Monday, March 9, 2009

Renal Adaptations to Hyperkalemia

Are ESRD patients "protected" from the arrhythmogenic effects of hyperkalemia if they are chronically exposed to elevated potassium levels? I'm not sure if there is a clear answer to this question, but it is certainly a relevant question. What do you do with the ESRD patient who comes into the Emergency Room at 7pm after skipping dialysis who has a K of 6.3? On the one hand, dialysis is a sure-fire way to rapidly lower the K and prevent any cardiac complication, which have the potential to be lethal. On the other hand, calling in the dialysis nurse and fellow uses valuable resources, and there is a belief by some that individuals who "live at a potassium in the 5's & 6's" are protected from the negative effects of hyperkalemia. What does the data show?

There certainly appears to be some degree of renal adaptation to hyperkalemia in chronic kidney disease. Early animal studies in which rats were exposed to varying degrees of infused potassium concentrations demonstrate that hyperkalemia dramatically regulates the degree of potassium secretion, primarily via aldosterone-mediated mechanism in the collecting duct. In addition, this 2002 Kidney International review argues that the hyperkalemia seen in CKD is an adaptive, physiologic response, reflecting a new steady state in which extracellular K rises to the level needed to stimulate K excretion so that it matches intake. There is less data as to what adaptive mechanisms are active in the complete absence of renal function, and furthermore, it's hard to know whether or not such adaptations to hyperkalemia would be operative in many ESRD patients where the K fluctuates dramatically with regards to pre- and post-K levels. One might expect different ion channels in the myocardium to be up/downregulated in order to guard against the cardiac effects of hyperkalemia, or perhaps key K transporters in skeletal muscle are upregulated to maintain the plasma K concentration within the appropriate range.

If anybody knows of other relevant studies looking at adaptations to hyperkalemia, let me know.

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