Hypokalemia

Potassium is one of the body's major ions. Nearly 98% of the body's potassium is intracellular. The ratio of intracellular to extracellular potassium is important in determining the cellular membrane potential. Small changes in the extracellular potassium level can have profound effects on the function of the cardiovascular and neuromuscular systems. The kidney determines potassium homeostasis, and excess potassium is excreted in the urine. The reference range for serum potassium level is 3.5-5 mEq/L, with total body potassium stores of approximately 50 mEq/kg (ie, approximately 3500 mEq in a 70-kg person). Hypokalemia is defined as a potassium level less than 3.5 mEq/L. Moderate hypokalemia is a serum level of 2.5-3 mEq/L. Severe hypokalemia is defined as a level less than 2.5 mEq/L.
Pathophysiology
Hypokalemia may result from conditions as varied as renal or GI losses, inadequate diet, transcellular shift (movement of potassium from serum into cells), and medications.
Frequency
United States
As many as 20% of hospitalized patients are hypokalemic; however, hypokalemia is clinically significant in only about 4-5% of these patients. Severe hypokalemia is relatively uncommon. Up to 14% of outpatients who undergo laboratory testing are found to be mildly hypokalemic. Approximately 80% of patients who are receiving diuretics become hypokalemic.
Sex
Incidence is equal in males and females.
Clinical
History
The history may be vague. Patients are often asymptomatic, particularly with mild hypokalemia. Symptoms are often due to the underlying cause of the hypokalemia rather than the hypokalemia itself. Hypokalemia should be suggested by a constellation of symptoms that involve the GI, renal, musculoskeletal, cardiac, and nervous systems. The patient's medications should be reviewed to ascertain whether any of them could cause hypokalemia. Common symptoms include the following:
Palpitations
Skeletal muscle weakness or cramping
Paralysis,