Chapter 13. Concepts of F&E & Acid Base Balance & Imbalance

Basic Concepts of Body Water Composition

  • Water as a Major Component:

    • Represents 50-60% of total body weight.

    • Men typically have more water in their bodies compared to women.

Fluid Imbalances

  • Dehydration:

    • More prevalent in the older population.

    • Important to understand fluid and electrolyte shifts in the body.

Fluid Compartments

  • Intracellular Fluid (ICF):

    • Fluid found inside cells.

  • Extracellular Fluid (ECF):

    • Fluid outside cells, which includes:

      • Interstitial Fluid: Fluid between cells.

      • Plasma: Component of blood.

      • Transcellular Fluid: Includes cerebrospinal fluid and more.

    • Fluid Distribution:

      • Approximately 25 liters of fluid is intracellular, and the remainder is extracellular, primarily in interstitial spaces.

Importance of Fluid-Electrolyte Balance

  • Homeostasis needs a stable balance of water and electrolytes.

  • Movement of electrolytes and fluids occurs through three processes:

    1. Filtration: Movement driven by hydrostatic pressure (water pressure).

    2. Diffusion: Movement of particles across a permeable membrane from high to low concentration.

    3. Osmosis: Movement of water through a semi-permeable membrane to achieve equilibrium.

  • Serum Osmolarity: Normal range is 270-300 mOsm/L.

    • Low Osmolarity: Fluid volume overload.

    • High Osmolarity: Indication of dehydration.

IV Fluid Categories

  • Classifications:

    • Isotonic: Osmolarity similar to blood, 270-300 mOsm/L.

      • Examples: Normal Saline, Lactated Ringer's, D5W (may change to hypotonic after administration).

    • Hypertonic: Higher osmolarity (>300 mOsm/L); pulls fluid out of cells.

      • Examples: 3% NaCl, 5% NaCl, D10W, and D20W.

    • Hypotonic: Lower osmolarity (< 270 mOsm/L); pulls fluid into cells.

      • Example: 0.25% NaCl.

Electrolytes Overview

  • Focus will be on Potassium, Calcium, Magnesium, and Sodium.

Essential Electrolyte Ranges:

  • Understand and memorize the ranges for clinical assessment.

  • Potassium: 3.5-5.0 mEq/L

  • Calcium: 9.0-10.5 mg/dL

  • Magnesium: 1.5-2.5 mEq/L

  • Sodium: 135-145 mEq/L

Fluid Intake and Balance

  • Obligatory Urine Output: 400-600 mL/day needed for waste excretion.

  • Fluid intake is driven by thirst response to increased osmolarity in the blood.

Hormonal Regulation of Fluid Balance

  • Aldosterone: Secreted by the adrenal cortex; controls sodium and water retention.

  • Antidiuretic Hormone (ADH): Produced by hypothalamus, secreted by posterior pituitary; regulates blood osmolality.

  • Natriuretic Peptides: Secreted from the heart; counteract fluid overload by promoting diuresis and helping to control blood pressure.

Dehydration

  • Common presentations:

    • Dry mucous membranes, increased heart rate, decreased peripheral pulses.

    • Assess urinary output: concentrated urine, dark color, strong odor.

    • Monitor weight changes, fluid intake, and loss patterns.

  • Treatment: Encourage fluid intake, monitor and replace electrolytes, manage IV fluids if severe.

Fluid Volume Overload

  • Occurs typically in patients with:

    • Congestive heart failure (CHF) or renal failure.

  • Assessment findings: Edema, increased blood pressure, altered mental status.

  • Treatment involves:

    • Diuretics, sodium restriction, and meticulous monitoring of intake and output (I&O).

    • Daily weight monitoring is vital: notify provider if weight change exceeds 3 lbs/week or 2 lbs/day.

Sodium: Clinical Relevance

  • Hyponatremia (Low Sodium):

    • Causes include actual loss (e.g., diuretics) and relative loss (e.g., dilutional due to fluid overload).

    • Symptoms: Stupor, confusion, muscle cramping, and cardiovascular changes.

    • Treatment involves hypertonic solutions (like 3% NaCl) with careful monitoring.

  • Hypernatremia (High Sodium):

    • Rare, occurs in only about 1% of hospitalized patients.

    • Symptoms: Agitation, confusion, muscular twitching, cardiovascular implications.

    • Management involves isotonic solutions and diuretics when indicated.

Potassium: Vital for Cardiac Function

  • Hypokalemia:

    • Causes: Diuretics, gastrointestinal losses.

    • Symptoms: Muscle weakness, arrhythmias (depressed ST segment, presence of U-waves).

    • Treatment focuses on potassium replacement and monitoring.

  • Hyperkalemia:

    • Causes: Renal failure, tissue damage, excess potassium intake.

    • Symptoms: Early signs of fatigue, muscle weakness, peaked T-waves on EKG.

    • Management may include insulin to shift potassium into cells, diuretics, or dialysis.

Calcium: Essential for Various Functions

  • Hypocalcemia:

    • Causes: Malabsorption, chronic renal disease, vitamin D deficiency.

    • Symptoms: Tetany, positive Chvostek's and Trousseau's signs.

    • Management involves calcium supplementation and monitoring.

  • Hypercalcemia:

    • Causes: Malignancy, vitamin D excess, prolonged immobilization.

    • Symptoms: Confusion, lethargy; increased risk for thromboembolic events.

    • Treatment includes hydration and possibly diuretics.

Magnesium: Impact on Neuromuscular Function

  • Hypomagnesemia:

    • Causes: Malnutrition, excessive diuretic use.

    • Symptoms include hyperactive deep tendon reflexes and muscle spasms.

    • Administer magnesium sulfate for correction.

  • Hypermagnesemia:

    • Causes: Renal failure, excessive intake.

    • Symptoms: Bradycardia, lethargy; severe cases can lead to respiratory failure.

    • Management includes hydration and discontinuing magnesium-containing medications.

Conclusion

  • Comprehensive monitoring of fluid and electrolyte balance is crucial in various clinical conditions.

  • Frequent reassessment and timely interventions are necessary to prevent severe complications that arise due to imbalances.