Evaluation of hypokalemia

Hypokalemia is defined as a serum potassium level <3.5 mEq/L. Moderate hypokalemia is defined as serum potassium levels of 2.5 to 3 mEq/L and severe hypokalemia defined as a serum potassium level <2.5 mEq/L.[1]Unwin RJ, Luft FC, Shirley DG. Pathophysiology and management of hypokalemia: a clinical perspective. Nat Rev Nephrol. 2011;7:75-84. http://www.ncbi.nlm.nih.gov/pubmed/21278718?tool=bestpractice.com The ratio of intracellular to extracellular potassium determines, in part, the cellular membrane potential. Therefore small changes in the extracellular potassium level can have large effects on the function of the cardiovascular and neuromuscular systems.

Hypokalemia is most commonly due to urinary or GI losses. A fall in serum potassium from 4.0 to 3.0 mEq/L represents an approximate loss of 200 to 400 mEq of potassium. However, these estimates do not always apply to patients with transcellular potassium redistribution. Clinical manifestations of hypokalemia are typically seen only if the serum potassium is <3.0 mEq/L.

Common acute manifestations are muscle weakness and ECG changes. More prolonged and profound hypokalemia may cause rhabdomyolysis, renal abnormalities, and cardiac arrhythmias.

The rapidity and method of potassium repletion depends on the:

• severity of hypokalemia

• presence of associated conditions

• presence or absence of signs and symptoms

• expectation of continued losses.

Obtaining an ECG is recommended for all patients with hypokalemia. Frequent monitoring of the serum potassium concentration is also recommended to ensure appropriate repletion and to avoid hyperkalemia.