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 and 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.
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 and 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 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, and 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).
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, and 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).
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.
It is not uncommon for an older cat to be diagnosed with both hyperthyroidism and CRF (DiBartola, Broome, Stein, and 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, and 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, and 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.
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.
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