Potassium

The body's normal daily potassium requirement is 0.5 to 1 mEq/kg (0.5-1 mmol/kg) or 40 to 80 mEq (40-80 mmol) to maintain a serum potassium concentration of 3.5 to 5 mEq/L (3.5-5 mmol/L). Potassium is the most abundant cation in the ICF, balancing the sodium contained in the ECF and maintaining electroneutrality of bodily fluids. Because the majority of potassium is intracellular, serum potassium concentration is not a good measure of total body potassium; however, clinical manifestations of potassium disorders correlate well with serum potassium. The acid-base balance of the body affects serum potassium concentrations: hyperkalemia is routinely seen in patients with decreased pH (acidosis). Potassium regulation is primarily under the control of the kidneys with excess dietary potassium being excreted in the urine. Although mild abnormalities of serum potassium are considered a nuisance, severe hy-

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perkalemia or hypokalemia can be life-threatening.

Hypokalemia (serum potassium less than 3.5 mEq/L [3.5 mmol/L]) is a common clinical problem. While generally asymptomatic, signs and symptoms of hypokalemia include cramps, muscle weakness, polyuria, electrocardiogram (ECG) changes (flattened T-waves and presence of U-waves), and cardiac arrhythmias (bradycardia, heart block, atrial flutter, premature ventricular contractions, and ventricular fibrillation). Causes of hypokalemia include GI losses (vomiting, diarrhea, or NG tube suction), renal losses (high aldosterone and low magnesium), inadequate potassium intake (in IV fluids or oral), or alkalosis. Many medications can precipitate hypokalemia. ^2-agonists (e.g., albuterol, available as generic) and insulin (multiple product formulations) lower potassium via cellular redistribution. The use of loop diuretics (furosemide [Lasix], also available as generic), thiazide diuretics (hydro-chlorothiazide, available as generic), high-dose antibiotics (penicillin, available as generic), and corticosteroids (prednisone, available as generic) cause renal potassium wasting. In addition, amphotericin B (available as generic), cisplatin (available as generic), and foscarnet (Foscavir, AstraZeneca) can also produce hypokalemia secondary to depletion of magnesium. Hypomagnesemia diminishes intracellular potassium concentration and produces potassium wasting. Given the potential for significant morbidity and mortality, serum potassium concentrations should be monitored

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closely for patients with known (or suspected) hypokalemia. Hypokalemia is a risk factor for digitalis toxicity.

Each 1 mEq/L (1 mmol/L) fall in serum potassium (i.e., from 4 to 3 mEq/L [4 to 3 mmol/L]) represents a loss of approximately 200 mEq (200 mmol) of potassium in the adult. However, when the serum potassium is below 3 mEq/L (3 mmol/L), each 1 mEq/L fall in serum potassium represents a 200 to 400 mEq (200-400 mmol) reduction in serum concentration in the adult patient. Potassium repletion should be guided by close monitoring of serial serum concentrations instead of using empirically chosen amounts. Of the five potassium salts available, potassium acetate (10.2 mEq/K+/g or 10.2 mmol/K+/g) and KCl (13.4 mEq/K+/g or 13.4 mmol/K+/g) are the most commonly used forms. When hypokalemia occurs in the setting of alkalosis, KCl is the preferred agent; in acidosis, potassium should be provided in the form of acetate, citrate, bicarbonate, or gluconate salt. Table 27-6 outlines the potassium content of each potassium salt preparation, and Table 27-7 lists each of the oral potassium replacement products. Potassium acetate and chloride are available for IV infusions as premixed solutions. The usual dose of these agents is 10 to 20 mEq (10-20 mmol)

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diluted in 1,000 mL of normal saline. ' '

Moderate hypokalemia is defined as a serum potassium of 2.5 to 3.5 mEq/L (2.5-3.5 mmol/L) without ECG changes. In this setting, potassium replacement can usually be given orally at a dose of 40 to 120 mEq/day (40-120 mmol/day). Anec-dotally, oral potassium supplementation (see Table 27-7) is often more effective in repleting moderate hypokalemia. For patients with an ongoing source of potassium loss, chronic replacement therapy should be considered. The potassium deficit is a rough approximation of the amount of potassium needed to be replaced and can be estimated as follows:

Table 27-6 Potassium Content in Various Potassium Salt Preparations

Potassium Salt

mEq/g immol/U

Potassium Gluconate"

A3

Potassium citrate'1

93

Potassium bicarbonate0

ion

Potassi urn acetale*

10.2

Potassium chloride^

13.4

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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