Learning Objectives
By the end of this section, you will be able to:
- Describe the principles of fluid and balances in the body
- Identify principles of electrolytes and balances in the body
- Explain the regulation mechanisms of fluid and electrolyte balance
The principle of fluid and electrolyte balance is one of the cornerstones of nursing practice. The human body must maintain strict balance between fluid levels and electrolyte concentrations in order for physiological processes to occur normally. To maintain this balance, there are multiple regulatory mechanisms that restore fluid and electrolyte balance. However, those regulatory mechanisms sometimes fail. Nurses must be knowledgeable about the signs and symptoms of a fluid and electrolyte imbalance so that they can intervene early and prevent serious complications.
Principles of Fluids and Balances in the Body
To ensure homeostasis and acid-base balance, the human body must maintain a consistent balance of fluid and electrolytes. Homeostasis refers to the process by which the human body maintains its balance by adjusting to internal and external stimuli. When homeostasis is not maintained, the patient is at risk for organ system dysfunction or even death. Nurses must recognize subtle signs of fluid and electrolyte imbalances. By doing so, they can intervene early and prevent patient complications.
Composition of Body Fluids
Body fluid is composed of water and solutes. A solute is any substance that is dissolved in a solution. Examples of solutes in body fluid are proteins, electrolytes, and metabolites. There are two main compartments of body fluid in the body: the intracellular compartment and the extracellular compartment. Approximately two-thirds of body fluid is found in the intracellular space and one-third is in the extracellular compartment (Figure 20.2) (Tobias & Mohiuddin, 2022).
Intracellular Fluids
The intracellular fluid is the body fluid found inside the body’s cells. Within this space, multiple chemical reactions occur. Therefore, it is important to maintain consistent solute concentrations. Alterations in solute concentration can change the acid-base balance inside the cell, which affects the structure and function of enzymes. An enzyme is a protein that catalyzes chemical reactions. When enzymes do not function normally, chemical reactions that normally take place inside the cells are significantly impacted (Brinkman & Sharma, 2023).
Extracellular Fluids
The extracellular fluid is the body fluid found outside of cells. It is subdivided into three categories: interstitial fluid, blood plasma, and transcellular fluid. The fluid that surrounds the cells is called interstitial fluid. Intravascular fluid, also known as blood plasma, is the liquid component of blood. It is whole blood minus the red blood cells, white blood cells, and platelets (Tobias & Mohiuddin, 2022). The fluid within epithelial-lined spaces is called transcellular fluid. Examples of transcellular fluid include cerebrospinal fluid, ocular fluid, and joint fluid. Transcellular fluid makes up less than 1 percent of total body fluid (Chen & Khalili, 2023).
Body Fluid Balance
Maintenance of fluid balance is necessary for optimal health. Nurses must recognize fluid imbalances because health problems can result from a patient having too much or too little fluid. Certain physiological conditions, such as renal disease and cardiac disease, can cause an excess accumulation of fluid, known as hypervolemia. On the other hand, decreased oral intake or excessive fluid loss can cause a negative fluid balance, known as hypovolemia. An optimal fluid balance for cellular processes is a net even, or euvolemic, fluid balance (Simpson & McIntosh, 2021).
In addition to problems related to total body fluid balance, fluid can be in the wrong compartment. For example, the patient can have an excess of extracellular fluid. A primary sign of excess extracellular fluid is edema, or swelling, caused by the accumulation of fluid in the body’s tissues. Extracellular fluid can also shift into the intracellular space, causing an excess of intracellular fluid. This process is seen in conditions such as cerebral edema. Having excess fluid in brain cells causes impaired neurological function. Fluid distribution in the body is largely determined by the solute concentration in both intracellular and extracellular fluid. Having a higher solute concentration in one compartment draws fluid into that compartment to maintain an equal solute concentration in both compartments (Simpson & McIntosh, 2021).
