Fundamentals of Fluid and Electrolyte Balance

After completing this chapter, the reader will be able to:

1.Define terminology related to fluids and electrolytes.

2.Identify the three fluid compartments within the body.

3.State the functions of body fluids.

4.Differentiate between active and passive transport.

5.Describe homeostatic mechanisms.

6.Compare and contrast the movement of water in hypotonic, hypertonic, and isotonic solutions.

7.Compare and contrast fluid volume deficit and fluid volume excess.

8.List the six major body systems assessed for fluid balance disturbances.

9.State the seven major electrolytes within the body fluids.

10.Contrast each of the seven electrolytes and their major roles in body fluids.

11.Identify signs and symptoms of both deficits and excesses of sodium, potassium, calcium, magnesium, chloride, and phosphate.

12.Identify patients at risk for electrolyte imbalances.

13.State the normal pH range of body fluids.

14.Identify regulatory organs of acid-base balance.

15.Compare clinical manifestations of acidosis and alkalosis.

Glossary ⬆ ⬇

Acidosis An actual or relative increase in the acidity of blood due to an accumulation of acids or an excessive loss of bicarbonate; blood pH below normal (<7.35)
Active transport The process by which a cell membrane moves molecules against a concentration or electrochemical gradient. Metabolic work is required
Alkalosis An actual or relative increase in blood alkalinity due to an accumulation of alkalis or a reduction of acids in the blood; blood pH above normal (>7.45)
Anion Negatively charged electrolyte
Antidiuretic hormone (ADH) A hormone secreted from the pituitary mechanism that causes the kidney to conserve water; sometimes referred to as the “water-conserving hormone”
Atrial natriuretic peptide (ANP) ANP is a cardiac hormone that is released when atria are stretched by high blood volume
Body fluid Body water in which electrolytes are dissolved
Brain natriuretic peptide (BNP) BNP is a cardiac hormone that is released when the ventricles are stretched by high blood volume. BNP levels are used in the evaluation of heart failure
Cation Positively charged electrolyte
Chvostek's sign A sign elicited by tapping the facial nerve about 2 cm anterior to the ear lobe, just below the zygomatic process; the response is a spasm of the muscles supplied by the facial nerve
Diffusion The movement of a substance from a region of high concentration to one of lower concentration
Extracellular fluid (ECF) Body fluid located outside the cells
Filtration The process of passing fluid through a filter using pressure
Fingerprinting edema A condition in which imprints are made on the hands, sternum, or forehead when the area is pressed firmly by the fingers
Fluid volume deficit (FVD) A fluid deficiency; hypovolemia; an equal proportion of loss of water and electrolytes from the body
Fluid volume excess (FVE) The state of exceeding normal fluid levels; hypervolemia; retention of both water and sodium in similar proportions to normal ECF
Homeostasis The state of dynamic equilibrium of the internal environment of the body that is maintained by the ever-changing processes of feedback and regulation in response to external or internal changes
Hypertonic Having a concentration greater than the normal tonicity of plasma; solution of higher osmotic concentration than that of an isotonic solution; greater than 375 mOsm/L
Hypotonic Having a concentration less than the normal tonicity of plasma; solution of lower osmotic concentration than that of an isotonic solution
Insensible loss Fluid loss that is not perceptible to the individual; nonvisible form of water loss that is difficult to measure (e.g., perspiration)
Interstitial fluid Body fluid between the cells
Intracellular fluid (ICF) Body fluid inside the cells
Intravascular fluid The fluid portion of blood plasma
Isotonic Having an osmotic pressure equal to that of blood; equivalent osmotic pressure; between 250 and 375 mOsm/L
Oncotic pressure The osmotic pressure exerted by colloids (proteins), as when albumin exerts oncotic pressure within the blood vessels and helps to hold the water content of the blood in the intravascular compartment
Osmolality The number of milliosmoles per kilogram of solvent
Osmolarity The number of milliosmoles per liter of solution
Osmosis The movement of water from a lower concentration to a higher concentration across a semipermeable membrane
pH A measure of hydrogen ion (H⁺) concentration; the degree of acidity or alkalinity of a substance
Sensible loss Output that is measurable (e.g., urine)
Solute The substance that is dissolved in a liquid to form a solution
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) A condition in which excessive ADH is secreted, resulting in hyponatremia
Tetany Continuous tonic spasm of a muscle
Trousseau's sign A spasm of the hand elicited when the blood supply to the hand is decreased or the nerves of the hand are stimulated by pressure; elicited within several minutes by applying a blood pressure (BP) cuff inflated above systolic pressure

