples and conducting a complete blood count, serum biochemistry profile and urinalysis, all of which are routine tests that are easy to conduct and are relatively inexpensive. The test results in dogs with acute renal failure may reveal elevated blood urea nitrogen (BUN), creatinine and phosphorus levels, abnormally low urine specific gravity and maybe evidence of a urinary tract infection or obstruction. High levels of circulating BUN, creatinine and phosphorus are caused by the kidneys’ inability to properly filter toxic waste products from the blood and flush them out in urine. Low urine-specific gravity means that the kidneys aren’t able to reabsorb water and concentrate urine normally, which makes it overly dilute, contributing to the dog’s dehydration, despite a high water intake.
More advanced blood tests can be conducted to detect the presence of ethylene glycol antifreeze and to detect Leptospira infection. Direct or indirect blood pressure tests are common. Abdominal ultrasounds and radiographs (X-rays) can reveal changes in kidney size, tissue or structure, cysts, tumors, urinary tract obstructions and other abnormalities.
If the initial diagnostic procedures point to acute renal failure, the dog may need to be hospitalized. A urinary catheter may be placed so that the medical team can monitor the dog’s urine output. The dog probably will be put on intravenous fluids to correct hydration and flush toxins into the urine. Fine needle aspirate samples of kidney tissues can be taken, with or without ultrasound guidance, so that the veterinarian can evaluate the kidneys’ cellular structure under magnification. This is especially useful for determining whether lymphosarcoma is responsible for any noticeable kidney enlargement. Biopsies can also be taken of kidney tissue and submitted to a pathology laboratory for assessment.
Special Notes
Urinary tract infections (UTIs) are common in dogs with kidney disease. Resolving those infections can help improve kidney function and alleviate discomfort in some dogs.
Effects of Acute Renal Failure – From The Dog’s Point of View
Kidney failure of any type, from any cause, eventually makes affected animals feel lousy. Dogs suffering from acute renal failure (ARF) usually become sick quickly, but most owners don’t notice the signs of ARF until their faithful companion is seriously ill, because the early stages of this disease are difficult to detect. At first, the dog will develop non-specific signs of weakness, lethargy and depression, which often go unnoticed even by the most attentive owners. The symptoms progress to gastrointestinal distress and other signs of general illness. By the time the dog is really obviously sick, more than 75% of its functional kidney tissue is usually damaged.
Symptoms of Acute Renal Failure – What the Owner Sees
The observable symptoms of acute renal failure usually appear suddenly, as the dog’s body tries to compensate for its kidneys’ inability to flush toxins out in the urine. Among the first signs noticed by most owners are increased thirst and water intake (polydipsia) and passage of unusually large amounts of urine (polyuria), and some animals may have bathroom accidents in the home. Occasionally, owners will notice a smaller urine output than normal, especially in late-stage disease. Other things that owners may see include:
- Abdominal discomfort and pain (enlarged, firm, sore kidneys)
- Lack of appetite
- Weight loss
- Weakness
- Lethargy; apathy; listlessness
- Depression
- Vomiting (+/- blood in vomitus)
- Constipation (+/- blood in stool)
- Diarrhea (+/- blood in stool)
- Blood in normal stool
- Bad breath from build-up of blood urea nitrogen in the blood stream
- Brownish discoloration of the tongue surface
- Bleeding problems (abnormal blood clotting; prolonged coagulation times)
- Changes in cognition or mental state; disorientation
- Dehydration (can become severe)
- Fever
- Oral ulcers
- Poor body condition (loss of muscle tone; dull, dry coat)
- Pale gums and other mucous membranes (pallor)
- Acute onset of blindness (from hypertension/high blood pressure)
- Ataxia (lack of coordination)
- Seizures, tremors, shivering, shaking (neurological signs with advanced disease)
- Collapse
- Coma
- Death
Polyuria and polydipsia (shortened to “PU/PD”) are associated with a wide number of medical disorders and, without more, cannot be used to diagnose ARF. However, excessive water intake and urine output almost always accompany renal failure, when it is present. In severe cases, dogs with ARF may develop high blood pressure, with the adverse effects associated with that condition.
