by Melissa Rodriguez, MD (’21)
Potassium is the second most common cation in the human body, with around 2% of it present extracellularly in the form of 3.5 to 5.5 mEq/L. Potassium moves along a gradient with sodium via the sodium-potassium-adenosine triphosphate (ATP) pump (which can be affected by things such as insulin, glucagon, catecholamines, acid-base status, etc). Hypokalemia is the presence of a serum potassium concentration less than 3.5 mEq/L, but it isn’t considered life threatening until around less than 2.5 mEq/L. In pediatrics the most common cause of hypokalemia is GI losses such as diarrhea and vomiting. Other reasons include urinary losses (diuretic use, DKA), inadequate potassium intake (eating disorders), and intracellular shifts of potassium (metabolic alkalosis, beta adrenergic agonist use, hyperthyroidism).
Hypokalemia can result in cellular membrane hyperpolarization and as such, impair muscle contractions. Potassium levels of 2.5 to 3 mEq/L can bring with them muscular weakness, myalgia, muscle cramps, and constipation. More severe hypokalemia can even lead to flaccid paralysis and hyporeflexia, which can result in severe (and rare) cases in respiratory depression. Early ECG changes include ST segment depression, T wave flattening, and presence of U waves. Treatment involves potassium replacement. In the presence of cardiac arrhythmias, extreme muscle weakness or respiratory depression, treatment includes IV potassium chloride. Less severe cases can be replaced with oral potassium supplements, of which many exist. The decision of which oral supplement to choose can be guided by other factors in the patient’s clinical presentation.
Potassium bicarbonate (KHCO3) is best utilized in patients with hypokalemia and metabolic acidosis, as seen in diarrhea.
Potassium phosphate (K3PO4) is good for cases of hypokalemia with hypophosphatemia such as in proximal tubular acidosis.
Potassium chloride (KCl) is useful for the presence of hypokalemia with hypochloremia and metabolic alkalosis, which can be seen in diuretic use or vomiting. KCl aids with resolving metabolic alkalosis (resolution of hypochloremia lessens renal bicarbonate reabsorption). It also raises serum potassium the quickest of all supplements given that chloride does not enter cells as easily as bicarbonate and promotes good maintenance of administered potassium in the extracellular fluid.
If hypomagnesemia is present with hypokalemia, magnesium should be replaced to promote potassium reabsorption at the kidneys (which is controlled by a magnesium powered electrolyte exchange pump).
Daly, K., & Farrington, E. (2013). Hypokalemia and Hyperkalemia in Infants and Children: Pathophysiology and Treatment. Journal of Pediatric Health Care, 27(6), 486–496. doi: 10.1016/j.pedhc.2013.08.003