Introduction ⬆ ⬇

Fluid and electrolyte balance in our bodies is critical to life. Every nurse must possess a fundamental understanding of the composition and distribution of body fluids and the maintenance of homeostasis. Any imbalance of fluids, such as dehydration or fluid excess, or electrolyte imbalance can be life-threatening. Nurses in all settings will monitor laboratory values as well as signs and symptoms of fluid and electrolyte indicators for evidence of imbalances.

Nursing Process ⬆ ⬇

The nursing process is a five- or six-step process for problem-solving to guide nursing action. Refer to Chapter 1 for details on the steps of the nursing process related to vascular access. The following tables focus on nursing diagnoses and nursing outcomes for patients with fluid, electrolyte, and acid-base imbalances. Nursing diagnoses should be patient specific and outcomes and interventions individualized. The Nursing Outcomes Classification (NOC) and Nursing Interventions Classification (NIC) presented here are suggested directions for development of outcomes and interventions.

Nursing diagnoses and interventions are specific to the underlying pathophysiological process. In addition, the following may be considered.

Nursing Diagnoses Related to Fluid and Electrolyte Imbalance	Nursing Outcomes Classification (NOC)	Nursing Interventions Classification (NIC)
Risk for activity intolerance related to: Decreased muscle strength, weakness or neuromuscular irritability secondary to electrolyte imbalance	Activity tolerance, energy conservation	Activity therapy; energy management
Decreased cardiac output related to: Altered heart rate; altered heart rhythm, altered contractility associated with reduced myocardial functioning from severe phosphorus depletion Altered heart rhythm associated with digitalis toxicity, electrolyte imbalance	Cardiac pump effectiveness, circulation status, tissue perfusion, vital signs	Cardiac care
Deficient fluid volume OR excess fluid volume related to: Compromised regulatory mechanisms; active fluid volume loss or gain; excessive or insufficient fluid intake; excessive sodium	Electrolyte and acid-base balance, fluid balance, hydration	Fluid management, hypovolemia management, shock management: volume, fluid monitoring
Risk for injury related to: Abnormal blood profile Alteration in cognitive functioning (drowsiness, weakness, sensory) and neuromuscular dysfunction, tetany due to electrolyte imbalances	Personal safety; risk control; safe home environment Knowledge to remain free of injury	Health education; environmental management; fall prevention
Deficient knowledge related to alteration in cognitive function; insufficient information	Knowledge of diet, disease process, health behavior, health resources, medication, treatment regimen	Teaching: Disease process, learning facilitation
Perfusion, tissue ineffective (peripheral) related to: Aggravating factors	Circulation status, fluid balance, hydration, tissue perfusion: peripheral	Circulatory care and monitoring
Impaired gas exchange related to: Alveolar-capillary membrane changes; ventilation-perfusion imbalance (hypercapnia, hypercarbia, hypoxemia, hypoxia)	Respiratory status: Gas exchange	Acid-base management, airway management

Sources: Ackley et al., 2020; Herdman et al., 2021.

