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Chronic Renal Failure and Treatment Options
for the Geriatric Cat:
A Literature Review
by Cynthia Jones
Spring 2005
Introduction
Chronic renal failure (CRF) appears
to have reached epidemic proportions in pet cats.
It is now recognized as a major cause
of morbidity and mortality in cats
(Hughes, Slater, Geller, Burkholder, & Fitzgerald, 2002).
One simple definition of CRF is
"the progressive and irreversible loss of renal function
during a relatively long period of time"
(Hughes et al, 2002).
The aim of this paper is to shed some light
on the different treatment options available for cats
once they have been given the CRF diagnosis.
Other disorders such as hypertension
that tend to co-exist, aggravate, or be associated with CRF
will also be discussed.
Dietary Management
CRF is characterized by impaired kidney function
that goes beyond the normal declines
in kidney size, renal blood flow
and glomerular filtration rate
that normally occur with aging
(AAFP/AFM, 2005).
Whether or not age alone
is a risk factor for CRF is debatable.
Experiments show that even after
significant reduction in renal mass,
the feline kidney can still concentrate urine
(AAFP/AFM, 2005).
One risk factor that may be modified
and used to halt the progression of CRF is diet.
Dietary management as part of CRF treatment
is controversial yet widely prescribed.
Despite numerous studies,
there is no consensus on the efficacy of such diets
(primarily protein restrictive)
in optimizing nutrition and limiting
progressive renal injury
(Polzin, Osborne, Ross, & Jacob, 2000).
Yet because diet is a relatively simple treatment option
that cat guardians can implement at home,
it remains the primary means
by which CRF is managed by veterinarians
(Polzin et al, 2000).
Along with protein restriction,
some studies have shown that phosphorus restriction
has some benefit in slowing the progression of CRF
(Polzin et al, 2000).
Because the kidneys tend to retain phosphorus in CRF,
about 60% of cats with CRF will develop hyperphosphataemia
(high phosphorus levels),
which in turn leads to hyperparathyroidism
(Polzin et al, 2000).
Polzin and colleagues (2000) point out that most renal diets
are naturally low in phosphorus because protein
is the major source of dietary phosphorus.
They also note that intestinal phosphorus binding agents
may be used in addition to diet
for cats whose serum phosphorus concentrations
do not normalize with diet alone.
More research is needed to gain direct experimental support
for linking phosphorus restriction
to a decreased rate of progression of CRF in cats
(Polzin et al, 2000).
Other CRF complicating factors
Polzin and colleagues (2000) bring up
in their report on dietary management
of feline CRF include acidity of the diet,
potassium levels, and sodium intake.
They conclude that when cats are fed reduced protein diets,
there is an increased need to maintain a normal acid-base balance.
Studies of normal cats fed
an acidifying and potassium restricted diet
showed a decrease in renal function
wherein potassium depletion
and acidosis appeared to be additive
(Polzin et al, 2000).
Renal function may improve with oral potassium therapy
for many cats with CRF
(Polzin et al, 2000).
Finally, although it is widely accepted
that sodium be limited in human patients with CRF,
there is no data to show that limiting dietary sodium intake
in cats with CRF is beneficial
(Polzin et al, 2000).
If cats in the final stages of CRF
become anorexic and appetite stimulants are ineffective,
Polzin and colleagues (2000) recommend
feeding renal failure diets
via gastrostomy or pharyngostomy tubes.
They claim that a high quality of life
is still possible after using these devices
and that the procedures also facilitate
administration of phosphorus binding agents,
alkalinizing drugs, and potassium supplements.
In addition to the level of protein,
the source of protein may also be a relevant factor
in the progression of renal damage
(Finco, Brown, S., Brown, C., Crowell, Sunvold, & Cooper, 1998).
However, some studies have shown that a high caloric intake
had more adverse affects on the kidneys than more protein
(Hughes et al, 2002).
The experiment conducted by Hughes and colleagues (2002)
focused on fiber intake and ad libitum or free feeding.
Their results show a positive association
between free feeding and CRF and decreased odds of CRF
when dietary fiber was increased
(Hughes et al, 2002).
They also cite more recent criteria
for normal creatinine values
and urine specific gravity at <2.0 mg/dl and >1.040, respectively.
Hughes and colleagues (2002) also experimented
with lifestyle variables such as amount
of playtime, flea collar use,
outdoor access versus indoor only, and more.
None of those variables were significant predictors of CRF
(Hughes et al, 2002).
