Intravenous fluids in a hospital have the same osmotic concentration as the cells in the body to prevent pain, as well as cell and tissue damage. Intravenous fluids should have the same osmotic pressure as the blood, because this won't cause any pain or damage to the blood vessels, regardless of how long the intravenous fluids are administered. The osmotic pressure also prevents the cell from bursting or dying by excess water as it regulates the flow of the water across the membranes or it stops it from flowing inward. This process of water movement or transport in a semipermeable membrane from a dilute solution to a concentrated solution is called osmosis.
Intravenous fluids are actually designed and created with the purpose of osmosis in mind and are meant to directly affect the osmotic pressure. IV fluids can be crystalloids (solutions that contain smaller water-soluble molecules) or colloids (solutions that contain larger insoluble molecules), which in turn can be isotonic, hypotonic, or hypertonic.
An isotonic solution has an equal concentration of solutes; the solute concentration inside the cell is equal to the solute concentration of solutes outside the cell. Isotonic solutions maintain the osmotic pressure both outside and inside the cell. A hypotonic solution has a lower concentration than other solutions and than those of the cells of the body. Due to the osmotic pressure, water will travel to the cell to expand it. A hypertonic solution has a higher solute concentration than other solutions. The osmotic pressure will cause the water to flow out of the cell in order to shrink it.