Intracellular and Extracellular Fluid Definitions and Transport Mechanisms

Key Definitions

• Intracellular Fluid (ICF): Fluid contained within the cells.
• Extracellular Fluid (ECF): Fluid outside the cells, including interstitial and intravascular fluids.
• Interstitial Fluid: Fluid present between cells in tissues.
• Intravascular Fluid: Fluid within blood vessels (e.g., plasma).
• Homeostasis: The biological system’s ability to maintain stable internal conditions despite external changes.

Fluid Transport Mechanisms

• Diffusion: Movement of solute molecules from a high to a low concentration across a semi-permeable membrane.
• Osmosis: Water moves across a semi-permeable membrane from an area of low solute concentration to high concentration.
• Filtration: Fluid passes through a filter under pressure, separating certain molecules.
• Active Transport: Movement of electrolytes from low to high concentration against the concentration gradient using ATP energy.

Intravenous (IV) Therapy

Overview

• Around 75% of hospitalized patients receive IV therapy.
• The human body is composed of 50-70% fluid, distributed as follows:
  • 1/3 in extracellular fluid (ECF), including:
    • Interstitial fluid
    • Plasma (intravascular fluid)
    • Transcellular fluid
  • 2/3 in intracellular fluid (ICF), including:
    • Fluid within cells
    • Red blood cells
    • Other cellular components

Uses of IV Therapy

• Maintain fluid and electrolyte balance.
• Administer medications continuously or intermittently.
• Provide venous access for emergencies.
• Transfuse blood and blood products.
• Deliver intravenous anesthetics.
• Correct nutritional imbalances.
• Administer diagnostic reagents.
• Monitor hemodynamic function.
• Manage acid-base imbalances.

Types of IV Fluids

1. Crystalloids

• Composed of water and electrolytes that can pass through semi-permeable membranes.
• Quickly leave the intravascular space and shift into interstitial fluid.
• Provide temporary fluid resuscitation, but large volumes are needed.

Types of Crystalloids

• Hypertonic: Draws fluid into the intravascular compartment.
• Hypotonic: Moves fluid from the intravascular compartment into the cells.
• Isotonic: Remains in the intravascular space, expanding blood volume.

Common Crystalloids & Their Uses

1. Dextrose 5% in Water (D5W) – Isotonic

   • Used for fluid loss, dehydration, and hypernatremia.
   • Caution: Can cause fluid overload in renal/cardiac patients.

2. 0.9% Sodium Chloride (Normal Saline) – Isotonic

   • Used for shock, blood transfusions, and resuscitation.
   • Caution: May cause electrolyte imbalances and overload.

3. Lactated Ringer’s (Hartmann’s) – Isotonic

   • Used for burns, dehydration, and blood loss.
   • Caution: Contains potassium, avoid in renal failure patients.

4. 0.45% Sodium Chloride (Half Normal Saline) – Hypotonic

   • Used for DKA and gastric fluid loss.
   • Caution: Increases intracranial pressure, avoid in trauma patients.

5. Dextrose 5% in 0.45% Normal Saline – Hypertonic

   • Used later in DKA.
   • Caution: Use only when blood sugar falls below 250 mg/dL.

6. Dextrose 5% in Normal Saline – Hypertonic

   • Used for shock treatment and Addison’s crisis.
   • Caution: Contraindicated for cardiac/renal patients.

7. Dextrose 10% in Water – Hypertonic

   • Used for water replacement and partial glucose nutrition.
   • Caution: Monitor blood sugar levels closely.

2. Colloids

• Contain large molecules (proteins or starches) that stay in blood vessels and expand intravascular volume.
• Draw water from cells into the bloodstream, providing short-term volume expansion.

Common Colloids & Their Uses

1. Albumin (Plasma Protein) – 4% or 20%

   • Maintains blood volume and pressure.
   • Caution: Risk of fluid overload and allergic reactions.

2. Dextran (Polysaccharide) – 40 or 70

   • Used for vascular expansion.
   • Caution: May cause fluid overload and increased bleeding risk.

3. Hetastarch (HES) – 6% or 10%

   • Expands vascular volume.
   • Caution: Contraindicated in heart failure and renal failure.

4. Mannitol (Alcohol Sugar) – 5% or 10%

   • Used for reducing cerebral edema and toxin elimination.
   • Caution: May cause electrolyte imbalances and dehydration.

3. Blood and Blood Products

• Plasma: Used for volume expansion after significant blood loss.
• Red Blood Cells (RBCs): Treats anemia and hemorrhage.
• White Blood Cells (WBCs): Helps fight infection.
• Platelets: Supports blood clotting in patients with thrombocytopenia.

Complications of IV Therapy

• Local Site Complications:
  • Extravasation (leakage of IV fluid into surrounding tissues)
  • Phlebitis (vein inflammation)
  • Hematoma (blood accumulation under skin)
  • Infection
• Systemic Complications:
  • Fluid overload → Pulmonary edema
  • Electrolyte imbalances → Arrhythmias
  • Allergic reactions
  • Air embolism

Electrolytes & Their Functions

Major Electrolytes

Electrolyte Imbalance Symptoms

• Hyponatremia: Fatigue, headache, muscle weakness.
• Hypernatremia: Thirst, flushed skin, confusion.
• Hypokalemia: Muscle weakness, cardiac arrhythmias.
• Hyperkalemia: Nausea, diarrhea, arrhythmias.
• Hypocalcemia: Muscle cramps, seizures, hypotension.
• Hypercalcemia: Fatigue, confusion, nausea.

Final Notes

IV therapy plays a critical role in maintaining fluid balance, delivering medications, and treating life-threatening conditions. Proper selection of fluids and monitoring for complications ensures patient safety and effective treatment. 🚑💉