Kidneys play a critical role in day-to-day functions. The kidneys remove metabolic waste from the bloodstream, and produce vital hormones that help control blood pressure and stimulate red blood cell production. The kidneys follow a complex system for managing and regulating waste; when this system breaks down, severe complications may occur to a dog’s other organs that can ultimately lead to death. There are two types of renal failure, acute and chronic. “Acute” renal failure means that the problem developed relatively quickly.
Acute Renal Failure
Causes
There are several things that may cause acute renal failure, especially certain poisons. These poisons include antifreeze, raisins and grapes, and certain drugs (aspirin or ibuprofen).
Symptoms
Early Stages:
Excessive thirst
Urine volume
Later Stages:
Lethargy
Poor or absent appetite
Vomiting
In severe kidney failure, the volume of urine may decrease or the pet may stop making urine altogether. Stomach or intestinal ulcers may also develop which results in either a black or tarry stool or vomiting of digested blood (looks like coffee grounds).
Diagnosis
Blood and urine tests are often used to diagnose acute kidney failure and to assess the severity. Other tests, including x-rays, ultrasound, and special blood tests are usually necessary to help determine what might have caused the kidney failure. Sometimes a biopsy of the kidney is recommended. However, the cause is not always discovered and may never be determined.
Treatment
IV Fluids: These fluids are used to restore food hydration and to flush out the substances that the kidneys should be removing from the bloodstream. Urine production is monitored throughout the IV fluid therapy as a decrease in urine can indicate the need for other therapies.
Medications: Antibiotics are given if the cause of the kidney failure is known or suspected to be an infection. More medications may be required depending on the clinical status of the patient.
Temporary Feeding Tube: As kidney failure drains the body’s resources and pet with kidney failure typically refuse to eat, a temporary feeding tube may be recommended.
Careful Monitoring: The clinical condition of the patient can change rapidly; therefore, careful monitoring is necessary. This may include repeatedly checking blood pressure, body weight, electrocardiogram, and blood tests. It may also be necessary to place a urinary catheter to measure urine volume.
Potassium
Potassium is normally found in low levels in the blood. In those with acute kidey failure, potassium levels may increase to dangerous levels. This increase in potassium slows the heartbeat and can cause the heart to stop. Alternatively, very high blood pressure could also develop causing the patient to need a blood pressure medication. High blood pressure can cause blood vessels in the eye or brain to burst.
Fluid Retention
Fluid retention may be present if the urine production is less than the IV fluid input. This may present as increased body weight, belly bloating, swollen legs, or shortness of breath if there is fluid buildup in the lungs.
Advanced Therapies
Not all animals with acute renal failure will respond to IV fluids. Advanced therapies such as peritoneal dialysis or hemodialysis may be necessary if there are dangerously high potassium levels, fluid in the lungs, or lack of improvement in lab results while a patient is receiving IV fluids.
Prognosis
Despite advances in treatment, acute kidney failure remains a serious and often fatal disease. About 60% of dogs and cats with this disease either die or are humanely euthanized due to the failure of a response with supportive care.
Dialysis is usually reserved for patients whose medical treatment failed, and the chance of death without dialysis is almost 100%. In these patients, 50% may recover with dialysis, depending on the cause of the kidney failure.
For patients that recover, recovery may be incomplete, leaving the patient with chronic kidney disease that requires life-long ongoing care.
Chronic Renal Failure
Chronic renal failure is the inability of the kidneys to efficiently filter the blood of waste products, not the inability to produce urine. Most dogs in kidney failure produce large quantities of urine, but the body’s toxic wastes are not being sufficiently eliminated.
Presence
Kidney tissue cannot be regenerated once it is destroyed, but the kidneys do have a large reserve capacity to perform their various functions. At least two thirds of the kidneys must be dysfunctional before clinical signs are present. This typically means the destruction has been occurring for months or years.
In dogs, CRF is associated with aging and can be considered to be “wearing out” of the kidney tissues. The age of onset is often correlated with the size of the dog. For most small dogs, early signs of kidney disease occur at about 10-14 years of age. Large dogs have a shorter lifespan and may undergo kidney failure as early as 7 years of age.
Symptoms
Early Signs:
Increased thirst and water consumption
Increased urination
More Advanced Signs:
Loss of appetite
Depression
Vomiting
Diarrhea
Very Bad breath
Ulcers in the mouth (occasionally)
Diagnosis
There are two basic tests to determine kidney function: a complete urinalysis and a blood chemistry analysis.
A urinalysis is required to evaluate the function of the kidneys. A low urine specific gravity is the earliest indication of kidney failure. An increase in protein in the urine is also indicative of decreased kidney function.
