| Author: Estella Wetzel
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Electrolytes work with fluids to maintain health and well-being. They're found in various concentrations, depending on whether they're inside or outside the cells. Electrolytes are crucial for nearly all cellular reactions and functions. Let's take a look at what electrolytes are, how they function, and what upsets their balance.
Electrolytes are substances that, when in solution, separate (or dissociate) into electrically charged particles called ions. Some ions are positively charged, and others are negatively charged. Several pairs of oppositely charged ions are so closely linked that a problem with one ion causes a problem with the other. Sodium and chloride are linked that way, as are calcium and phosphorus.
A variety of diseases can disrupt the normal balance of electrolytes in the body. Understanding electrolytes and recognizing imbalances can make your patient assessment more accurate.
Anions and cations
Anions are electrolytes that generate a negative charge; cations are electrolytes that produce a positive charge. An electrical charge makes cells function normally. (See Looking on the plus and minus sides.)
The anion gap is a useful test for distinguishing types and causes of acid-base imbalances because it reflects serum anion-cation balance. (The anion gap is discussed in chapter 3, Balancing acids and bases.)
Balancing the pluses and minuses
Electrolytes operate outside the cell in extracellular fluid (ECF) compartments and inside the cell in intracellular fluid (ICF) compartments. Individual electrolytes differ in concentration, but electrolyte totals balance to achieve a neutral electrical charge (positives and negatives balance each other). This balance is called electroneutrality.
Memory JoggerTo remind yourself about the difference between anions and cations, remember that the T in “cation” looks like the positive symbol, “+.”
Hooking up with hydrogen
Most electrolytes interact with hydrogen ions to maintain acid-base balance. The major electrolytes have specialized functions that contribute to metabolism and fluid and electrolyte balance.
Major electrolytes outside the cell
Sodium and chloride, the major electrolytes in ECF, exert most of their influence outside the cell. Sodium concentration affects serum osmolality (solute concentration in 1 L of water) and ECF volume. Sodium also helps nerve and muscle cells interact. Chloride helps maintain osmotic pressure (water-pulling pressure). Gastric mucosal cells need chloride to produce hydrochloric acid, which breaks down food into absorbable components.
More outsiders
Calcium and bicarbonate are two other electrolytes found in ECF. Calcium is the major cation involved in the structure and function of bones and teeth. Calcium is needed to:
Bicarbonate plays a vital role in acid-base balance.
Major electrolytes inside the cell
Potassium, phosphorus, and magnesium are among the most abundant electrolytes inside the cell. The body uses phosphorus to convert energy.
Potent potassium
Potassium plays an important role in:
Fundamental phosphorus
The body contains phosphorus in the form of phosphate salts. Sometimes, the words phosphorus and phosphate are used interchangeably. Phosphate is essential for energy metabolism. Combined with calcium, phosphate plays a key role in bone and tooth mineralization. It also helps maintain acid-base balance.
Magnificent magnesium
Magnesium acts as a catalyst for enzyme reactions. It regulates neuromuscular contraction, promotes normal functioning of the nervous and cardiovascular systems, and aids in protein synthesis and sodium and potassium ion transportation.
Electrolyte movement
When cells die (e.g., from trauma or chemotherapy), their contents spill into the extracellular area and upset the electrolyte balance. In this case, elevated levels of intracellular electrolytes are found in plasma.
Although electrolytes are generally concentrated in a specific compartment, they aren't confined to these areas. Like fluids, they move around trying to maintain balance and electroneutrality.
Electrolyte balance
Fluid intake and output, acid-base balance, hormone secretion, and normal cell function all influence electrolyte balance. Because electrolytes function both collaboratively, with other electrolytes, and individually, imbalances in one electrolyte can affect balance in others. (See Understanding electrolytes.)
Electrolyte levels
Even though electrolytes exist inside and outside the cell, only the levels outside the cell in the bloodstream are measured. Although serum levels remain fairly stable throughout a person's life span, understanding which levels are normal and which are abnormal is critical to reacting quickly and appropriately to a patient's electrolyte imbalance.
Consider what you know about the patient when you see abnormal test results. The patient's condition determines how often electrolyte levels are checked. Results for many laboratory tests are reported in milliequivalents per liter (mEq/L), which is a measure of the ion's chemical activity, or its power. (See Interpreting serum electrolyte test results, for a look at normal and abnormal electrolyte levels in the blood.)
See the whole picture
When you see an abnormal laboratory test result, consider what you know about the patient. For instance, a serum potassium level of 7 mEq/L for a patient with previously normal serum potassium levels and no apparent reason for the increase may be an inaccurate result. Perhaps the patient's blood sample was hemolyzed from trauma to the cells, which can occur when drawing the blood or during transport to the lab.
With that said, look at the whole picture before you act, including what you know about the patient, patient's signs and symptoms, and patient's electrolyte levels. (See Documenting electrolyte imbalances.)
Many activities and factors are involved in regulating fluid and electrolyte balance. A quick review of some of the basics will help you understand this regulation better.
Fluid and solute movement
As discussed in chapter 1, active transport moves solutes upstream and requires pumps within the body to move the substances from areas of lower concentration to areas of higher concentration—against a concentration gradient. Adenosine triphosphate is the energy that moves solutes upstream.
