Feline renal insufficiency (Proceedings)
Stages, diagnostics, and treatment for renal disease.
1) I much prefer creatinine over BUN
a) The BUN is influenced by many non-renal factors
i) High protein diet: increase BUN
ii) GI bleeding: increase BUN
iii) Increased protein catabolism: increase BUN
(1) Corticosteroids, burns, fever, tetracycline
iv) Dehydration: increase BUN
v) Prerenal renal failure: increase BUN
vi) Polyuria: decrease BUN
vii) Severe liver disease: decrease BUN
b) Creatinine is lowered when there is extreme weight loss to the point of emaciation.
2) Stages of renal disease
a) Renal insults
i) Bacterial infections, toxins, trauma, aminoglycosides, urethral obstruction, etc.
ii) Generally, these result in loss of some renal function but it is less than 75% so the creatinine and USG remain normal.
iii) There may be a few days of lethargy and anorexia but often PU/PD does not occur.
b) Renal insufficiency
i) Loss of 75-85% of renal function
ii) Creatinine typically = 2.5-5.5 (when the normal range is up to 2.4)
iii) No or mild clinical signs (which may be missed by the owners)
(1) PU/PD, reduced appetite, slight weight loss.
c) Renal failure
i) Loss of >85% of renal function
ii) Lab findings
(1) Creatinine = 5.5 – 20
(2) Hyperphosphatemia
(3) Acidosis (+/-)
(4) Anemia of chronic disease
iii) Clinical findings
(1) Anorexia, dehydration, very sick cat
(2) The clinical signs increase in severity as the creatinine rises.
3) Further diagnostics
a) All of these cats should have a urine culture
i) 22% positive: J Fel Med Surg April 07, p.124.
b) Ultrasound and possibly biopsy should be performed if:
i) The cat is less than 10 years of age.
ii) One or both kidneys are enlarged.
iii) One or both kidneys are painful.
c) Sizing kidneys
i) Palpation
ii) Radiographs: Normal is 2.0-2.5 X the length of the body of L2.
iii) Ultrasound: 38-42 mm in a young cat.
d) Urine culture – by cystocentesis.
4) Home Maintenance
a) Indications
i) Cats presented for PU/PD and treated as above for renal insufficiency.
ii) Cats treated for renal failure in the hospital and converted to renal insufficiency.
iii) Cats diagnosed with renal insufficiency on geriatric profiles.
b) Expectations: to add 1-3 years of life to the cat.
c) Steps of Treatment
i) Renal diet
(1) Reduced protein (controversial – has been and will be)
(2) Reduced phosphorus
(3) Non acidifying
(4) Low sodium
(5) Good choices that I carry in my practice (because cats are so picky about what they eat)
(a) Purina: NF canned and dry
(b) Eukanuba: Multistage Renal canned and dry
(c) Hill's: k/d canned (regular and minced) and dry
(6) Best palatability (in my experience)
(a) Purina's NF dry
(b) Hill's k/d minced canned.
(7) Avoid diets that acidify the urine
(a) Aggravate acidosis
(b) Predispose the cat to calcium oxalate stones which are much more common in older cats than struvite stones.
ii) Potassium orally: 2-4 mEq/d or 500-1000 mg/d
(1) The cycle:
(a) Renal failure causes polyuria.
(b) Potassium is lost in increasing amounts resulting in hypokalemia.
(c) Hypokalemia is harmful to the kidneys of the cat.
(d) Acidosis causes a shift of potassium from within the cells (where it works) to the blood.
(i) This results in muscle weakness in spite of improving potassium blood levels.
DiBartola in JAVMA, 3/1/93
"Chronic renal disease initiates a self-perpetuating cycle of declining renal function and increasing potassium depletion."
DiBartola in Sherding, 1994 ed.
"Potassium depletion leads to functional and morphologic abnormalities in the kidneys characterized by decreased GFR and defective renal concentrating ability." DiBartola in JAVMA, 3/1/93
"Dietary potassium supplementation may stabilize or improve renal function and should be a part of chronic renal disease management."
(1) Potassium tastes badly so administration can be a problem.
(2) You must find a method that is hassle-free or it will not be done long-term.
(3) Options
(a) Tumil-K: powder (good in canned food); tablets; gel
(b) Generic potassium gluconate (RenaCare)
(c) Compounded chewables or liquids (relatively expensive)
(d) Potassa-chew: V.E.T. Pharmaceuticals: 1-866-838-1995
(e) Renal K powder; excellent palatability
(f) Pill Pockets: very well accepted by cats.
iii) Subcutaneous fluids: by the owner or your technician
(1) 150 ml 2X per week; increase based on creatinine level and creatinine trend
(2) Use 18 gauge needles unless owner specifies otherwise
(3) Potassium can be added to SQ fluids
(a) KCl up to 35 mEq per liter (more causes SQ inflammation)
(b) I recommend it if fluids are given 3X per week or more due to increased loss of potassium due to the amount of fluid being given.
(c) I consider it a replacement of this lost potassium and not a replacement for oral potassium.
(d) Subcutaneous Fluid Catheter
(i) Not my Plan A, but a good Plan B.
(ii) SurgiVet (formerly Cook) Tube available from DVM Solutions (1-866-373-9626).
1. A 9" or 12" long catheter that is placed along the dorsal midline (or nearby). It is multifenestrated so the fluid is dispersed across a larger area. The external fluid line fitting is sutured to the skin. It is designed for 12+ month in-dwell time.