Chapter Highlights ⬆ ⬇

Fluid is distributed in three compartments: intracellular (40%), intravascular (5%), and interstitial (15%). Water accounts for 60% of TBW for an average adult and 80% for full-term infants.
Fluid is transported passively by filtration, diffusion, and osmosis.
Electrolytes are actively transported by ATP on cell membranes and by the sodium-potassium pump.
The osmolarity of IV solutions has the following ranges:
- Isotonic solutions: 250 to 375 mOsm/L
- Hypotonic solutions: Less than 250 mOsm/L
- Hypertonic solutions: Greater than 375 mOsm/L
The homeostatic organs that regulate fluid and electrolyte balance include the kidneys; heart and blood vessels; lungs; and adrenal, parathyroid, and pituitary glands.
There are six areas to assess for fluid balance: neurological status; cardiovascular, respiratory, and integumentary systems; special senses; and body weight.
Fluid imbalances fall into two categories:
- FVD caused primarily by disorders of the GI system. Signs and symptoms reflect a dehydrated individual. Treatment is aimed at rehydration with isotonic sodium chloride.
- FVE caused primarily by cardiovascular dysfunction, renal or endocrine dysfunction, and too rapid administration of IV fluids. Signs and symptoms reflect fluid overload. Treatment is aimed at decreasing the sodium level, using diuretics to increase the excretion of fluids, and treating the underlying cause.
The seven major electrolytes and their symbols are:
- Cations: Sodium: Na⁺, potassium: K⁺, calcium: Ca²⁺, magnesium: Mg²⁺
- Anions: Chloride: Cl^-, phosphate: HPO₄^-, bicarbonate: HCO₃^-
Key nursing interventions for electrolyte imbalances reflect collaborative practice and are specific to the imbalance.
Key laboratory values include:
- Sodium (N⁺): 135 to 145 mEq/L
- Potassium (K⁺): 3.5 to 5.0 mEq/L
- Calcium (Ca²⁺): 4.5 to 5.5 mEq/L or 9 to 11 mg/dL
- Magnesium (Mg²⁺): 1.5 to 2.5 mEq/L or 1.8 to 3.0 mg/dL
- Phosphorus (HPO₄^-): 2.5 to 4.5 mg/dL
- Chloride (Cl^-): 95 to 108 mEq/L
Critical guidelines for potassium infusion include:
- Never give potassium by IV push.
- Concentrations of potassium greater than 60 mEq should not be given in a peripheral vein.
- Concentrations greater than 8 mEq/100 mL can cause pain and irritation of peripheral veins, leading to phlebitis.
- Do not add potassium to a hanging container.
- Administer potassium at a rate not exceeding 10 mEq/hr through peripheral veins.
Calcium and phosphate have a reciprocal relationship: When one is elevated, the other is decreased.
Patients with calcium imbalances may need seizure precautions. The most dangerous symptom of hypocalcemia is laryngospasm.
The four major acid-base imbalances in the body are respiratory acidosis (carbonic acid excess), respiratory alkalosis (carbonic acid deficit), metabolic acidosis (base bicarbonate deficit), and metabolic alkalosis (bicarbonate excess).
Acid-base balance is maintained through three major reaction-specific buffer systems that regulate hydrogen ion concentration: the carbonic acid-bicarbonate system, the phosphate buffer system, and the protein buffer system.

Critical Thinking: Case Study

A 28-year-old woman who became ill on a cruise to the Bahamas was admitted to the hospital after 6 days of severe diarrhea and poor intake. She weighed 120 lb on admission (132 lb before illness). Her BUN was 40 mg/dL, and serum creatinine was 1.3 mg/dL. Her potassium level was 3.2 mEq/mL, and sodium was 133 mEq/mL. Her skin turgor was poor, and urine output was 15 mL/hr (specific gravity 1.030). Blood gases were pH 7.47 and HCO₃^- 30 mEq/L; BP was 120/80 mm Hg recumbent and fell to 98/60 mm Hg when the patient was upright. Her pulse was 110, weak, and regular, with respiratory rate of 14. Her reflexes were hyperactive, and she complained of “tingling of fingers.”

Case Study Questions

1.What percentage of body weight did she lose?

2.What concerns would the nurse have regarding the patient's laboratory test results?

3.What nursing diagnoses would apply to this woman?

4.What nursing interventions would be implemented?

5.What collaborative orders would you anticipate?

Media Link: Chapter post tests and answers are provided on FADavis.com, along with case studies and critical thinking activities.

References ⬆

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section name header

Learning Objectives ⬇

Glossary ⬆ ⬇

Introduction ⬆ ⬇

Nursing Process ⬆ ⬇

Chapter Highlights ⬆ ⬇

References ⬆