Management of Fluid and Electrolyte problems in Children

Potassium ions are important in the maintenance of resting potentials across cell membranes. Imbalances of potassium homeostasis affect many biologic processes which rely on these membrane potentials.

This is important with respect to cardiac muscle cell contractility and changes in plasma [K⁺] may lead to arrythmias.

The kidneys are responsible for maintaining plasma [K⁺].

Potassium is the main intracellular cation. 98% of body potassium is inside cells. It is held inside cells by a charge gradient which maintains a negative charge within cells. This is achieved by:

1. A Na⁺K⁺ ATPase creates a high intracellular [K⁺]. 3 Na+ are pumped out and only 2 K⁺ enter the cell.
2. K⁺ diffuses out of cells, down the concentration gradient. Potassium ions diffuse through cell membranes more rapidly than sodium ions. The majority of the intracellular anions are large macromolecules and therefore cannot diffuse out of the cells.

What factors influence potassium shift from the ICF to the ECF?

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