Fluid Volume Deficit
Also referred to as hypovolemia or dehydration, fluid volume deficit is a medical condition in which fluid loss exceeds fluid intake. A fluid volume deficit can occur in any age group, but children under the age of two and older adults are at greater risk. Common causes of fluid volume deficit include vomiting, diarrhea, fever with excessive sweating, and inadequate oral intake. Nurses must recognize signs of dehydration to intervene early. Possible signs of dehydration in infants and young children include crying without tears, no wet diapers for three hours or more, irritability, sunken eyes, and a sunken fontanel. Mild cases of fluid volume deficit can be treated with oral rehydration. More severe cases require intravenous fluid administration.
Clinical Judgment Measurement Model
Take Action: Recommend Laboratory Analysis
The nurse is admitting a 9-month-old infant with a three-day history of vomiting and diarrhea. When completing the admission assessment, the nurse notes the infant’s eyes are sunken and anterior fontanelle (or fontanel) is depressed. Recognizing that the infant’s physical assessment is concerning for dehydration, the nurse analyzes other cues to see if additional diagnostic tests may be warranted. The nurse considers possible treatment options for dehydration and determines intravenous fluid may be needed. The nurse reviews the medical orders and notes that the infant is ordered a clear liquid diet, and no baseline laboratory values were requested. The nurse pages the on-call provider to discuss the patient’s clinical status. During the conversation, the nurse recommends sending a basic metabolic panel to monitor the patient’s hydration status and placing a peripheral IV.
Fluid Volume Overload
Also referred to as hypervolemia, fluid volume overload is a medical condition in which an excessive amount of fluid is retained in the intravascular fluid compartment. Certain medical conditions place patients at risk for developing fluid volume overload. These conditions include heart failure, kidney failure, cirrhosis, and pregnancy. Patients with fluid volume overload often present with pitting edema, ascites, and dyspnea and crackles in the lung fields. Treatment of fluid volume overload often involves restricting sodium and fluid intake. It may also include diuretic use to help remove excess fluid.
Cultural Context
Preference for Traditional Medicines
Heart failure is a common chronic condition that often improves with diet and lifestyle modifications such as sodium restriction and fluid restriction. When providing education about heart failure management, nurses should be cognizant of how cultural preferences influence the patient’s response to education about diet and lifestyle modification. Many ethnic groups in the United States may prefer traditional medicine practices and be more likely to adhere to diet and fluid recommendations if the practitioner takes into consideration their cultural preferences. For example, many people in the Hispanic/Latino community may use traditional remedies such as herbal teas or treatments derived from curanderismo (traditional folk healing). If a practitioner acknowledges and integrates these practices, such as recommending safe herbal teas that complement medical treatments, patients may be more receptive to following dietary and fluid intake guidelines. Similarly, Chinese patients may rely on traditional Chinese medicine (TCM), which includes practices such as acupuncture, tai chi, and the use of specific herbs and foods for their medicinal properties. Practitioners who understand and respect TCM can provide dietary recommendations that align with these practices, such as suggesting foods that balance yin and yang, thereby increasing patient adherence to medical advice. Nurses should be knowledgeable about the diet and traditional medicine beliefs of the patient population they serve. By doing so, their patients are more likely to be receptive to the education (Kulakaç et al., 2022).
Principles of Electrolytes and Balances in the Body
Electrolytes are different from other solutes because they have an electrical charge, either positive or negative, when dissolved in water. The electrical charge of electrolytes is important for multiple cellular processes, including initiation of muscle contractions, initiation of nerve signals, maintenance of acid-base homeostasis, and distribution of fluid across different compartments. There are multiple regulatory systems within the human body that maintain electrolytes within a narrow range so that they are able to fulfill their function in maintaining homeostasis.
Electrolyte Composition of Body Fluids
Body fluid composition is maintained in a normal physiological range by regulatory mechanisms that control water and solute concentrations in both the intracellular and extracellular spaces. There is a narrow range of normal electrolyte values that body fluid composition should stay within, and slight abnormalities can have serious consequences. For this reason, it is important for nurses to know normal electrolyte ranges, understand the cause of electrolyte imbalances, recognize the signs and symptoms of an imbalance, and identify appropriate treatments (Table 20.1).
| Electrolyte | Functions in the Body | Normal Adult Range |
|---|---|---|
| Bicarbonate | Maintains acid-base homeostasis | 22–29 mEq/L |
| Calcium | Necessary for muscle contractions, nerve impulses, blood clotting, and healthy bones and teeth | 8.6–10.2 mg/dL |
| Chloride | Helps maintain fluid balance and is an important component of stomach acid | 96–106 mEq/L |
| Magnesium | Necessary for muscle and cardiac contractions, bone strength, and muscle formation | 1.5–2.4 mEq/L |
| Phosphate | Essential for energy production, bone and teeth formation, and cell signaling | 3.4–4.5 mg/dL |
| Potassium | Helps maintain fluid balance, controls heart contractions, and regulates heart rhythm | 3.5–5.1 mEq/L |
| Sodium | Regulates fluid balance and necessary for nerve and muscle contractions | 135–145 mEq/L |
Life-Stage Context
Dehydration Risk in Children Under the Age of 2
Infants and young children under the age of 2 are at a higher risk of dehydration than other age groups. Children in this age group have immature immune systems and are more susceptible to infections, such as gastroenteritis, which can cause vomiting and diarrhea. Children under the age of 2 also have a higher metabolic rate, which results in more insensible fluid loss. Lastly, they are unable to communicate their needs to hydrate themselves (Vega & Avva, 2024).
Sodium
Sodium (Na+) is the most abundant electrolyte in the extracellular fluid compartment. The concentration of sodium plays an important role in maintaining an appropriate fluid balance in the intravascular and interstitial spaces. Sodium ions play a pivotal role in regulating extracellular fluid volume and are essential for generating the action potential, which is the voltage difference across a cell membrane. The action potential is determined by the balance of ions between the intracellular and extracellular fluid. Action potentials are vital for the proper functioning of neurons, pacemaker cells in the heart, muscles, and nerves.
The normal serum sodium range is 135 to 145 mEq/L. A common phrase in fluid and electrolyte physiology is “water follows sodium.” A high serum sodium levels pulls fluid out of the intracellular space and a low serum sodium level moves fluid into the intracellular space, causing cells to swell. The brain cells are particularly sensitive to these fluid shifts in response to changes in serum sodium levels. Signs of hypernatremia, or an elevated serum sodium level, include mental confusion, irritability, seizures, severe thirst, and dry mucous membranes. Signs of hyponatremia, or a low serum sodium level include headache, confusion, nausea, seizures, and coma (Allen & Sharma, 2023; Barker & VonColln-Appling, 2023).
Patient Conversations
Resistance to Diet Modifications
Scenario: Julian is a 19-year-old with type 1 diabetes, hypertension, and kidney disease. He receives health care at a family practice clinic that provides services to the uninsured. Over the last six months, his blood pressure has increased; however, he is resistant to taking new medications or making any diet or lifestyle changes. He came to the clinic today to meet with the nurse case manager for the diabetes team.
Nurse: Hi, Julian. My name is Rebecca. I’m a nurse who helps patients who have diabetes.
Patient: Hi, Rebecca. It’s nice to meet you. I’m really stressed out because I lost my insurance and it’s hard for me to buy my medications.
Nurse: That sounds really stressful. We have a prescription assistance program. Often, we can provide you with samples of the medications that you need until we can work out a permanent solution. In the meantime, I’d like to talk about other things you can do to help manage your condition, such as diet and exercise modification.
Patient: What do you mean? I’m a type 1 diabetic. I need insulin! Why are you bothering to talk to me about stupid stuff like diet?
Nurse: I understand that you need insulin, and I’ll make sure you leave the clinic today with the medicine you need. However, with the kidney disease and high blood pressure along with the diabetes, lifestyle modifications are oftentimes needed in addition to medications. Has anyone talked to you about the effect of sodium on blood pressure and kidney disease?
Patient: No. And I don’t see why it matters. Having a chronic illness sucks. It’s not my fault I’m a diabetic.
Nurse: Of course, it’s not your fault. I’m not judging you or trying to make you feel bad. I just want to make sure you understand what’s going on inside your body so that you can make the best decisions for yourself.
Patient: Hmmm, okay.
Nurse: High blood sugar and high blood pressure both negatively impact your kidneys. When you add a high-salt diet on top of that, it can make the kidney damage worse. You’ve just started showing signs of kidney disease and I want to help you protect your kidneys to minimize potential harm to your body. Does that make sense?
Patient: I guess so.
Nurse: Okay, let’s talk about some things you can do at home. First of all, limiting your salt intake is important. Salt draws fluid into your bloodstream and makes your blood pressure higher. If you cut back on processed foods that contain a lot of salt—such as canned soups, bacon, chips, frozen pizzas, Ramen noodles, and things like that—you might feel better and see improvements in your blood pressure. Also, it would be great to exercise three times per week. You don’t need to join a fancy gym or anything, you can just go for a thirty-minute brisk walk or maybe ride your bike. How does trying those things sound to you?
Patient: I don’t really see why exercising and decreasing my salt intake is important for a diabetic, but I could try.
Nurse: Trust me, those small lifestyle changes will help. I’d like to see you back in the clinic in two weeks for another blood pressure check and to track your progress with exercise and diet. Now I’m going to talk to your provider to make sure I have the most updated information for your prescription medications. How do you feel about the plan?
Patient: Okay. I was scared about not being able to afford my insulin. If you can help with that I’ll try to limit my salt intake and think about the exercise.
Nurse: Great. I know managing diabetes is stressful. I’ll make sure you have the insulin sorted out before you leave today, and I’ll see you back in my office in two weeks. Deal?
Patient: Yeah, thanks for your help.
Potassium
Potassium (K+) is the most abundant electrolyte within the intracellular fluid. Serum potassium levels are maintained inside the cell via active transport using the sodium–potassium pump. Serum potassium levels are regulated by the hormone aldosterone in the kidneys. Normal potassium levels are needed for cardiac function, neural function, and muscle contractility (Sur & Mohiuddin, 2022).
The normal serum potassium range is 3.5 to 5.1 mEq/L. An increased serum potassium level greater than 5.1 mEq/L is referred to as hyperkalemia. Signs of hyperkalemia, or an elevated potassium level, include irritability, gastrointestinal cramping, diarrhea, and peaked T waves on an electrocardiogram. If hyperkalemia worsens, the patient may progress to cardiac dysrhythmias or cardiac arrest (Barker & VonColln-Appling, 2023). Common causes of hyperkalemia are kidney failure, metabolic acidosis, use of potassium-sparing diuretics, and/or administration of potassium supplements. Mild hyperkalemia often involves adjustments to medications and decreasing potassium oral intake. For more severe cases, sodium polystyrene (Kayexalate) is often administered either orally or rectally. Kayexalate binds potassium so it can be excreted via the gastrointestinal tract. For severe symptomatic hyperkalemia, temporary hemodialysis may be used (Sur & Mohiuddin, 2022).
Hypokalemia refers to a decreased serum potassium level or a level less than 3.5 mEq/L. Potential causes of hypokalemia include excessive vomiting, diarrhea, use of potassium-wasting diuretics, and a low potassium diet. Signs of hypokalemia, or having a low serum potassium level, include muscle weakness, lethargy, and a thready pulse (Cleveland Clinic, 2022). Treatment of hypokalemia revolves around replacing the missing potassium. Mild hypokalemia is often treated with oral potassium supplements. More severe cases may require intravenous potassium administration. Because potassium is excreted by the kidneys, it is imperative to confirm that the patient has adequate urine output prior to giving a potassium replacement (Barker & VonColln-Appling, 2023).
