Blood substitutes
Blood substitutes are used to fill fluid volume and/or carry oxygen and other gasses in the cardiovascular system. Substances called perfluorochemicals (PFC) have the ability to carry oxygen and carbon dioxide. Perfluorochemicals will not mix with blood, therefore emulsions must be made by dispersing small drops of PFC in water. This liquid is then mixed with antibiotics, vitamins, nutrients and salts, producing a mixture that contains about 80 different components, and performs many of the vital functions of natural blood. As of 1990, most blood substitutes tended to raise blood pressure.Recent research on blood substitutes has yeilded encouraging results. New studies have found that the size of PFC particles is about 40 times smaller than the diameter of an RBC red blood cell. This small size can enable PFC particles to traverse capillaries through which no RBCs are flowing. This seems to hold promise of benefit in the case of certain damaged, blood-starved tissue.
Also in need of mention are volume expanders. The simplest is saline (salt) solution, which is both inexpensive and compatible with blood. There are also fluids with special properties, such as dextran, Haemaccel, and lactated Ringer's solution.
When blood is lost, compensatory mechanisms start up. The heart pumps more blood with each beat. Since the lost blood was replaced with a suitable fluid, the now diluted blood flows more easily, even in the small vessels. As a result of chemical changes, more oxygen is released to the tissues. These adaptations are so effective that even if only half of the red cells remain, oxygen delivery may be about 75 percent of normal. A patient at rest uses only 25 percent of the oxygen available in his blood.
