Show Notes

  • Potassium is a monovalent cation that plays a key role in many of our body’s foundational activities via the sodium-potassium exchange pump, which creates the electrochemical gradients that generate action potentials. Action potentials allow our neurons to transmit signals and our muscles to contract.
  • The ratio between potassium levels inside and outside a cell determines the resting potential.
    • In skeletal muscle, low potassium outside of the cell makes the resting potential more negative, and thus makes it more difficult to depolarize, which causes weakness and paralysis.
    • In cardiac muscle, low serum potassium actually drives sodium into the cell, bringing the heart closer to depolarization, hence the risk for arrhythmias with  hypokalemia.
  • How does this translate clinically?
    • Serum potassium levels less than 2.5 mEq can precipitate ileus, hyporeflexia, rhabdomyolysis, and EKG changes, including U waves.
    • When serum potassium falls below 2 mEq, this can progress to paralysis, respiratory failure, and cardiac arrhythmias.
    • Notably, acuity matters – a quick drop can cause these changes to occur more quickly or at higher levels.
  • We obtain potassium through the food we eat. We excrete some through our GI tract, but most of it is excreted in our kidneys (around 90%).
    • Interestingly, our kidneys are actually programmed to excrete more potassium during the day, in part due to circadian rhythms and in part triggered by eating food containing potassium.
  • Regarding the evidence for potassium repletion: the data simply doesn’t exist. None of the trials we found actually looked at repletion itself. What clinical studies have been able to tell us is this: high and low serum potassium levels correlate with mortality.
    • Lower potassium levels correlated strongly with increased mortality in patients with heart failure and acute MI. This is likely due to the fact that low potassium serves as a proxy measure of worsening disease (and possibly, poorer diet), as well as putting the heart at risk for arrhythmias at very low levels, as discussed above.

References

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