Why are the kidneys important?
The kidneys are one of the most important organs of
the body. The kidneys play multiple roles in maintaining an optimal
environment within the body for everyday function and survival. They help to maintain the correct levels of body fluids and
electrolytes, stimulate the bone marrow to produce new red blood cells,
aid in the control of blood pressure and play a critical role in
removing waste products from the body.
When the kidneys don’t function properly, the pet can become
dehydrated and suffer from electrolyte imbalances, become anemic and
toxins can build up in the blood causing the pet to become ill.
How do the kidneys work?
Mammals have two kidneys,
one on each side in the region of the mid to lower back. Each kidney is connected to the urinary bladder by a small
tube called the ureter. The
urinary bladder is emptied to the outside of the body by a single larger
tube called the urethra. The
kidneys are made up of millions of “nephrons”.
The nephron is the functional unit of the kidney and together,
they regulate the amount of water, electrolytes, waste products and
other substances that are excreted in the urine or reabsorbed into the
blood depending on the needs of the body.
When the body is dehydrated, the kidneys reabsorb more water,
which makes the urine more concentrated.
If the pet drinks a large amount of water, the nephrons allow
more water to pass through into the urine, making it more dilute.
The nephrons act in a similar manner in regulating the other
substances that pass through the kidney.
There are millions of nephrons in the kidneys, which allow them
to sustain a certain amount of damage.
The kidneys cannot however, replace damaged nephrons, so once
damage occurs, it is irreversible. Because of their large reserve capacity, we typically do not
start to see signs of kidney disease until at least half of the total
nephrons are damaged. This
makes it difficult to evaluate renal failure in a pet until it has
progressed significantly.
What is renal failure?
Renal failure results from
damage to the nephrons, causing them to not function properly.
Renal failure can be divided into acute (a rapid onset) or
chronic (slowly progressive over time).
Acute renal failure is often the result of major damage to the
kidneys, such as infection, decreased blood flow to the kidneys, drugs
that can be harmful to the kidneys, toxins such as antifreeze, or
blockage of urine outflow from the kidneys, such as stones lodged in the
ureters or urethra. The pet
usually becomes sick shortly after the kidney has been damaged.
Depending on the cause and if acute renal failure is discovered
early enough, it can sometimes be reversed and the kidneys can recover.
At the other extreme, irreversible damage can occur where the
kidney is unable to be repaired and the disease can be fatal.
Chronic renal failure is often more gradual in onset and by the
time the pet is showing clinical signs it is difficult to pinpoint what
initially caused the insult to the kidneys.
As animals age, the number of functional neprons begins to
decrease. This is
especially true in older cats and the decrease in functional nephrons
often results in chronic renal failure.
There is no way to cure chronic renal failure and it will
continue to progress as more nephrons become non-functional.
In many cases, pets with chronic renal failure can be treated
with medications, fluid therapy and dietary changes to help them feel
better and slow the progression of the disease for months or even years.
Can my pet be tested for renal failure?
Blood work and urinalysis
are helpful tests for looking at kidney function.
With blood work, substances that are eliminated from the blood by
the kidney can be evaluated. The
major substances evaluated are BUN (blood urea nitrogen) and creatinine.
These become elevated with renal failure because the kidneys
aren’t working well enough to clear them from the blood.
There are many other toxins that build up in the body with renal
failure. Most of these lead
to the clinical signs that we see, but they are difficult to evaluate
with tests. Unfortunately, two thirds of the nephrons must be lost
before the BUN and creatinine become elevated.
Urinalysis can evaluate the ability of the kidneys to concentrate
the urine as well as look for any evidence of infection, crystals or
other substances such as protein that shouldn’t be in the urine under
normal circumstances. Your
veterinarian may also suggest other tests such as radiographs or
ultrasound to get an idea of the size, shape and architecture of the
kidneys.
What are the signs of renal failure?
With acute renal failure, the pet will often become
depressed, have a decreased appetite or vomiting, foul smelling breath
and may have reduced or no urination.
The clinical signs are usually rapid in onset. With chronic renal
failure, the initial clinical signs are usually drinking more water and
urinating more frequently. As
the disease progresses, the pet may have a decreased appetite, weight
loss, intermittent vomiting, lethargy, weakness, poor hair coat, ulcers
in the mouth and foul smelling breath.
Many of these clinical signs can occur with medical conditions
other than renal failure and it is important to seek veterinary
attention for your pet if they are experiencing any of these clinical
signs.
How do you treat renal failure?
The treatment of renal failure is performed on a
case-by-case basis to meet the individual needs of each patient.
If the initial cause of the kidney insult can be identified, your
veterinarian will aim treatment efforts at correcting or removing the
source of the problem. In
many cases, intravenous fluid therapy is required in attempt to diurese
the kidneys to aid in flushing many of the built up waste products, such
as BUN and creatinine out of the body.
Fluid therapy might also be required to correct electrolyte
imbalances. Other
medications might be used to help the kidneys filter fluids more
effectively or to help increase the blood flow to the kidneys.
Some pets with renal failure also develop high blood pressure. If this is a problem, medication to control the blood
pressure might also be indicated.
Medications can be used on a long-term basis at home to help with
the other clinical signs such as nausea, decreased appetite and anemia.
Fluids can also be administered under the skin at home.
Your veterinarian may prescribe a special diet for your pet that
is lower in proteins, salt and other substances that may be difficult
for the failing kidneys to eliminate in the urine.
It is important for a pet with kidney disease to always have
access to fresh water. Since
the kidneys can’t concentrate the urine adequately, they need to drink
more to make up for water that is lost in the urine. Your veterinarian
will be able to formulate the best treatment protocol for you and your
pet.
