Blood, Electrolytes, and Intravenous Infusions
2-5
2-5. ELECTROLYTES
The amounts of intracellular and extracellular fluids contained in a person's body are extremely important to his healthy physiology. Losses of body fluids by vomiting, diarrhea, or excessive perspiration can produce illness or even death. Whenever body fluids are lost, the substances dissolved in the fluids are also lost. Certain inorganic substances are found in the body's fluids. These are called "electrolytes." Examples of electrolytes are potassium and chloride. These electrolytes exist in their "ion" state in the body fluids. This means that each ion can combine with one or more ions to form needed body compounds or can produce electro-chemical equilibrium (or balance). One example of this is the osmotic pressure that causes water to flow across a cell membrane. The relationship between the concentrations of sodium and potassium electrolytes in the cells and the extracellular fluid causes the water to flow into and out from the cells. There is usually a low level of sodium in the cells and a high concentration of potassium. The milliequivalent (mEq) is a unit of measure for the electrolyte.
a. The movement of electrolytes is governed by their electrical charge. Some are positively charged and are called "cations." Others are negatively charged and called "anions." Below are the major electrolytes, their chemical abbreviations, and the amount of each contained in a liter of extracellular fluid.
Sodium (Na
+) 140 mEqChloride (Cl
–) 100 mEqBicarbonate (HCO
3 –) 27 mEqPotassium (K
+) 4 mEqMagnesium (Mg
+2) 3 mEq+2). There are 3 mEq of magnesium in each liter of extracellular fluid. Therefore, each liter of extracellular fluid has 6 positive ions of magnesium (+2 x 3 = +6) available to combine with other negative ions. If the compound, magnesium chloride is needed, these six positive ions could combine with six negative ions from the 100 mEq of chloride contained in a liter of extracellular fluid (each electrolyte of chloride has one negative charge, shown as Cl–). This would yield the required magnesium chloride by neutralizing the positive and negative ions.(1) Certain compounds can be formed by combining these charged cations and anions.
(a) To form magnesium chloride: Each ion of magnesium has two positive charges (Mg
(b) To form sodium bicarbonate: Each ion of sodium has one positive charge (Na
+). There is one negative charge of bicarbonate (HCO3–) in each ion of bicarbonate. If the compound, sodium bicarbonate is required, each positive sodium ion can combine with a negative bicarbonate ion to yield the required amount of sodium bicarbonate. This neutralizes the positive and negative ions of both the sodium and the bicarbonate used(2) When the body loses fluids, the number and kind of electrolyte(s) lost will depend on whether the fluid has been lost from interstitial or intravascular spaces or both.
b. Intracellular fluid contains the following kinds and amounts of electrolytes per liter:
Potassium (K
+) 160 mEqPhosphate (PO
4–3) 110 mEqMagnesium (Mg
+2) 25 mEqSodium (Na
+) 5 mEqChloride (Cl
–) 3 mEq
c. Each electrolyte has certain functions in order to help the body maintain homeostasis.
(1) Sodium. As you can see, sodium is the most abundant positive electrolyte (or cation) in the extracellular fluid and is also present in intracellular fluid. The main function of sodium is in maintaining normal osmotic pressure.
(2) Chloride. Chloride is the most abundant negative electrolyte (or anion) in extracellular fluid and is present in intracellular fluid as well. Chloride is essential to maintain normal osmotic pressure and is found in the stomach fluid.
(3) Potassium. Potassium is the most abundant electrolyte in the intracellular fluid. Potassium is also required for osmotic pressure but has other vital functions. Potassium is required to
convert dextrose (a sugar) into body energy and is required as an aid in transmitting nerve impulses within the heart.
(4) Bicarbonate. Bicarbonate helps to maintain the acid-base balance within the body (see paragraph 2-6).
(5) Phosphate. Phosphate is required for the formation of bones, teeth, and body enzymes (see paragraph 2-10 for a discussion of enzymes).
(6) Magnesium. Magnesium is essential for the formation of enzymes within the body.
(7) Calcium. Calcium is essential for the formation of bones and teeth. Calcium is needed to help in blood clotting and in maintaining the rhythm of the heart beat
d. If a liter of body fluid is lost from extracellular fluids, all the electrolytes must be replaced along with the water. If a liter of fluid is lost by a severe case of diarrhea, the electrolytes would be of a different type and amount than those from the extracellular fluid. Therefore, both the source of the lost fluid and the amount must be considered when giving replacement fluids.
