Fluid and Electrolyte Balance

Introduction

• The human body is composed of approximately 45-75% water.
• Fluid percentage varies by age and tissue composition (adipose vs. muscle).
  • Infants: ~75% fluid (high protein, low fat).
  • Elderly: ~45% fluid.
  • Adults: ~60% fluid.
  • Higher adipose tissue = lower fluid percentage; higher muscle tissue = higher fluid percentage.

Fluid Distribution in the Body

• Intracellular Fluid (ICF): Makes up 2/3 of total body fluid.
• Extracellular Fluid (ECF): Remaining 1/3 of body fluid.
  • Interstitial Fluid: ~2/3 of ECF.
  • Blood Plasma: ~8% of ECF.

Composition of Body Fluid Compartments

• Intracellular Fluid (ICF):
  • High in potassium, magnesium, phosphate, negatively charged proteins.
• Extracellular Fluid (ECF):
  • High in sodium, calcium, chloride, bicarbonate.
  • Blood plasma contains proteins like albumin, which helps maintain osmotic pressure.

Fluid Movement and Osmolarity

• Fluid moves between compartments based on osmolarity.
• Water moves from hypotonic (low solute) to hypertonic (high solute) areas to balance concentrations.

Fluid Intake and Output

• Average Fluid Intake: 2500 mL/day.
  • 2300 mL from food and drink.
  • 200 mL from metabolic water production.
• Fluid Output: Also 2500 mL/day.
  • 1500 mL in urine (majority).
  • Remaining from perspiration, exhalation, and feces.

Sensible vs. Insensible Water Loss

• Sensible Loss: Measurable (urine, feces).
• Insensible Loss: Not measurable (evaporation from skin and lungs).

Factors Affecting Fluid Balance

• Sensible Water Loss: Urine and feces.
• Insensible Water Loss: Respiration and transpiration.
• Obligatory Water Loss: Always occurs, like transpiration and minimal urine.
• Facultative Water Loss: Regulated by hormones based on the body's needs.

Fluid Imbalance Types

• Isotonic Imbalances:
  • Volume Depletion: More isotonic fluid loss than gain (causes: hemorrhage, burns, etc.).
  • Volume Excess: More isotonic fluid gain than loss (causes: excessive IV fluids).
• Osmolar Imbalances:
  • Dehydration: Water loss greater than solute loss (causes: sweating, diabetes, alcohol).
  • Hypotonic Hydration: Water gain greater than solute gain (causes: excessive water intake).
• Fluid Sequestration: Normal fluid level but distributed abnormally.

Clinical Implications

• Dehydration Effects: Can lead to cell crenation, possible dehydration of cells.
• Hypotonic Hydration Risks: Can cause cerebral edema, convulsions, coma, and death.
• Fluid Sequestration Examples:
  • Edema: Fluid accumulation in interstitial spaces.
  • Ascites: Fluid build-up in the peritoneal cavity, often due to liver issues.
  • Pericardial Effusion & Pleural Effusion: Fluid accumulation around the heart and lungs, respectively.

Conclusion

• Fluid and electrolyte balance is critical for maintaining homeostasis and is regulated by multiple body systems.
• Imbalances can have serious health consequences, requiring careful monitoring and management.

• End of Lecture on Fluid and Electrolyte Balance Part 1. Further details on regulation of fluid balance will be covered in the next lecture.