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.
History
The history may be vague. 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, paresthesias
- Constipation
- Nausea or vomiting
- Abdominal cramping
- Polyuria, nocturia, or polydipsia
- Psychosis, delirium, or hallucinations
- Depression
Physical
Findings may include the following:
- Signs of ileus
- Hypotension
- Ventricular arrhythmias
- 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)
Causes
- Renal losses
- Renal tubular acidosis
- Hyperaldosteronism
- Magnesium depletion
- Leukemia (mechanism uncertain)
- GI losses
- Vomiting or nasogastric suctioning
- Diarrhea
- Enemas or laxative use
- Ileal loop
- Medication effects
- Diuretics (most common cause)
- Beta-adrenergic agonists
- Steroids
- Theophylline
- Aminoglycosides
- Transcellular shift
- Insulin
- Alkalosis
- Malnutrition or decreased dietary intake, parenteral nutrition
What is the treatment for low potassium?
Serum potassium levels above 3.0 mEq/liter are not considered dangerous or of great concern; they can be treated with potassium replacement by mouth. Levels lower than 3.0 mEq/liter may require intravenous replacement. Decisions are patient-specific and depend upon the diagnosis, the circumstances of the illness, and the patient's ability to tolerate fluid and medication by mouth.
Over the short term, with self-limited illnesses like gastroenteritis with vomiting and diarrhea, the body is able to regulate and restore potassium levels on its own. However, if the hypokalemia is severe, or the losses of potassium are predicted to be ongoing, potassium replacement or supplementation may be required.
In those patients taking diuretics, often a small amount of oral potassium may be prescribed since the loss will continue as long as the medication is prescribed. Oral supplements may be in pill or liquid form, and the dosages are measured in mEq. Common doses are 10-20mEq per day. Alternatively, consumption of foods high in potassium may be suggested for replacement. Bananas, apricots, oranges, and tomatoes are high in potassium content. Since potassium is excreted in the kidney, blood tests that monitor kidney function may be ordered to predict and prevent potassium levels from rising too high.
When potassium needs to be given intravenously, it must be given slowly. Potassium is irritating to the vein and must be given at a rate of approximately 10 mEq per hour. As well, infusing potassium too quickly can cause heart irritation and promote potentially dangerous rhythms like ventricular tachycardia.
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