There are three key types of intravenous fluid. Crystalloid solutions, which include hypotonic, isotonic, and hypertonic solutions are the most common, while colloid solutions are less prevalent. Blood and blood products are also given via intravenous (IV) therapy. Synthetic blood replacement fluid could become of a new kind of intravenous fluid but is still experimental in 2011.
Many of the best known types of intravenous fluid fall under the general class of crystalloid solutions. These solutions contain chemicals with small molecules which can easily pass through the walls of capillaries into the body's cells. Crystalloid kinds of intravenous fluid are divided into three groups, depending on whether they have more, less, or the same amount of electrolytes as plasma, which is the primary liquid component of blood.
Hypotonic crystalloid fluids, such as half-strength saline solution with 0.45% salt, have fewer electrolytes than plasma and are frequently used to hydrate patients. Isotonic fluids match the body's electrolyte level. These solutions, which include a 5% dextrose sugar solution, 0.9% saline solution, and lactated Ringer's solution, serve a range of functions. Hypertonic fluids, which have high concentrations of electrolytes, include double-strength 10% dextrose and 5% dextrose in saline solution. These fluids can fill blood vessels while also delivering sugar, and are useful in treating diabetics. Many specialty pharmaceuticals that are delivered intravenously are mixed with one of these types of fluid.
Colloid solutions, such as albumin and dextran, carry large molecules which typically cannot permeate the capillary wall. They do an excellent job of increasing blood volume both by staying in the vessels and by their ability, similar to hypertonic crystalloid fluids, to pull fluid out of the body and into the circulatory system. These solutions tend to be expensive and hard to store and administer.
Blood and blood products are natural products but are also frequently administered through an IV line and can also be classified as one of the types of intravenous fluid. Plasma can be used in transfusions to replace fluids while blood constituents like white blood cells and platelets can be transfused to solve specific health problems. Transfusions do carry health risks beyond the risks of other IV fluid replacement.
In the first decade of the 21st century, a fourth type of intravenous fluid began to emerge. Synthetic blood-replacement fluids would have the ability to carry oxygen similar to that of the hemoglobin in red blood cells. The hope is that they will be able to combine the convenience and affordability of crystalloid solutions with the oxygen-carrying capacity of human blood. As of 2011, though, synthetic blood fluids using perfluorochemicals as an oxygen-carrier remain under clinical trials in the US.