Clinical Safety and Procedures (QSEN)
QSEN Competency: What To Do If a Patient Requires Intravenous (IV) Potassium Supplements
Disclaimer: Always follow the agency’s policies.
| Steps | Description/Rationale |
|---|---|
| Assess the patient’s fluid status and renal function. | IV potassium should only be given to patients who are well-hydrated and who have normal renal function. Patients who are dehydrated or have decreased renal clearance of potassium could develop life-threatening hyperkalemia during IV potassium administration. |
| Assess and document the patient’s IV access. | Potassium salts are highly caustic to veins. Ideally potassium should be administered via a central line. If it is not infused via a central line, it should be infused via a large, high-flow vein. |
| Place the patient on a bedside cardiac monitor and record a set of baseline vital signs prior to administration. | Intravenous potassium administration can cause cardiac arrhythmias. Continuously monitor the patient to prevent complications. |
| Verify the dose of IV potassium ordered with a second nurse. | An accidental overdose of potassium can be life-threatening. Always double-check the dose of potassium ordered with a second RN. Both RNs should document the administration on the medication administration record (MAR). |
| Start the infusion of potassium slowly, at a maximum rate of 20 mEq/hr. | Rapid administration of potassium can cause cardiac arrest. |
| After the infusion is complete, send a follow-up serum potassium level. Make sure the blood is not drawn from the same line used to infuse the potassium. | Following up on the patient’s potassium level is important to ensure the patient’s safety. High potassium levels are associated with cardiac arrhythmias and cardiac arrest. The post-infusion level must be drawn from a different line because potassium can stick to IV tubing and could alter the results of the follow-up potassium level. |
Calcium
Calcium (Ca2+) is more common in the extracellular fluid than in the intracellular fluid. However, most of the total body calcium is stored in the bones. Calcium is important for bone and teeth structure, nerve transmission, and muscle contraction. Serum calcium levels are regulated by parathyroid hormone, dietary intake, and physical activity. Physical activity promotes the incorporation of calcium into bones, contributing to bone density, whereas extended periods of immobility may lead to the release of calcium from bones into the bloodstream. Dietary sources of calcium include dairy products, green leafy vegetables, and whole grains.
The normal serum calcium range is 8.6 to 10.2 mg/dL (Barker & VonColln-Appling, 2023; Drake & Gupta, 2024). Having an elevated serum calcium level is known as hypercalcemia. Possible causes of hypercalcemia are prolonged immobilization that causes calcium to leach out of bones into the serum. It can also be caused by certain types of cancer, such as parathyroid tumors, that increase the secretion of parathyroid hormone (PTH). Hypercalcemia primarily affects the gastrointestinal and musculoskeletal systems. Symptoms of hypercalcemia include nausea, vomiting, constipation, and skeletal muscle weakness. Mild hypercalcemia may be treated with dietary modifications such as decreasing intake of calcium and increasing intake of phosphorus, which binds to calcium and makes it inactive. Patients with limited mobility and hypercalcemia may benefit from weight-bearing exercise to stop the leaching of calcium from the bones into the serum. More severe or chronic hypercalcemia may require hemodialysis or surgical removal of the parathyroid gland (Barker & VonColln-Appling, 2023).
Having a low serum calcium level, known as hypocalcemia, can be caused by hypoparathyroidism, vitamin D deficiency, and or renal disease. Without adequate levels of PTH, not enough calcium is reabsorbed by the kidneys. Vitamin D deficiency causes hypocalcemia because vitamin D is necessary for absorption of dietary calcium from the gastrointestinal tract. In patients with renal disease, the kidneys may excrete too much calcium, resulting in hypocalcemia. The primary symptom of hypocalcemia is paresthesia, or numbness and tingling sensation. Hypocalcemia paresthesia is felt in the lips, tongue, hands, and feet. Patients with hypocalcemia may also experience muscle cramps and tetany, or involuntary muscle contractions. Chvostek’s sign, an involuntary twitching of the facial muscle when the facial nerve is tapped, is a classic sign of hypocalcemia (Omerovic & M Das, 2023). Trousseau’s sign, or the involuntary spasm of the hand when a blood pressure cuff is inflated above the diastolic blood pressure for three minutes, is also a classic sign of hypocalcemia (Patel & Hu, 2023). Most cases of hypocalcemia can be treated with dietary modifications. Patients are encouraged to increase calcium and vitamin D intake and decrease phosphorus intake. Severe cases of hypocalcemia may be treated with intravenous calcium replacements (Drake & Gupta, 2024).
