Fluids and Electrolytes Study Notes

Prepared By: Patricia Marie L. Gaddi, RN
Key Components: Sodium (Na), Magnesium (Mg), Calcium (Ca), Electrolytes (K, Cl, PO₄, HCO₃)

Key Ions:
- Sodium ions (Na⁺)
- Potassium ions (K⁺)
- Calcium ions (Ca²⁺)
- Magnesium ions (Mg²⁺)
Importance: Maintains electrolyte homeostasis, essential for nerve impulses and muscle contraction.

Definition: Total body water and electrolytes are maintained within normal levels, ensuring proper distribution within the body compartments.
Interdependence: Abnormalities in fluid often lead to abnormalities in electrolytes and vice versa.

Importance of Retaining Fluid: More significant in infants due to their higher body water percentage compared to adults.
- Adult Water Composition: Approximately 60% of total weight
- Infant Water Composition: 75% to 80%
- Children Water Composition: 65% to 75%

Brain: 90% water
Blood: 83% water
Muscle: 73% water
Bone: 22% water
Functions:
- Transports nutrients and oxygen into cells
- Moisturizes air in lungs and aids metabolism
- Protects joints and organs, facilitating absorption of nutrients
- Detoxifies the body

Electrolyte: Any compound that dissolves in water to yield ions, which are charged particles.
Fluid: Refers to water and the chemical components it contains; principal components of body fluids.

ELECTROLYTE	MAIN LOCATION	NORMAL VALUE	MAIN PURPOSE	COMMON FOOD SOURCES
Sodium (Na⁺)	Extracellular (ECF)	135–145 mEq/L	Controls water balance, blood pressure, nerve impulses	Table salt, processed foods, canned goods
Potassium (K⁺)	Intracellular (ICF)	3.5–5.0 mEq/L	Muscle contraction, especially heart rhythm	Banana, orange, avocado, spinach, etc.
Calcium (Ca²⁺)	Mostly Extracellular	8.5–10.5 mg/dL	Bone strength, muscle contraction, blood clotting	Milk, cheese, yogurt, sardines, etc.
Magnesium (Mg²⁺)	Intracellular	1.5–2.5 mEq/L	Nerve & muscle relaxation	Nuts, seeds, whole grains, dark chocolate
Chloride (Cl⁻)	Extracellular	98–106 mEq/L	Fluid balance, works with sodium	Table salt, tomatoes, olives, seaweed
Phosphate (PO₄³⁻)	Intracellular	2.5–4.5 mg/dL	Energy production (ATP), bones & teeth	Meat, dairy products, beans, nuts
Bicarbonate (HCO₃⁻)	Extracellular	22–26 mEq/L	Maintains acid–base balance	Produced by kidneys; small amounts in mineral water

Cations: Positively charged ions (e.g., Na⁺, K⁺, Ca²⁺).
Anions: Negatively charged ions (e.g., Cl⁻, PO₄³⁻).
Non-electrolytes: Substances that do not ionize and therefore do not carry an electrical charge (e.g., glucose).

Osmolality: Measure of total solute concentration per kilogram of solvent.
Osmolarity: Measure of total solute concentration per liter of solution.
Definitions:
- Solute: Substance being dissolved.
- Solution: Homogeneous mixture of solutes in a solvent.
- Solvent: Substance that dissolves a solute (liquid or gas).
- Valence: Degree of combining power of an ion.

Needs at least 1500 mL of water daily plus 700 mL from food and 300 mL from oxidation of food.
Roles:
- Transport of nutrients and wastes
- Solvent for electrolytes and non-electrolytes
- Maintenance of body temperature
- Facilitation of digestion and elimination
- Maintenance of acid-base balance
- Lubrication of joints

Extracellular Fluid Compartment: 25% of body weight.
- Plasma: 7%
- Extracellular Fluid: 26%
- Contains sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), sugars, proteins.
Intracellular Fluid (ICF): 67% of body weight.
- Fluid inside all cells; approximately two-thirds of all body water.
- Rich in potassium (K⁺); site of cell metabolism.
Transcellular Fluid: Found in cerebrospinal canals, lymph, synovial joints, and eyes.

Osmosis: Movement of water only from low solute concentration to high solute concentration (no energy required).
Diffusion: Movement of solutes from high concentration to low concentration.
Filtration: Movement of water and small solutes from high pressure to low pressure (uses pressure).
Active Transport: Movement of solutes against concentration gradient using energy (ATP).

Isotonic: Same solute and water concentration as body fluids (e.g., 0.9% saline).
- Medical Use: Maintain hydration without causing cell shrinkage or swelling.
Hypotonic: Lower solute concentration compared to body fluids; causes water to move into cells leading to swelling (e.g., 0.45% saline).
- Medical Use: Caution needed to avoid cell bursting.
Hypertonic: Higher solute concentration compared to body fluids; causes water to move out of cells leading to shrinkage (e.g., 3%-5% NaCl).
- Medical Use: Treat cerebral edema; restore blood volume in hypovolemia.

Isotonic Dehydration: Equal loss of water and electrolytes. Causes include vomiting, diarrhea, and burns.
Hypertonic Dehydration: Greater loss of water than electrolytes. Causes include hyperventilation, renal failure.
Hypotonic Dehydration: Less common, results from fluid shifts causing decrease in plasma volume. Causes include chronic illness and excessive fluid replacement.

Isotonic Overhydration: Retention of isotonic fluids, leading to increased ECF. Causes include poorly controlled IV therapy.
Hypotonic Overhydration: Excess fluid hypotonic to normal body fluids causing fluid shifts into cells. Causes include early renal failure.
Hypertonic Overhydration: Rare, caused by excessive sodium intake leading to fluid shifts into ECF while ICF contracts.

Increased volume of ECF and decreased osmolality stimulate the thirst center in the hypothalamus, prompting water intake.

Importance of fluid and electrolyte homeostasis in health, understanding transport mechanisms, dehydration, and overhydration management for effective clinical practice.