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Fluid and Electrolytes, Acid-Base Balance

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By Marianne Belleza, R.N.

Fluid and electrolyte balance is a dynamic process that is crucial for life and homeostasis.

  • Fluid occupies almost 60% of the weight of an adult.
  • Body fluid is located in two fluid compartments: the intracellular space and the extracellular space.
  • Electrolytes in body fluids are active chemicals or cations that carry positive charges and anions that carry negative charges.
  • The major cations in the body fluid are sodium, potassium, calcium, magnesium, and hydrogen ions.
  • The major anions are chloride, bicarbonate, sulfate, and proteinate ions.

Table of Contents


Homeostasis is the dynamic process in which the body maintains balance by constantly adjusting to internal and external stimuli.

Negative and Positive Feedback

  • Feedback is the relaying of information about a given condition to the appropriate organ or system.
  • Negative feedback. Negative feedback occurs when the body reverses an original stimulus for the body to regain physiologic balance.
  • Positive feedback. Positive feedback enhances or intensifies the original stimulus.
  • Examples. Blood pressure control and maintenance of normal body temperature are examples of negative feedback while blood clotting after an injury and a woman in labor are examples of positive feedback.

Systems Involved in Feedback

The major systems involved in feedback are the nervous and endocrine systems.

  • Nervous system. The nervous system regulates homeostasis by sensing system deviations and sending nerve impulses to appropriate organs.
  • Endocrine system. The endocrine system uses the release and action of hormones to maintain homeostasis.

Body Fluids

Fluids make up a large portion of the body, which is approximately 50%-60% of the total body weight.

Location of Fluids

  • Main compartments. Body fluids are divided into two main compartments: the intracellular fluid and the extracellular fluid compartments.
  • Intracellular fluid. Intracellular fluid functions as a stabilizing agent for the parts of the cell, helps maintain cell shape and assists with transport of nutrients across the cell membrane, in and out of the cell.
  • Extracellular fluid. Extracellular fluid mostly appears as interstitial tissue fluid and intravascular fluid.

Fluid Regulation Mechanisms

  • The thirst center. The thirst center in the hypothalamus stimulates or inhibits the desire for a person to drink.
  • Antidiuretic hormone. ADH regulates the amount of water the kidney tubules absorb and is released in response to low blood volume or in response to an increase in the concentration of sodium and other solutes in the intravascular fluids.
  • The RAA system. The RAA system controls fluid volume, in which when the blood volume decreases, blood flow to the renal juxtaglomerular apparatus is reduced, thereby activating the RAA system.
  • Atrial natriuretic peptide. The heart also plays a role in correcting overload imbalances, by releasing ANP from the right atrium.

Normal Intake and Output

  • Daily intake. An adult human at rest takes appropriately 2,500 ml of fluid daily.
  • Levels of intake. Approximate levels of intake include fluids 1, 200 ml, foods 1, 000 ml, and metabolic products 30 ml.
  • Daily output. Daily output should be approximately equal in intake.
  • Normal output. Normal output occurs as urine, breathing, perspiration, feces, and in minimal amounts of vaginal secretions.

Overhydration and Edema

  • Overhydration. Overhydration is an excess of water in the body.
  • Edema. Edema is the excess accumulation of fluid in interstitial tissue spaces, also called third-space fluid.
  • Cause of edema. Edema is caused by a disruption of the filtration and osmotic forces of the body’s circulating fluids.
  • Treatment of edema. Diuretics are commonly given for systemic edema.


  • Dehydration. Dehydration is a deficiency of body water or excessive loss of water.
  • External causes. External causes of dehydration include prolonged sun exposure and excessive exercise, as well as diarrhea, vomiting, and burns.
  • Treatment of dehydration. Supplemental fluids and electrolytes are often administered.


An electrolyte is a substance that will disassociate into ions when dissolved in water.

  • Origins. Electrolytes are found in the form of inorganic salts, acids, and bases.
  • Active chemicals. Electrolyte concentrations are measured according to their chemical activity and expressed as milliequivalents.
  • Ions. Each chemical element has an electrical charge, either positive or negative.
  • Intracellular electrolytes. Important intracellular electrolytes are potassium, magnesium, sulfate, and phosphate, and the most dominant cation is potassium while the most dominant anion is phosphate.
  • Extracellular electrolytes. Important extracellular electrolytes include sodium, chlorine, calcium, and bicarbonate, and the most essential cation is sodium while chlorine is the most important anion.

Fluid and Electrolyte Transport

Total electrolyte concentration affects the body’s fluid balance.

  • The body cells. Nutrients and oxygen should enter body cells while waste products should exit the body.
  • The cell membrane. The cell membrane separates the intracellular environment from the extracellular environment.
  • Permeability. The ability of a membrane to allow molecules to pass through is known as permeability.

Permeability of Membranes

  • Freely permeable membranes. These membranes allow almost any food or waste substance to pass through.
  • Selectively permeable. The cell membrane is selectively permeable, meaning that each cell’s membrane allows only certain specific substances to pass through.

Passive Transport

  • Passive transport. Passive transport mechanisms include diffusion, osmosis, and filtration.
  • Diffusion. Diffusion, or the process of “being widely spread”, is the random movement of molecules from an area of higher concentration to an area of lower concentration.
  • Osmosis. Osmosis is the diffusion of a pure solvent, such as water, across a semipermeable membrane in response to a concentration gradient in situations where the molecules of a higher concentration are non-diffusible.
  • Filtration. Filtration is the transport of water and dissolved materials concentration already exists in the cell.

Active Transport

  • Mechanisms. Active transport mechanisms require specific enzymes and energy expenditure in the form of adenosine triphosphate (ATP).
  • Processes. Active transport processes can move solutes “uphill”, against the normal rules of concentration and pressure.

Fluid and Electrolyte Balance

Fluid and electrolyte balance is vital for the proper functioning of all body systems.

  • Osmolarity. This is the property of particles in a solution to dissociate into ions.
  • Electroneutrality. This is the balance of positive and negative charges.

Acid-Base Balance

Acid-base balance is another important aspect of homeostasis.

Acid, Bases, and Salts

  • Acid. An acid is one type of compound that contains the hydrogen ion.
  • Base. A base or alkali is a compound that contains the hydroxyl ion.
  • Salt. Salt is a combination of a base and an acid and is created when the positive ions of a base replace the positive hydrogen ions of an acid.
  • Important salts. The body contains several important salts like sodium chloride, potassium chloride, calcium chloride, calcium carbonate, calcium phosphate, and sodium phosphate.

Potential of Hydrogen

  • pH. The symbol of pH refers to the potential or power of hydrogen ion concentration within the solution.
  • Low pH. If the pH number is lower than 7, the solution is an acid.
  • High pH. If the pH is greater than 7, a solution is basic or alkaline.
  • Neutral pH. If the pH is 7, then the solution is neutral.
  • Changes. A change in the pH of a solution by one pH unit means a tenfold change in hydrogen concentration.


  • Buffers. A buffer is a chemical system set up to resist changes, particularly in hydrogen ion levels.
  • Bicarbonate buffer system. Sodium bicarbonate and carbonic acid are the body’s major chemical buffers.
  • Carbon dioxide. The major compound controlled by the lungs is CO2, and the respiratory system can very rapidly compensate for too much acid and too little acid by increasing or decreasing the respiratory rate, thereby altering the level of CO2.
  • Bicarbonate. Bicarbonate ions are basic components in the body, and the kidneys are key in regulating the amount of bicarbonate in the body.
  • Measurement of arterial blood gas. The pH level and amounts of specific gases in the blood indicate if there is more acid or base and their associated values.
  • Respiratory acidosis. Respiratory acidosis occurs when breathing is inadequate and PaCO2 builds up.
  • Respiratory alkalosis. Respiratory alkalosis occurs as a result of hyperventilation or excess aspirin intake.
  • Metabolic acidosis. In metabolic acidosis, metabolism is impaired, causing a decrease in bicarbonates and a buildup of lactic acid.
  • Metabolic alkalosis. Metabolic alkalosis occurs when bicarbonate ion concentration increases, causing an elevation in blood pH.


