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A patient with history of arrhythmias undergoing cardiac surgery is noted to be hypokalemic. After the patient receives potassium replacement, there is no increase in serum potassium levels. Repletion of what electrolyte would MOST likely increase the patient’s serum potassium?
A. Magnesium ✔
B. Phosphorus X
C. Calcium X
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Potassium is an important cation for nerve conduction within both the cardiac and nervous systems. Abnormalities of potassium concentration can play a major role in arrythmias, muscle weakness, and ileus. Most of the body’s potassium is intracellular, with approximately 2% existing in the extracellular space. Hypokalemia may occur secondary to a diminished intake of potassium and excessive renal and gastrointestinal losses or transcellular shifts.
Magnesium has a vital role in potassium maintenance, and a deficiency of both magnesium and potassium can further increase the risk of malignant arrhythmias. Magnesium regulates the activity of the renal outer medullary potassium (ROMK) channel, which allows potassium to be excreted. A normal magnesium level closes ROMK channels, thus maintaining potassium levels. However, a low magnesium level allows more ROMK channels to open, leading to potassium loss.
Magnesium also has a role as a cofactor in sodium-potassium-adenosine-triphosphatase and in potassium’s intracellular/extracellular balance.
Neither calcium nor phosphorus plays a significant role in potassium homeostasis.
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Date of last update: March 18, 2025