In summary, inconclusive data shouldn't rule out
dietary management as a useful tool
in fighting the progression of CRF
and possibly preventing its development
in the first place.
Protein, phosphorus, potassium,
pH, fiber, sodium, and calories
may all work together
to aid or hinder the progression
and development of CRF.
Patterns of usual dietary intake
and not just individual nutrients
should also be considered as "ad libitum" feeding
has been shown in some studies
to contribute to the development of CRF
(Hughes et al, 2002).
Guardians of older cats should own a scale
and use it frequently to monitor any weight loss
in their cats as weight loss may be an early sign
of decreased renal function before it can be detected
by clinical tests
(Hughes et al, 2002).
Feline Renal Transplantation
When subcutaneous fluid therapy,
low protein diets, and phosphate binders
are unsuccessful at treating CRF,
some cats are considered candidates for transplantation
if they are free of any other disease
and have a packed cell volume of at least 30%
(Bernsteen, Gregory, Kyles, Wooldridge, & Valverde, 2000).
Bernsteen and colleagues (2000) claim
that renal transplantation can offer long-term survival
with a normal quality of life for CRF cats.
There must be a kidney donor and a guardian
willing to commit to properly medicating the cat
long-term and providing careful post-operative care
(Bernsteen et al, 2000).
Long-term complications include rejection
and infections due to immunosuppression.
There is also an increased risk of cancer and diabetes
among transplant recipients
(Bernsteen et al, 2000).
For cats with end stage renal failure,
transplantation is a therapeutic option
with a success rate of 60 to 70% of cats
surviving greater than one year after the procedure.
There is no age restriction
if the cat is in stable condition before anesthesia
(Bernsteen et al, 2000).
The following tests are recommended to determine
if a cat is a good candidate for transplantation:
complete blood count (CBC), serum chemistry profile,
urinalysis, urine protein creatinine ratio,
urine culture and sensitivity, thyroid (T4) level,
feline leukemia virus and feline immunodeficiency (FELV/FIV) tests,
toxoplasma titers, blood type, electrocardiogram and echocardiogram,
thoracic radiographs, and abdominal ultrasound
(Bernsteen et al, 2000).
Findings that would preclude transplantation include:
cardiac disease of any type, FELV positive status,
active FIV infection, urinary tract infection,
inflammatory bowel disease,
uncontrolled hyperthyroidism, neoplasia, diabetes,
poor body condition or cachexia
and fractious temperament
(Bernsteen et al, 2000).
It's important to recognize that no matter
how carefully selected a cat is for the procedure,
transplantation is a serious surgery with serious risks.
It is never performed on an emergency basis
or prophylactically
(Bernsteen et al, 2000).
Renal transplantation may be considered a last resort
or final attempt at a good quality of life for CRF cats
that would be unable to survive otherwise
(Bernsteen et al, 2000).
Hemodialysis
When fluid administration
and other conventional therapies fail
and/or serum creatinine levels are greater than 6 mg/dL,
hemodialysis may provide the necessary support
the kidneys need to regenerate and repair
(Elliott, 2000).
Hemodialysis uses the extracorporeal blood circulation
to exchange solute through an artificial kidney
called a dialyzer
(Elliott, 2000).
It may also be recommended
when the blood urea nitrogen (BUN) exceeds 90 mg/dL
and when the cat's quality of life decreases significantly
(Elliott, 2000).
It is also helpful before and after renal transplantation
by improving the condition of the cat
both pre and post-operatively
(Elliott, 2000).
The following CRF related conditions
are indications for hemodialysis:
high BUN and creatinine (see paragraph above for values),
fluid overload, severe metabolic acidosis,
hyperkalemia, acute renal graft rejection
and acute exacerbations of chronic renal failure
(Elliott, 2000).
Technically demanding
and requiring sophisticated delivery equipment,
hemodialysis must be done properly
by specifically trained and dedicated staff
(Elliott, 2000).
Complications range from neurologic
to respiratory to gastrointestinal
and confound the course of many patients
(Elliott, 2000).
The goal should be to improve the patient's quality of life
rather than merely prolonging it.
Factors such as distance to a hemodialysis center,
financial status, and education are important
when considering hemodialysis as a treatment option.
Elliott (2000) cites Michigan State University's
Veterinary Clinic as the regional hemodialysis referral center
in the Midwest.
Comorbid Conditions
It is not uncommon for an older cat
to be diagnosed with both hyperthyroidism and CRF
(DiBartola, Broome, Stein, & Nixon, 1996).
Yet the diagnosis of renal disease
may be complicated by hyperthyroidism
because the condition may cause a reduction
in serum creatinine concentration
due to the loss of muscle mass
(DiBartola et al, 1996).
In other words,
because high serum creatinine levels
are an important indicator of renal disease,
CRF may go unrecognized in the hyperthyroid cat.
Results of a study on hyperthyroid cats
conducted by DiBartola and colleagues (1996)
indicate that after treatment
with radioactive iodine and methimazole,
cats tested with higher mean serum creatinine
and BUN concentrations
30 to 90 days after treatment was initiated.
The experimenters concluded that the observed increases
in creatinine and BUN levels were due to correction
of the hyperthyroid state
(DiBartola et al, 1996).
Systemic hypertension or high blood pressure
is said to occur in about 60 to 70% of cats with CRF
(Bartges, Willis, & Polzin, 1996).
Sodium retention and extracellular volume expansion
often occur with CRF and can contribute
to the development of hypertension
(Bartges et al, 1996).
Bartges and colleagues (1996) recommend
administering antihypertensive drugs
such as amlodipine to decrease blood pressure.
They conclude that blood pressure
must be carefully monitored in cats with CRF.
Hyperaldosteronism is an endocrine condition
that may occur in cats and is the result
of high aldosterone (PAC) levels
(Javadi, Djajadiningrat-Laanen, Kooistra, van Dongen,
Voorhout, van Sluijs, van den Ingh, Boer, & Rijnberk, 2005).
Aldosterone may contribute to kidney damage
by causing thrombosis and fibrosis
(Javadi et al, 2005).
According to Javadi and colleagues (2005),
no effective treatment is known at this time
and further study is needed to delineate the role
of aldosterone in the progression of renal disease.
Conclusion
Some non-conservative treatment options
for feline CRF have been discussed here
in part due to a surprising lack of literature
found on the subject of fluid (rehydration) therapy
despite its frequent usage and acceptance in CRF treatment.
Dietary management of CRF has been studied prolifically
but the results remain inconclusive.
The recently published
Panel Report on Feline Senior Care
from the American Association of Feline Practitioners
and the Academy of Feline Medicine (2005)
cites phosphorus, protein, and potassium
as the main nutrients of concern for cats with CRF.
Disorders that commonly coexist with CRF
include hyperphosphataemia, hypertension,
hyperthyroidism, and hyperaldosteronism.
Renal transplantation and hemodialysis
aim to increase the quality of life
and seem to be a last resort for guardians of CRF cats
who have the local resources/access, finances,
and education to provide for such treatment
if their cat meets the treatment qualifications.
References
American Association of Feline Practitioners/Academy of Feline Medicine.
(2005).
Panel Report on Feline Senior Care.
Journal of Feline Medicine and Surgery,
7:3-32.
Bartges, J, Willis, M, Pozin, J.
(1996).
Hypertension and Renal Disease.
Veterinary Clinics Of North America:
Small Animal Practice,
26:6. 1131-1345.
Bernsteen, L, Gregory, C, Kyles, A, Wooldridge, J, and Valverde, C.
(2000).
Renal Transplantation in Cats.
Clinical Techniques in Small Animal Practice,
15:1, 40-45.
DiBartola, S, Broome, M, Stein, B and Nixon, M.
(1996).
Effect of Treatment of Hyperthyroidism on Renal Function in Cats.
JAVMA,
208:6, 875-878.
Elliott, D.
(2000).
Hemodialysis.
Clinical Techniques in Small Animal Practice,
15:3, 136-148.
Hughes, K, Slater, M, Geller, S, Burkholder, W, and Fitzgerald, C.
(2002).
Diet and Lifestyle Variables as Risk Factors
for Chronic Renal Failure in Pet Cats.
Preventive Veterinary Medicine,
55:1-15.
Javadi, S, Djajadiningrat-Laanen, S, Kooistra, H, van Dongen, A,
Voorhout, G, van Sluijs, F, van den Ingh, T, Boer, W, and Rijnberk, A.
(2005).
Primary Hyperaldosteronism,
a Mediator of Progressive Renal Disease in Cats,
28:85-104.
Polzin, D, Osborne, C, Ross, S and Jacob, F.
(2000).
Dietary Management of Feline Chronic Renal Failure:
Where Are We Now? In What Direction are We Headed?
Journal of Feline Medicine and Surgery,
2:75-82.
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