Parenterals Tonicity

What happens to solvent molecules during osmosis in an open system?

• In an open system, solvent molecules move across a semi-permeable membrane, but the liquid level and vapor pressure remain equal on both sides.

What is osmotic pressure?

• Osmotic pressure is the amount of pressure required to make the fluid levels equal on both sides of a semi-permeable membrane.

How does osmosis function differently in a closed system, like a cell?

• In a closed system, changes in volume on each side of the membrane are significant, causing the membrane to move. Osmotic pressure can reverse this movement.

What factors influence osmotic pressure?

• Osmotic pressure is influenced by the number of molecules or ions in the solution, a concept called a “colligative property.”

What is the difference between osmolarity and osmolality?

• Osmolarity is the number of osmotically active particles per liter of solution.

• Osmolality is the number of osmotically active particles per kilogram of solvent.

How much osmotic pressure does a 1 Osmolar aqueous solution exert?

• 22.4 atmospheres at 0°C.

What effect does a 1 Osmolar solution have on freezing and boiling points?

• A 1 Osmolar aqueous solution will freeze at -1.86°C and boil at 100.52°C.

What is the difference between osmolarity and tonicity?

• Osmolarity measures solute concentration per liter and has units (osmoles/L).

• Tonicity describes how a solution affects a cell’s volume and has no units.

Can isosmotic solutions always be considered isotonic?

• No, isosmotic solutions have the same solute concentration, but they are not always isotonic.

• Tonicity depends on whether solutes can enter the cell.

Why is understanding tonicity important in medical treatments?

• Tonicity is essential in intravenous (IV) therapy, as using the wrong IV solution can harm or even kill patients.

How do normal saline and D-5-W solutions differ in terms of tonicity?

Both are isosmotic at 278 mOsmol/L.

However:

• Normal saline is isotonic because NaCl does not enter cells.

• D-5-W (5% dextrose) is hypotonic because glucose enters cells, causing them to swell.

Are hyposmotic solutions always hypotonic?

• Yes, hyposmotic solutions (low solute concentration) are always hypotonic, meaning they will cause cells to swell.

How can the same solution be isotonic to one cell type but hypotonic to another?

• For example, a sucrose solution is isotonic to mammalian cells (they lack sucrose transporters).

• However, it is hypotonic to plant cells, which have sucrose transporters that allow sucrose to enter.

Why is a 5% dextrose solution hypotonic?

• A 5% dextrose solution is hypotonic because dextrose (glucose) can enter cells, reducing the solution’s osmotic effect and causing cells to absorb water and swell.