Introduction
Feline chronic kidney disease (CKD) is a common disease, where nutritional management is crucial. Poor body condition is associated with a poorer prognosis and poor appetite is perceived as a significant quality of life concern by owners. Clinical trials have shown improved survival and quality of life using renal diets to manage the disease.1 The main points are summarized by Elliott.2 However, benefits of renal diets will not be seen if the patient will not eat them. The main characteristic of renal diets is phosphorus restriction characteristics of renal diets are. They are also moderate in high quality protein, moderate in sodium, high in B vitamins and they are alkalinizing (likely the only feline diets to do so). The potassium content is also a bit above typical maintenance diets although it varies from brand to brand. Some of them include long chain omega 3 fatty acids.
Nutritional Factors
Energy
Renal diets are high in energy density (thus, low in fiber and high in fat, as a palatable source of energy) to facilitate calorie intake even in the face of a waxing and waning appetite. Dry foods are more energy dense than canned.
Phosphorus
Phosphorus restriction (below 1 g/1000 Kcal, in general) is indicated to address renal secondary hyperparathyroidism. The IRIS society (http://www.iris-kidney.com) recommends the use of low phosphorus diets early in the disease, but phosphate binders will be need at later stages, where dietary restriction is not enough.2
Sodium
Sodium is not truly restricted, because a very low sodium diet can stimulate the renin angiotensin aldosterone axis and result in hypertension.3 However, the content is moderate, with the idea of reducing the work load of the kidneys to maintain adequate blood pressure. Most maintenance diets provide 1 g/1000 Kcal, and renal diets range from 0.5 to 1 g/1000 Kcal.
Potassium
Potassium varies amongst renal diets (from 1.5 to 3.5 g/1000 Kcal, approximately). The best choice will depend on the patients since some renal patients will be hypokalemic (common in cats) but some will be hyperkalemic, for example late stage patients and those receiving ACE inhibitors.
Protein
Protein should be provided in adequate amounts and be of a high biological value, to avoid creating essential amino acid deficiencies. Renal diets usually provide less protein than maintenance diets to reduce the amount of nitrogenous waste products and thus reduce the incidence of uremia, although it does not seem to help slow down progression overall.2 The NRC4 minimum protein requirement is around 16% protein calories, while AAFCO's is 22%. Most renal diets range from 22 to 27%, and all of them provide all amino acid requirements. However, in patients with poor appetite that do not eat enough, the energy deficiency will result in muscle mobilization and in a decreased protein intake, making them prone to protein malnutrition.
B Vitamins & Acid-Base Balance
B vitamin losses occur due to polyuria and their intake can be reduced due to hyporexia. Also, CKD can result in acidosis, thus, renal diets promote alkalinization.
Omega 3 Fatty Acids
EPA and DHA have shown positive effects on experimental canine CKD, and one retrospective study in cats suggested that diets rich in these fatty acids could result in longer survival.5
Nutritional Plan
A complete nutritional evaluation (http://www.wsava.org/guidelines/global-nutrition-guidelines) should be carried out before making recommendations. These recommendations should include:
1. When to start dietary management: Clinical studies have seen benefits of renal diets in stages II to IV. Patients with stage I do not require a diet change, unless they have proteinuria, where they will benefit from a low protein diet. The better the patient feels, the easier to switch diets, thus, stage II is the best time.
2. What to feed: The recommendations is to choose a commercial renal diets from a reputable brand. The choice will depend on price, availability, palatability, and nutrient characteristics (protein, phosphorus, potassium, EPA+DHA, etc). Treats, if tolerated, can be given, as long as they provide less than 10% of the total daily calories. Consult a specialist (www.acvn.org, www.esvcn.eu) to get a home cooked diet formulated.
3. How much to feed: The amount of food should be enough to maintain a stable body weight and ideal body condition score (BCS). Label instructions are a good start (or formulas, such as http://www.wsava.org/sites/default/files/Calorie%20requirements%20simple%20cat.pdf) but they will need twice a month adjustments, since the error of the formulas used to estimate energy needs is high. Patients with low BCS should be fed 20% more of label instructions/formulas. If the cat is overweight, consider not addressing obesity unless the BCS is very high (8 or 9/9) or if it is affecting quality of life.