A blood biochemistry analysis assesses the function of various internal organs. A measurement of two waste products in the blood, blood urea nitrogen (BUN) and blood creatinine (CREA), indicates decreased kidney function. Tests to measure the blood levels of other substances (albumin, globulin, potassium, sodium, phosphorus, and calcium) are also important in determining the extent of the failure and in creating a treatment plan.
A newer, blood test to assess levels of SDMA have been used to determine the presence of early renal failure. SDMA concentrations increase above the normal reference interval before serum creatinine becomes elevated. This allows the vet to provide treatment at a much earlier stage of the disease.
A dog in compensated chronic kidney failure with marginal kidney functions may have normal levels of BUN and creatinine, but will have a low urine specific gravity.
A dog with a low urine specific gravity as well as elevated BUN and CREA is said to be azotemic.
How does my vet determine the degree of kidney failure?
Your vet will use the IRIS (The International Renal Interest Society) staging system. This system is based on serum creatinine levels, with sub-staging based on the presence of protein in the urine and measuring your dog’s blood pressure. This system of staging will allow our vets to gain a better understanding of how to proceed with treatment, monitor progress, and to estimate the pet’s prognosis.
Treatment
Treatment will vary based on the results from the blood tests. Early diagnosis and aggressive treatment allow many dogs to live a normal lifestyle for many months or years. Treatment typically occurs in two phases: first, flushing the kidneys and removing toxin build-up from the blood and next providing treatments to manage the disease and delay its progression.
First Phase
A high dose of IV fluids are given to flush out the kidneys and bloodstream. This process is called diuresis and helps mildly damaged kidney cells to function again and create a healthier environment for healing. Fluid therapy includes replacement of various electrolytes, especially potassium. Other aspects important in initial treatment include proper nutrition and medication to control vomiting and diarrhea. This first phase often reduces discomfort in the pet once completed.
Second Phase
The goal of this phase is to keep the kidneys functioning as long and normally as possible. This is typically accomplished with one or more of the following:
Diet - The ideal diet for dogs with advanced stages of kidney failure is lower in protein, low in phosphorus, and is not acidified. This diet helps reduce the amount of protein waste and metabolic toxins that may make your pet feel sick and lethargic. A decreased protein diet also helps to decrease the workload on the kidneys.
Phosphate Binder - Phosphorus is removed from the body by the kidneys. When kidney function is impaired, phosphorus begins to build-up in the blood. Elevated blood phosphorus levels contribute to lethargy and a decrease in appetite. Certain drugs can bind excess phosphorus in the intestinal tract to avoid absorption into the bloodstream.
Home Fluid Therapy - Once your pet is stabilized, maintenance fluids can be given under the skin at home. This prevents dehydration, and continuously flushes toxins from the kidneys. This is usually done anywhere from twice daily to once a week. Most dogs tend to do best when they receive small amounts daily. Although this technique sounds beyond one’s capabilities, many are surprised at the ease of the technique and how well dogs tolerate it.
Therapy for Proteinuria - Dogs with protein in their urine have an increased progression of CRF. ACE inhibitors will help lower pressure in the kidneys and decrease the amount of protein in the urine.
Medication to Regulate the Parathyroid Gland and Calcium Levels - Calcium and phosphorus should remain at a 2:1 ratio in the blood. The increase in blood phosphorus levels secondary to kidney failure stimulates the parathyroid gland to increase the blood calcium level by removing it from bones. Although this helps with normalizing the ratio, it makes the bones brittle and easily breakable. Calcitriol can be used to reduce the function of the parathyroid gland and to increase calcium absorption from the intestinal tract.
Medication to Stimulate the Bone Marrow to Produce New RBCs - The kidneys also produce erythropoietin which stimulates the bone marrow to produce new red blood cells. However, when this production is diminished due to kidney failure, the pet may become anemic (low red blood cell count). Synthetic erythropoietin may stimulate the bone marrow to make red blood cells and correct the anemia in most patients. Unfortunately, in some cases, the drug cannot be used long term as the body will recognize the product as foreign and create antibodies against it.
Prognosis
The prognosis is variable depending on the pet’s response to the initial stage of treatment and your ability to perform follow-up care. Veterinarians encourage treatment in most situations due to a good response and the ability to maintain a good quality of life. Treatment and follow-up care are relatively easy and inexpensive and extend the length and quality of life for the patient.
Source:
Blue Pearl Veterinary Partners: https://bluepearlvet.com/medical-articles-for-pet-owners/acute-renal-failure-in-dogs/
VCA Animal Hospitals: https://vcahospitals.com/know-your-pet/kidney-failure-chronic-in-dogs