Pushing fluids
The sodium-potassium pump, an example of an active transport mechanism, moves sodium ions from ICF (an area of lower concentration) to ECF (an area of higher concentration). With potassium, the reverse happens: A large amount of potassium in ICF causes an electrical potential at the cell membrane. As ions rapidly shift in and out of the cell, electrical impulses are conducted. These impulses are essential for maintaining life.
Organ and gland involvement
Most major organs and glands in the body—the lungs, liver, adrenal glands, kidneys, heart, hypothalamus, pituitary gland, skin, gastrointestinal (GI) tract, and parathyroid and thyroid glands—help to regulate fluid and electrolyte balance.
As part of the renin-angiotensin-aldosterone system, the lungs and liver help regulate sodium and water balance as well as blood pressure. The adrenal glands secrete aldosterone, which influences sodium and potassium balance in the kidneys. These levels are affected because the kidneys excrete potassium, or hydrogen ions, in exchange for retained sodium.
The heart says no
The heart counteracts the renin-angiotensin-aldosterone system when it secretes atrial natriuretic peptide (ANP), causing sodium excretion. The hypothalamus and posterior pituitary gland produce and secrete an antidiuretic hormone that causes the body to retain water which, in turn, affects solute concentration in the blood.
Where electrolytes are lost
Sodium, potassium, chloride, and water are lost in sweat and from the GI tract; however, electrolytes are also absorbed from the GI tract. Discussions of individual electrolytes in upcoming chapters explain how GI absorption of foods and fluids affects their balance.
The glands play on
The parathyroid glands also play a role in electrolyte balance, specifically the balance of calcium and phosphorus. The parathyroid glands (usually two pairs) are located behind and to the side of the thyroid gland. They secrete parathyroid hormone, which draws calcium into the blood from the bones, intestines, and kidneys and helps move phosphorus from the blood to the kidneys, where it's excreted in urine.
The parafollicular cells in the thyroid gland are also involved in electrolyte balance by secreting calcitonin. This hormone lowers an elevated calcium level by preventing calcium release from bone. Calcitonin also decreases intestinal absorption and kidney reabsorption of calcium.
Kidney involvement
Remember filtration? It's the process of removing particles from a solution by allowing the liquid portion to pass through a membrane. Filtration occurs in the nephron (the anatomic and functional unit of the kidneys). As blood circulates through the glomerulus (a tuft of capillaries), fluids and electrolytes are filtered and collected in the nephron's tubule.
Some fluids and electrolytes are reabsorbed through capillaries at various points along the nephron; others are secreted. Age can play an important role in the way kidneys function—or malfunction. (See Who's at risk?)
A juggling act
A vital part of the kidneys' job is to regulate electrolyte levels in the body. Normally functioning kidneys maintain the correct fluid level in the body. Sodium and fluid balances are closely related. When too much sodium is released, the body's fluid level drops.
The kidneys also rid the body of excess potassium. When the kidneys fail, potassium builds up in the body. High levels of potassium in the blood can be fatal. (For more information about which areas of the nephron control fluid and electrolyte balance, see How the nephron regulates fluid and electrolyte balance.)
How diuretics affect balance
Many patients—whether in a medical facility or at home—take a diuretic to increase urine production. Diuretics are used to treat many disorders, such as hypertension, heart failure, electrolyte imbalances, and kidney disease.
Keeping a close watch
The health care team monitors the effects of a diuretic, including its effect on electrolyte balance. A diuretic may cause electrolyte loss, whereas an IV fluid causes electrolyte gain. Older adults, who are at risk for fluid and electrolyte imbalances, need careful monitoring because a diuretic can worsen an existing imbalance.
When you know how the nephron functions normally, you can predict a diuretic's effects on your patient by knowing where along the nephron the medication acts. This knowledge and understanding can help you provide optimal care for a patient taking a diuretic. (See How medications affect nephron activity.)
IV fluids
Like diuretics, IV fluids affect electrolyte balance in the body. When providing IV fluid, keep in mind the patient's normal electrolyte requirements. For instance, the patient may require:
Improving your IV IQ
To evaluate IV fluid treatment, ask:
For more about IV fluids, see chapter 19, IV fluid replacement. (For the electrolyte content of some commonly used IV fluids, see IV fluid components.)
If you answered all six questions correctly, congratulations! You understand balance so well, you're ready to walk the high wire.
If you answered four or five correctly, great! You still have all the qualities of a well-balanced individual!
If you answered fewer than four correctly, no need to feel too unbalanced! Just review the chapter and you'll be fine.
References
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Potter, P. A., Perry, A. G., Stockert, P. A., Hall, A. M., & Felver, L. (2021). Chapter 42: Fluid, electrolyte and acid-base balance. In Ostendorf, W. R. (Ed.), Fundamentals of nursing (10th ed., pp. 943–991). Elsevier Mosby.
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Tkacs, N., Herrmann, L., & Johnson, R. (2021). Advanced physiology and pathophysiology: essentials for clinical practice. Springer Publishing Company.
Walker, M. D. (2016). Fluid and electrolyte imbalances: interpretation and assessment. Journal of Infusion Nursing, 39(6), 382–386.
In this chapter, you'll learn: