What exactly is a 'blood substitute'?
The term 'blood substitute' is a little misleading
since their development so far has concentrated primarily on only the blood's
function to carry oxygen to our tissues. A more accurate term for blood substitutes
being developed would be either:
- Cell-free oxygen carriers
- Oxygen therapeutics
- Red cell substitutes
Essentially, blood substitutes are fluids which, when injected
into the human blood stream, contribute significantly to the
transport of oxygen around the body.
What constitutes a suitable substitute?
Scientists have identified that an ideal blood substitute
should have several key properties. These would ensure that
a substitute would be free of all of the problems associated
with donated human blood when it is used in transfusion. Such
properties include:
- Adequate oxygen uptake in the lungs
- Adequate oxygen delivery to the tissues
- Long circulation time
- Non-toxic
- Rapidly excreted without causing harm
- Stable at room temperature and readily available for use
- Easily sterelisable (i.e. easy to ensure absence of pathogens
such as viruses)
- Cheap to manufacture
- Long shelf life and easy to store
- Widely applicable (i.e. no need for crossmatching or compatibility
testing)
- Free of any side effects
There are 3 key advantages to a blood substitute that meets
all of these criteria, and it is these that make the prospect
of developing an effective substitute very exciting:
- Unlike red blood cells, a blood substitute could be sterilised,
this would mean the problems of disease spreading would
be removed from transfusions.
- Problems of human error, (mismatching of blood types)
with donated blood would be removed since a substitute would
not contain the properties of blood that cause this.
- A blood substitute could be stored stably for a long time,
which would allow for transport to third world countries
or to a battlefield, or site of natural disaster without
the need for refrigerators. Effectively there would be trouble
free availability of blood.