There are different fluid volume disturbances that may affect an individual.

  • Fluid volume deficit or hypovolemia occurs when the loss of ECF volume exceeds the intake of fluid.
  • Fluid volume excess or hypervolemia refers to an isotonic volume expansion of the ECF caused by the abnormal retention of water and sodium in approximately the same proportions in which they normally exist in the ECF.

Disturbances in electrolyte balances are common in clinical practice and must be corrected.

  • Hyponatremia refers to a serum sodium level that is less than 135 mEq/L
  • Hypernatremia is a serum sodium level higher than 145 mEq/L.
  • Hypokalemia usually indicates a deficit in total potassium stores.
  • Hyperkalemia refers to a potassium level greater than 5.0 mEq/L.
  • Hypocalcemia are serum levels below 8.6 mg/dl.
  • Hypercalcemia is calcium level greater than 10.2 mg/dl.
  • Hypomagnesemia refers to a below-normal serum magnesium concentration.
  • Hypermagnesemia are serum levels over 2.3 mg/dl.
  • Hypophosphatemia is indicated by a value below 2.5 mg/dl.
  • Hyperphosphatemia is a serum phosphorus level that exceeds 4.5 mg/dl in adults.


Nurses need an understanding of the pathophysiology of fluid and electrolyte balance to anticipate, identify, and respond to possible imbalances.

  • Concentrations. Electrolyte concentrations vary from those in the ICF to those in the ECF.
  • Sodium. Sodium ions outnumber any other cations in the ECF; therefore it is essential in the fluid regulation of the body.
  • Potassium. The ECF has a low concentration of potassium and can tolerate only small changes in its concentrations.
  • Maintenance. The body expends a great deal of energy in maintaining the sodium and potassium concentrations through cell membrane pumps that exchange sodium and potassium ions.
  • Osmosis. When two different solutions are separated by a membrane that is impermeable to the dissolved substances, fluid shifts from the region of low solute concentration to the high solute concentration until the solutions are of equal concentration.
  • Diffusion. Diffusion is the natural tendency of a substance to move from an area of higher concentration to an area of lower concentration.


Causes of fluid and electrolyte imbalances are discussed below in general.

  • Fluid retention. Retention of sodium is associated with fluid retention.
  • Loss of sodium. Excessive loss of sodium is associated with decreased volume of body fluid.
  • Trauma. Trauma causes release of intracellular potassium which is extremely dangerous.
  • Loss of body fluids. FVD results from loss of body fluids and occurs more rapidly when coupled with decreased fluid intake.
  • Fluid overload. Fluid volume excess may be related to a simple fluid overload or diminished function of the homeostatic mechanisms responsible for regulating fluid balance.
  • Low or high electrolyte intake. Diets low or excessive in electrolytes could also cause electrolyte imbalances.
  • Medications. There are certain medications that could lead to electrolyte imbalances when taken against the physician’s orders.

Clinical Manifestations

Signs and symptoms that occur in fluid and electrolyte imbalances are discussed below.

  • Fluid volume deficit. Clinical signs and symptoms include acute weight loss, decreased skin turgor, oliguria, concentrated urine, orthostatic hypotension, a weak, rapid heart rate, flattened neck veins, increased temperature, thirst, decreased or delayed capillary refill, cool, clammy skin, muscle weakness, and cramps.
  • Fluid volume excess. Clinical manifestations of FVE include edema, distended neck veins, and crackles.
  • Hyponatremia. Signs and symptoms include anorexia, nausea and vomiting, headache, lethargy, dizziness, confusion, muscle cramps and weakness, muscular twitching, seizures, dry skin, and edema.
  • Hypernatremia. The signs and symptoms are thirsts, elevated body temperature, hallucinations, lethargy, restlessness, pulmonary edema, twitching, increased BP, and pulse.
  • Hypokalemia. Clinical manifestations are fatigue, anorexia, muscle weakness, polyuria, decreased bowel motility, paresthesia, ileus, abdominal distention, and hypoactive reflexes
  • Hyperkalemia. Signs and symptoms include muscle weakness, tachycardia, paresthesia, dysrhythmias, intestinal colic, cramps, abdominal distention, and anxiety.
  • Hypocalcemia. The signs and symptoms are numbness, tingling of fingers, toes, and circumoral region, positive Trousseau’s sign and Chvostek’s sign, seizures, hyperactive deep tendon reflexes, irritability, and bronchospasm.
  • Hypercalcemia. The signs and symptoms include muscle weakness, constipation, anorexia, nausea and vomiting, dehydration, hypoactive deep tendon reflexes lethargy, calcium stones, flank pain, pathologic fractures, and deep bone pain.
  • Hypomagnesemia. Clinical manifestations include neuromuscular irritability, positive Trousseau’s and Chvostek’s sign, insomnia, mood changes, anorexia, vomiting, and increased deep tendon reflexes.
  • Hypermagnesemia. Signs and symptoms are flushing, hypotension, muscle weakness, drowsiness, hypoactive reflexes, depressed respirations, and diaphoresis.
  • Hypophosphatemia. Signs and symptoms include paresthesias, muscle weakness, bone pain and tenderness, chest pain, confusion, seizures, tissue hypoxia, and nystagmus.
  • Hyperphosphatemia. Clinical manifestations are tetany, tachycardia, anorexia, nausea and vomiting, muscle weakness, and hyperactive reflexes.


Fluid and electrolyte imbalances could result in complications if not treated promptly.

  • Dehydration. Fluid volume deficit could result in dehydration of the body tissues.
  • Cardiac overload. Fluid volume excess could result in cardiac overload if left untreated.
  • SIADH. Water is retained abnormally in SIADH.
  • Cardiac arrest. Too much potassium administered could lead to cardiac arrest.

Assessment and Diagnostic Findings

The following are laboratory studies useful in diagnosing fluid and electrolyte imbalances:

  • BUN. BUN may be decreased in FVE due to plasma dilution.
  • Hematocrit. Hematocrit levels in FVD are greater than normal because there is a decreased plasma volume.
  • Physical examination. A physical exam is necessary to observe the signs and symptoms of the imbalances.
  • Serum electrolyte levels. Measurement of electrolyte levels should be performed to check for the presence of an imbalance.
  • ECG. ECG changes can also contribute to the diagnosis of fluid and electrolyte imbalance.
  • ABG analysis. ABG analysis may reveal acid-base imbalances.

Medical Management

Treatment of fluid and volume imbalances needs accuracy to avoid consequences that can result in complications.

  • Isotonic electrolyte solutions. These solutions are used to treat the hypotensive patient with FVD because they expand plasma volume.
  • Accurate I&O. Accurate and frequent assessments of I&O should be performed when therapy should be slowed or increased to prevent volume deficit or overload.
  • Dialysis. Hemodialysis or peritoneal dialysis is performed to remove nitrogenous wastes and control potassium and acid-base balance, and remove sodium and fluid.
  • Nutritional therapy. Treatment of fluid and electrolyte imbalances should involve restrictions or enforcement of the concerned electrolyte.

Pharmacologic therapy

  • AVP receptor agonists. These are new pharmacologic agents that treat hyponatremia by stimulating free water excretion.
  • Diuretics. To decrease fluid volume in FVE, diuretics are administered.
  • IV calcium gluconate. If serum potassium levels are dangerously elevated, it may be necessary to administer IV calcium gluconate.
  • Calcitonin. Calcitonin can be used to lower the serum calcium level and is particularly useful for patients with heart disease or heart failure who cannot tolerate large sodium loads.

