Fluid and Electrolyte Series: Balancing act Na+ Sodium K+ Potassium
Ann Crawford PhD, RN
Helene Harris MSN, RN

July 2011 
Volume 41  Number 7
Pages 44 - 50
  PDF Version Available!

FLUID CIRCULATING throughout the body contains electrolytes: elements or minerals that, when dissolved in water or another solvent, dissociate into ions and carry an electrical charge, either positive (cations) or negative (anions). Electrolyte concentrations differ in extracellular and intracellular fluids, but overall the total concentration of cations and anions in each fluid compartment should be equal or balanced.1,2 Electrolyte abnormalities occur when this balance is upset.This article reviews the normal functions of two key electrolytes, sodium and potassium, and discusses nursing assessment and intervention when imbalances occur. For a review of how various I.V. fluids act within the body, see the first article in this series, "I.V. Fluids: What Nurses Need to Know," in the May issue of Nursing2011.Note: Normal value ranges may vary slightly for different age groups, between males and females, and among different analytical labs. Always refer to individual reference lab data to verify normal serum electrolyte ranges used in your institution.The normal serum value for sodium, the most abundant cation in extracellular fluid, is 135 to 145 mEq/L. Sodium is the primary determinant of extracellular fluid osmolality, so it has a principal role of controlling water distribution and fluid balance throughout the body. (See Osomolality or osmolarity: What's the difference?) Remember that water follows sodium, so high levels of sodium in a fluid compartment will draw water with it. Some diuretics utilize this principle to achieve diuresis. Sodium also functions to: * promote transmission of nerve impulses * maintain intracellular osmolality * activate several enzymatic reactions * assist with regulation of acid-base balance * promote myocardial, skeletal, and smooth muscle contractility.1,2Sodium is actively absorbed by the intestines and excreted by the kidneys. The body possesses an intricate system of safeguards and feedback mechanisms to monitor and maintain the sodium

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