In this episode, I’ll discuss how correction of hypokalemia in a hyponatremic patient makes inadvertent overcorrection of hyponatremia more likely.
Shout out to “Pharmacy Alex” for inspiring this episode!
During the correction of hyponatremia, care is taken to not correct the serum sodium too quickly. This is because the over-correction of sodium levels carries a risk of osmotic demyelination and permanent brain damage.
The recommended safe limit of sodium correction has been continually lowered. While many years ago an increase of 12 mEq/L in 24 hours was considered safe, recent recommendations for an upper limit of 9, 8 and even 6 mEq/L have been made.
This lower limit of correction is rational because a 4-6 mEq/L increase should reverse severe symptoms of hyponatremia and having lower targets makes preventing over-correction easier.
Some patients, such as those with severe vomiting or diarrhea, present with both hyponatremia and hypokalemia.
Clinicians should be aware that correction of hypokalemia at the same time as correction of hyponatremia can lead to overcorrection of serum sodium to dangerous levels.
Because potassium is just as osmotically active as sodium, intracellular sodium will move out into the extracellular fluid in exchange for potassium. In addition, the extra chloride from potassium chloride can also force free water into cells, effectively raising serum sodium.
If you need to replace both sodium and potassium, take into account the effects of potassium first, then figure out if additional sodium is needed.
For example, if a patient’s total body water is 40 liters and you are giving 100 mEq potassium chloride, this should raise the serum sodium by 2.5 mEq/L.
Oral potassium and hypertonic IV potassium solutions can be expected to cause this issue with possible overcorrection of serum sodium. However a hypotonic IV solution of potassium will likely not cause overcorrection of serum sodium, because of the additional free water contained in such a solution. Therefore clinicians should be especially vigilant for this issue if using small fluid volumes in potassium replacement minibags such as 20 mEq in 50 mL sterile water, or if using compounded IV potassium in a 0.9% sodium chloride diluent.
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