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On the relationship between potassium and acid-base balance
Summarized from Lee Hamm l, Hering-Smith K, Nakhoul N. Acid-base and potassium homeostasis. Seminars in Nephrology 2013; 33: 257-64
The notion that acid-base and potassium homeostasis are linked is well known. Students of laboratory medicine will learn that in general acidemia (reduced blood pH) is associated with increased plasma potassium concentration (hyperkalemia), whilst alkalemia (increased blood pH) is associated with reduced plasma potassium concentration (hypokalemia).
A frequently cited mechanism for these findings is that acidosis causes potassium to move from cells to extracellular fluid (plasma) in exchange for hydrogen ions, and alkalosis causes the reverse movement of potassium and hydrogen ions.
As a recently published review makes clear, all the above may well be true, but it represents a gross oversimplification of the complex ways in which disorders of acid-base affect potassium metabolism and disorders of potassium affect acid-base balance. The review begins with an account of potassium homeostasis with particular detailed attention to the renal handling of potassium and regulation of potassium excretion in urine.
This discussion includes detail of the many cellular mechanisms of potassium reabsorption and secretion throughout the renal tubule and collecting duct that ensure, despite significant variation in dietary intake, that plasma potassium remains within narrow, normal limits. There follows discussion of the ways in which acid-base disturbances affect these renal cellular mechanisms of potassium handling.
For example, it is revealed that acidosis decreases potassium secretion in the distal renal tubule directly by effect on potassium secretory channels and indirectly by increasing ammonia production.
The clinical consequences of the physiological relation between acid-base and potassium homeostasis are addressed under three headings: Hyperkalemia in Acidosis; Hypokalemia with Alkalosis; and Hypokalemia with Acidosis. Among the topics discussed under these headings is the important revelation that a variety of mechanisms account for the hyperkalemia in acidosis.
So that for example, the mechanisms for the hyperkalemia associated with diabetic ketoacidosis differ from the mechanisms of the hyperkalemia associated with lactic acidosis. Other conditions associated with disturbances of both acid-base and potassium homeostasis that are discussed in this section include: renal disease, primary hyperaldosteronism, Addison’s disease, chronic diarrhea and renal tubule acidosis.
This review article, which is one of eleven contained in the May issue of Seminars in Nephrology all devoted to different aspects of potassium homeostasis, provides much detail of an aspect of acid-base pathophysiology that often receives minimal explanation in medical texts.
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