Fluids and Electrolytes Nursing Care Management and Study Guide

Fluid and electrolyte balance keeps every patient alive, and small shifts show up fast on the floor as confusion, arrhythmias, falling output, or crackles. Fluid makes up about 60% of an adult's weight and sits in two compartments, intracellular and extracellular. Electrolytes are the charged chemicals dissolved in that fluid: cations carry positive charges, anions carry negative. The major cations are sodium, potassium, calcium, magnesium, and hydrogen ions; the major anions are chloride, bicarbonate, sulfate, and proteinate ions.

Homeostasis

Homeostasis is the body constantly adjusting to internal and external stimuli to hold balance. Feedback relays information about a condition to the organ or system that can act on it. Negative feedback reverses the original stimulus to restore balance (blood pressure control, body temperature). Positive feedback intensifies the original stimulus (blood clotting after injury, labor). The nervous and endocrine systems drive most feedback: the nervous system senses deviations and fires nerve impulses to the right organs, and the endocrine system releases hormones to maintain balance.

Body Fluids

Fluids make up roughly 50% to 60% of total body weight, split between intracellular and extracellular compartments. Intracellular fluid stabilizes cell structure, maintains cell shape, and helps move nutrients across the membrane. Extracellular fluid appears mostly as interstitial tissue fluid and intravascular fluid.

Fluid Regulation Mechanisms

Four mechanisms keep volume in range. The thirst center in the hypothalamus drives or suppresses the urge to drink. ADH regulates how much water the kidney tubules reabsorb and is released in response to low blood volume or a rise in sodium and other solutes. The renin-angiotensin-aldosterone (RAA) system controls fluid volume: when blood volume drops, reduced flow to the renal juxtaglomerular apparatus activates it. The heart corrects overload by releasing atrial natriuretic peptide (ANP) from the right atrium.

Normal Intake and Output

An adult at rest takes in about 2,500 ml of fluid daily: roughly 1,200 ml as fluids, 1,000 ml from foods, and 30 ml from metabolic products. Daily output should about equal intake and occurs as urine, breathing, perspiration, feces, and minimal vaginal secretions.

Overhydration, Edema, and Dehydration

Overhydration is excess water in the body. Edema is excess fluid in the interstitial spaces (third-space fluid), caused by disruption of the body's filtration and osmotic forces; diuretics are commonly given for systemic edema. Dehydration is a deficiency or excessive loss of body water from prolonged sun exposure, excessive exercise, diarrhea, vomiting, or burns; treat with supplemental fluids and electrolytes.

Electrolytes

An electrolyte dissociates into ions when dissolved in water and is found as inorganic salts, acids, and bases. Concentrations are measured by chemical activity and expressed in milliequivalents. The dominant intracellular electrolytes are potassium (dominant cation) and phosphate (dominant anion), along with magnesium and sulfate. The key extracellular electrolytes are sodium (most essential cation) and chloride (most important anion), along with calcium and bicarbonate.

Fluid and Electrolyte Transport

Total electrolyte concentration drives fluid balance. Nutrients and oxygen enter cells while waste exits, all across the cell membrane that separates the intracellular from the extracellular environment. Permeability is the membrane's ability to let molecules pass. Freely permeable membranes pass almost any substance; the cell membrane is selectively permeable, allowing only specific substances through.

Passive transport needs no energy and includes diffusion (random movement of molecules from higher to lower concentration), osmosis (movement of a solvent such as water across a semipermeable membrane along a concentration gradient), and filtration (movement of water and dissolved materials by pressure). Active transport requires enzymes and energy as adenosine triphosphate (ATP) and can move solutes uphill against concentration and pressure gradients.

Acid-Base Balance

An acid contains the hydrogen ion; a base or alkali contains the hydroxyl ion; a salt forms when the positive ions of a base replace the hydrogen ions of an acid (sodium chloride, potassium chloride, calcium chloride, calcium carbonate, calcium phosphate, sodium phosphate). pH is the power of hydrogen ion concentration: below 7 is acid, above 7 is basic or alkaline, and 7 is neutral. A change of one pH unit means a tenfold change in hydrogen ion concentration.

Buffers resist changes in hydrogen ion levels. Sodium bicarbonate and carbonic acid are the body's major chemical buffers. The lungs control CO2 and can compensate rapidly by changing the respiratory rate; the kidneys regulate bicarbonate. Arterial blood gas shows whether acid or base predominates. Respiratory acidosis occurs when breathing is inadequate and PaCO2 builds up; respiratory alkalosis follows hyperventilation or excess aspirin intake; metabolic acidosis comes from impaired metabolism with falling bicarbonate and lactic acid buildup; metabolic alkalosis occurs when bicarbonate rises and blood pH climbs.

