Hypokalemia

From Felipedia

Potassium disorders are common in feline medicine^[1]. Hyperkalemia is far more common than hypokalemia due to the retention of potassium in kidney diseases. Hypokalemia is common in anorexic cats that have been vomiting for 2-3 days.

Hypokalemia is common in Burmese cats with hypokalemic polymyopathy and in cases of chronic diuresis such as diabetes insipidus, diabetes mellitus and a small percentage of cats with chronic renal disease.

Potassium is the major intracellular cation in mammalian cells and is largely responsible for maintenance of intracellular volume. Serum potassium concentrations slightly exceed plasma concentrations because potassium is released from platelets during the clotting process. Potassium is responsible for maintaining resting cell membrane potential. Therefore, disorders of potassium concentration affect excitable membranes. Clinical signs are related to disturbances in skeletal (weakness) and cardiac (arrhythmia) muscles. Internal distribution of potassium is affected by acid-base equilibrium. These changes, however, are only clinically relevant during acute mineral acidosis (e.g. infusion of HCl). Extrapolation of information obtained in experimental animals to the clinical setting has led to misconceptions regarding the effects of acid-base changes in potassium balance^[2].

Causes

Hypokalemia arises from decreased intake, translocation of potassium from ECF to ICF, and excessive loss of potassium by either gastrointestinal or urinary routes. The history often provides information about the likely source of potassium loss (e.g. chronic vomiting, diuretic administration) or the possibility of translocation (e.g. insulin administration). Muscular weakness, polyuria and polydipsia, anorexia, and tachycardia are the most common clinical signs associated with hypokalemia. Cats are usually presented with ventroflexion of the neck. Electrocardiographic changes in hypokalemia are not specific, although supraventricular and ventricular arrhythmias may occur. Hypokalemia renders arrhythmias refractory to therapy and favors digitalis toxicity. Other complications of hypokalemia include polymyopathy and respiratory muscle paralysis. Cats fed highly acidifying diets also low in potassium content may develop hypokalemic nephropathy. Decreased intake of potassium alone is unlikely to cause hypokalemia, but it may be a contributing factor. Administration of potassium-deficient fluids to an anorectic animal also may result in hypokalemia^[3].

Translocation of potassium into cells may occur with sodium bicarbonate administration, and insulin and catecholamine release. Insulin promotes uptake of glucose and potassium by hepatic and skeletal muscle cells and may contribute to hypokalemia when glucose-containing fluids are administered. Gastrointestinal loss of potassium from vomiting or diarrhea is a very important cause of hypokalemia in cats. Urinary loss of potassium is another important cause of hypokalemia. Chronic renal disease was the most common associated disorder observed in a survey of cats with hypokalemia. Urinary losses of potassium also may occur in renal tubular acidosis and during the post-obstructive diuresis that follows relief of urethral obstruction and post administration of loop or thiazide diuretics^[4].

Hypokalemia can occur at any stage in chronic renal disease. Elliott et al reports that hypokalemia occurs in 15% of stage II, 25% of stage II and 30% of cats in stage IV disease^[5]. Hypokalemia is typically mild, and is not associated with overt clinical signs; however, clinicians should not await signs before treating for hypokalemia. Clinical improvement has been noted following potassium supplementation. Hypokalemia also appears to be associated with increased risk of systemic hypertension in cats with chronic renal disease^[6].

Hypokalemia arises from decreased intake, translocation of potassium from ECF to ICF, and excessive loss of potassium by either gastrointestinal or urinary routes. The history often provides information about the likely source of potassium loss (e.g. chronic vomiting, diuretic administration) or the possibility of translocation (e.g. insulin administration). Muscular weakness, polyuria and polydipsia, anorexia, and tachycardia are the most common clinical signs associated with hypokalemia. Cats are usually presented with ventroflexion of the neck. Electrocardiographic changes in hypokalemia are not specific, although supraventricular and ventricular arrhythmias may occur. Hypokalemia renders arrhythmias refractory to therapy and favors digitalis toxicity. Other complications of hypokalemia include polymyopathy and respiratory muscle paralysis. Cats fed highly acidifying diets also low in potassium content may develop hypokalemic nephropathy. Decreased intake of potassium alone is unlikely to cause hypokalemia, but it may be a contributing factor. Administration of potassium-deficient fluids to an anorectic animal also may result in hypokalemia^[7].

Translocation of potassium into cells may occur with sodium bicarbonate administration, and insulin and catecholamine release. Insulin promotes uptake of glucose and potassium by hepatic and skeletal muscle cells and may contribute to hypokalemia when glucose-containing fluids are administered. Gastrointestinal loss of potassium from vomiting or diarrhea is a very important cause of hypokalemia in cats. Urinary loss of potassium is another important cause of hypokalemia. Chronic renal disease was the most common associated disorder observed in a survey of cats with hypokalemia. Urinary losses of potassium also may occur in renal tubular acidosis and during the postobstructive diuresis that follows relief of urethral obstruction and post administration of loop or thiazide diuretics.

Treatment

Treatment of hypokalemia should be directed at correcting the underlying disease process and providing potassium supplementation. Parenteral therapy is usually attempted with KCl, although KH2PO4 also can be used. Potassium-containing fluids can be administered intravenously or subcutaneously, although slow intravenous infusion usually is preferred. Maintenance supplementation (20-30 mEq/K/L) usually corrects mild hypokalemia (serum K > 3,0 mEq/L). Higher maintenance values should be used in patients with serum K close to 3,0 mEq/L. When potassium concentration is < 3,0 mEq/L, potassium supplementation in mEq of KCl per liter of fluid can be estimated as:

• K supplement = 4 - (patient’s K) X 35.

Potassium should not be given at a concentration greater than 80 mEq/L or at a rate faster than 0,5 mEq/Kg/h to avoid acute hyperkalemia and its adverse effects. Fluids containing > 60 mEq/L potassium should be administered carefully because of the potential for sclerosis of peripheral vessels. Infusion of potassium-containing fluids may be associated with an initial decrease in serum potassium concentration. This can be minimized by using a glucose-free solution and by starting oral potassium supplementation as soon as possible. Potassium gluconate usually is recommended for oral supplementation. In cats, the initial dose is 5-8 mEq/day divided BID or TID, followed by a maintenance dose of 2-4 mEq/day. The dose should be adjusted based on clinical improvement and serial measurements of potassium concentration.

References

1. ↑ Thiesen, SK et al (1997) Muscle potassium and potassium gluconate supplementation in normokalaemic cats with naturally occurring chronic renal failure. J Vet Intern Med 11:212
2. ↑ DiBartola SP, de Morais HA (2006) Disorders of potassium: Hypokalemia and hyperkalemia, in DiBartola SP (ed): Fluid, Electrolyte, and Acid-Base Disorders. 3rd ed., Philadelphia, Elsevier, pp 91-121.
3. ↑ Kogika MM, de Morais HA (2008) Hypokalemia: A quick reference. Vet Clin N Am Small Anim Pract 38:481-484
4. ↑ August, JR (2006) Consultations in feline internal medicine. Vol 5. Elsevier Saunders, USA
5. ↑ Elliott, J & Syme, HM (2003) Response of cats with chronic renal failure to dietary potassium supplementation. J Vet Intern Med 17:418
6. ↑ Syme, HM et al (2002) Incidence of hypertension in cats with naturally occurring chronic renal failure. J Am Vet Med Assoc. 220:1799
7. ↑ Kogika MM, de Morais HA (2008) Hypokalemia: A quick reference. Vet Clin N Am Small Anim Pract 38:481-484, 2008.