Chapter 25

Chapter 25: Fluid, Electrolyte, and Acid-Base Balance

Lesson 25.1: Fluids and Electrolytes

  • Functions of Water in the Body:

    • Transport: Water is a medium for transporting substances to and from cells.

    • Heat Regulation: Aids in maintaining body temperature.

    • H+ Balance: Helps in maintaining hydrogen ion concentration.

    • Enzymatic Action: Serves as a medium for digestion processes.

  • Major Electrolytes and Their Functions:

    • Sodium (Na+): Regulates water balance and distribution.

    • Potassium (K+): Key for nerve impulse transmission, muscle contractions, and plasma acid-base balance.

    • Calcium (Ca2+): Vital for muscle activity and blood coagulation.

    • Magnesium (Mg2+): Involved in nerve impulse transmission and muscle contractions.

    • Phosphate (HPO4^2-): Essential for ATP production.

    • Chloride (Cl-): Component of hydrochloric acid, helps maintain acid-base balance.

    • Bicarbonate (HCO3-): Crucial for acid-base balance.

  • Distribution of Body Fluids:

    • Body fluids are distributed among fluid compartments:

      • Intracellular (within cells)

      • Extracellular (outside cells)

        • Intravascular (within blood vessels)

        • Interstitial (between cells)

        • Transcellular (various body secretions).

  • Signs & Symptoms of Fluid and Electrolyte Imbalances:

    • Dehydration: thirst, weakness, dizziness, decreased urine production.

    • Fluid volume excess: weight gain, slowed bounding pulse, elevated blood pressure.

Composition of Body Fluids

  • Body fluids mostly composed of water and electrolytes.

  • Water constitutes more than half of the body weight.

  • Electrolytes are minerals/salts that dissolve and dissociate into ions.

Importance of Water

  • Critical Functions:

    • Transports substances.

    • Regulates heat.

    • Maintains acid-base balance.

    • Facilitates enzymatic reactions.

  • Variation: Water composition varies by age, sex, and health.

  • Infants and elderly are at higher risk of dehydration.

Sources and Loss of Water

  • Daily intake:

    • Oral: 1500 mL

    • Food: 800 mL

    • Metabolism: 200 mL

    • Total: 2500 mL

  • Daily output:

    • Urine: 1500 mL

    • Perspiration: 400 mL

    • Feces: 200 mL

    • Expired air: 400 mL

    • Total: 2500 mL

Electrolyte Normal Ranges

  • Sodium: 135-145 mEq/L

  • Potassium: 3.5-5 mEq/L

  • Calcium: 8.4-10.6 mg/dL

  • Magnesium: 1.3-2.5 mg/dL

  • Phosphate: 2.5-4.5 mg/dL

  • Chloride: 96-106 mEq/L

  • Bicarbonate: 22-26 mEq/L

Non-Electrolytes

  • Includes amino acids, glucose, fatty acids, which remain bound in solution.

Blood Composition and Fluid Distribution

  • Normal blood volume: 4-6 L, consisting of erythrocytes, leukocytes, platelets, and plasma.

  • Plasma proteins maintain osmotic pressure, which affects circulation and blood volume.

Mechanisms of Fluid and Electrolyte Movement

  • Thirst Mechanism: Regulated by hypothalamus based on electrolyte concentration.

  • Kidney Function: Manages fluid retention via hormones (e.g., aldosterone, ADH).

Transport Mechanisms

  • Diffusion: Substances move from high to low concentration until evenly distributed.

  • Osmosis: Movement of water across a semipermeable membrane.

  • Filtration: Movement of fluids through a membrane due to hydrostatic pressure.

  • Active Transport: Requires energy (ATP) to move substances against concentration gradients.

Fluid Volume Deficit and Dehydration

  • At-Risk Groups: Individuals unable to intake fluids (e.g., impaired swallowing), or those losing excessive fluids (e.g., vomiting, diarrhea).

  • Dehydration: Results in cellular shrinkage due to water moving out of cells. Treated via oral or IV fluids.

Signs and Symptoms of Dehydration

  • Thirst, weakness, dizziness, hypotension, decreased urine production, dry mucous membranes, rapid pulse.

Fluid Volume Excess

  • Can occur due to excessive intake or inadequate excretion. Signs include weight gain, elevated blood pressure, and potential edema.

Electrolyte Imbalances: Sodium, Potassium, Calcium, Magnesium

  • Hyponatremia: Sodium deficit due to excessive fluid intake or loss.

  • Hypernatremia: Sodium excess often from water loss.

  • Hypokalemia: Low potassium, often due to dietary deficiencies or excessive loss.

  • Hyperkalemia: High potassium from conditions like renal failure or tissue damage.

  • Hypocalcemia/Hypercalcemia: Calcium imbalances linked to dietary deficiencies or malignancies.

  • Hypomagnesemia/Hypermagnesemia: Magnesium levels affected by dietary issues and renal function.

Acid-Base Balance

  • pH Range: Normal serum pH is 7.35 - 7.45. Death is possible outside 6.8 - 7.8.

  • Bicarbonate as a Buffer: Normal range is 22-26 mEq/L; assists in neutralizing excess acids.

  • Control Mechanisms:

    • Blood buffer systems

    • Lungs handle CO2

    • Kidneys help regulate bicarbonate levels.

Acid-Base Imbalances

  • Respiratory Acidosis: Caused by increased CO2 due to obstruction or lung disease.

  • Metabolic Acidosis: Loss of bicarbonate or increase in H+ levels due to kidney failure or shock.

  • Respiratory Alkalosis: Caused by hyperventilation or anxiety.

  • Metabolic Alkalosis: Caused by vomiting or diuretic therapy.