Overview
This lecture covers the basics of IV fluids, focusing on the differences between hypotonic, isotonic, and hypertonic crystalloids, their mechanisms, indications, and clinical implications.
IV Fluids and Osmosis
- IV fluids are used when patients cannot take fluids orally, need rapid infusion, or have electrolyte imbalances.
- Crystalloids are IV solutions mainly composed of water and dissolved salts or sugars.
- Osmosis is the movement of water across a semi-permeable membrane from low to high solute concentration.
- Understanding fluid movement requires comparing the solution to the cell (solution vs. cell).
Hypotonic Solutions
- Hypotonic solutions have lower solute concentration than the cell, causing water to enter and swell the cell.
- Common hypotonic solutions: 0.45% saline (half normal), 0.225% saline (quarter normal), 0.33% saline (one-third normal).
- Indicated for cellular dehydration but contraindicated in increased intracranial pressure.
Isotonic Solutions
- Isotonic solutions have equal solute concentration to the cell, resulting in no net water movement.
- Main isotonic solutions: 0.9% saline (normal saline), lactated Ringer's (LR), D5W (5% dextrose in water), 5% dextrose in 0.225% saline.
- Used for increasing extracellular fluid without changing cell size, especially after blood loss, vomiting, diarrhea, or surgery.
Hypertonic Solutions
- Hypertonic solutions have higher solute concentration than the cell, causing water to move out and shrink the cell.
- Common hypertonic solutions: 3% saline, 5% saline, 10% dextrose in water, 5% dextrose in 0.9% or 0.45% saline, 5% dextrose in lactated Ringer's.
- Indicated for hyponatremia or cerebral edema and usually require central venous access.
Key Terms & Definitions
- Osmosis — movement of water across a semi-permeable membrane from lower to higher solute concentration.
- Crystalloids — IV fluids containing water and dissolved substances like salts or sugars.
- Hypotonic — solution with lower solute concentration than the cell; causes cell swelling.
- Isotonic — solution with solute concentration equal to the cell; no change in cell size.
- Hypertonic — solution with higher solute concentration than the cell; causes cell shrinkage.
Action Items / Next Steps
- Review the different types of IV fluids and their indications.
- Memorize which solutions are hypotonic, isotonic, and hypertonic.
- Understand osmosis and how it affects cell size depending on the fluid given.