(iii) Protocol for Placement and Management
(iv) Insertion
1. Make is simply making a 1 cm incision on the dorsal midline and sliding the catheter (with metal stylet) through the subcutis. The plastic fitting is sutured to the skin. The suturing should be much more elaborate than just using the two holes in the wings. Secure it cranially, caudally, and on the right and left. Four doses of an injectable antibiotic (Baytril, Cefazolin, etc.) are given/dispensed to cover any infection that occurs at the time of insertion. They are injected through the catheter with about 5 cc of saline.
2. Complications: 1) Scratching at the fitting (for 2-3 days): Place a bandage around the chest with the cap exposed and leave it for 2-3 days. 2) Fibrin buildup that inhibits the flow of fluids: Have the owner do a heparin flush after each fluid treatment, (Hep saline = 5 ml [1000 u/ml] heparin in 1 liter of fluid) 3) Infection: Culture and treat accordingly through the catheter. Do not remove it!
(v) Infection prevention: 1) Have the owner soak the cap in Clorox (1/2 cup per gallon of water) during the fluid infusion 2) Rinse the cap with sterile saline or LRS prior to its replacement in the catheter.
iii) Famotidine (Pepcid): PRN
(1) For appetite stimulation by resolving nausea that accompanies low gastric pH
(2) 2.5 mg q12h
iv) Phosphate binder: PRN (usually not needed)
(a) Phosphate control
(i) Feed a renal diet for one month then check serum phosphorus level
1. If < 5.0, no Pi binder is needed
2. If 5.0+, use a Pi binder
3. If the cat will not eat a renal diet or the owner will not feed a renal diet:
a. If < 5.0, no Pi binder is needed.
i. If 5.0+, use a Pi binder
(ii) Phosphate binders
1. If total calcium (or ionized Ca) is normal, any type is acceptable.
2. If iCa is elevated, do not use a calcium-containing binder
a. Ca acetate: PhosLo
b. Ca carbonate: Epakitin
c. Instead, use aluminum hydroxide
i. Amphojel @ 100 mg/kg divided BID; available as 600 mg tablet; average dose: 1/2 tablet BID with food
d. USP grade powder: Spectrum Chemical (www.spectrumchemical.com); 500 gm for $45.65 + shipping; Mix in canned food or "shake in a baggy" with dry food.
i. Dose: 1/4 teaspoon per cat BID in food.
ii. Dose can be increased 2-4X if needed to reduce phosphorus to < 5.0.
v) Drugs to increase food intake
(1) Famotidine (see above)
(2) Cyproheptadine
(3) Mirtazapine: 15 mg tablet: 1/4 to 1/8 tablet q2-3d (benzodiazepine derivative)
(4) FortiFlora (Purina): sold for diarrhea control but cats eat much better with it in their food.
(5) Benazepril (main "side effect" is appetite stimulation and weight gain).
vi) Hypotensive agents
(1) 50% of cats with chronic renal disease are hypertensive
(2) Amlodipine (Norvasc) is clearly the drug of choice.
(3) ACE-inhibitors will lower blood pressure but not very much
vii) Benazepril
(1) AJVR, 3/01: Shown to slow progressive deterioration of the kidneys in cats.
(2) Actions (per Novartis)
(a) Inhibits the Renin-Angiotensin-Aldosterone System
(b) Vasodilation of the glomerular efferent arteriole
(c) Reduces glomerular pressure (relieves glomerular hypertension)
(d) Decreases protein loss
(e) Increases glomerular filtration leading to increased clearance of creatinine and urea.
(3) Dose: Up to 5 kg: 2.5 mg/d; Over 5 kg: 5 mg/d
(4) Watch for development of hyperkalemia (very unlikely)
viii) Summary
(1) Level One
(a) Creatinine ~ 2.5-4.0
(b) Renal diet + potassium + benazepril + calcitriol
(c) Note: Do not begin potassium and benazepril at the same time or there is a good chance of anorexia. Make the transition to the new diet first, then add benazepril (or potassium). After it has been taken for one week, add potassium (or benazepril).
(2) Level Two
(a) Creatinine ~ 4.0-6.0 or increasing creatinine values over time
(b) Add SQ fluids to above
(3) Others: On a PRN basis.
b) Rechecks
i) Most vital tests: creatinine, phosphorus, calcium, potassium (initially), PCV, blood pressure.
ii) First should be 2 weeks after all recommendations are being performed
(1) May take 4-6 weeks.
(2) Primarily to check compliance as there should be no change in the creatinine level.
(3) Also, to check for hyperkalemia and hypercalcemia.
iii) Every 3 months thereafter.
c) Compliance
i) Differentiate insufficiency from failure
ii) Have a plan and make it understandable
iii) Make do-able recommendations
iv) Plan rechecks (to check cat and owner compliance)
v) Give the client a reasonable goal
d) Microalbuminuria in cats
i) Elevated in the following (3 or more positives obtained 2 or more weeks apart)
(1) Primary renal disease
(2) Renal injury secondary to other systemic disease.
(3) Inflammatory disease, chronic infections, metabolic disease
(a) Hypertension, Cushing's Syndrome, Diabetes Mellitus, Hyperthyroidism
(4) Neoplasia
(5) False positives due to pyuria and gross hematuria.