Nursing Management

Nurses may use effective teaching and communication skills to help prevent and treat various fluid and electrolyte disturbances.

Nursing Assessment

Close monitoring should be done for patients with fluid and electrolyte imbalances.

  • I&O. The nurse should monitor for fluid I&O at least every 8 hours, or even hourly.
  • Daily weight. Assess the patient’s weight daily to measure any gains or losses.
  • Vital signs. Vital signs should be closely monitored.
  • Physical exam. A physical exam is needed to reinforce other data about a fluid or electrolyte imbalance.


The following diagnoses are found in patients with fluid and electrolyte imbalances.

  • Excess fluid volume related to excess fluid intake and sodium intake.
  • Deficient fluid volume related to active fluid loss or failure of regulatory mechanisms.
  • Imbalanced nutrition: less than body requirements related to inability to ingest food or absorb nutrients.
  • Imbalanced nutrition: more than body requirements related to excessive intake.
  • Diarrhea related to adverse effects of medications or malabsorption.

Nursing Care Planning & Goals

Main Article: 10 Fluid And Electrolyte Imbalances Nursing Care Plans

Planning and goals for fluid and electrolyte imbalances include:

  • Maintenance of fluid volume at a functional level.
  • Display of normal laboratory values.
  • Demonstration appropriate changes in lifestyle and behaviors including eating patterns and food quantity/quality.
  • Reestablishment and maintenance of normal pattern and GI functioning.

Nursing Interventions

There are specific nursing interventions for fluid and electrolyte imbalances that can aid in alleviating the patient’s condition.

  • Monitor turgor. Skin and tongue turgor are indicators of the fluid status of the patient.
  • Urine concentration. Obtain urine sample of the patient to check for urine concentration.
  • Oral and parenteral fluids. Administer oral or parenteral fluids as indicated to correct the deficit.
  • Oral rehydration solutions. These solutions provide fluid, glucose, and electrolytes in concentrations that are easily absorbed.
  • Central nervous system changes. The nurse must be alert for central nervous system changes such as lethargy, seizures, confusion, and muscle twitching.
  • Diet. The nurse must encourage intake of electrolytes that are deficient or restrict intake if the electrolyte levels are excessive.


Evaluation of the care plan can check the effectiveness of the treatments. The interventions are deemed effective if the client has:

  • Maintained fluid volume at a functional level.
  • Displayed normal laboratory results.
  • Demonstrated appropriate changes in lifestyle and behaviors including eating patterns and food quantity/quality.
  • Reestablished and maintained normal pattern and GI functioning.

Discharge and Home Care Guidelines

After hospitalization, treatment and maintenance of the condition must continue at home.

  • Diet. A diet rich in all the nutrients and electrolytes that a person needs should be enforced.
  • Fluid intake. Fluid intake must take shape according to the recommendations of the physician.
  • Follow-up. A week after discharge, the patient must return for a follow-up checkup for evaluation of electrolyte and fluid status.
  • Medications. Compliance with prescribed medications should be strict to avoid recurrence of the condition.

Documentation Guidelines

Data should be documented for future medical and legal references. The nurse must document:

  • Individual findings, including factors affecting ability to manage body fluids and degree of deficit.
  • I&O, fluid balance, changes in weight, urine specific gravity, and vital signs.
  • Results of diagnostic testing and laboratory studies.
  • Plan of care.
  • Client’s responses to treatment, teaching, and actions performed.
  • Attainment or progress toward desired outcome.
  • Modifications to plan of care.

See Also

Related posts:

Marianne leads a double life, working as a staff nurse during the day and moonlighting as a writer for Nurseslabs at night. As an outpatient department nurse, she has honed her skills in delivering health education to her patients, making her a valuable resource and study guide writer for aspiring student nurses.

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