Fluid and Electrolytes

Balance and Homeostasis

  • Fluid Balance: Maintained by:

    • Fluctuations in intake and output influenced by trauma, surgery, diseases, aging, or environmental factors.

    • Nursing Role: Identify risks, recognize imbalances, and intervene appropriately.

  • Homeostasis: Achieved through the balance of fluids and electrolytes.

Body Fluids and Solutes

Body Fluids

  • Functions:

    • Maintain blood volume.

    • Regulate body temperature.

    • Transport materials to/from cells.

    • Medium for cellular metabolism.

  • Fluid Composition by Compartments:

    • Intracellular Fluid (ICF): Inside cells, essential for metabolism and cellular function.

    • Extracellular Fluid (ECF): Outside cells; includes:

      • Interstitial Fluid (ISF): Between cells; excess = edema.

      • Intravascular Fluid (IVF): Plasma, transports blood cells.

      • Transcellular Fluid: Specialized fluids (e.g., CSF, pleural, digestive juices).

Solutes in Body Fluids

  • Crystalloids: Dissolve easily; include electrolytes (carry charges, e.g., Na⁺, K⁺) and non-electrolytes (e.g., glucose, amino acids).

  • Colloids: Large particles like proteins (e.g., albumin); do not dissolve easily or pass through membranes.

  • Electrolytes: Dissociate into charged ions to:

    • Conduct electrical impulses across cells.

    • Maintain homeostasis, regulate fluid balance, and acid-base balance.

Body Water Across the Lifespan

  • TBW (Total Body Water):

    • Higher in infants (75%), lower in elderly or obese individuals (45%).

    • Men (60%) > Women (50%) due to higher lean body mass.

    • Risk Factors for Imbalances: Lower body water content increases susceptibility.

  • Body Weight as Indicator:

    • 1L of water = 2.2 lbs (1 kg).

    • Daily weight changes are key for fluid volume assessment.

Fluid Movement

  • Processes:

    • Passive Movement: No energy required.

      • Osmosis: Water moves from low to high solute concentration across a semipermeable membrane.

      • Filtration: Water and solutes move together from high to low pressure.

    • Active Movement: Energy required (e.g., sodium-potassium pump).

  • Osmotic Pressure: Force due to solute concentration differences.

  • Osmolality (Tonicity): Solute concentration measured in mOsm/kg; impacts fluid shifts between compartments.

Effects of Osmolality on Cells:

  • Isotonic Fluids: Same osmolality as blood; no cellular changes. (e.g., 0.9% NS, LR).

  • Hypotonic Fluids: Lower osmolality than blood; causes cellular swelling. (e.g., 0.45% NS).

  • Hypertonic Fluids: Higher osmolality than blood; causes cellular shrinkage. (e.g., D5 NS).

Electrolytes

General Functions:

  • Transmit nerve impulses.

  • Regulate acid-base balance and fluid osmolality.

  • Maintain blood volume.

Electrolytes by Type:

  1. Sodium (Na⁺):

    • Range: 135–145 mEq/L.

    • Function: Regulates fluid volume, stimulates nerve impulse conduction, supports muscle contraction.

    • Imbalances:

      • Hyponatremia (<135): Caused by water excess or sodium loss.

        • Signs: Confusion, seizures, weakness.

        • Intervention: Fluid restriction, seizure precautions.

      • Hypernatremia (>145): Caused by sodium excess or water loss.

        • Signs: Dry mucous membranes, altered LOC.

        • Intervention: Limit salt, increase water.

  2. Potassium (K⁺):

    • Range: 3.5–5.0 mEq/L.

    • Function: Maintains cardiac rhythm, regulates nerve impulses.

    • Imbalances:

      • Hypokalemia (<3.5): Caused by diuretics, fluid loss.

        • Signs: Weak pulse, arrhythmias.

        • Intervention: Increase intake (bananas, potatoes).

      • Hyperkalemia (>5): Caused by renal failure, cell trauma.

        • Signs: Muscle weakness, cardiac arrhythmias.

        • Intervention: Reduce intake, administer diuretics.

Fluid Volume Deficits (FVD)

  • Isotonic FVD: Equal loss of water and sodium.

    • Causes: Hemorrhage, burns, vomiting.

    • Signs: Thirst, poor skin turgor, orthostatic hypotension.

  • Hypertonic FVD: More water loss than sodium, causing cell shrinkage.

    • Causes: DKA, excessive fluid loss.

    • Signs: Dry mucous membranes, neurologic changes (confusion, lethargy).

  • Assessment Indicators:

    • Weight loss: 5% significant, 8% severe, 15% fatal.

    • Vitals: Tachycardia, thready pulse, hypotension.

    • I&O: Negative fluid balance.

    • Skin/Mucous Membranes: Poor turgor, dry mucosa.

Fluid Volume Excess (FVE)

  • Positive Fluid Balance: Intake > output.

  • Causes: Excessive intake, kidney dysfunction.

  • Signs: Edema, elevated BP, crackles in lungs.

Regulation of Fluid Balance

Hormonal Regulation:

  • ADH (Antidiuretic Hormone):

    • Secreted in response to high plasma osmolality.

    • Promotes water reabsorption in kidneys.

  • RAAS (Renin-Angiotensin-Aldosterone System):

    • Regulates BP and extracellular fluid balance via sodium and water retention.

  • Thirst Mechanism: Major driver of fluid intake, declines with age.

Assessment of Fluid Status:

  • Key Factors:

    • Vital Signs.

    • Daily Weights: Same time, scale, clothes.

    • Intake/Output: Measure trends.

    • Lab Values: Electrolytes, BUN, urine osmolality.

  • Loss Types:

    • Sensible: Measurable (e.g., urine, diarrhea).

    • Insensible: Non-measurable (e.g., sweat, respiratory loss).

Fluid Therapy

IV Fluids:

  1. Isotonic: Expand intravascular volume. (e.g., 0.9% NS, LR).

  2. Hypotonic: Treat cellular dehydration. (e.g., 0.45% NS).

  3. Hypertonic: Pull water from cells to ECF. (e.g., D5 NS, 3% saline).