Classification

Fluid volume deficit (hypovolemia) occurs when loss of ECF volume exceeds fluid intake. Fluid volume excess (hypervolemia) is an isotonic expansion of the ECF from abnormal retention of water and sodium in about the proportions they normally exist.

Electrolyte disturbances are common and must be corrected:

• Hyponatremia: serum sodium less than 135 mEq/L
• Hypernatremia: serum sodium higher than 145 mEq/L
• Hypokalemia: a deficit in total potassium stores
• Hyperkalemia: potassium greater than 5.0 mEq/L
• Hypocalcemia: serum levels below 8.6 mg/dl
• Hypercalcemia: calcium greater than 10.2 mg/dl
• Hypomagnesemia: below-normal serum magnesium
• Hypermagnesemia: serum levels over 2.3 mg/dl
• Hypophosphatemia: value below 2.5 mg/dl
• Hyperphosphatemia: serum phosphorus exceeding 4.5 mg/dl in adults

Pathophysiology

Electrolyte concentrations differ between the ICF and ECF. Sodium outnumbers every other cation in the ECF and is essential to fluid regulation. The ECF holds little potassium and tolerates only small changes in it. The body spends significant energy running cell membrane pumps that exchange sodium and potassium. In osmosis, when two solutions are separated by a membrane impermeable to the solute, fluid shifts from low to high solute concentration until they equalize. In diffusion, a substance moves from higher to lower concentration on its own.

Causes

Sodium retention drives fluid retention, while excessive sodium loss decreases body fluid volume. Trauma releases intracellular potassium, which is dangerous. Fluid volume deficit results from loss of body fluids and moves faster with reduced intake. Fluid volume excess relates to fluid overload or to diminished homeostatic regulation. Diets too low or too high in electrolytes, and medications taken against orders, also cause imbalances.

Clinical Manifestations

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

Complications

Untreated, these imbalances escalate. Fluid volume deficit leads to tissue dehydration; fluid volume excess leads to cardiac overload. Water is retained abnormally in SIADH. Too much potassium administered can cause cardiac arrest.

Assessment and Diagnostic Findings

BUN may fall in FVE from plasma dilution. Hematocrit runs higher than normal in FVD from decreased plasma volume. A physical exam confirms the signs of imbalance. Serum electrolyte levels confirm the imbalance, ECG changes support the diagnosis, and ABG analysis reveals acid-base disturbances.

Medical Management

Isotonic electrolyte solutions treat the hypotensive FVD patient by expanding plasma volume. Assess I&O accurately and frequently so therapy can be slowed or increased to prevent deficit or overload. Hemodialysis or peritoneal dialysis removes nitrogenous wastes, controls potassium and acid-base balance, and removes sodium and fluid. Nutritional therapy restricts or supplements the electrolyte involved.

Pharmacologic therapy: AVP receptor agonists treat hyponatremia by stimulating free water excretion. Diuretics reduce fluid volume in FVE. IV calcium gluconate is given when serum potassium is dangerously elevated. Calcitonin lowers serum calcium and is useful for cardiac patients who cannot tolerate large sodium loads.

Nursing Management

Assessment

Monitor I&O at least every 8 hours, or hourly when indicated. Weigh the patient daily to catch gains or losses, monitor vital signs closely, and use the physical exam to reinforce other data.

Diagnosis

• Excess fluid volume related to excess fluid 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 medication effects or malabsorption

Planning and Goals

• Maintain fluid volume at a functional level
• Display normal laboratory values
• Demonstrate appropriate lifestyle and behavior changes, including eating patterns and food quantity and quality
• Reestablish and maintain a normal GI pattern

Interventions

Check skin and tongue turgor as indicators of fluid status. Obtain a urine sample to check concentration. Give oral or parenteral fluids as indicated to correct a deficit; oral rehydration solutions supply fluid, glucose, and electrolytes in easily absorbed concentrations. Stay alert for CNS changes such as lethargy, seizures, confusion, and muscle twitching. Encourage intake of deficient electrolytes or restrict those that are excessive.

Evaluation

Care is effective when the patient meets the planned goals: fluid volume held at a functional level, normal laboratory values, appropriate lifestyle and behavior changes, and a reestablished normal GI pattern.

Discharge and Home Care

Enforce a diet rich in the nutrients and electrolytes the patient needs and set fluid intake per the physician's recommendations. The patient returns a week after discharge for a followup checkup to reassess electrolyte and fluid status. Stress strict compliance with prescribed medications to prevent recurrence.

Documentation

Document individual findings, including factors affecting fluid management and degree of deficit; I&O, fluid balance, weight changes, urine specific gravity, and vital signs; diagnostic and laboratory results; the plan of care; the patient's responses to treatment and teaching; attainment of or progress toward outcomes; and any modifications to the plan.