Author: David Garth, MD, Attending Physician, Department of Emergency Medicine,
Mary Washington Hospital
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.1,2,3
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.
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.
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.
Incidence is equal in males and females.
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:
- Skeletal muscle weakness or cramping
- Paralysis, paresthesias
- Nausea or vomiting
- Abdominal cramping
- Polyuria, nocturia, or polydipsia
- Psychosis, delirium, or hallucinations
Findings that are consistent with severe hypokalemia may include the following:
- Signs of ileus
- Ventricular arrhythmias5
- Cardiac arrest
- Bradycardia or tachycardia
- Premature atrial or ventricular beats
- Hypoventilation, respiratory distress
- Respiratory failure
- Lethargy or other mental status changes
- Decreased muscle strength, fasciculations, or tetany
- Decreased tendon reflexes
- Cushingoid appearance (eg, edema)
- Renal losses
- Renal tubular acidosis
- Magnesium depletion
- Leukemia (mechanism uncertain)
- GI losses (source may be medical or psychiatric6 , ie, anorexia or bulimia)
- Vomiting or nasogastric suctioning
- Enemas or laxative use
- Ileal loop
- Medication effects
- Diuretics (most common cause)
- Beta-adrenergic agonists
- Transcellular shift
- Malnutrition or decreased dietary intake, parenteral nutrition