Assessment of hypokalaemia

Hypokalaemia is defined as a serum potassium level <3.5 mmol/L (<3.5 mEq/L). Moderate hypokalaemia is defined as serum potassium levels of 2.5 to 3 mmol/L (2.5 to 3 mEq/L) and severe hypokalaemia defined as a serum potassium level <2.5 mmol/L (<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.

Hypokalaemia is most commonly due to urinary or GI losses. A fall in serum potassium from 4 to 3 mmol/L (4 to 3 mEq/L) represents an approximate loss of 200 to 400 mmol (200 to 400 mEq) of potassium. However, these estimates do not always apply to patients with transcellular potassium redistribution. Clinical manifestations of hypokalaemia are typically seen only if the serum potassium is <3.0 mmol/L (<3.0 mEq/L).

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

The rapidity and method of potassium repletion depends on the:

• severity of hypokalaemia

• presence of associated conditions

• presence or absence of signs and symptoms

• expectation of continued losses.

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