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Fluid and Electrolyte Balance Study Notes

Fluid and Electrolyte Balance

Learning Objective

  • Relate principles of nursing care to disturbances in fluid volume and electrolytes.

Importance of Fluid and Electrolyte Balance

  • Essential for maintaining homeostasis in the body.

  • Equilibrium of intake and output is crucial for all body systems.

  • Regulated by:

    • Kidneys

    • Pulmonary system

    • Hormonal and neural functions.

Body Fluid Compartments

  • Total body fluid is divided into two major compartments:

    1. Intracellular Fluid (ICF): within the body cells.

    2. Extracellular Fluid (ECF): outside cells, further divided into three subcompartments:

    • Interstitial Fluid: surrounds and bathes tissue cells.

    • Intravascular Fluid: plasma and blood vessels.

    • Transcellular Fluid: includes fluids in various spaces (e.g., GI, cerebrospinal fluid).

Total Body Water (TBW)

  • Composed of:

    • ICF: 40%

    • ECF: 20% (15% interstitial, 5% intravascular, ~1-2L transcellular)

  • Example: TBW of a 70-kg male is about 60% (40 L). Varies with age, sex, body fat.

Electrolytes

  • Substances that separate into ions in solution (cations and anions).

  • Important for carrying electrical impulses for cell communication.

  • Major electrolytes include sodium, potassium, calcium, magnesium, bicarbonate, chloride, phosphorus, and sulfate.

Homeostasis

Definition

  • Process maintaining a stable internal environment despite external changes.

Principles of Homeostasis in Fluids and Electrolytes

  1. Anions and cations must be balanced to remain electrically neutral.

  2. Fluid compartments should remain in osmotic equilibrium.

Fluid Movement

  • Occurs via processes:

    • Osmosis: movement of water through a semipermeable membrane from low to high solute concentration.

    • Diffusion: movement of molecules from high to low concentration.

    • Hydrostatic Pressure: force within the fluid compartment.

    • Osmolality: concentration of solutes in body fluids.

    • Active Transport: energy-requiring movement across membranes.

Osmolality

Description

  • Refers to particles dissolved in serum and urine, mainly sodium, urea, and glucose.

Normal Serum Osmolality

  • 275 to 295 mOsm/kg.

Fluid Concentration Types

  1. Iso-osmolar: equal to body fluids.

  2. Hypo-osmolar: less concentrated than body fluids.

  3. Hyperosmolar: more concentrated than body fluids.

Causes of Fluid Concentration Changes

  • Hypo-osmolality: fluid overload, excessive water intake.

  • Hyper-osmolality: dehydration, increased sodium intake, diabetes.

Fluid Replacement Therapy

Fluid Intake and Loss

  1. Insensible Loss: loss of fluid via skin/lungs, not measurable.

  2. Sensible Loss: measurable losses through urine, feces, sweat.

Recommended Daily Water Intake

  • 2300-2900 mL.

Daily Water Loss

  • Kidneys (1200-1500 mL), skin (500-600 mL), lungs (500 mL), GI (200 mL).

Types of Intravenous Solutions for Replacement

Crystalloids

  • Solutions containing fluids and electrolytes that can cross capillary membranes.

  • Classifications:

    • Isotonic: same osmolality as blood (e.g., Normal Saline).

    • Hypotonic: lower osmolality than blood (e.g., 0.45% NaCl).

    • Hypertonic: higher osmolality (e.g., 3% NaCl).

Colloids

  • Contain large molecules that remain in the vascular space, increasing osmotic pressure.

Blood and Blood Products

  • Includes PRBCs, plasma, and platelets administered based on patient needs.

Nursing Process: Fluid Imbalance (FVD and FVE)

Recognize Cues

  • Assess for signs of FVD (e.g., thirst, weight loss) and FVE (e.g., edema, jugular vein distension).

Analyze Cues

  • Patient history and laboratory values are essential.

Generate Solutions

  • For FVD, prioritize fluid and electrolyte balance.

  • For FVE, consider fluid restriction and diuretics.

Patient Teaching

  • Educate on recognizing signs of liquid imbalances and dietary restrictions (low sodium).

Potassium Imbalance

  • Hypokalemia: < 3.5 mEq/L, due to loss from vomit, diarrhea, or diuretics.

  • Hyperkalemia: > 5.0 mEq/L, caused by kidney failure or potassium-sparing medications.

Sodium Imbalance

  • Hyponatremia: < 135 mEq/L; causes include diuretics and kidney disease.

  • Hypernatremia: > 145 mEq/L; causes include dehydration or excess sodium intake.

Calcium Imbalance

  • Hypocalcemia: < 8.6 mg/dL; causes can include vitamin D deficiency.

  • Hypercalcemia: > 10.2 mg/dL; may lead to kidney stones and muscle weakness.

Magnesium Imbalance

  • Hypomagnesemia: < 1.5 mEq/L; may lead to increased neuromuscular excitability.

  • Hypermagnesemia: > 2.5 mEq/L; may cause weakness and hypotension.

Phosphorus Imbalance

  • Hypophosphatemia: < 2.4 mEq/L; typical in malnutrition.

  • Hyperphosphatemia: > 4.4 mEq/L; often related to chronic kidney disease.