4. How to feed: In thin patients and in patients with poor appetite, either multiple times a day or ad libitum feeding are indicated. Overweight patients should be fed portion controlled amounts to prevent further weight gain. Patients that are losing weight due to a poor appetite might need assisted feeding via feeding tubes that can also be used for hydration and to medicate the patient.
5. Medical management of appetite: Complications of CKD such as hypertension, dehydration, hypokalemia and anemia can contribute to inappetence and therefore should be managed when identified. Cats with CKD likely suffer from nausea, vomiting and inappetence as a result of uremic toxins affecting the chemoreceptor trigger zone in the brain as little evidence for stomach lesions has been found.6 Centrally acting anti-emetics such as maropitant, ondansetron and dolasetron should be considered for management. When given orally daily for two weeks, maropitant was demonstrated to palliate vomiting in cats with Stage II and III CKD in a recent study.7
Mirtazapine (1.89 mg every other day) is an effective appetite stimulant in cats with CKD and can significantly increase appetite and weight as was demonstrated in a placebo-controlled, double-masked crossover clinical trial.8 Mirtazapine demonstrates anti-nausea properties in addition to its appetite-stimulating properties.8 This drug can be a useful adjunct to the nutritional management of cats with CKD.
The use of H2 blockers or proton pump inhibitors anecdotally appears to palliate inappetence in some patients, however, both the degree of hyperacidity present in CKD and the efficacy of these medications in feline CKD remains unproven. Omeprazole has been demonstrated to be superior to famotidine in inhibiting acid production with 1 mg/kg twice daily dosing.9
If cats are too nauseous or critical to even consider oral feeding, or have not responded to appetite encouragement after 3–5 days, placement of an enteral feeding tube should be considered.
6. Monitoring: In addition to standard CKD monitoring (via physical exam, bloodwork, urinalysis, medical history), regular nutritional evaluations (including weight, BCS, muscle mass, food intake, etc.) are important to adjust the plan.
References
1. Ross SJ, Osborne CA, Kirk CA, Lowry SR, Koehler LA, Polzin DJ. Clinical evaluation of dietary modification for treatment of spontaneous chronic kidney disease in cats. J Am Vet Med Assoc. 2006;229(6):949–957.
2. Elliott DA. Nutritional management of chronic renal disease in dogs and cats. Vet Clin North Am Small Anim Pract. 2006;36:1377–1384.
3. Buranakarl C, Mathur S, Brown SA. Effects of dietary sodium chloride intake on renal function and blood pressure in cats with normal and reduced renal function. Am J Vet Res. 2004;65(5):620–627.
4. National Research Council. Nutrient Requirements of Dogs and Cats. Washington, DC: National Academies Press; 2006.
5. Plantinga EA, Everts H, Kastelein AM, Beynen AC. Retrospective study of the survival of cats with acquired chronic renal insufficiency offered different commercial diets. Vet Rec. 2005;157(7):185–187.
6. McLeland SM, Lunn KF, Duncan CG, Refsal KR, Quimby JM. Relationship between serum creatinine, serum gastrin, calcium-phosphorus product and uremic gastropathy in cats with chronic kidney disease. J Vet Intern Med. 2014;28:827–837.
7. Quimby JM, Brock WT, Moses K, Bolotin D, Patricelli K. Chronic use of maropitant for the management of vomiting and inappetence in cats with chronic kidney disease: a blinded placebo-controlled clinical trial. J Feline Med Surg. 2015;17:692–697.
8. Quimby JM, Lunn KF. Mirtazapine as an appetite stimulant and anti-emetic in cats with chronic kidney disease: A masked placebo-controlled crossover clinical trial. Vet J. 2013;197:651–655.
9. Parkinson S, Tolbert K, Messenger K, et al. Evaluation of the effect of orally administered acid suppressants on intragastric pH in cats. J Vet Intern Med. 2015;29:104–112.