Page 120 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

110 ELECTROLYTE DISORDERS

BOX 5-2 Causes of Hyperkalemia

Pseudohyperkalemia Decreased Urinary Excretion
Thrombocytosis Urethral obstruction
Hemolysis Ruptured bladder
Anuric or oliguric renal failure
Increased Intake Hypoadrenocorticism
Unlikely to cause hyperkalemia in presence of normal renal Selected gastrointestinal diseases (e.g., trichuriasis,
function unless iatrogenic (e.g., continuous infusion of salmonellosis, perforated duodenal ulcer)
potassium-containing fluids at an excessively rapid rate) Late pregnancy in Greyhound dogs (mechanism unknown
Translocation (ICF ! ECF) but affected dogs had gastrointestinal fluid loss)
Chylothorax with repeated pleural fluid drainage
Acute mineral acidosis (e.g., HCl, NH 4 Cl) {
Hyporeninemic hypoaldosteronism
Insulin deficiency (e.g., diabetic ketoacidosis)
Drugs
Acute tumor lysis syndrome
Angiotensin-converting enzyme inhibitors (e.g., enalapril)*
Reperfusion of extremities after aortic thromboembolism in
Angiotensin receptor blockers (e.g., losartan)*
cats with cardiomyopathy
Cyclosporin and tacrolimus*
Hyperkalemic periodic paralysis (one case report in a pit bull) Potassium-sparing diuretics (e.g., spironolactone,
Mild hyperkalemia after exercise in dogs with induced amiloride, triamterene)*
hypothyroidism Nonsteroidal anti-inflammatory drugs*
Infusion of lysine or arginine in total parenteral nutrition Heparin*
solutions Trimethoprim*
Drugs
Nonspecific b-blockers (e.g., propranolol)*
Cardiac glycosides (e.g., digoxin)*
*Likely to cause hyperkalemia only in conjunction with other contributing factors (e.g., other drugs, decreased renal function, concurrent
administration of potassium supplements).
{
Not well documented in veterinary medicine.

associated with a significant increase in serum potassium and spasm. 131 It is caused by a mutation in the a subunit of
concentration after the same dogs had been trained for 6 the sodium channel of skeletal muscle that results in
weeks. In racing greyhounds, no change in serum potas- impaired channel inactivation. 35,90
sium concentration was observed immediately after Decreased urinary excretion is the most important
racing, despite development of marked lactic acidosis. 98 cause of hyperkalemia in small animal practice. The most
Severe rhabdomyolysis and lethal hyperkalemia (serum common associated disorders are urethral obstruction,
potassium concentrations of 10.9 to 12.6 mEq/L) ruptured bladder, anuric or oliguric renal failure, and
occurred in three cats with hypertrophic muscular dystro- hypoadrenocorticism. The time required for develop-
phy after restraint and anesthesia. 78 The sarcolemma of ment of hyperkalemia in cats after urethral obstruction
muscle cells in dystrophin-deficient animals is thought is variable, but it may occur within 48 hours. 71,73 After
to be more sensitive to injury by anesthetic agents and relief of obstruction, hyperkalemia resolves within 24
intense activity resulting in release of intracellular hours, whereas azotemia and hyperphosphatemia require
contents. Life-threatening hyperkalemia developed in 48 to 72 hours to resolve. 73 After experimental bladder
16 of 46 (35%) cats with aortic thromboembolism treated rupture in dogs, azotemia, hyperphosphatemia, and mild
with streptokinase because of reperfusion of ischemic hyponatremia developed within 24 hours, whereas
muscle tissue and possibly decreased renal excretion hyperkalemia did not develop until after 48 hours. 33 In
associated with renal artery thrombosis. 134 Acute tumor a retrospective clinical study of uroperitoneum in cats,
lysis syndrome complicated by renal failure and hyperkalemia was detected in 13 of 24 (54%) animals
hyperkalemia has been reported in dogs and cats with evaluated. 13
lymphoma treated by radiation and chemother- In chronic renal failure, normal potassium balance is
apy. 34,109,110,199 There is one case report of a young pit maintained, and hyperkalemia is uncommon and
bull dog with episodic hind limb and neck weakness. develops only if oliguria occurs. This renal adaptation is
Exercise or potassium challenge resulted in mild accomplished by increased FE K in remnant nephrons
hyperkalemia. 101 This case may represent an example of (Fig. 5-14). 24,25,179 Fecal excretion of potassium also
hyperkalemic periodic paralysis. In quarter horses, increases during chronic progressive renal disease and
hyperkalemic periodic paralysis is an autosomal dominant represents an extrarenal adaptation to maintain potassium
trait thatcauses recurrentepisodesofmusclefasciculations balance (see Fig. 5-3). However, patients with chronic