A decrease in PaCO2 of 10 mm Hg will result in which change in serum potassium concentration?

A decrease in PaCO2 of 10 mm Hg will result in which change in serum potassium concentration?

• A. A decrease in [K+] of 0.5 mEq/L
• B. A decrease in [K+] of 1.0 mEq/L
• C. No change in [K+]
• D. An increase in [K+] of 0.5 mEq/L

Answer: (A)

A fall in PaCO2 causes respiratory alkalosis. In alkalosis, potassium shifts from the extracellular space into cells to help maintain electroneutrality, so serum potassium falls. The typical magnitude of this shift is about 0.5 mEq/L for a 10 mm Hg decrease in PaCO2, which matches the option describing a 0.5 mEq/L decrease. A larger drop (1.0 mEq/L) is less likely for just a 10 mm Hg change, while no change or an increase would contradict the intracellular shift that occurs with alkalemia.

A fall in PaCO2 causes respiratory alkalosis. In alkalosis, potassium shifts from the extracellular space into cells to help maintain electroneutrality, so serum potassium falls. The typical magnitude of this shift is about 0.5 mEq/L for a 10 mm Hg decrease in PaCO2, which matches the option describing a 0.5 mEq/L decrease. A larger drop (1.0 mEq/L) is less likely for just a 10 mm Hg change, while no change or an increase would contradict the intracellular shift that occurs with alkalemia.