Link to Learning
This video about Chvostek’s and Trousseau’s signs helps you gain an understanding of how to elicit these signs.
Magnesium
Magnesium (Mg2+) is an important electrolyte for cardiac, nerve, and muscle function. Approximately 50 percent of the body’s magnesium is stored in the bones. The remaining magnesium is primarily stored in the intracellular fluid. The normal serum magnesium level is 1.5 to 2.4 mEq/L (Barker & VonColln-Appling, 2023). Maintaining serum magnesium levels is necessary for normal cardiac function, nerve stimulation, muscle contractions, and immune health.
Having an elevated serum magnesium level is known as hypermagnesemia. Many cases of hypermagnesemia are caused by medication misuse, such as taking excessive magnesium supplements or using magnesium-containing laxative or antacids. It can also be caused by renal failure. Patients presenting with hypermagnesemia may have bradycardia, lethargy, hyporeflexia, muscle weakness, and tremors. Severe cases may lead to cardiac arrest. Mild cases of hypermagnesemia can be treated by increasing fluid intake and limiting oral intake of magnesium. In severe cases, dialysis is needed to lower magnesium levels (Barker & VonColln-Appling, 2023).
Having a low serum magnesium level is referred to as hypomagnesemia. The most common cause of hypomagnesemia is inadequate dietary intake of magnesium. Patients with alcohol use disorder are at high risk for hypomagnesemia because they tend to have a poor diet and have impaired nutrient absorption from the gastrointestinal tract. It can also be secondary to loop diuretic use, which causes the excretion of magnesium in the urine. Common signs and symptoms of hypomagnesaemia include vomiting, lethargy, weakness, and leg cramps. Severe cases can lead to cardiac dysrhythmia, or an abnormal heart rhythm or heart rate. Mild cases of hypomagnesemia can be treated with increasing oral intake of magnesium. More severe cases require IV replacement of magnesium (Allen & Sharma, 2023).
Chloride
Chloride (Cl–) is the second-most common electrolyte in the extracellular fluid. It plays a key role in regulation of body fluids, electrolyte balance, and acid-base balance. Chloride is almost always bound to other electrolytes, such as sodium, which makes it unusual for a patient to have an isolated chloride abnormality. If the serum chloride level is out of range, most often another electrolyte, such as sodium, is also out of range. The presence of a chloride deviation is most often associated with an underlying acid-base imbalance. The normal serum chloride range is 96 to 106 mEq/L (Wu & Yan, 2023).
Having an elevated serum chloride level, known as hyperchloremia, can occur when water loss exceeds sodium and chloride losses. Because chloride is an anion that is commonly used in chemical reactions, hyperchloremia is also seen in patients with acid-base imbalances. Symptoms of hyperchloremia are linked to the underlying cause of the electrolyte imbalance. The treatment is to treat the underlying cause (Song et al., 2022).
Having a low serum chloride level, known as hypochloremia, is usually caused by nasogastric suctioning, vomiting, or the excessive use of loop diuretics. Loop diuretics excrete both potassium and chloride and gastric contents contain hydrochloric acid (HCL). Therefore, losing large amounts of gastric contents causes hypochloremia. There have also been cases of hypochloremia related to malnutrition (Signorelli et al., 2020). There are no specific symptoms of hypochloremia. The treatment is to fix the underlying cause of the electrolyte disorder (Signorelli et al., 2020).
