Page 268 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Metabolic Acid-Base Disorders 259

Distal RTA has been reported in two cats with pyelo- to moderate renal insufficiency. 65 The hyperchloremic
nephritis caused by Escherichia coli. 77,236 Clinical signs metabolic acidosis observed in these patients has been
included polyuria, polydipsia, anorexia, lethargy, enlarged called Type 4 RTA. This syndrome has not been
kidneys, and isosthenuria. In one cat, urine pH was 5.0 at characterized in veterinary medicine but should be con-
the time pyelonephritis was first diagnosed, but distal sidered in dogs and cats with hyperkalemia and mild to
RTA was documented at a later time by the presence of moderate hyperchloremic metabolic acidosis after
hyperchloremic metabolic acidosis, alkaline urine pH, hypoadrenocorticism has been ruled out by an
and failure to lower urine pH after oral administration adrenocorticotropic hormone (ACTH) response test.
of NH 4 Cl. 77 Findings were similar for the other cat, The diagnosis may be established by finding an inappro-
but hyperphosphaturia and persistent hypokalemia also priately decreased plasma aldosterone concentration in
were detected. 236 Distal RTA and hepatic lipidosis were the presence of hyperkalemia.
reported in another cat without urinary tract infection 29
and in a cat with concurrent hyperaldosteronism and Carbonic Anhydrase Inhibitors
severe hypokalemia. 228 Distal renal tubular acidosis also Carbonic anhydrase inhibitors, such as acetazolamide,
has been reported in association with immune-mediated decrease proximal tubular reabsorption of HCO 3 in
hemolytic anemia in three dogs. 215 Distal renal tubular the kidneys by noncompetitive inhibition of luminal
acidosis is associated with some immune-mediated and cellular carbonic anhydrase. Hypokalemia is caused
diseases in human patients, but not specifically by increased sodium delivery to the distal nephron and
immune-mediated hemolytic anemia. The clinical its reabsorption there in exchange for potassium. As
features of proximal (type 2) and distal (type 1) RTA hyperchloremic metabolic acidosis develops, the filtered
are summarized in Table 10-2. load of HCO 3 decreases and the effect of carbonic
Hyporeninemic hypoaldosteronism, characterized by anhydrase inhibitors on HCO 3 reabsorption is limited.

hyperkalemia with decreased plasma renin and aldoste- Acetazolamide given at 7 to 10 mg/kg three times daily
rone concentrations, occurs in some human patients, causes self-limited hyperchloremic metabolic acidosis,
notably those with diabetes mellitus who also have mild mild to moderate hypokalemia, and mild hypocalcemia
in dogs. 107,201 The effects of acetazolamide were greatest
after 3 days of administration, and blood chemistry
TABLE 10-2 Clinical Features of results stabilized after 5 days of administration. 201 Acet-
azolamide is used most commonly in small animal prac-
Proximal and Distal
tice for the treatment of glaucoma.
Renal Tubular Acidosis
Ammonium Chloride
Proximal Distal
Clinical Feature RTA RTA Administration of NH 4 Cl is equivalent to administration
of HCl because the NH 4 is converted in the liver to urea
þ
þ
Hypercalciuria Yes Yes and H . Ammonium chloride has been used commonly
Hyperphosphaturia Yes Yes as a urinary acidifier in dogs and cats. A study of cats
Urinary citrate Normal Decreased receiving 800 mg of NH 4 Cl per day as a powder or tablet
Bone disease Less severe More severe showed that venous blood pH and HCO 3
Nephrocalcinosis No Yes concentrations were decreased to values at the lower
Nephrolithiasis No Yes (calcium end of the normal range. 211 A combination product sup-
phosphate) plying 580 mg each of NH 4 Cl and D,L-methionine had a
Hypokalemia Mild Mild to severe
more notable effect on venous blood pH and HCO 3
Potassium wasting Worsened by Improved by
concentrations than that observed with 800 mg of
NaHCO 3 NaHCO 3 NH 4 Cl alone, but results were still within the reported
Alkali required for treatment >10 mEq/ <3 mEq/kg/ 212
kg/day day normal range. In another study of cats, NH 4 Cl at
Other defects of proximal Yes No 300 mg/kg/day did not significantly alter venous blood

tubular function* pH, P CO 2 ,orHCO 3 concentration, but 400 mg/kg/

Reduction in plasma HCO 3 Moderate Variable (can day significantly decreased blood HCO 3 concentration
be severe) during the course of the study. 85 Ammonium chloride at
Fe HCO3 at normal plasma >15% <5% a dosage of 535 mg/kg/day administered to dogs over 6
HCO 3 concentration days caused hyperchloremic metabolic acidosis and was

Urine pH during acidemia <5.5 >6.0
associated with hypokalemia, presumably related to
Urine pH after Nh 4 cl <5.5 >6.0 150
increased aldosterone secretion. In another study of
dogs, NH 4 Cl at 200 mg/kg/day reduced urine pH to
Fe, fractional excretion.
*Decreased fractional reabsorption of sodium, potassium, phosphate, approximately 5.0 and produced mild metabolic acidosis
urate, glucose, and amino acids. without change in serum potassium concentration. 208