April 23, 2021
Today’s VETgirl online veterinary continuing education sponsored blog is written by Dr. Lindsey Bullen, DACVN. Thanks to Royal Canin for sponsoring this blog. Please note the opinions in this blog are the expressed opinion of the author, and not directly endorsed by VETgirl.
Nutrition for the Nephron Blog
By Dr. Lindsey Bullen, DACVN
In this VETgirl online veterinary continuing education blog, Dr. Lindsey Bullen, DACVN, reviews nutritional support of our feline friends with chronic kidney disease (CKD). While CKD is both common and is relatively straight forward to understand, managing cats with CKD can pose a challenge even to the most experienced of veterinary professionals. Understanding both the ‘how’ and the ‘why’ to treat (along with some extra tid bits) can both help relieve any stress associated with treating the CKD cat, as well as improve clinical outcome and client experience.
The kidney + chronic kidney disease (CKD)
While the kidneys represent around 0.5% of total body weight, they receive approximately 25% of total cardiac output because they have a big job to do! Among other things, the kidneys are responsible for:
1. Waste excretion (ex: BUN, creatinine, drug metabolites, etc.)
2. Regulation (ex: electrolytes, pH, fluids, etc.)
3. Production/ secretion of hormones (ex: erythropoietin, calcitriol, renin, etc.)
With CKD, the kidneys are no longer functioning optimally. Depending on which part of the nephron (functional unit of the kidney) is affected/ damaged, possible diagnostic abnormalities can include:
2. Elevated waste products (BUN, creatinine, drug metabolites)
3. Elevated electrolytes (phosphorus, calcium, potassium, magnesium, sodium)
4. Decreased electrolytes (potassium, calcium, etc.)
5. Dilute urine concentration
Since CKD severity and signs fall along a spectrum, medical and nutritional treatment should ideally match the severity of the patient’s disease. The International Renal Interest Society (IRIS) has developed staging guidelines that categorize a patient’s level of disease.
Feline IRIS Staging
Studies show that CKD progression can be slowed and severity of signs reduced with dietary manipulation; thus, diet is considered one of the mainstays of treatment. While not an exhaustive list, the following nutrients are important in all CKD patients, though the target dietary levels will be different for each individual case.
Hyperphosphatemia can occur due to reduced renal excretion. Unfortunately, while a product of CKD, hyperphosphatemia can in turn cause progression by increasing the rate of interstitial fibrosis, nephrocalcinosis, and tubular atrophy. Additionally, hyperphosphatemia can lead to renal secondary hyperparathyroidism by decreasing the conversion of calcidiol to calcitriol (leads to hypocalcemia). Renal therapeutic diets contain reduced phosphorus levels.
Protein is essential to supporting a patient’s normal metabolic functions (including maintaining normal mass). However, protein breakdown results in production of BUN and BUN increases in CKD due to reduced excretion. Additionally, if the patient has renal proteinuria, excess dietary protein can contribute to mesangial cell toxicity and glomerulofibrosis. In general, renal diets contain reduced dietary protein levels while keeping the protein source highly bioavailability.
With decreased renal function, the fractional excretion (FE) of sodium will increase. Because CKD patients vary their FE over a progressively narrowing range, their ability to handle high salt loads is reduced. Additionally, literature suggests that excess sodium may increase workload and oxygen demands, which may contribute to renal hypoxia. Renal diets contain reduced dietary salt.
Hypokalemia may be seen in patients with polyuria, anorexia, vomiting or a combination thereof. When this occurs, choosing a renal diets containing increased dietary potassium (ideally before considering additional supplementation) is warranted. Alternatively, hyperkalemia may be observed in oliguric or anuric patients. In this case, choosing a renal diet with reduced potassium would be optimal prior to starting a potassium binder.
Appetite Modulation and more
Did you know there are over 20 different renal therapeutic diets for BOTH dogs and cats??? In general, renal diets modulate the above nutrients to support the renal patient. While there are many similarities between renal diets, the exact nutrient profile, flavor, ingredients, etc. can be very different. Thus, if a patient won’t eat one diet… it is possible (and even likely) that they will like at least one of the other 19+.
Unfortunately, a CKD cat with the refined palate may still refuse all appropriate commercial options.
The following tips may help get the finicky kitty to eat:
Treat all clinical signs!
• If the patient is nauseated/ vomiting, antiemetic therapy is imperative
• If the patient is dehydrated, supplemental water should be provided orally, IV, etc.
• Concerns for gastric ulceration? The use of gastroprotectants is warranted.
Toppers and Palatants
• Calories from toppers/ treats/ palatants should (ideally) not be more than 10% of total daily caloric intake
• Examples toppers include- baby food, yogurt, cottage cheese, sour cream, broth, Purina Fortiflora (very tasty!)
• Kitties prefer meat/ acidic flavors
Warm the diet
o This increases the flavor and aroma
o Be warned… if the pet is nauseated…treat the nausea first!
o Safer for immunocompromised pets
o Washes out rancid/ residual smells and flavors
Consider glass or ceramic bowls
o Plastic bowls can absorb smells and flavors (yuck!)
o Metal bowls can leave bad tastes in the mouth
Consider an appetite stimulant (alphabetized below)
- Capromorelin (Elura in cats; Entyce in dogs)
- Ghrelin agonist; mimics normal physiology
- 2mg/kg in cats; dosed orally once daily
- May see hypersalivation, vomiting, transient bradycardia and hypotension, transient hyperglycemia
- Antihistamine (antagonized 5HT receptors)
- Takes time (~ 3 days) to see effects
- 1-2mg cat; dosed twice daily (taper recommended when discontinuing)
- May see paradoxical excitement and CNS depression
- Mirtazapine (Mirataz in cats)
- Antidepressant (stimulates 5HT1 and antagonizes 5HT2 and 3 receptors)
- Transdermal- 1.5 inches inside pinnae once daily (alternate ears)
- Oral- 1.9mg/cat every other day
- May cause sedation, alterations to behavior and mentation
Consider a tailored homemade diet formulated by a veterinary nutritionist
- Can be tailored to the pet’s disease state(s) and flavor/ ingredient preferences
- Gives client feeling of involvement and control
- Can be very dangerous if incomplete and/or unbalanced!
- Can find board certified nutritionists in your area at ACVN.org/ directory
- Consider assisted feeding
- A great option in pets that need a little more TLC!
- Can be used to supplement nutritional support
- Can be used to provide supplemental water without causing fear or pain
- Can be used for medication administration
Regardless what renal diet and adjunct therapies are recommended, the most important thing to remember in treating the feline CKD patient is communication. It is important to listen to and address our clients’ concerns so that we can maintain a lasting and positive relationship (without which we cannot successfully treat the patient). It is equally important to share and educate our clients on why the diet and therapies we recommend are superior to others (most clients like to be informed). With a strong and collaborative relationship, our clients will be more likely to try different diets, treatments, and plans!