Bicarbonate
Bicarbonate (HCO3–) is one of the major anions, or negatively charged electrolytes, in the extracellular fluid. Bicarbonate is a base (a molecule that can donate a hydroxide ion (OH–) in chemical reactions). Its main function is to act as a buffer and uphold homeostasis in pH, which refers to the concentration of hydrogen ions in a given solution. Bicarbonate is generated spontaneously from carbon dioxide and water, or via the catalytic activity of the enzyme carbonic anhydrase. The kidneys help maintain optimal bicarbonate levels by either excreting or reabsorbing bicarbonate. The normal serum bicarbonate range is 22 to 29 mEq/L (Moustafa et al., 2022).
Phosphate
Phosphate (PO43–) is an important electrolyte in the human body that is needed for energy production, cell membrane formation, and deoxyribonucleic acid (DNA). Bones contain about 85 percent of the body’s phosphate. The remaining 15 percent is found in the intracellular fluid compartment. The body obtains phosphate from dietary intake. Foods high in phosphate include dairy products, egg yolk, and chocolate. The kidneys regulate phosphate levels by excreting phosphate in the urine.
The normal serum phosphate range is 3.4 to 4.5 mg/dL (Lewis, 2023; Sharma et al., 2024). Having an elevated serum phosphorus level is known as hyperphosphatemia. Having elevated phosphate levels does not cause any symptoms. However, because phosphate levels and calcium levels are inversely related, patients with hyperphosphatemia may develop symptomatic hypocalcemia. Mild hyperphosphatemia can be treated with decreasing oral intake of phosphorus. Patients may also be prescribed phosphorus-binding agents that bind phosphate and help with excretion. As a last resort, hemodialysis can be used to correct hyperphosphatemia.
Having a low serum phosphate level is referred to as hypophosphatemia. Chronic hypophosphatemia can be caused by parathyroid gland tumors, vitamin D deficiency, prolonged use of phosphate binders, and malnutrition. Acute hypophosphatemia can be the result of burns, diuretic use, and diabetic ketoacidosis. Mild hypophosphatemia is usually asymptomatic. However, severe cases can cause muscle weakness, seizures, and even death. The primary treatment of hypophosphatemia is to treat the underlying cause. If needed, phosphorus supplements can be given both orally and intravenously (Sharma et al., 2024).
Link to Learning
West Coast University provides a concise review of the principles of fluid and electrolyte balances in the human body.
Regulation of Fluid and Electrolyte Balance
The fluid compartments of the body are interdependent. Homoeostasis of the different compartments depends on their interactions with each other. Fluid and electrolytes can move between the compartments by passive or active transport. Active transport requires energy expenditure and passive transport does not. The movement of solutes through a transmembranous protein (a gatekeeper that controls what gets into and out of a cell) using energy expenditure is called active transport. The movement of solvents and solutes across cell membranes based on the concentration gradients, or the process of substances moving from an area of high concentration to an area of low concentration, is known as passive transport. Passive transport is subdivided into two categories: osmosis and diffusion. Through the principles of active and passive transport, the human body maintains fluids, electrolytes, and other solutes in optimal concentrations for chemical reactions and cellular processes to occur (Chen & Lui, 2023).
Osmosis
The passage of a solvent, or a liquid, through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration is called osmosis. The solvent passes through the membrane from the solution with the higher concentration of solutes to the side with the lower concentration until the two solutions are equal in concentration. The rate of osmosis largely depends on the osmotic pressure, which is determined by the concentration of solutes. The higher the osmotic pressure, the faster the fluid moves. The rate of osmosis is also dependent on the permeability of the membrane and the electric potential across the cell membrane (Lopez & Hall, 2023).
Diffusion
The passage of solutes (e.g., electrolytes, proteins, and metabolites) through a semipermeable membrane that separates solutions with two different solute concentrations is called diffusion (Figure 20.3). It is very similar to osmosis in that the diffusion rate is driven by the concentration of solutes. However, it differs from osmosis in that diffusion is the passive transport of solutes, instead of solvents (liquids). Solutes move via diffusion from the solution with the higher concentration to the solution with the lower concentration until the two solutions have equal concentrations (Lopez & Hall, 2023).
