Lecture Notes on Fluids and Electrolytes

Key Concepts

• Importance of maintaining homeostasis in body fluids and solutes.
• Different transport processes: diffusion, osmosis, and active transport.
• Importance of hydrostatic pressure and oncotic pressure.

Cell Membrane Transport

Structure

• Phospholipid Bilayer: Medium for substance exchange, featuring hydrophilic heads and hydrophobic tails.
• Channel Carrier Proteins: Assist in transport of specific molecules.

Diffusion

• Simple Diffusion: Passive transport, no energy required. Moves molecules from high to low concentration (e.g., oxygen, carbon dioxide).
• Facilitated Diffusion: Also passive, uses helper proteins for large or charged molecules (e.g., glucose, ions).

Active Transport

• Movement from low to high concentration against the gradient.
• Requires energy in the form of ATP, uses special protein channels.

Osmosis

• Water movement across a semi-permeable membrane from high to low water concentration.
• Important in balancing solute concentration inside and outside the cell.

Hydrostatic and Oncotic Pressure

Hydrostatic Pressure

• Pushes water across capillary walls.
• High in arteries, lower in veins, involved in filtration.

Oncotic Pressure (Colloidal Osmotic Pressure)

• Pulls water across capillary walls using proteins like albumin.
• Important in maintaining blood plasma volume.

Hormonal Regulation of Fluid Balance

Renin-Angiotensin-Aldosterone System (RAAS)

• Activated by low blood pressure; increases blood volume and pressure.
• Involves Angiotensin II, aldosterone, and ADH.

Thirst Mechanism

• Triggered by high blood osmolality, stimulates ADH release.

Natriuretic Peptides

• Prevent fluid overload by counteracting RAAS effects.

Lab Values and Diagnostics

Complete Blood Count (CBC)

• Monitors cells in blood: RBC, WBC, and platelets.

Metabolic Panels

• Assess electrolyte status, renal function, and liver performance.

Coagulation Levels

• Important for patients on anticoagulants.

Lipid Panels

• Assess cardiovascular risk.

Drug Levels

• Monitor for drugs with narrow therapeutic windows.

Arterial Blood Gases (ABGs)

• Evaluate acid-base balance and respiratory/metabolic function.

Electrolyte Imbalances

Sodium

• Major extracellular cation, vital for nerve and muscle function.
• Normal range: 135-145 mEq/L.
• Hyponatremia: Caused by fluid overload or diuretics.
• Hypernatremia: Caused by dehydration or high sodium intake.

Potassium

• Major intracellular cation, crucial for cardiac and muscle function.
• Normal range: 3.5-5 mEq/L.
• Hypokalemia: Caused by diuretics or renal issues.
• Hyperkalemia: Caused by renal failure or tissue damage.

Calcium

• Important for bones and muscle function.
• Normal range: 8.5-10.5 mg/dL.
• Hypocalcemia: Caused by lack of vitamin D or hypoparathyroidism.
• Hypercalcemia: Caused by hyperparathyroidism or excess calcium intake.

Magnesium

• Intracellular cation, affects muscle and nerve function.
• Normal range: 1.5-2.5 mg/dL.
• Hypomagnesemia: Caused by poor absorption or chronic alcoholism.
• Hypermagnesemia: Rare, often due to excessive supplementation.

Phosphate

• Vital for energy transfer and bone mineralization.
• Hypophosphatemia: Caused by malnutrition or hyperparathyroidism.
• Hyperphosphatemia: Typically due to renal failure or hypoparathyroidism.

IV Fluid Types

Isotonic Solutions

• Same osmolarity as blood, used for fluid replacement (e.g., Normal Saline).

Hypotonic Solutions

• Lower osmolarity, rehydrates cells (e.g., 0.45% Saline).

Hypertonic Solutions

• Higher osmolarity, draws water out of cells (e.g., 3% Saline).

Fluid Volume Disorders

Hypervolemia (Fluid Overload)

• Causes include heart failure, excessive IV fluids.
• Symptoms include edema, hypertension, pulmonary congestion.

Hypovolemia (Fluid Deficit)

• Causes include dehydration, hemorrhage.
• Symptoms include hypotension, tachycardia, dry mucous membranes.

Hypovolemic Shock

• Severe volume depletion, requires urgent fluid replacement.
• Monitor vital signs and fluid balance closely.

These notes cover the key points from the lecture on fluids and electrolytes, providing a comprehensive overview of the physiological processes and clinical considerations.