Dogs at Increased Risk
Acute renal failure tends to occur more often in the fall and winter months, when dogs have increased access to ethylene glycol antifreeze. Cold, damp weather support the infectious leptospirosis microorganisms. Frequently, dogs with ARF are younger than those that develop chronic renal failure. Large breed, free-roaming dogs seem to be predisposed to this condition, probably due to their increased access to poisonous plants, chemicals, snakes, 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 suffer from kidney stones or other types of kidney disease. Systemic illness, dehydration, low blood pressure (hypotension), advancing age and administration of certain drugs can also put dogs at an increased risk of developing acute renal failure.
Treatment Goals
The goals of treating acute renal failure (ARF) are to alleviate the symptoms of circulating toxic waste build-up, correct electrolyte abnormalities, eliminate dehydration, restore normal urine production and concentration, delay progression of disease and improve the dog’s overall quality of life.
Treatment Options for Acute Renal Failure
It is critical to flush circulating toxic waste products from the blood of dogs in acute renal failure. Free access to fresh water is essential for dogs in renal failure. They must be able to drink enough water to compensate for their increased urine output, or they will develop life-threatening dehydration. Unfortunately, most decompensated animals will not voluntarily drink enough water to accomplish this. Dogs that are dehydrated, anorexic and vomiting usually need to be hospitalized so that they can start immediate, aggressive intravenous fluid and electrolyte replacement therapy to try and force toxins into the urine. After fluid and electrolyte balances are corrected, fluids can be given under the skin (subcutaneously), rather than directly into a vein. Many owners can do this stage of treatment at home.
If an ingested poison such as antifreeze is suspected as the cause of the crisis, activated charcoal or other substances may be given to bind the toxic material and speed its elimination through vomiting or in urine or feces.
Dietary changes can be helpful when they are customized to the individual dog. Dogs that are vomiting often are kept off food for a few days and may need to get their calories through a liquid diet using a feeding tube. Protein is poorly metabolized by dogs in renal failure, and phosphorus and sodium tend to accumulate in their blood. Most commercial kidney diets have less protein, phosphorus and sodium than maintenance diets. Some dogs resist sudden dietary changes, especially when they aren’t feeling well. When a sick dog refuses to eat and starts dropping weight, it becomes increasingly difficult for his body to fight disease. It can become more important for a dog with ARF to get enough calories than it is for him to eat a perfectly balanced diet. Tasty, calorie-packed meals may be the best choice, at least in the short term. A number of medications are available to decrease stomach acidity, reduce nausea, decrease stomach acidity and soothe sore gums, if vomiting and oral or gastric ulcers are involved. Drugs that are metabolized by the kidneys or are known to cause kidney damage should not be used in ARF patients unless absolutely necessary. If leptospirosis is the cause of acute kidney failure, intravenous and oral medications are available to resolve the infection. Blood pressure irregularities may be manageable with medication.
Kidney transplants are gradually becoming available at a handful of veterinary teaching hospitals and referral centers for dogs with renal failure. Kidney dialysis is another potential therapy, although it is extremely expensive and rarely used in veterinary medicine. Dialysis involves routing the dog’s blood through special catheters into a machine that performs the filtering functions of normal kidneys. The procedure lasts 3 to 4 hours and must be done several times a week. Dialysis is slowly becoming available at a limited number of highly specialized veterinary facilities for short-term management of dogs with ARF.
Prognosis
The outlook for dogs with ARF is hard to predict. Dogs with infectious or obstructive causes tend to have a slightly better prognosis than those with toxic causes. Life expectancy can range from days to years, depending on the stage of disease at the time of diagnosis. Unfortunately, the prognosis for any affected dog is unfavorable. If management attempts are unsuccessful, euthanasia may be the only humane option.
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