There are a few different kinds of intravenous (IV) fluids given to patients in hospitals, ambulances, and emergency settings. Each type of IV therapy depends on what a patient requires for treatment, and intravenous fluids have drastically different effects on the body depending on which are used. Aside from fluids that deliver medications, an IV drip can consist of colloids, or fluids that stay inside the blood vessels, or crystalloids, which can have different effects depending on how concentrated the electrolytes are within the fluids. Blood, red blood cells, plasma, and platelets can also be injected intravenously, while alternative fluids that can carry oxygen are also available.
Colloid-based fluids stay inside the blood vessels because it contains molecules and proteins too big to pass into the surrounding cells. The fluids increase blood volume and also cause water from cells to enter the bloodstream. Long-term use can dehydrate cells, and colloid fluids are difficult to store outside of a hospital.
The most viable intravenous fluids used before patients enter hospitals are crystalloid solutions. Depending on the concentration of electrolytes, the fluids behave differently in terms of how water is distributed. Tonicity defines how many electrolytes are concentrated in the solution in relation to the human body, and how the fluid gets across membranes based on this relationship is called osmosis. Fluids that have equal electrolytes to the body plasma are called isotonic crystalloids, while hypertonic crystalloids are higher in tonicity and cause fluids to fill the blood vessels. Hypotonic fluids have a lower tonicity, so they allow water to move from inside blood vessels toward cells.
Body fluids tend to move toward areas where the electrolytes or molecule count are higher. Medical personnel administer fluids based on knowledge of what a patient needs. It is extremely important to give the proper concentration of fluid, because the wrong one can be fatal for someone who is sick or injured.
Another type of intravenous therapy is the injection of blood, or components of it. Blood volume can be increased and the concentration of red blood cells with hemoglobin, which carries oxygen, is raised. Synthetic intravenous fluids include oxygen-carrying solutions, which can carry oxygen throughout the body similar to how blood does and are easily transported into the field where injuries may have led to extreme blood loss. All IV fluid bags are required to have a label indicating the type, amount of, and expiration date of the solution.