Blood substitutes
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Blood substitutes are used to fill fluid volume and/or carry oxygen and other gases 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 yielded encouraging results. New studies have found that the size of PFC particles is about 40 times smaller than the diameter of a red blood cell (RBC). 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.
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Volume expanders
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.
Towards artificial blood
Artificial blood is supposed to replace biological blood, especially in humans. Unfortunately, oxygen transport (the function that distinguishes real blood from other volume expanders) has been very difficult to reproduce. In 1990s significant progress was achieved, and the first blood substitute approved (initially in South Africa) for use in humans was Hemopure, a solution made from cow hemoglobin. Perfluorochemicals can undergo oxygen transport effectiveily, but must be emulsified first, also PFCs do not last long in the body as they are removed by the kidneys and vaporize away in the blood-air interface in the lungs. Complete FDA approval of PFCs is still lacking.
In December 2003 a new artificial whole blood, PolyHeme began field tests on emergency patients. PolyHeme is the 15th experiment to be approved by the Food and Drug Administration since 1996. Patient consent is not necessary under the special category created by the FDA for these experiments.
Artificial blood, produced in large quantities, would remove the need for blood donors. It could also be equipped with special properties, like the ability to transport an increased amount of oxygen, which would be useful for someone who suffered massive blood loss. Artificial blood would also most likely have a universal blood type, so it could be used on anyone.
Apart from attempts to create blood by genetic engineering, work is being conducted on nanotechnology-based blood.
The United States Army is experimenting with varieties of dried blood, which takes up less room, weighs less and can be used much longer than blood plasma. These properties make it ideal for first aid during combat. Water has to be added prior to use.
Uses outside medicine
Artificial blood is also used in movie-making. For example, when a director needs to simulate an actor being shot or cut, special props using animal blood, tinted water or ketchup are utilized.
See also
External links
- Detailed overview of Artificial bloods understudy (http://medind.nic.in/maa/t03/i1/maat03i1p45.pdf) (PDF)
- How Can Blood Save Your Life? (http://www.watchtower.org/library/hb/index.htm?article=article_00.htm) - the Jehovah's Witnesses perspective
- Artificial cells & organs research (http://www.medicine.mcgill.ca/artcell/)
- Respirocytes: A Mechanical Artificial Red Cell (http://www.foresight.org/Nanomedicine/Respirocytes1.html)
- South Africa Approves First Blood Substitute (http://www.redcross.org/news/bm/intl/010419sub.html)ja:無輸血治療