Page 122 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

112 ELECTROLYTE DISORDERS

150 hyperkalemia) can occur in dogs with gastrointestinal dis-
ease related to trichuriasis, salmonellosis, or perforated
120 53,123
duodenal ulcer. Hyperkalemia in affected dogs with
105 trichuriasis is not caused by a deficiency of aldosterone
because plasma aldosterone concentrations have been
90 found to be normal or high. 87 Hyperkalemia and
FE K (%) 75 hyponatremiaalsohavebeenobservedindogsandcatswith

60 chylous pleural and peritoneal effusions, in a dog with
pleural effusion caused by a lung lobe torsion, in a dog with
45 a neoplastic pleural effusion, in a dog with portal hyperten-
sion and peritoneal effusion associated with Bartonella
30
henselae infection, and in cats with peritoneal effusion
15 caused by neoplasia or feline infectious peritonitis. {
The hyperkalemia observed in these situations is thought
to arise from decreased renal excretion of potassium as a
15 30 45 60 75 90 105 120 135 150
consequence of volume depletion (e.g., gastrointestinal
GFR (mL/min)
Figure 5-14 Nomogram relating fractional potassium excretion fluid loss and third-space loss of fluid) and decreased distal
(FE K ) to glomerular filtration rate (GFR). Values for patients with an renal tubular flow. Hyperkalemia and hyponatremia also
intact hormonal and renal tubular secretory mechanism for have been reported in three female Greyhounds late in
potassium (closed triangles) are used to delineate the hatched area. pregnancy. 175 The underlying mechanism was unknown,
The open squares and circles indicate patients with selective but all of the dogs had a history of vomiting or diarrhea.
aldosterone deficiency and renal tubular secretory defects, Hyporeninemic hypoaldosteronism is an important cause
respectively. (From Batlle DC,Arruda JA, Kurtzman NA. of unexplained asymptomatic hyperkalemia in human
Hyperkalemic distal renal tubular acidosis associated with patients, but this disorder has rarely been recognized in
obstructive uropathy. N Engl J Med 1981;304:373–380.) 47
veterinary medicine. Many affected human patients
have mild to moderate renal insufficiency caused by
catabolic state and acute metabolic acidosis may contribute diabetic glomerulosclerosis or interstitial renal disease.
to translocation of potassium from ICF to ECF. Most of them have low plasma renin and aldosterone
Hyperkalemia, hyponatremia, and Na/K ratios less concentrations. Even in patients with normal plasma aldo-
than 27:1 are usually, but not always, found in dogs sterone concentrations, the concentration of this hormone
and cats with hypoadrenocorticism.* In dogs with must be considered abnormal in light of the hyperkalemia.
hypoadrenocorticism, hyperkalemia has been reported Resting plasma cortisol concentrations and response to
in 74% to 96%, hyponatremia in 56% to 100%, and ACTH are normal. Hyperchloremic metabolic acidosis
Na/K ratios less than 27:1 in 85% to 100% of cases. and hypertension may be observed. It is unclear whether
Hyperkalemia was found in 9 of 10 cats with hypoadreno- low aldosterone concentrations are a consequence of
corticism, whereas hyponatremia and Na/K ratios less diminished renin secretion and lack of trophic effect of
than 27:1 were found in all 10 affected cats. 150 Treatment angiotensin II on the zona glomerulosa of the adrenal cor-
is begun immediately after a presumptive diagnosis of tex or whether there is a primary adrenal defect in aldoste-
hypoadrenocorticism is made, but conclusive diagnosis rone secretion. To document this syndrome in veterinary
requires results of an ACTH stimulation test. patientswouldrequiredemonstrationofsubnormalplasma
If sodium intake is sufficient to maintain normal ECF renin and aldosterone concentrations or a subnormal
volume and distal tubular flow rate, an animal with increase in aldosterone after volume contraction or ACTH
hypoadrenocorticism may be able to maintain potassium administration. Normally, aldosterone concentrations
207
balance. Treatment of dogs with hypoadrenocorticism increase in response to ACTH in the dog. In this study,
with fluids alone also often decreases serum potassium one dog with diabetes mellitus was suspected to have
concentration into the normal range. However, usually hyporeninemic hypoaldosteronism based on a subnormal
these animals are presented with anorexia and vomiting aldosterone response to ACTH.
that contribute to decreased ECF volume and urine Several drugs may contribute to hyperkalemia, espe-
output, and without adequate endogenous mineralo- cially when used in combination with one another, in
corticoids, they are unable to excrete sufficient potassium conjunction with potassium supplementation, or in
to prevent frank hyperkalemia. patients with renal sufficiency. 148 Nonspecific b-blockers
Electrolyte abnormalities similar to those found in (e.g., propranolol) interfere with catecholamine-
dogs with hypoadrenocorticism (i.e., hyponatremia and mediated uptake of potassium by liver and muscle by

*References 113, 150, 151, 154, 161, 168, 174, 192, 206. { References 21, 105, 111, 193, 206, 210.