Hypokalemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Assistant Editor(s)-In-Chief: Jack Khouri
Overview
Hypokalemia is a potentially fatal condition in which the body fails to retain sufficient potassium to maintain health. It is defined as a serum potassium level below 3.5 mEq/L. The condition is also known as potassium deficiency.
Historical Perspective
The prefix hypo- means low (contrast with hyper-, meaning high). The middle kal refers to kalium, which is Neo-Latin for potassium. The end portion of the word, -emia, means "in the blood" (note, however, that hypokalemia is usually indicative of a systemic potassium deficit).
Pathophysiology
Potassium is the most abundant intracellular cation. Any derangement of potassium serum levels can disturb the transmembrane potential and renders excitable cells (nerve and muscle) hyperpolarized and less excitable. However, cardiac cells don't obey this rule and become hyperexcitable.
Potassium regulation is essential to maintain a normal activity of excitable cells. Failure to regulate potassium serum levels can have severe consequences on several organs especially the heart and the nervous system. Normally, total potassium excretion in stool is low and most ingested potassium is absorbed. The kidney is the main regulator of potassium balance through excretion (the kidney excretes 90-95% of dietary potassium); the gut excretes a minimal amount of dietary potassium (approximately 10%).
Causes
The etiology of hypokalemia can be quite difficult to diagnose. As a matter of fact, many organ systems are involved in the regulation of potassium level and any derangement to their normal function can cause hypokalemia. Drugs, diarrhea, kidney disease, endocrine diseases and many others are potential culprits.
Hypokalemia can be the consequence of decreased ingestion, increased losses (renal, GI or excessive sweating) or transcellular shift from the extracellular to the intracellular compartment. The most common causes are diarrhea, vomiting and diuretic use (mostly loop and thiazide diuretics).
Diagnosis
Diagnosis relies on a constellation of findings including:
History
It should include the past medical history to point out some relevant diseases and conditions that can result in hypokalemia (eg hyperthyroidism, hyperaldosteronism, Cushing's disease,etc). The medication history should be detailed given the long list of medications that can be culprit.
Symptoms
Mostly constitutive with predominance of muscle weakness and cramping. The heart can be affected; ECG can reveal arrhythmias and other major changes. The kidney can be involved: nephrogenic diabetes insipidus and hyponatremia can occur.
Laboratory findings
Many labs can be helpful. The transtubular potasium gradient (TTKG), urine potassium and urine chloride levels can help define the etiology of hypokalemia.
Treatment
The oral route is the safest. There are many oral potassium salts that can be prescribed including potassium chloride KCl (the most popular) and the organic alkalinizing salts that are metabolized to potassium bicarbonate KHCO3 in the body. Severe hypokalemia ca be treated via IV KCl infusion with doses that shouldn't exceed 60 mEq/L unless ECG monitoring is provided. A central line can be used for administration of greater concentrations of KCl.