BLOOD COMPONENT THERAPY
A major advance in the field of blood banking has been the development
of blood component therapy. It is beyond the scope of this chapter to describe the
various separation steps in detail, but a superficial outline of the scheme by which
various blood components are derived is shown in Figure
47-10
. The basic philosophy is based on the concept that patients are
best treated by administration of the specific fraction of blood that they lack.
This concept has presented problems to the surgical team, who often desire whole
blood.
Packed Red Blood Cells
PRBCs contain the same amount of hemoglobin as whole blood, but
much of the plasma has been removed. The hematocrit value is 40% in whole blood
and 70% in packed erythrocytes ( Table
47-15
). The position of the American Association of Blood Banks has been
that transfusion of whole blood is required primarily for blood loss acute enough
to cause hypovolemic shock. More specifically, they state that the primary indication
for whole blood is for patients who are actively bleeding and have sustained a loss
of greater than 25% of their total blood volume. In other words, whole blood provides
oxygen-carrying capacity and intravascular blood volume expansion. Less severe degrees
of hemorrhage may be effectively treated with PRBCs, retaining the plasma and the
TABLE 47-15 -- Comparison of whole blood and packed red blood cells
|
Value |
Whole Blood |
Packed Red Blood Cells |
|
Volume (mL) |
517 |
300 |
|
Erythrocyte mass (mL) |
200 |
200 |
|
Hematocrit (%) |
40 |
70 |
|
Albumin (g) |
12.5 |
4 |
|
Globulin (g) |
6.25 |
2 |
|
Total protein (g) |
48.8 |
36 |
|
Plasma sodium (mEq) |
45 |
15 |
|
Plasma potassium (mEq) |
15 |
4 |
|
Plasma acid (citric-lactic) (mEq) |
80 |
25 |
|
Donor-to-recipient ratio |
1 unit per patient |
1 unit per 4–6 patients |
|
From Landers DF, Hill GE, Wong KC, et al: Blood transfusion-induced
immunomodulation. Anesth Analg 82:187, 1996. |
components thereof for other patients (see Fig.
47-10
). Many blood banks have religiously followed this principle, and
whole blood cannot be obtained in the operating rooms except by special request.
In essence, blood bankers are saying that except for a rare situation (e.g., hypovolemic
shock), whole blood is not necessary.
Because of this trend, some hospitals do not have whole blood
readily available. This may force the surgical team to use PRBCs for losses of blood
more than 1000 to 1500 mL/70 kg. One fear has been that if large volumes of PRBCs
reconstituted with a crystalloid are given, serum albumin deficiencies may result.
However, administration of saline-reconstituted RBCs for losses of blood less than
2500 mL/70 kg usually does not induce low serum levels of albumin, although fibrinogen
concentration can be decreased in the recipient.
The administration of PRBCs is facilitated by reconstituting them
with a crystalloid or colloid; however, not all crystalloids are suitable. If the
solution contains calcium, clotting occurs. Lactated Ringer's solution is usually
not recommended for use as a diluent for PRBCs ( Table
47-16
). Conversely, using flow rates and clot formation, Cull and colleagues
[134]
found lactated Ringer's solution and normal
saline to be equally acceptable. A more important factor may be whether the diluent
is hypotonic with respect to plasma. If so, the RBCs will swell and eventually lyse.
Solutions that cause hemolysis are listed in Table
47-16
. Clinicians who fear that the crystalloid-reconstituted RBCs may
cause low serum concentrations may be tempted to use a plasma derivative, such as
Plasmanate.[135]
However, these solutions also
can cause hemolysis. The osmolality of Plasmanate is only 180 mOsm/kg. Solutions
recommended for reconstituted packed erythrocytes are 5% dextrose in 0.4% saline,
5% dextrose in 0.9% saline, 0.9% saline, and Normosol-R with a pH of 7.4.
 |