Active Transport
The phospholipid layer and the electrochemical gradient of cell membranes prevent the movements of some substances across the membrane. Active transport, or the movement of solutes through a transmembrane protein using energy expenditure, is the mechanism that cells use to overcome the impediment posed by the cell membrane, or to move solutes against a concentration gradient. By active transport, cells accumulate needed resources inside the cells. Examples of solutes moved via active transport include electrolytes, sugar, and amino acids (Chen & Lui, 2023). An example of active transport is the sodium–potassium pump. The sodium–potassium pump is located on the outer plasma membrane of cells and maintains a higher concentration of sodium extracellularly and a high concentration of potassium intracellularly. Without the sodium–potassium pump, the concentrations of sodium and potassium would equalize across the cell membrane through the process of diffusion (Pirahanchi & Aeddula, 2023).
Capillary Filtration
The process of delivering oxygen and other nutrients and removing cellular waste through the capillary system is called capillary filtration. Capillaries are the smallest blood vessels in the circulatory system. They connect arteries, which deliver oxygen and nutrients to target tissue, to veins, which transport waste products back to the heart and lungs. Capillaries form a bed, or network, of multiple capillaries. One end of the capillary bed is the arterial side, and the other end is the venous side. The pressure on the arterial side is greater, which pushes nutrients and oxygen from the arterial capillary bed into the surrounding tissue. The pressure on the venous side of the capillary bed is lower, which causes waste products to be reabsorbed from the tissue into the capillary bed (Pias, 2021).
Link to Learning
This video reviews how the capillary bed helps deliver oxygen and remove waste products in the body.
Body Systems and Organs
In addition to active and passive transport, various body systems are responsible for regulating fluid and electrolytes to maintain body homeostasis. Hormones also play an integral role in stimulating various organ systems to either excrete or reabsorb electrolytes. Total body fluid is regulated by the renal system. In response to pressure in the renal tubules, the kidneys suppress or excrete antidiuretic hormone. When total body fluid is down, or the patient is hypovolemic, more antidiuretic hormone (ADH) is released, which causes the kidneys to reabsorb more water. When fluid volume in the renal tubules is high, the kidneys suppress ADH, resulting in hypervolemia and more dilute urine. Table 20.2 explains how different body systems regulate serum electrolyte levels.
| Electrolyte | Primary Fluid Compartment | Body System and Hormones that Regulate Serum Levels | Signs and Symptoms of Excess | Signs and Symptoms of Deficit |
|---|---|---|---|---|
| Sodium (Na+) | Extracellular | Renal system Aldosterone |
Confusion, irritability, seizures, thirst, dry mucous membranes | Headache, confusion, seizures, coma |
| Potassium (K+) | Intracellular | Renal system Aldosterone, insulin, epinephrine, and glucocorticoids |
Irritability, gastrointestinal cramping, peaked T waves on ECG, cardiac arrest | Muscle weakness, lethargy, thready pulse, flattened or inverted T waves on ECG, U wave on ECG, ST segment depression on ECG |
| Calcium (Ca2+) | Extracellular | Skeletal system Parathyroid hormone, vitamin D, and calcitonin |
Nausea, vomiting, constipation, skeletal muscle weakness | Muscle tingling, muscle cramps, tetany |
| Magnesium (Mg2+) | Intracellular | Renal system Parathyroid hormone and vitamin D |
Bradycardia, lethargy, hyporeflexia, muscle weakness | Nausea, vomiting, tremors, tetany, dysrhythmias |
| Chloride (Cl–) | Extracellular | Renal system Aldosterone |
Dependent upon the primary electrolyte that is causing the chloride excess | Dependent upon the primary electrolyte that is causing the chloride deficiency |
| Bicarbonate (HCO3–) | Extracellular | Renal System Aldosterone |
Confusion, numbness in the face, hands, or feet, nausea, vomiting | Increased heart rate, headache, deep breathing |
| Phosphate (PO43–) | Intracellular | Renal system and gastrointestinal system Parathyroid hormone and vitamin D |
Bone pain, loss of appetite, weakness, irritability | Muscle cramps, bone and joint pain, rash, itchy skin |