Functional Aspects of Hemoglobin
in the acid-citrate-dextrose (ACD) medium used by many
blood banks. As a result, oxygen affinity is increased and
the ability of blood that is transfused to supply oxygen
to the tissues is decreased. Volunteers who received such
blood had an increase in oxygen affinity that did not return
to normal for 6-24 hours. The therapeutic significance of
these changes is not clear. The greatest effects should occur
in patients who receive numerous transfusions over a pe-
riod of about
hours, so that a significant fraction of their
circulating erythrocytes has increased oxygen affinity.
Traditionally, red cell survival has been the main crite-
rion of the quality of stored blood. However, cell survival
does not necessarily correspond to maintenance of ade-
quate organic phosphate levels. Studies on the composition
of the storage medium needed to prevent this metabolic
loss of organic phosphates show the following:
1. Citrate-phosphate-dextrose (CPD) medium is better
than ACD for maintaining organic phosphate levels
and for preventing a reduction in
because of the higher pH of CPD. In 1971, 90% of
blood banks in the United States used ACD and only
10% used CPD; by 1975, the reverse was true. The
shelf life of cells is the same for both media
(21 days), but cells stored in CPD function better
physiologically when transfused.
2. Supplementation with inosine generates a supply of
-phosphate and provides a potential glycolytic
substrate that can be metabolized to 2,3-DPG.
Pyruvate and fructose, which help maintain a supply
of oxidized NAD+, potentiate the effect of inosine.
This modification must be balanced against the
possibility of hyperuricemia (Chapter 27) caused by
transfusion of large amounts of inosine-containing
3. Supplementation with dihydroxy acetone phosphate
could provide a glycolytic substrate without the risk
In addition to carrying oxygen from the lungs to the tissues,
hemoglobin helps move carbon dioxide from tissues back
to the lungs, where it can be eliminated. This CO
ment is accomplished with little or no change in blood pH,
owing to the buffering capacity of hemoglobin (Chapter 1).
Figure 28-10 summarizes the pathways and intermediates
involved. Of particular importance are the following:
F IG U R E 2 8 -1 0
Interchange of carbon dioxide and oxygen between tissues and lungs. The reactions at right occur in plasma and
erythrocytes in tissue capillaries during oxygen delivery to tissue cells; the reactions at left occur in the lungs during
release and O
uptake. The cyclic nature of these changes (lungs to capillaries to lungs) should be noted.